Introduction, Alkanes, Alkenes and Alkynes..pdf

Basic Organic Chemistry. Lecturer: Dr.
Nabaz Abdulmajeed.
1
Basic Organic Chemistry
Lecturer: Nabaz Abdulmajeed Muhammad Salih Perxdry (PhD in Chemistry).
nabazsalih82@gmail.com
Peer Reviewer: Dr. Akram Noori Mohammed .

Chemistry
Chemistry is the branch of science that deals with the properties,
composition, and structure of elements and compounds, how they
can change, and the energy that is released or absorbed when they
change.
Chemistry sometimes is called the "central science" because it
connects other sciences to each others, such as biology, physics,
geology and environmental science.
Matter is as anything that has both mass and volume (occupies
space). Matter is everything around you. Matter is anything made of
atoms and molecules, e.g. trees, air.
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Properties of matter
1. Chemical property: is a characteristic or behavior of a substance
that may be observed when it undergoes a reaction. Do change the
chemical nature of matter, such as flammability, reactivity, pH, toxicity,
chemical stability, and heat of combustion.
2. Physical properties: is a characteristic of matter that is not
associated with a change in its chemical composition. Do not change
the chemical nature of matter physical properties of matter are
categorized as either intensive or extensive.
a. Intensive properties that do not depend on the amount of the
matter present such as color, odor, conductivity, hardness, melting and
freezing point, boiling point and density.
b. Extensive properties that do depend on the amount of matter
present such as mass, weight , volume and length.
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1. Element is made up of the same kind of atoms. Their atoms with
specific properties.
2. Compounds is composed of two or more elements of different
kinds. The properties of a compound are different than the
elements from which it is made.
3. Molecules such as O2, H2 and Cl2.
4. Mixture material that is made up of 2 or more substances that
can be separated physically for example column chromatography,
HPLC or recrystallization.
Composition of Matter:
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Understanding the structure of atoms is critical to
understanding the properties of matter.
Atoms are composed of
1. Protons – positively charged particles are located in the nucleus.
2. Neutrons – neutral particles are located in the nucleus.
3. Electrons – negatively charged particles
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Helium atom
+
N
N
+
-
-
proton
electron neutron
Shell
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Atomic orbital
 Atomic orbital show probability of presence of electron in different
distance and direction according to nucleus, and its orbitals.
Atomic orbitals differ in terms of
1. Energy.
2. Shape.
3. Direction
 Orbitals is a region around the nuclear in the atom where there is a
high probability (90-95)% of finding a electron.
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Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
X
A
Z
Mass Number
Atomic Number
Element Symbol
 Atoms with the same atomic number have the same chemical
properties and belong to the same element.
 Every different atom has a characteristic number of protons in the
nucleus.
He
4
2
Mass Number
Atomic Number
Element Symbol
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Isotopes are atoms of the same element (X) with different numbers
of neutrons in the nucleus
H
1
1 H (Deuterium)
1
2 H (Tritium)
1
3
U
92
235 U
92
238
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Atomic Structure
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Aufbau Principle: orbitals fill in order of increasing energy from
lowest energy to highest energy.
Hund's Rule: when orbitals of equal energy are available but
there are not enough electrons to fill all of them, one electron is
added to each orbital before a second electron is added to any
one of them.
Pauli Exclusion Principle: only two electrons can occupy any
atomic orbital, and to do so these two must have opposite
spins.
Valence shell: the outermost shell of an atom containing the
valence electrons.
Valence electrons : electrons in the valence shell of an atom
these electron are used to form chemical bonds and also used
in chemical reactions.
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The historical name of subshell:
s sharp
p principal
d diffuse
f fundamental

Electron Configuration of Atoms
• Is a particular distribution of electrons among
available subshells.
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It is important to know:
 Carbon: normally forms four covalent bonds and has no unshared
pairs of electrons.
 Hydrogen: forms one covalent bond and has no unshared pairs of
electrons.
 Nitrogen: normally forms three covalent bonds and has one
unshared pair of electrons.
 Oxygen: normally forms two covalent bonds and has two unshared
pairs of electrons.
 Halogen: normally forms one covalent bond and has three
unshared pairs of electrons.
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Ions are charged atoms.
 Cations – have more protons than electrons and are positively
charged.
 Anions – have more electrons than protons and are negatively
charged.
Ionization energy: it is the energy that is needed to remove an
electron from the valence shell of the atom.
Neutral atoms have the same number of protons and electrons.
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Halogens
Hydrogen
Oxygen
Nitrogen
Carbon
Elements
1
1
2
3
4
Valence electron
3
0
2
1
0
Lone pairs
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An ion is formed when an atom, or group of atoms, has a
net positive or negative charge (why?).
If a neutral atom looses one or more electrons it becomes a
cation.
If a neutral atom gains one or more electrons
it becomes an anion.
Na
11 protons
11 electrons Na+ 11 protons
10 electrons
Cl
17 protons
17 electrons Cl-
17 protons
18 electrons
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The Nature of Chemical Bonds
Ionic Bonds: is a chemical bond formed by the electrostatic
attraction between positive and negative ions , NaCl.
Covalent Bonds: is a chemical bond involving the sharing of a pair
of electrons between two adjacent atoms in a molecule.
(Bonding forces are due to the attraction between nuclei and
electron pairs).
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Bond polarity
Electronegativity: the relative ability of a bonded atom to attract the
shared electrons.
Which bond is more polar or dipolar?
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If the difference in electronegativity (∆EN) is between (0.0 to 0.4 non-
polar covalent bond), (>0.4 to 1.7 polar covalent bond or 1.7 to 4.0
ionic bond) present.
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However, it is possible for both electrons to come from the same
atom (coordinate covalent bond).
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Intermolecular attractive forces (Electrostatic) that are involved in
the solubilization process are:
1. Van der Waals Attraction (London force)
■ Weakest intermolecular.
■Occurs between nonpolar groups (e.g. hydrocarbons like CH3-CH3).
When a non-polar molecule dissolves in a non-polar solvent, there is
an induced dipole-induced dipole interaction between temporary
dipoles on solute and solvent.
2. Dipole-Dipole Interaction
occur when the partial charges formed within one molecule are
attracted to an opposite partial charge in a nearby molecule.
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Basic Organic Chemistry. Lecturer: Dr. Nabaz Abdulmajeed.

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■Hydrogen bonding is a special kind of dipole-dipole force that
occurs when a H atom is bonded to one of the very electronegative
atoms O, N and F. in a nearby molecule. Electronegative atoms must
have at least a lone pair of electrons.
N: H O
H

C
O
O H
O
H
H
 +
+
+

N: H O
H

C
O
O H
O
H
H
 +
+
+

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3.Ion-Dipole Bonding
■electrostatic between a cation/anion and a dipole.
■relatively strong.
N
+
H
O
H
H


C
O
O
-
H
O
H

+

Polar and non-polar Molecules
Nonpolar molecule: either has nonpolar bonds or polar bonds whose
dipoles moment cancel to zero H2, Cl2.
Polar molecule: has polar bonds with dipoles moment that do not
cancel to zero.
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Polar Molecules
 Linear molecules, like H-Cl, with a polar bond are always polar
molecules. We can represent this with a vector, called the dipole
moment of the molecule.
 Molecules with polar bonds are not necessary to be polar
molecules. Take carbon tetrachloride, CCl4, as an example.
 Each C-Cl bond is polar with an electronegativity difference of 0.61
units.
We can represent the polarity of each bond as a vector, showing
electrons in the bond going closer to the more electronegative
chlorine atom.
The vector sum of the 4 bond vectors is zero. They cancel out. So this
is a non-polar molecule.

For elements in the periodic table, the electronegativity increases
from left to right in a row, and from bottom to top in a column.
Replace one of the Cl atoms with an H atom. Now the vectors don't
cancel and the molecule has a net dipole moment.

Lewis Dot structure (or Lewis diagram or a Lewis
electron dot diagram or electron dot diagram
A Lewis Structure is a very simplified representation of the valence
shell electrons in a molecule. It is used to show how the electrons
are arranged around individual atoms in a molecule. Electrons are
shown as "dots" or for bonding electrons as a line between the two
atoms. The goal is to obtain the "best" electron configuration, i.e.
the octet rule and formal charges need to be satisfied.
Lewis structure does NOT attempt to explain the geometry of
molecules, how the bonds form, or how the electrons are shared
between the atoms. It is the simplest and most limited theory on
electronic structure.
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Lewis Dot Symbols of Monoatomic Elements

Number of covalent bonds:
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Steps for drawing a Lewis structure:
1. Count all the valence electrons.
2. Determine the central atom.
3. Draw a skeletal structure by draw single bonds to the central atom.
4. Put all remaining valence electrons on atoms as lone pairs.
5. Turn lone pairs into double or triple bonds or make multiple bonds
if all octets are not filled.

Resonance or (mesomerism) is a way of describing delocalized
electrons within certain molecule.
Resonance structures have the same relative placement of atoms but
different locations of bonding and lone electron pairs.
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Inductive effect is an electronic effect due to the polarisation of σ
bonds within a molecule or ion. This is typically due to an
electronegatvity difference between the atoms at either end of the
bond.
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Curly arrows represent reaction mechanisms
Nucleophiles donate electrons from available, high-energy orbitals
represented by one of the following:
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Electrophiles accept electrons into empty low-energy orbitals
represented by one of the following:
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Reactions are like Words
Mechanisms are like Grammar
Stereochemistry = exact arrangement in space of the atoms in a
molecule.
Synthesis = making molecules from simpler starting materials.
Terms in Organic Chemistry
Need both to “Speak”
Organic chemistry
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Pharmaceutical Organic chemistry: is a research area incorporating
with different branches of chemistry and biology in the research for
better and new drugs (Drug Discovery).
Generally pharmaceutical organic Chemists can:
 Make new compounds.
 Determine their effect on biological processes.
 Alter (change) the structure of the compound for optimum (best)
effect.
and minimum side effects.
 Study uptake, distribution, metabolism and excretion
of drugs.

Molecular Model of Aspirin

Functional Groups
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Functional groups: an atom or group of atoms or bonds within
molecules that shows a characteristic set of predictable physical and
chemical behaviors.
A particular functional group, in whatever compounds it is found to
have:
1. Similar reactivity for compounds having the same functional group
(Undergo the same types of chemical reactions).
2. Serve as the units by which we classify organic compounds into
families.
4. Serve as a basis for naming organic compounds.
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Why functional groups are important in organic chemistry?
Because they are sites predictable chemical and physical behaviors.
Why functional groups are important in pharmacy?
Functional groups provide specific properties and behaviors, that
allow drug molecules to exert their desired pharmacodynamic and
pharmacokinetic effects.
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Most organic molecules contain more than one functional group, and
most functional groups can react in more than one way, so organic
chemists often have to predict which functional group will react,
where it will react, and how it will react.
There are three main types of selectivity:-
• Chemoselectivity: which functional group will react?
• Regioselectivity: where it will react?
• Stereoselectivity: how it will react? (stereochemistry of the
products)
Selectivity

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Drug Functional Groups
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• Overall water/lipid solubility
• Route of administration
• Ability to interact with specific biological targets
• Mechanism of action
• Route of metabolism and elimination
• Duration of action
• Tendency to cause adverse effects or drug interactions
Significant roles of functional groups
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Acidity and Basicity
 Acidic and/or basic properties of organic medicinal agent are
important in both:
1- Pharmaceutical phase (dosage formulation, etc.) and
2- Pharmacological phases (disposition, structure at target site, etc.).

Arrhenius acid is a substance that produces H+ (H3O+) in water
Arrhenius base is a substance that produces OH- in water
Arrhenius Concept of Acids and Bases

Acid: is the species donating the proton in a proton-transfer
reaction.
Brønsted-Lowry Concept of Acids and Bases
Base: is the species accepting the proton in a proton-transfer
reaction.
acid
conjugate
base
base conjugate
acid

Lewis Concept of Acids and Bases
Acid: as an electron pair acceptor.
Base: as an electron pair donor.
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 This concept broadened the scope of acid-base theory to
include reactions that did not involve H+. The Lewis
concept embraces many reactions that we might not
think of as acid-base reactions.
 Boron trifluoride accepts the electron pair, so it is a Lewis
acid. Ammonia donates the electron pair, so it is the Lewis
base.

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Common basic organic functional groups
 Aliphatic: 1º (R-NH2), 2º (R2NH) and 3º (R3N)- amines
 Heterocyclic amines
 Aromatic amines (Ar-NH2)
R N
R
R
+ H3O+
H2O
+
R N+
R
R
H
+ H2O
H3O+
+
N N+
R
Aliphatic amines
Heteroaromatic amines
NH3
+
NH2
+ H3O+ H2O
+
Aromatic amines
N N
H
N NH
Pyridine
Piperidine
Imidazole
H
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Acidic and basic functional groups are capable of ionization and can
become negatively or positively charged, respectively.

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Common acidic organic functional groups
 Carboxylic acid (-COOH)
 Phenol (Ar-OH)
 Sulfonamide (R-SO2NH2)
 Imide (R-CO-NH-CO-R)
 -Carbonyl group (-CO-CHR-CO-)
R C
O
O H
+ H2O R C
O
O
-
+ H3O
+
O
H
R + H2O
O-
R
Carboxylic acid
Phenol
H3O
+
R
NH3
+
H2O
+
NH2
R
+
H3O
+
+
Aniliniumcation
R SO2NH2
H3O
+
+
H2O
+ R SO2NH-
Sulfonamide
R
O
N
O
R
H + H2O +
R
O
N
-
O
R
H3O+
Imide
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Acids
Imides
H3O+
R
O
N-
O
R
+
H2O
+
R
O
N
O
R
H
Sulfonamides
R SO2NH-
+ H2O
+ H3O+
+ H3O+
Phenols
Carboxylic acids
O-
H2O
+
O
H
H3O+
+
R C
O
O-
H2O
+
R C
O
O H
ArSO2NHR
Aromatic amines
+ H2O
H3O+
+
NH2 NH3
+
Heteroaromatic amines
Aliphatic amines
N+
R
N
+ H3O+ H2O
+
R N+
R
R
H+ H2O
H3O+
+
R N
R
R
Bases
Ionization of Acidic and Basic Functional Groups
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Forming Covalent Bonds
 Valence Bond Theory
How two electron sharing between atoms?
Take those atomic orbitals (s, p) mix to form hybrids
of atomic orbitals. Then overlapping of hybrid
orbitals .
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 Resonance is a scientific exercise within the Valence Bond
Theory of bonding that describes the delocalization of electrons
within molecules. It involves constructing multiple Lewis
structures that, when combined, represent the full electronic
structure of the molecule.
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 What is the difference between electronegativity and inductive
effect?
The difference in atoms electronegative values within a molecule
causes the inductive effect.

Forming Covalent Bonds
Molecular Orbital Theory
Formed as a result from the overlaps of two atomic orbitals, wherein
pair of electrons occupying. Since orbitals are wave functions, they
can combine either constructively (forming a bonding molecular
orbitals), or destructively (forming an antibonding molecular orbitals)
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Organic Chemistry
Is that branch of chemistry that deals with the structure, properties,
synthesis and reactions of the carbon compounds and only a few
others elements-chiefly, hydrogen, oxygen, nitrogen, sulfur, halogens,
and phosphorus.
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Basic Organic Chemistry; Dr. Nabaz
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Most Familiar compounds are “organic”
1) Cotton in clothing. 2) Plastics.
2) Gasoline. 4) Drugs.
3) Food. 6) Dyes.
(Natural Products vs. Synthetic Organic compounds)
 Natural products are compounds we find in the environment.
 Synthetic organic compounds do not occur naturally and must be
synthesized from simpler compounds.

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The mechanism you need to know
There are four main mechanism in organic chemistry:
1. Addition.
2. Substitution.
3. Elimination.
4. Rearrangement

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1. Addition Reaction:

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2. Substitution reaction: it’s that reaction in which the electron-
withdrawing group is replaced by another group or atom. The
substitution either is electrophilic substitution or nucleophilic
substitution.

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3. Elimination: it’s that reaction in which the electron-withdrawing
group is eliminated (removed) by another group or atom.
4. Rearrangement

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Reactive Carbon Intermediates
 Reactive intermediates are short-lived species.
 They are never present in high concentrations because they react
as quickly as they are formed.

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Carbocation Structure
 A carbocation (also called a carbonium ion or a carbenium ion) is a
positively charged carbon.
 Carbon is sp2 hybridized with a vacant p orbital.

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Carbocation Stability
Stabilized by alkyl substituents in three ways:
1. Inductive effect: Donating of electron density along the sigma
bonds.

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2b. Resonance: Unsaturated
carbocations are also stabilized by
resonance stabilization. If a pi
bond is adjacent to a carbocation,
the filled p orbitals of the bond
will overlap with the empty p
orbital of the carbocation.
2a. Hyper conjugation: Overlap of sigma
bonding orbitals with empty p orbital.

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Free Radicals
 Carbon is sp2 hybridized with one electron in the p orbital.

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Stability of Carbon Free Radicals
1. Inductive effect:
 Stabilized by alkyl substituents, more highly substituted radicals
are more stable.

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2. Resonance: Unsaturated radicals are also stabilized by
resonance stabilization. Overlap with the p orbitals of a π bond allows
The odd electron to be delocalized over two carbon atoms.

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Carbanions
 Eight electrons on carbon: six bonding plus one lone pair.
 Carbon has a negative charge.
 Carbanions are nucleophilic and basic.

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A carbene has both a lone pair of electrons and an empty p orbital, so
it can react as a nucleophile or as an electrophile.
Carbenes

1. Petroleum or (crude oil):
The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and
aromatic hydrocarbons while the other organic compounds contain
nitrogen, oxygen and sulfur, and trace amounts of metals such as iron,
nickel, copper and vanadium.
Sources of Alkanes
2. Natural gas: is a gaseous mixture of hydrocarbons recovered from
natural sources. It is mostly about 70% methan (CH4, b.p. = -162
o
C)
with 10% ethane (CH3CH3, b.p. = -88
o
C) and 15% propane (CH3CH2CH3,
b.p. = -42
o
C)
Metals source in crude oil:
1. inorganic salt (sodium, potassium,
calcium, barium, and cesium salts).
2. Organometallic compound.

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Once crude oil is extracted from the ground, it must be transported
and refined into petroleum products that have any value. Petroleum
refining processes are the chemical engineering processes and other
facilities used in petroleum refineries (also referred to as oil refineries)
to transform crude oil into useful products such as liquefied petroleum
gas (LPG), gasoline or petrol, kerosene, jet fuel, diesel oil and fuel oils.
The process of crude oil refining
1

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Refining crude petroleum into usable fuel and other
petroleum products.
Schematic of a refinery tower
Refinery tower

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 Alkanes are aliphatic hydrocarbons having C—C and C—H  bonds.
 They can be categorized as the following
A. Non-cyclic alkanes have the general molecular formula {CnH2n+2}
(where n = an integer).
B. Cycloalkanes have the general molecular formula {CnH2n}.
Alkanes

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 Methane and ethane are difficult to liquefy, so they are usually
handled as compressed gases. Upon cooling to cryogenic (very low)
temperatures, however, methane and ethane become liquids.
 Propane and butane are easily liquefied at room temperature
under modest pressure. These gases, often obtained along with
liquid petroleum, are stored in low pressure cylinders of liquefied
petroleum gas (LPG).
Physical properties of Alkane
 Alkanes are water insoluble because they are not polar.
C1 – C4 are gases
C5 – C17 are liquids
> C17 are solids

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Hybridization

The shape, structure and reactivity of carbon compounds depend on different types of
hybridization (sp3,sp2,sp). Hybridized orbitals are formed when electrons are excited from their
ground state and when mixing of orbitals take place.

Hybridization of Alkane
 Hybridization:
(1) Sp3 orbitals : Methane (Tetrahedral).
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Bond lengths are measured in picometers (pm).

Ethane:
CH3-CH3
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Tetrahedral and chirality in drugs
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Classification of non-cyclic alkanes
1. Straight chain alkanes: the alkanes in which all the carbon atoms
are attached by covalent bonds in a continuous chain are called
straight chain alkanes or normal alkanes.
2. Branched chain alkanes: the alkanes in which all the carbon atoms are
not in a continuous chain and some of them are linked to other carbon
atoms to make branches are called branched chain alkanes.

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 The molecular formulas show the correct number of each
type of atom in the molecule.
 The electron dot diagrams (Lewis structures) show the
arrangement of those atoms and all of the valence electrons.
 The structural formulas show the arrangement of the atoms
and the covalent bonds between them.
 The condensed structure does not show bonds but lists
atoms, and polyatomic groups are inside parenthesis.
 The Skeletal Structure
Molecular
Formula
Electron Dot
Diagram
Line-Bond
Structural
Formula
Condensed
Structure
Skeletal
Structure
CH2O
: O :
::
H : C : H
CH3CH2CH3

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• All C atoms in an alkane are surrounded by four groups, making
them sp3 hybridized and tetrahedral, and all bond angles are
109.5°.
Lewis Structure 3-D representation Ball- and- stick model
Note: In the 3-D drawing that each C atom has two bonds in the
plane (solid lines), one bond in front on a (wedge) and one bond
behind the plane on a (dashed line).

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 All of the alkanes containing 4 or more carbon atoms show
structural isomerism, meaning that there are two or more different
structural formula that you can draw for each molecular formula.
 Constitutional isomers: They have the same molecular formula but
differ in the connectivity; without any reference to space or
configuration and conformation.
Isomerism
There are three different ways to arrange five carbons

The IUPAC names of straight chain alkanes consists of two parts:
A prefix: Indicates the number of carbon atoms in the chain.
The suffix –ane show the compound is a saturated hydrocarbon;
alkane.
The first 4 alkanes (i.e., methane, ethane, propane and butane) have
got the special names historically, but the alkanes from pentane
onwards are named according to the latin or greek numerals to
indicate the number of carbon atoms. However, this naming system
becomes very hard to apply for numerous isomers of higher alkanes.
Alkanes - Nomenclature
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Alkyl group
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Is alkane minus one hydrogen, replace the –ane suffix with –yl.
Example: methyl group (CH3-) is CH4 minus (1 hydrogen atom), we can
also abbreviate this group as Me-

Alkyl group Structure IUPAC name Abbreviation
CH3- CH3- methyl Me-
CH3CH2- ethyl Et-
CH3CH2CH2- n-propyl n-Pr
CH3CHCH3 isopropyl or i-
propyl
i-Pr
CH3CH2CH2CH2- n-butyl n-Bu
CH3CH2CHCH3 sec-butyl s-Bu
(CH3)2CHCH2- isobutyl or i-butyl i-Bu
(CH3)3C- tert-butyl or t-butyl t-Bu
C6H5- phenyl Ph
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Some common alkyl groups.
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The names of the secondary-butyl (sec-butyl) and tertiary-butyl (tert-butyl or t-
butyl) groups are based on the degree of alkyl substitution of the carbon atom
attached to the main chain.

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Types of Alkyl group
Carbon in alkanes and other organic compounds are classified by
atoms the number of other carbons directly bonded to them.

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Classification of hydrogen atoms depending on the type of carbon
atom to which they are bonded; or same to (-OH, -Br).

Substituted Alkanes - IUPAC Nomenclature
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Prefix + Parent chain + Suffix
Prefix: What and where are the substituents?
Parent chain: the longest continuous chain containing the
principal functional group that defines the root name; other
groups attached to this chain are called substituents.
Suffix: What is the functional group?
Alkane end with suffix ane.
Alkene end with suffix ene.
Alkynes end with suffix yne.

F Cl Br I
fluoro chloro bromo iodo
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Principal Functional group: is the highest priority group
according to the order preference.
 If only a single functional group is present, it becomes the
principal functional group, and it will determine the root name.
-COOH, -SO3H, -COOR, -COCl, -CONH2, -CN, HC=O
(Aldehyde), C=O (Ketone), -OH, -SH, -NH2, >C=C, Alkyne,
Alkane, Ether, X (F, Cl, Br, I), NO2.
 If you got halogens as a branch call them as the following:-

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Prefixes ( Alkane – H = Alkyl)

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When there are two longest chains of equal length, use the chain
with the greater number of substituents as the main chain. The
following compound contains two different seven-carbon chains and
is named as a heptane. We choose the chain on the right as the main
chain because it has more substituents (in red) attached to the chain.

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The most interesting and useful aspect of organic
chemistry is the study of reactions.
 We cannot remember thousands of specific organic reactions,
but we can organize the reactions into logical groups based on
how the reactions take place and what intermediates are
involved.

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The overall reaction, with the reactants on the left and the products
on the right, is only the first step in our study of a reaction. If we truly
want to understand a reaction, we must also know the mechanism,
the step-by-step pathway from reactants to products. To know how
well the reaction goes to products, we study its thermodynamics, the
energetics of the reaction at equilibrium. The amounts of reactants
and products present at equilibrium depend on their relative
stabilities. Even though the equilibrium may favor the formation of a
product, the reaction may not take place at a useful rate. To use a
reaction in a realistic time period (and to keep the reaction from
becoming violent), we study its kinetics, the variation of reaction
rates with different conditions and concentrations of reagents.
Understanding the reaction's kinetics helps us to propose reaction
mechanisms that are consistent with the properties we observe.

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1. The mechanism is the complete, step-by-step description of
exactly which bonds break and which bonds form in what order to
give the observed products.
2. Thermodynamics is the study of the energy changes that
accompany chemical and physical transformations. It allows us to
compare the stability of reactants and products and predict which
compounds are favored by the equilibrium.
3. Kinetics is the study of reaction rates, determining which
products are formed fastest. Kinetics also helps to predict how the
rate will change if we change the reaction conditions.

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Synthesis of the alkanes
Industrial Laboratory
Large amounts (tons) Small amounts (grams)
Lowest cost Non-profit
Mixtures often okay Pure substances
Dedicated apparatus Flexible apparatus

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Methods of preparation:-
1. By Corey- House Synthesis
2. By Grignard Reagents
3. By Hydroboration of Alkenes
4. By Hydrogenation of Alkenes((>C=C<) : Sabatier and Senderen's Method
5. By Reduction of Alcohols, Aldehydes, Ketones or Fatty Acids and their Derivatives
6. By Reduction of Carbonyl Compounds
7. By the Hydrolysis of AI or Be Carbides
8. By the Reduction of Alkyl Halides
9. Decarboxylation
10. Kolbe's Electrolysis Method
11. Wurtz Reaction
Laboratory methods of synthesis

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1. Hydrogenation of alkenes and alkynes:

A. Hydrolysis of a Grignard reagent (two steps)
i) R—X + Mg  RMgX (Grignard reagent)
ii) RMgX + H2O  RH + Mg(OH)X
SB SA WA WB
2. Reduction of an alkyl halide:
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B. with an active metal and an acid.
R—X + metal/acid  RH
active metals = Sn, Zn, Fe, etc.
acid = HCl, etc. (H+)
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3. Alkylation of terminal alkynes:
C. Reduction with LiAlH4

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4. Corey–House synthesis
Is an organic reaction that involves the reaction of a organocopper
reagent, usually a lithium dialkylcuprate (R2CuLi) (Gilman reagent) with
an alkyl (pseudo) halide (R'X) to form a new alkane, as well as
organocopper species and lithium halide as by products; used to
prepare symmetrical and unsymmetrical alkane.
As a result of the reaction between methyl bromide (an alkyl halide)
and lithium metal in the environment of dry ether, methyl lithium and
lithium bromide are produced.

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5. Decarboxylation
Decarboxylation refers to the process of removal of CO2 from the
molecules having carboxylic group (-COOH) group. Saturated
monocarboxylic acid salt of sodium or potassium on dry distillation
with soda lime (NaOH+ CaO)gives alkane. The alkane formed by
decarboxylation process always contains one carbon atom less than
the original acid.

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6. Kolbes Synthesis

7. Wurtz Reaction
The intramolecular version of the reaction has also found application
in the preparation oaf strained ring compounds:
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The Wurtz Coupling is one of the oldest organic reactions, and
produces the simple dimer derived from two equivalents of alkyl
halide.

Mechanism of the Wurtz Reaction
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Side products:

Reactivity of Alkane
Alkanes are the least reactive class of organic compounds. Their low
reactivity is reflected in another term for alkanes: paraffins. The
name paraffin comes from two Latin terms, parum, meaning "too
little," and affinis, meaning "affinity." Chemists found that alkanes
do not react with strong acids or bases or with most other reagents.
They attributed this low reactivity to a lack of affinity for other
reagents, so they coined the name "paraffins."
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Alkane + H2SO4  No reaction (NR)
Alkane + NaOH  NR
Alkane + Na  NR
Alkane + KMnO4  NR
Alkane + H2, Ni  NR
Alkane + Br2  NR
Alkane + H2O  NR
Alkanes are typically non-reactive, they don’t react with acids, bases,
active metals, oxidizing agents, reducing agents, halogens, etc.)
Reactions of alkanes:
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Alkanes are the only family of organic molecules that have no
functional group. Consequently, they undergo very few reactions.
1. Combustion (oxidation).
2. Pyrolysis (cracking).
3. Halogenation (use slide).
Reactions of Alkane:-

1. Combustion
CnH2n+2 + (n) O2, flame  n CO2 + (n+1) H2O + heat
gasoline, diesel, heating oil…
2. Pyrolyis (cracking)
Combustion is a rapid oxidation that takes place at high temperatures,
converting alkanes to carbon dioxide and water. Little control over the
reaction is possible, except for moderating the temperature and
controlling the fuel/air ratio to achieve efficient burning.
Combustion

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Unfortunately, the burning of gasoline and fuel oil pollutes the air
and depletes the petroleum resources needed for lubricants and
chemical feedstocks. Solar and nuclear heat sources cause less
pollution, and they do not deplete these important natural
resources. Facilities that use these more environment-friendly heat
sources are, however, more expensive than those that rely on the
combustion of alkanes.

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The heat of combustion (∆Hcomb) is the amount of heat liberated
when one mole of material undergoes combustion at 1 atm pressure
to produce gaseous CO2 and liquid water.
Heat of Combustion
Note, the total amount of heat liberated increases with the size of
the hydrocarbon, but that doesn't make it a better fuel. On a per
weight basis, methane is a better fuel than the octane.

Alkane, 400-600 oC  smaller alkanes + alkenes + H2
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Cracking is a process for breaking down larger alkanes into smaller
alkanes by heating. The mixture of larger alkanes is heated in the
absence of oxygen at high temperatures (~500 ℃) for only a few
minutes in the presence of catalysts. By this method, alkanes of size
C12 and larger can be turned into gasoline-size alkanes (C5 to C10). ;
cracking without hydrogen gives mixtures of alkanes and alkenes.
2. Pyrolyis (Cracking and Hydrocracking)
Note: Petroleum Technologies exist to interconvert the
various hydrocarbons using catalysts.

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Since the 1920s, it has been known that highly branched alkanes
perform better in the internal combustion engine than straight-
chain alkanes. Catalytic isomerization changes straight-chain
alkanes into the more useful branched alkanes.
Isomerization

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Catalytic Reforming Alkanes are transformed into cycloalkanes and
aromatic hydrocarbons by catalytic reforming.
The aromatic hydrocarbons produced by catalytic reforming are used
as additives in gasoline and as starting materials for the
petrochemical industry. Production of these aromatics is in the
billions of pounds per year in the United States.
Catalytic Reforming

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3. Halogenation of alkanes:
Alkanes are notoriously unreactive compounds because they are non-
polar and lack functional groups at which reactions can take place.
Free radical halogenation therefore provides a method by which
alkanes can be functionalized.
Alkanes undergo halogenation by treating with bromine or chlorine
solution in the presence of heat or UV light. In this reaction, one or
more hydrogens in the alkane is replaced by a halogen; as a result, the
corresponding haloalkane is generated.

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Fluorination reactions generally proceed too quickly to be useful. This
reaction is explosive even in the cold and dark, and you tend to get
carbon and hydrogen fluoride produced.
CH4+2F2→C+4HF
Iodination reactions go too slowly, but oxidizing agents like HNO3 and
HIO3 are used in the iodination because the reaction is reversible in
nature, we use oxidizing agents like HNO3 or HIO3 to destroy HI. These
oxidizing agents further oxidize HI to I2and make the reaction
irreversible.

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Halogenations usually result in the formation of a mixture of
products rather than a single product. Because number of similar C-H
bonds, so selective reactions are difficult to achieve.
Methane and chlorine when heated to a high temperature in the
presence of light react as follows.
By controlling the reaction conditions and the ratio of chlorine to
methane. It is possible to favour formation of one or another of the
possible chlorinated methane products.

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The mechanism for this reaction takes place in three steps.
1. Initiation Step:
The Cl-Cl bond of elemental chlorine undergoes homolysis when
irradiated with UV light, and this process yields two chlorine atoms,
also called chlorine radicals.

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2. Propagation Step:
A chlorine radical abstracts a hydrogen atom from methane to produce
the methyl radical. The methyl radical in turn abstracts a chlorine
atom from a chlorine molecule and chloromethane is formed. The
second step of propagation also regenerates a chlorine atom. These
steps repeat many times until termination occurs.

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3. Termination Step:
Termination takes place when a chlorine atom reacts with another
chlorine atom to generate Cl2, or chlorine atom can react with a
methyl radical to form chloromethane which constitutes a minor
pathway by which the product is made. Two methyl radicals can also
combine to produce ethane, a very minor by product of this reaction.
The reaction does not stop at this step, however because the
chlorinated methane product can react with additional chlorine to
produce polychlorinated products.

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A. Initiating step:
1)Cl—Cl  2 Cl•
B. Propagating steps:
2) Cl• + CH3—H  H—Cl + CH3•
3) CH3• + Cl—Cl  CH3—Cl + Cl•
Then, 2), 3), 2), 3)…
C. Terminating steps:
4) 2 Cl•  Cl—Cl
5) CH3• + Cl•  CH3—Cl
6) 2 CH3•  CH3—CH3
In Summary. General mechanism for the chlorination of
methane involves three steps:

CH3CH3 + Cl2, hv  CH3CH2-Cl + HCl
ethane ethyl chloride
CH3CH2CH3 + Cl2, hv  CH3CH2CH2-Cl + CH3CHCH3
propane n-propyl chloride Cl
isopropyl chloride
45%
55%
CH3CH3 + Br2, hv  CH3CH2-Br + HBr
ethane ethyl bromide
CH3CH2CH3 + Br2, hv  CH3CH2CH2-Br + CH3CHCH3
propane n-propyl bromide Br
isopropyl bromide
3%
97%
Gives a mixture of both the possible alkyl halides
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A. Initiating step:
1. Cl—Cl  2 Cl•
B. Propagating steps:
1. abstraction of 1o hydrogen:
Cl• + CH3CH2CH3  CH3CH2CH2• + HCl
or abstraction of 2o hydrogen:
Cl• + CH3CH2CH3  CH3CHCH3 + HCl
•
CH3CH2CH2• + Cl2  CH3CH2CH2Cl + Cl•
or CH3CHCH3 + Cl2  CH3CHCH3 + Cl•
• Cl
Mechanism to chlorination of propane
139

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C. Terminating steps:
Science
Write the mechanism for free-radical bromination of
propane. Make sure you show all electron

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Homolytic and Heterolytic cleavages

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Definitions of primary, secondary, and tertiary hydrogens..
There are six primary hydrogens in propane and only two secondary hydrogens, yet
the major product results from replacement of a secondary hydrogen

Chlorination Energy Diagram

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Q: Tertiary hydrogen atoms react with chlorine about 5.5 times as fast
as primary ones. Predict the product ratios for chlorination of
isobutane and yield?

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Rate of Substitution in the Bromination of Propane

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Bromination Energy Diagram for the Propane

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Conformations: are different arrangements of atoms that are
interconverted by rotation about single bonds.
Conformations
Rotation occurs here

Conformations of non-cyclic Alkanes
1. Sawhorse projections
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151
• The staggered and eclipsed conformations of ethane interconvert at room
temperature, but each conformer is not equally stable.
• The staggered conformations are more stable (lower in energy) than the
eclipsed conformations.
• Electron-electron repulsion between bonds in the eclipsed conformation
increases its energy compared with the staggered conformation, where
the bonding electrons are farther apart.
These C-H bonds are farther apart, in the
following staggered conformation of ethane
These C-H bonds are closer together, in the
following eclipsed conformation of ethane
Side view
Less stable
Side view
More stable
Dihedral angle: is the angle that separates a bond on one atom from a
bond on an adjacent atom.
Torsional energy: is the energy difference between staggered and
eclipsed conformers.
Torsional strain: it is resistance to rotation.

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A Newman projection, useful in alkane stereochemistry to visualizes
chemical conformations of a carbon-carbon chemical bond from front
to back, with the front carbon represented by a dot and the back
carbon as a circle (see below).
2. Newman projection

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How to draw Newman projection

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Correct
Incorrect

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Newman projection of ethane

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Ethane Conformational Analysis

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Newman projection for Propane C1-C2

Proane Conformational Analysis

• Highest energy has methyl groups eclipsed.
• Steric hindrance
• Dihedral angle = 0 degrees
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=>
totally eclipsed
(1) Butane Conformers C2-C3

• Gauche, staggered conformer
• Methyls closer than in anti conformer
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=>
gauche
(2) Butane Conformers C2-C3

• Methyl groups eclipsed with hydrogens
• Higher energy than staggered conformer
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eclipsed
(3) Butane 3 Conformers C2-C3

• Lowest energy has methyl groups anti.
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anti
(4)Butane Conformers C2-C3

Butane C2-C3
Newman Conformational Analysis
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Cycloalkanes are named by using similar rules of the
alkane, but the prefix cyclo immediately precedes the
name of the parent.
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B. Cycloalkanes have the general molecular formula {CnH2n}.
Prefix Parent Suffix

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2. If there is an alkyl straight chain that has a greater number of
carbons than the cycloalkane, then the alkyl chain must be used as
the primary parent chain. Cycloalkane acting as a substituent to an
alkyl chain has an ending "-yl" and, therefore, must be named as a
cycloalkyl.
1. Find the parent cycloalkane.

3. Name and number the substituents. No number is needed to
indicate the location of a single substituent.
4. For rings with more than one substituent, begin numbering at one
substituent and proceed around the ring to give the second
substituent the lowest number.
5. With two different substituents, number the ring to assign the
lower number to the substituents alphabetically.
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6. If the substituents of the cycloalkane are related by the cis or
trans configuration, then indicate the configuration by placing "cis-"
or "trans-" in front of the name of the structure.

7. Alcohol Substituents on Cycloalkanes
Alcohol (-OH) substituents take the highest priority for carbon atom numbering in
IUPAC nomenclature. The carbon atom with the alcohol substituent must be labeled
as 1. Molecules containing an alcohol group have an ending "-ol", indicating the
presence of an alcohol group. If there are two alcohol groups, the molecule will have
a "di-" prefix before "-ol" (diol). If there are three alcohol groups, the molecule will
have a "tri-" prefix before "-ol" (triol), etc.

Some organic compounds are identified using common names that
do not follow the IUPAC system of nomenclature. Many of these
names were given long ago before the IUPAC system was adopted,
and are still widely used. Additionally, some names are descriptive of
shape and structure, like those below:
Common Names

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Physical Properties of Cycloalkanes
1. Cyclopropane and cyclo butane are gases, next three members are
liquid and higher members are solid.
2. These are insoluble in water but soluble in alcohol or acetone.
3. Their density increases with increase in molecular weight. Lower
members are lighter than water and floats over it; therefore
cyclohexane floats over water.
4. The boiling points increase with increase in molecular weight. The
boiling point are also higher than their corresponding alkenes and
alkanes.

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Preparation of Cycloalkanes
(a) From dihalogen compounds: α-γ elimination from dihalides having
halogen atoms on two ends of carbon chain (α-γ dihalides) with Na or
Zn dust gives rise to the formation of cycloalkanes.

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(b) Clemmensen Reduction: The reduction of cyclic ketones by Zn-
Hg/HCI gives cycloalkanes.
Mechanism of the Clemmensen Reduction

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(c) From alkenes:
Simmons-smith reaction: Alkenes on treating with CH2I2 in presence of
Cu-Zn or by carbene insertion to diazomethane (CH2N2) in presence of U.V. light gives
derivatives of cycloalkanes.
Mechanism of the Simmons-Smith Reaction
Ultrasonication improves the rate of formation of these organozinc compounds, as
with many organometallic reactions occurring at a surface.

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 Cycloalkanes are similar to alkanes in their general physical
properties, but they have higher boiling points, melting points,
and densities than alkanes. This is due to stronger London
forces because the ring shape allows for a larger area of contact.
Containing only C–C and C–H bonds.
 Cycloalkanes are very similar to the alkanes in reactivity, except for
the very small ones, especially cyclopropane. It is significantly
more reactive than what is expected because of the bond angles
in the ring. Normally, when carbon forms four single bonds, the
bond angles are approximately 109.5°. In cyclopropane, the
bond angles are 60°.
Reactivity

179
Stabilities of Cycloalkanes; Ring Strain
Why are five-membered and six-membered rings more common than
the other sizes?
Adolf von Baeyer first attempted to explain the relative stabilities of
cyclic molecules in the late nineteenth century, and he was awarded a
Nobel Prize for this work in 1905. Baeyer reasoned that the carbon
atoms in acyclic alkanes have bond angles of 109.5°. (We now explain
this bond angle by the tetrahedral geometry of the sp3 hybridized
carbon atoms.)

181
Why cyclopropane bears more ring strain per methylene group than
any other cycloalkane?Two factors contribute to this large ring strain.
 First is the angle strain required to compress the bond angles from
the tetrahedral angle of 109.5° to the 60° angles of
cyclopropane. The bonding overlap of the carbon--carbon sp3
orbitals is weakened when the bond angles differ so much from
the tetrahedral angle. The sp3 orbitals cannot point directly toward
each other, and they overlap at an angle to form weaker "bent
bonds" .

Functional group = carbon-carbon double bond
sp2 hybridization => flat, 120o bond angles
σ bond & π bond => H2C=CH2
C C
H H
H H
2p
(sp2
C + 1sH)
(sp2
C + sp2
C)
overlap
p orbitals C C
H H
H H
 bond
no free rotation
H
C
H
C
H
H
trigonal planar
sp2
cis-2-butene trans-2-butene
182
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Alkenes are sometimes called olefins, a term derived from olefiant
gas, meaning "oil-forming gas." This term originated with early
experimentalists who noticed the oily appearance of alkene
derivatives.
Alkenes CnH2n “unsaturated” hydrocarbons

• Ethylene (Trigonal planar)
– C2H4
  bond
– P bond
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Ethylene
184
9/6/2023 Basic Organic Chemistry. Lecturer:
Dr.Nabaz Abdulmajeed.

185
Diagram shows several Drugs contain double bonds:

Nomenclature, alkenes:
1. The systematic (IUPAC) name of an alkene is obtained by
Choosing the parent chain = longest continuous carbon chain that
contains the C=C then change suffix ane of alkane to -ene in
alkene.
2. Prefix a location for the carbon-carbon double bond using the
principle of lower number.
186
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Basic Organic Chemistry. Lecturer:

9/6/2023 188
3. A compound with two double bonds is a diene. A triene has three
double bonds, and a tetraene has four. Numbers are used to specify
the locations of the double bonds.

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4. If a chain has more than one substituent, the substituents are
cited in alphabetical order.
5. If the same number for the alkene functional group suffix is
obtained in both directions, the correct name is the name that contains
the lowest substituent number

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Common Names Most alkenes are conveniently named
by the IUPAC system, but common names are
sometimes used for the simplest compounds

191
Alkenes as Substituents:
Alkenes named as substituents are called alkenyl groups. They can be named
systematically (ethenyl, propenyl, etc.), or by common names, Common alkenyl
substituents are the vinyl, allyl, methylene, and phenyl groups.

Geometric isomers” (Cis & Trans isomer)
192
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H
C
H3C
C
Cl
CH2CH3
H
C
H3C
C
CH2CH3
Cl
(E)-3-chloro-2-pentene (Z)-3-chloro-2-pentene
CH3 > H
Cl > CH2CH3

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E2 elimination takes place by a concerted one-step reaction. A strong
base abstracts a proton on a carbon next to the one bearing a halogen.
The leaving group (halide) leaves simultaneously.
1a. Dehydrohalogenation by the E2 Mechanism
Alkene Synthesis

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Dehydrohalogenation is the elimination of a hydrogen and a
halogen from an alkyl halide to form an alkene.
Second-order elimination is a reliable synthetic reaction,
especially if the alkyl halide is a poor SN2 substrate. E2
dehydrohalogenation takes place in one step, in which a strong base
abstracts a proton from one carbon atom as the leaving group leaves
the adjacent carbon.

9/6/2023 195
A bulky base can minimize the amount of substitution. Large alkyl
groups on a bulky base hinder its approach to attack a carbon atom
(substitution), yet it can easily abstract a proton (elimination). Some of
the bulky strong bases commonly used for elimination are t-butoxide
ion, diisopropylarnine, triethylamine, and 2,6-dimethylpyridine.
Use of a Bulky Base

196
Bulky bases can also accomplish dehydrohalogenations that do not
follow the Zaitsev rule. Steric hindrance often prevents a bulky base
from abstracting the proton that leads to the most highly substituted
alkene. In these cases, it abstracts a less hindered proton, often the one
that leads to formation of the least highly substituted product, called
the Hofmann product. The following reaction gives mostly the
Zaitsev product with the relatively unhindered ethoxide ion, but mostly
the Hofmann product with the bulky t-butoxide ion.
Formation of the Hofmann Product:

9/6/2023 197
1b.Dehydrohalogenation by the E1 Mechanism
First-order dehydrohalogenation usually takes place in a good ionizing
solvent (such as an alcohol or water), without a strong nucleophile or
base to force second-order kinetics, The substrate is usually a
secondary or tertiary alkyl halide, First-order elimination requires
ionization to form a carbocation, which loses a proton to a weak base
(usually the solvent), El dehydrohalogenation is generally accompanied
by SN 1 substitution, because the nucleophilic solvent can also attack
the carbocation directly to form the substitution product.

9/6/2023 199
2. Debromination of Vicinal Dibromides
Debrornination is formally a reduction because a molecule of Br2 (an
oxidizing agent) is removed. The reaction with iodide takes place by
the E2 mechanism, with the same geometric constraints as the E2
dehydrohalogenation.

3. Dehydration of alcohols
Elimination of H-OH from an alcohol by (E1 or E2) mechanism, When
heated (50 oC) with strong acids catalysts (most commonly H2SO4,
H3PO4), alcohols typically undergo a 1,2- or β-elimination reactions to
generate an alkene and water.
200
E2 mechanism which proceeds via a transition state, (1o alcohols).

E1 mechanism which proceeds via a carbocation intermediate, that can
often undergo rearrangement, (3o alcohols).
201

Addition Reactions
A - B A
B
Important characteristics of addition reactions
 Orientation (Regioselectivity)
If the doubly bonded carbons are not equivalent which one get the A
and which gets the B.
 Stereochemistry: geometry of the addition.
Syn addition: Both A and B come in from the same side of the alkene.
Both from the top or both from the bottom.
Anti Addition: A and B come in from opposite sides (anti addition).
9/6/2023 202

Electrophilic Addition
Step 1: Pi electrons attack the electrophile.
203
C C + E
+
C
E
C +
C
E
C + + Nuc:
_
C
E
C
Nuc
 Step 2: Nucleophile attacks the carbocation.

Carbocation's Mechanism
Br
Br
Mirror objects
:Br
-
:Br
-
9/6/2023 204

9/6/2023 205
The addition of H2 occurs only in the presence of a metal catalyst
such as palladium (Pd). The metal provides a surface that binds both
the alkene and H2, and this speeds up the rate of reaction.
Hydrogenation of an alkene forms an alkane since the product has
only C-C single bonds. Reaction is heterogeneous (process is not in
solution).
1.Reduction of Alkenes: (Hydrogenation)

206
9/6/2023

Hydrogen Addition- Selectivity
 Selective for C=C. No reaction with C=O, C=N
 Polyunsaturated liquid oils become solids
 If one side is blocked, hydrogen adds to other
 STEREOSPECIFIC
207
9/6/2023

2a. Addition of Hydrogen Halides to Alkenes and Alkynes
Alkenes and alkynes undergo hydrogen halides (HX) addition. The
addition of HX to an alkene gives the corresponding alkyl halides.
However, the addition reaction of an alkyne with HX provides a
geminal dihalide. All hydrogen halides (HF, HCl, HBr, and HI) can
participate in this reaction, but of course, with different reaction
rates. Addition HX such as HBr or HCl to alkene gives an alkyl
halide. As the atomic size of X gets bigger, the H-X bond becomes
weaker due to the poor overlap of orbitals. So, the reactivity of HX
proportionally increases with increasing the atomic size of
halogen (X). The reactivity order of hydrogen halides (HX) is as
follows
9/6/2023
208
HI > HBr > HCl > HF

Addition of hydrogen halides to symmetric alkenes and
alkynes:
9/6/2023
209

Addition of Hydrogen Halides to asymmetric Alkenes
Protonation of double bond yields the most stable carbocation.
Positive charge goes to the carbon that was not protonated.
210
X
+ Br
_
+
+
CH3 C
CH3
CH CH3
H
CH3 C
CH3
CH CH3
H
H Br
CH3 C
CH3
CH CH3
9/6/2023
CH3 C
CH3
CH CH3
H
+
Br
_
CH3 C
CH3
CH CH3
H
Br

9/6/2023 211
There are m any examples of reactions where the proton adds to the
less substituted carbon atom of the double bond in order to produce
the more substituted carbocation. The addition of HBr (and other
hydrogen halides) is said to be regioselective because in each case,
one of the two possible orientations of addition results preferentially
over the other. Markovnikov's Rule a Russian chemist, Vladimir
Markovnikov, first showed the orientation of addition of HBr to
alkenes in 1869. Markovnikov stated: MARKOVN IKOV'S RULE:
The additio n of a proton acid to the double bond of an alkenere sults
in a product with the acid proton bonded to the carbon atom that
already holds the greater number of hydrogen atoms.

2b. Free-Radical Addition of HBr.
 In the presence of peroxides, HBr adds to an alkene to form the
“anti-Markovnikov” product.
 Only HBr has the right bond energy.
 HCl bond is too strong.
 HI bond tends to break heterolytically to form ions.
212
9/6/2023

Free Radical Initiation
• Peroxide O-O bond breaks easily to form
free radicals.
213
+
R O H Br R O H + Br
O O
R R +
R O O R
heat
• Hydrogen is abstracted from HBr.
Electrophile
9/6/2023

Propagation Steps
• Bromine adds to the double bond.
214
+
C
Br
C H Br
+ C
Br
C
H
Br
Electrophile
C
Br
C
C C
Br +
• Hydrogen is abstracted from HBr.
9/6/2023

 Tertiary radical is more stable, so that intermediate forms faster.
215
CH3 C
CH3
CH CH3 Br
+
CH3 C
CH3
CH CH3
Br
CH3 C
CH3
CH CH3
Br
X
9/6/2023
Propagation Steps
 Bromine adds to the double bond.

Rearrangement of Carbocations
Expected product is not the major product; rearrangement of carbon skeleton
occurred. The methyl group moved. Rearranged.
9/6/2023 216

9/6/2023 217
Some electrophilic addition reactions give products
that are clearly not the result of the addition of an
electrophile to the sp2 carbon bonded to the greater
number of hydrogens and the addition of a nucleophile
to the other sp2 carbon. For example, the addition of
HBr to 3-methyl-1-butene forms 2-bromo-3-
methylbutane (minor product) and 2-bromo-2-
methylbutane (major product)
Rearrangement of Carbocations

9/6/2023 218
2-Bromo-3-methylbutane is the product you would
expect from the addition of (H+) to the sp2 carbon
bonded to the greater number of hydrogens and Br- to
the other sp2 carbon. 2-Bromo-2-methylbutane is
an ―unexpected‖ product, even though it is the major
product of the reaction

9/6/2023 219
Because a shift of hydrogen with its pair of electrons is involved
in the rearrangement, it is called a hydride shift. More
specifically it is called a 1,2-hydride shift. A methyl group can
shift with its pair of electrons to the adjacent positively charged
carbon to form a more stable tertiary carbocation. This kind of
shift is called a 1,2-methyl shift. Carbocation rearrangements
also can occur by ring expansion, another type of 1,2-shift. In
the following example, a secondary carbocation is formed
initially:

• Markovnikov product is formed.
220
+
CH3 C
CH3
CH CH3 O
H H
H
+
+ H2O
+
H
CH3
CH
CH3
C
CH3
H2O
CH3 C
CH3
CH CH3
H
O
H H
+
H2O
CH3 C
CH3
CH CH3
H
O
H
9/6/2023
 Reverse of dehydration of alcohol.
 Use very dilute solutions of H2SO4 or H3PO4 to drive equilibrium toward
hydration.
3. Hydration of Alkenes

4. Addition of Alcohols
Alcohols react with alkenes in the same way that water does. Like
the addition of water, the addition of an alcohol requires an acid
catalyst. The product of the reaction is an ether.
221
9/6/2023

9/6/2023 222
5. Addition of Halogens to Alkenes
Alkenes upon halogenation, specifically bromination and chlorination.
The halogenation of alkenes provides vicinal halides, compounds
bearing the halogens on adjacent carbons.
However, F2 and I2 are not synthetically useful for halogenation as F2
reacts explosively with the alkene while the reaction with I2 gives an
unstable product that subsequently undergoes degradation. For
example, ethene reacts explosively with fluorine to give carbon and
hydrogen fluoride gas and the iodination of 2-butene gave unstable
2,3-diiodobutane.

 Bromine and chlorine add to alkenes to give 1,2-dihaldes, an industrially
important process
– F2 is too reactive and I2 does not add
 Cl2 reacts as Cl+ Cl-
– Br2 is similar
9/6/2023 223

Mechanism:
The halogen bond is relatively weak and polarizable. When the
electron-rich π bond approaches the halogen, it causes one of the
atoms to have a partial positive charge. It now becomes the
electrophile that is subsequently attacked by alkenes. The bromine-
bromine breaks down heterolytically, and a cyclic bromoinum ion
intermediate is generated. Finally, the nucleophilic attack of the
bromide anion at the rigid three-membered ring ultimately gives the
product.
The halogenation of alkenes is always conducted in a neutral organic
solvent such as carbon tetrachloride (CCl4) or dichloromethane
(CH2Cl2) that cannot act as a nucleophile when the cyclic halonium
ion is formed.
9/6/2023
224

Bromonium Ion Mechanism
• Electrophilic addition of bromine to give a cation is followed by cyclization
to give a bromonium ion
• This bromonium ion is a reactive electrophile and bromide ion is a good
nucleophile
• Stereospecific anti addition
225

• Br+ adds to an alkene producing a cyclic ion. (Br-Br bond is polarized by
the p electrons)
• Bromonium ion, bromine shares charge with carbon
– Gives trans addition
Mechanism of Bromine Addition
Halide ion approaches from side opposite the three-membered ring.
C
C
Br
Br
C
C
Br
Br
9/6/2023 226

Test for Unsaturation
• Add Br2 in CCl4 (dark, red-brown color) to an alkene in the
presence of light.
• The color quickly disappears as the bromine adds to the
double bond.
• “Decolorizing bromine” is the chemical test for the presence
of a double bond.
227
9/6/2023

6. Addition of Hypohalous Acids to Alkenes: Halohydrin
Formation
 This is formally the addition of HO-X to an alkene to give a 1,2-halo
alcohol, called a halohydrin
 The actual reagent is the dihalogen (Br2 or Cl2 in water in an organic
solvent)
228
9/6/2023

A halohydrin is an alcohol with a halogen on the adjacent carbon
atom. In the presence of water, halogens add to alkenes to form
halohydrins. The halogen adds to the alkene to give a halonium ion,
which is strongly electrophilic. Water acts as a nucleophile to open
the halonium ion and form the halohydrin.
229
Br2 forms bromonium ion, then water adds. Orientation toward stable C+
species. Aromatic rings do not react
Mechanism of Formation of a Bromohydrin
more + charge on the
more substituted
carbon

7. Epoxidation
• Alkene reacts with a peroxyacid to form an epoxide (also
called oxirane).
• Usual reagent is peroxybenzoic acid.
230
C
C + R C
O
O O H C
C
O
R C
O
O H
+
9/6/2023
One-step concerted reaction. Several bonds break and form
simultaneously.
O
C
O
R
H
C
C
O
O
H
O
C
O
R
C
C
+
Mechanism

8. Syn Dihydroxylation of Alkenes
 Alkene is converted to a cis-1,2-diol,
 Two reagents:
1. Cold, dilute aqueous potassium permanganate, followed by hydrolysis with base.
2. Osmium tetroxide (expensive), followed by hydrogen peroxide or NMO
C
C
Os
O O
O
O
C
C
O O
O
O
Os C
C
OH
OH
+ OsO4
H2O2
9/6/2023 231

9. Oxidative Cleavage
• Both the pi and sigma bonds break.
• C=C becomes C=O.
• Two methods:
– Warm or concentrated or acidic KMnO4.
– Ozonolysis
• Used to determine the position of a double bond in an unknown.
232
9/6/2023

Permanganate Oxidation of Alkenes
Potassium permanganate (KMnO4) can produce carboxylic
acids and carbon dioxide if H’s are present on terminal =CH2
• Permanganate is a strong oxidizing agent.
• Glycol initially formed is further oxidized.
• Disubstituted carbons become ketones.
• Monosubstituted carbons become carboxylic acids.
• Terminal =CH2 becomes CO2.
233
9/6/2023

234
C
C
CH3 CH3
H CH3 KMnO4
(warm, conc.)
C C
CH3
CH3
OH
OH
H3C
H
C
O
H3C
H
C
CH3
CH3
O
C
O
H3C
OH
+
9/6/2023

Ozonolysis
• Reaction with ozone forms an ozonide.
• Ozonides are not isolated, but are treated with a mild reducing
agent like Zn or dimethyl sulfide.
• Milder oxidation than permanganate.
• Products formed are ketones or aldehydes.
235
9/6/2023
C
C
CH3 CH3
H CH3 O3
C
H3C
H
O O
C
CH3
CH3
O
Ozonide
+
(CH3)2S
C
H3C
H
O C
CH3
CH3
O CH3 S
O
CH3
DMSO

Alkynes are hydrocarbons that contain carbon-carbon triple bonds.
Alkynes are also called acetylenes because they are derivatives of
acetylene, the simplest alkyne; with general molecular formula CnH2n-
2, for an acyclic (noncyclic) alkyne, and that for a cyclic alkyne is
CnH2n-4.
9/6/2023 236
Alkynes
The relatively weak π- bonds allow alkynes to react easily. Like
alkenes, alkynes are stabilized by electron-donating alkyl groups.
Internal alkynes, therefore, are more stable than terminal alkynes, so
alkyl groups stabilize alkenes, alkynes, carbocation's, and alkyl radicals.

• Acetylene (Linear)
– C2H2
– One -bond
– & two -bonds
237

Alkynes are not as common in nature as alkenes, but some plants do
use alkynes to protect themselves against disease or predators.
Cicutoxin is a toxic compound found in water hemlock, and capillin
protects a plant against fungal diseases.
9/6/2023 238
The alkyne functional group is not common in drugs, but parsalmide
is used as an analgesic, and ethynyl estradiol (a synthetic female
hormone) is a common ingredient in birth control pills. Dynemicin A
is an antibacterial compound that is being tested as an antitumor agent.

239
Drugs Containing Alkyne functional Group with
linear shape
Rasagiline (Azilect)
Selegiline
Treat symptoms in early Parkinson's disease (PD)

Nomenclature of Alkynes
1. The systematic name of an alkyne is obtained by replacing the ―ane
ending of the alkane name with ―yne. If the triple bond is at the end
of the chain, the alkyne is classified as a terminal alkyne. Alkynes with
triple bonds located elsewhere along the chain are called internal
alkynes. For example, 1-butyne is a terminal alkyne, whereas 2-
pentyne is an internal alkyne. The IUPAC rules you learned in alkane
and alkenes, apply to alkynes as well:
9/6/2023 240

2. When additional functional groups are present, the suffixes are
combined to produce the compound names of the:
-alkenynes (a double bond and a triple bond),
-alkynols (a triple bond and an alcohol), and so on.
-The new IUPAC system (placing the number right before the group)
helps to clarify these names. The IUPAC rules give alkenes and
alcohols higher priority than alkynes, so the numbering begins at the
end closer to these higher-priority groups.
9/6/2023
241

Common Names
9/6/2023 242
The common names of alkynes describe them as derivatives of
acetylene. Most alkynes can be named as a molecule of acetylene with
one or two alkyl substituents. This nomenclature is like the common
nomenclature for ethers, where we name the two alkyl groups bonded
to oxygen.

Many of an alkyne's chemical properties depend on whether there is an
acetylenic hydrogen (H -C=C), that is, whether the triple bond comes
at the end of a carbon chain. Such an alkyne is called a terminal alkyne
or a terminal acetylene. If the triple bond is located somewhere other
than the end of the carbon chain, the alkyne is called an internal alkyne
or an internal acetylene.
9/6/2023 243

Physical Properties
All hydrocarbons have similar physical properties. In other words,
alkenes and alkynes have physical properties similar to those of
alkanes. All are insoluble in water and all are soluble in solvents with
low polarity such as benzene and ether. They are less dense than water
and, like other homologous series, have boiling points that increase
with increasing molecular weight. Alkynes are more linear than
alkenes, and a triple bond is more polarizable than a double bond.
These two features cause alkynes to have stronger Van der Waals
interactions. As a result, an alkyne has a higher boiling point than an
alkene containing the same number of carbon atoms. Internal alkenes
have higher boiling points than terminal alkenes. Similarly, internal
alkynes have higher boiling points than terminal alkynes. Notice that
the boiling point of cis-2-butene is slightly higher than that of trans-2-
butene because the cis isomer has a small dipole moment, whereas the
dipole moment of the trans isomer is zero. 244

Boiling points of Hydrocarbons:
9/6/2023 245

Preparation of Acetylene
9/6/2023 247
coke (roasted coal)
The synthesis of acetylene from natural gas is a simple process. Natural
gas consists mostly of methane, which forms acetylene when it is
heated for a very short period of time.

Reaction of alkynes
Alkynes, like alkenes, undergo electrophilic addition reactions. The
same electrophilic reagents that add to alkenes also add to alkynes and
that again like alkenes electrophilic addition to a terminal alkyne is
regioselective: When an electrophile adds to a terminal alkyne, it adds
to the sp carbon that is bonded to the hydrogen. The addition reactions
of alkynes, however, have a feature that alkenes do not have: Because
the product of the addition of an electrophilic reagent to an alkyne is an
alkene, a second electrophilic addition reaction can occur.
9/6/2023 248

1. Addition of Hydrogen
9/6/2023 249
a. Catalytic Hydrogenation to Alkanes

b. Catalytic Hydrogenation to cis Alkenes
9/6/2023 250
Lindlar catalyst is a poisoned palladium catalyst, composed of
powdered barium sulfate coated with palladium, poisoned with
quinoline. Nickel boride ( Ni2B ) is a newer alternative to Lindlar's
catalyst that is more easily made and often gives better yields.

9/6/2023 251
c. Metal-Ammonia Reduction to trans Alkenes.

2. Addition of Halogens
9/6/2023 253
Alynes undergo halogenation in the same way as alkenes to give
dihalo alkenes, which upon further halogen addition, resulting
tetrahalides.

3. Addition of Hydrogen Halides
When a hydrogen halide adds to a terminal alkyne, the product has the
orientation predicted by Markovnikov's rule. A second molecule of HX
can add, usually with the same orientation as the first. /
9/6/2023 254

Although the addition of a hydrogen halide to an alkyne can generally
be stopped after the addition of one equivalent of hydrogen halide, a
second addition reaction will take place if excess hydrogen halide is
present. The product of the second addition reaction is a geminal
dihalide, a molecule with two halogens on the same carbon.
―Geminal‖ comes from geminus, which is Latin for ―twin.‖
9/6/2023 255

Addition of a hydrogen halide to an internal alkyne forms two geminal
dihalides because the initial addition of the proton can occur with
equal ease to either of the sp carbons.
9/6/2023 256
If, however, the same group is attached to each of the sp carbons of
the internal alkyne, only one geminal dihalide is obtained.

An alkyl peroxide has the same effect on the addition of HBr to an
alkyne that it has on the addition of HBr to an alkene, it reverses the
order of addition because the peroxide causes Br. to become the
electrophile.
9/6/2023 257

9/6/2023 258
4. Addition of Water
Alkynes also undergo the acid-catalyzed addition of water. The
product of the reaction is an enol. An enol has a carbon–carbon
double bond and an OH group bonded to one of the sp2 carbons.
(The ending ―ene‖ signifies the double bond, and ―ol‖ the OH.

9/6/2023 259
The enol immediately rearranges to a ketone. A carbon doubly bonded
to an oxygen is called a carbonyl group. A ketone and an enol differ
only in the location of a double bond and a hydrogen. Such isomers
are called tautomers. The ketone and enol are called keto–enol
tautomers. Interconversion of the tautomers is called
tautomerization. The keto and enol tautomers come to equilibrium in
solution, and the keto tautomer, because it is usually much more
stable than the enol tautomer, predominates at equilibrium.

Addition of water to an internal alkyne that has the same group
attached to each of the sp carbons forms a single ketone as a product.
But if the two groups are not identical, two ketones are formed
because the initial addition of the proton can occur to either of the sp
carbons.
9/6/2023 260

Terminal alkynes are less reactive than internal alkynes toward the
addition of water. Terminal alkynes will add water if mercuric ion is
added to the acidic mixture. The mercuric ion acts as a catalyst to
increase the rate of the addition reaction.
9/6/2023 261

Carbon forms nonpolar covalent bonds with hydrogen because carbon
and hydrogen, having similar electronegativity's, share their bonding
electrons almost equally. However, not all carbon atoms have the same
electronegativity. An sp hybridized carbon is more electronegative than
an sp2 hybridized carbon, which is more electronegative than an sp3
hybridized carbon, which is just slightly more electronegative than a
hydrogen.
9/6/2023 262
Acidity of Hydrogen`s Bonded to an sp Hybridized Carbon;
Formation of Acetylide Ions

Because the electronegativity of carbon atoms follows the order
sp > sp2> sp3, ethyne is a stronger acid than ethene, and ethene is a
stronger acid than ethane.

9/6/2023 264
We can compare the acidities of these compounds with the acidities of
hydrogens attached to other second-row elements.

The corresponding conjugate bases of these compounds have the
following relative base strengths because the stronger the acid, the
weaker is its conjugate base.
9/6/2023 265
In order to remove a proton from an acid, the base that removes the
proton must be stronger than the base that is generated as a result of
proton removal .In other words, you must start with a stronger base
than the base that will be formed. The amide ion (-NH2) can remove a
hydrogen bonded to an sp carbon of a terminal alkyne to form a
carbanion called an acetylide ion, because the amide ion is a stronger
base than the acetylide ion.

9/6/2023 266
If hydroxide ion were used to remove a hydrogen bonded to an
sp carbon, the reaction would strongly favor the reactants
because hydroxide ion is a much weaker base than the
acetylide ion that would be formed.

Alkylation of Acetylide Ions
9/6/2023 267
An acetylide ion is a strong base and a powerful
nucleophile. It can displace a halide ion from a suitable
substrate, giving a substituted acetylene.

9/6/2023 268
If this SN2 reaction is to produce a good yield, the alkyl halide must be
an excellent SN2 substrate: It must be primary, with no bulky
substituents or branches close to the reaction center. In the following
examples, acetylide ions displace primary halides to form elongated
alkynes.

9/6/2023 269
If the back-side approach is hindered, the acetylide ion may
abstract a proton, giving elimination by the E2 mechanism.
In this example, the dihalide used is a geminal dihalide, which means
that both halogens are connected to the same carbon atom.
Alternatively, alkynes can also be prepared from vicinal dihalides, in
which the two halogens are connected to adjacent carbon atoms:

Whether the starting dihalide is geminal or vicinal, the alkyne is
obtained as the result of two successive elimination reactions. The
first elimination can be readily accomplished using many different
bases, but the second elimination requires a very strong base. Sodium
amide (NaNH2), dissolved in liquid ammonia (NH3), is a suitable base
for achieving two successive elimination reactions in a single reaction
vessel. This method is used most frequently for the preparation of
terminal alkynes, because the strongly basic conditions favor
production of an alkynide ion, which serves as a driving force for the
overall process:
9/6/2023 270

Base-Catalyzed Rearrangements
9/6/2023 271
Unfortunately, the double dehydrohalogenation is limited by the
severe conditions. Under extremely basic conditions, an
acetylenic triple bond can migrate along the carbon chain by
repeated deprotonation and reprotonation.

Addition of Acetylide Ions to Carbonyl Groups
9/6/2023 272

Commercial Use of Ethyne
9/6/2023 274

Course Reading List and References:
Text Book:
1. Robert Thornton Morrison, Robert Neilson Boyd and S. K.
Bhattacharjee (2010). Organic Chemistry, 7th ed., Pearson
education: 1509 pp.
2. David R. Klein, (2017). Organic Chemistry, 3rd ed., John Wiley &
Sons: 1319 pp.
3. Leroy G. Wade Jr, Jan William Simek, (2016). Organic Chemistry,
9th ed., Pearson: 736 pp.
4. Jonathan Clayden, Nick Greeves and Stuart Warren (2012). Organic
Chemistry, 2nd ed., Oxford University Press: 1265 pp.
5. Fieser (1941). Experiments in Organic Chemistry, 2nd ed., D C
HEATH & CO: 500 pp.
Basic Organic Chemistry. Lecturer: Dr. Nabaz Abdulmajeed.
275 9/6/2023

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