Alkanes and Cycloalkanes chemistry.pptx

To identify and name different
types of alkanes and
cycloalkanes based on their
molecular structure and
properties.
To understand the various
methods and reactions
involved in the preparation
of alkanes and
cycloalkanes.

To emphasize the
importance of alkanes
and cycloalkanes for
specific purposes.
To analyze the different
reactions of alkanes and
cycloalkanes and their
implications in organic
chemistry.

Alkanes are organic compounds that
consist entirely of single-bonded
carbon and hydrogen atoms and lack
any other functional groups.
Alkanes have the general formula:
CnH2n+2

Alkanes are also saturated
hydrocarbons. Alkanes are the
simplest and least reactive
hydrocarbon species containing only
carbons and hydrogens.

Alkanes, the simplest hydrocarbons,
are found in all shapes and sizes and
occur widely in nature. They are the
major constituents of petroleum, a
complex mixture of compounds that
includes hydrocarbons such as
hexane and decane.

Methane (CH4) and ethane (C2H6)
are the first two members of the
alkane family. The shape of methane is
tetrahedral. Each carbon atom in
ethane is also tetrahedral, and all bond
angles are approximately 109.5°.

• Linear straight-chain alkanes
are alkanes that have all their carbon
atoms connected in a single, unbranched
chain. For example, methane, ethane,
propane, and butane are linear straight-
chain alkanes.

Methane, CH4, has a single carbon atom,
and ethane, CH3CH3, has two. All C atoms
in an alkane are sur- rounded by four
groups, the sp³ hybridized and tetrahedral,
and all bond angles are 109.5.
The three-carbon alkane CH3CH2CH3
propane, has molecular formula C3H8. Each
carbon in the three-dimensional drawing
has two bonds in the plane (solid lines), one
bond in front (on a wedge), and one bond
behind the plane (on a dashed wedge).

2. Branched alkanes
are alkanes that have one or more carbon atoms
connected to more than two other carbon atoms,
forming branches or side chains. For example, 2-
methylpropane, also known as isobutane, is a
branched alkane with a methyl group attached to
the second carbon atom of the main chain.

Butane and 2-methylpropane are isomers,
two different compounds with the same
molecular formula. They belong to one of
the two major classes of isomers called
constitutional or structural isomers.
Butane is the fuel in this lighter. Butane
molecules are present in the liquid and
gaseous states in the lighter.

3. Cycloalkanes
are alkanes that have their carbon atoms
arranged in a ring or a cycle. For example,
cyclopropane, cyclobutene , and
cyclopentane , are cycloalkanes with three,
four, and five carbon atoms in a ring,
respectively

Secretion of undecane by a cockroach
causes other members of the species
to aggregate. Undecane is a
pheromone, a chemical substance used
for communication in an animal
species, most commonly an insect
population.
Cyclohexane is one component of
the mango, the most widely
consumed fruit in the world.

Secretion of undecane by a
cockroach causes other members
of the species to aggregate.
Undecane is a pheromone, a
chemical substance used for
communication in an animal species,
most commonly an insect population.

The names of all alkanes end with -ane.
Whether or not the carbons are linked
together end-to-end in a ring (called
cyclic alkanes or cycloalkanes) or
whether they contain side chains and
branches, the name of every carbon-
hydrogen chain that lacks any double
bonds or functional groups will end with
the suffix -ane.

Alkanes with unbranched carbon chains are
simply named by the number of carbons in the
chain. The first four members of the series (in
terms of number of carbon atoms) are named
as follows:
CH4 = methane = one hydrogen-saturated
carbon
C2H6 = ethane = two hydrogen-saturated
carbons
C3H8 = propane = three hydrogen-saturated
carbons
C4H10 = butane = four hydrogen-saturated
carbons

Alkanes with five or more carbon atoms
are named by adding the suffix -ane to
the appropriate numerical multiplier,
except the terminal -a is removed from
the basic numerical term. Hence, C5H12
is called pentane, C6H14 is called
hexane, C7H16 is called heptane and so
forth.

Straight-chain alkanes are sometimes
indicated by the prefix n- (for normal) to
distinguish them from branched-chain
alkanes having the same number of carbon
atoms. Although this is not strictly
necessary, the usage is still common in
cases where there is an important
difference in properties between the
straight-chain and branched-chain
isomers: e.g. n-hexane is a neurotoxin while
its branched-chain isomers are not.

1. Find and name the longest continuous carbon chain.
2.Identify and name groups attached to this chain.
3.Number the chain consecutively, starting at the end nearest a
substituent group.
4.Designate the location of each substituent group by an
appropriate number and name.
5.Assemble the name, listing groups in alphabetical order using
the full name (e.g. cyclopropyl before isobutyl).
The prefixes di, tri, tetra etc., used to designate several groups of
the same kind, are not considered when alphabetizing.

Preparation of Alkanes
Alkanes are referred to as saturated
hydrocarbons, that is, hydrocarbons having all
carbon atoms bonded to other carbon atoms or
hydrogen atoms with sigma bonds only. As the
alkanes possess weak Van Der Waals forces, the
first four members, C1 to C4 are gases, C5 to
C17 are liquids and those containing 18 carbon
atoms or more are solids at 298 K. They are
colorless and odorless. They are prepared in
laboratories and industries through various
techniques

Preparation of Alkanes from alkyl
halides
Alkane can be produced from alkyl
halides predominantly by two ways:
• Alkanes can be prepared from
alkyl halides (except fluorides)
through reduction with zinc and
dilute hydrochloric acid.
CH3-Cl + H2 → CH4 + HCl

2.Wurtz reaction
In dry ethereal solution, on treating alkyl
halides with sodium metal, the production of
alkanes is higher. By this reaction, we can
achieve higher alkanes with an even number
of carbon atoms.
CH3-Br + 2Na + BrCH3 → CH3-CH3 + 2NaBr

Preparation of Alkanes from unsaturated
hydrocarbon
Alkane can be prepared from alkene and
alkyne through the process of hydrogenation.
In this process, dihydrogen gas is added to
alkynes and alkenes in the presence of a
catalyst. These catalysts are finely divided
and may include nickel, palladium or platinum
to form alkanes. With the help of nickel as the
catalyst, this reaction takes place at an
elevated temperature, whereas the reaction
takes place at room temperature with
platinum as the catalyst.

Complete combustion
(given sufficient oxygen)
of any hydrocarbon
produces carbon
dioxide and water.

The hydrocarbons become harder
to ignite as the molecules get
bigger. This is because the bigger
molecules don't vaporize so easily
- the reaction is much better if the
oxygen and the hydrocarbon are
well mixed as gases. .

If the liquid is not very volatile, only
those molecules on the surface can
react with the oxygen. Bigger
molecules have greater Van der Waals
attractions which makes it more
difficult for them to break away from
their neighbors and turn to a gas.
.

Provided the combustion is complete, all
the hydrocarbons will burn with a blue
flame. However, combustion tends to be
less complete as the number of carbon
atoms in the molecules rises. That means
that the bigger the hydrocarbon, the
more likely you are to get a yellow,
smoky flame.

Incomplete combustion (where there is not enough oxygen
present) can lead to the formation of carbon or carbon
monoxide. As a simple way of thinking about it, the hydrogen
in the hydrocarbon gets the first chance at the oxygen, and
the carbon gets whatever is left over!
.The presence of glowing carbon particles in a
flame turns it yellow, and black carbon is often
visible in the smoke. Carbon monoxide is
produced as a colorless poisonous gas.
.

Halogenation is the replacement of one
or more hydrogen atoms in an organic
compound by a halogen (fluorine,
chlorine, bromine or iodine). Unlike the
complex transformations of combustion,
the halogenation of an alkane appears to
be a simple substitution reaction in
which a C-H bond is broken and a new
C-X bond is formed.
The chlorination of methane, shown
below, provides a simple example of this
reaction.
CH4 + Cl2 + energy → CH3Cl + HCl

The relative amounts of the various
products depend on the proportion of
the two reactants used. In the case of
methane, a large excess of the
hydrocarbon favors formation of methyl
chloride as the chief product; whereas,
an excess of chlorine favors formation
of chloroform and carbon tetrachloride.
CH4 + Cl2 + energy → CH3Cl + CH2Cl2
+ CHCl3 + CCl4 + HCl

Alkanes with two or more carbons can be
twisted into a number of different three-
dimensional arrangements of their atoms
by rotating about one or more carbon–
carbon bonds. Any three-dimensional
arrangement of atoms that results from
rotation about a single bond is called a
conformation.

Conformation
Any three-dimensional arrangement of atoms in a molecule
that results by rotation about a single bond.
Staggered conformation
A conformation about a carbon–carbon single bond in
which the atoms on one carbon are as far apart as possible
from the atoms on the adjacent carbon.
Newman projection
A way to view a molecule by looking along acarbon–carbon
bond

Line-angle formula
An abbreviated way to draw structural formulas in
which each vertex and each line ending represents
a carbon.
Alkanes have the general molecular formula
CnH2n2. Thus, given the number of carbon atoms
in an alkane, it is easy to determine the number of
hydrogens in the molecule and also its molecular
formula.

Constitutional isomers are compounds that
have the same molecular formula, but
different structural formulas. By “different
structural formulas,” we mean that these
compounds differ in the kinds of bonds they
have (single, double, or triple) or in their
connectivity (the order of attachment
among their atoms).

For the molecular formulas CH4, C2H6, and C3H8,
only one order of attachment of atoms is possible.
For the molecular formula C4H10, two orders of
attachment of atoms are possible. In one of these,
named butane, the four carbons are bonded in a
chain; in the other, named 2-methylpropane, three
carbons are bonded in a chain, with the fourth carbon
as a branch on the middle carbon of the chain.
Butane and 2-methylpropane are constitutional
isomers; they are different compounds and have
different physical and chemical properties. Their
boiling points, for example, differ by approximately
11°C. We will discuss how to name alkanes in the next
section.

To find out whether two or more
structural formulas represent
constitutional isomers, write the molecular
formula of each and then compare them.
All compounds that have the same
molecular formula, but different structural
formulas, are constitutional isomers.

The name of every organic molecule has three parts:
• The parent name indicates the number of carbons in the longest
continuous carbon chain in the molecule.
2. The suffix indicates what functional group is present.
3. The prefix reveals the identity, location, and number of
substituents attached to the carbon chain.
Prefix + Parent + Suffix
What and where What is the longest What is the
are the substituents carbon chain functional group
.

Ideally, every organic compound should have a
name from which its structural formula can be
drawn. For this purpose, chemists have adopted
a set of rules established by an organization
called the International Union of Pure and Applied
Chemistry (IUPAC).
The IUPAC name of an alkane with an
unbranched chain of carbon atoms consists of
two parts: (1) a prefix that indicates the number
of carbon atoms in the chain and (2) the ending -
ane to show that the compound is a saturated
hydrocarbon. Table 3.2 gives the prefixes used to
show the presence of 1 to 20 carbon atoms.

In fact, they were well established even before
there were hints of the structural theory
underlying the discipline. For example, the
prefix but- appears in the name butyric acid, a
compound of four carbon atoms formed by
the air oxidation of butter fat (Latin: butyrum,
butter). Prefixes to show five or more carbons
are derived from Greek or Latin numbers.
The IUPAC name of an alkane with a branched
chain consists of a parent name that indicates
the longest chain of carbon atoms in the
compound and substituent names that
indicate the groups bonded to the parent
chain.

A substituent group derived from an alkane by
the removal of a hydrogen atom is called an
alkyl group and is commonly represented by
the symbol R-.
We name alkyl groups by dropping the -ane
from the name of the parent alkane and
adding the suffix -yl.
The prefix sec- is an abbreviation for
secondary, meaning a carbon bonded to two
other carbons. The prefix tert- is an
abbreviation for tertiary, meaning a carbon
bonded to three other carbons.

Note that when these two prefixes are
part of a name, they are always italicized. The
rules of the IUPAC system for naming alkanes
are as follows:
1. The name for an alkane with an
unbranched chain of carbon atoms consists
of a prefix showing the number of carbon
atoms in the chain and the ending -ane.
2. For branched-chain alkanes, take the
longest chain of carbon atoms as the parent
chain, and its name becomes the root name.

3. Give each substituent on the parent chain a name
and a number. The number shows the carbon atom
of the parent chain to which the substituent is
bonded. Use a hyphen to connect the number to the
name;
4. If there is one substituent, number the parent
chain from the end that gives it the lower number;
5. If there are two or more identical substituents,
number the parent chain from the end that gives the
lower number to the substituent encountered first.
The number of times the substituent occurs is
indicated by the prefix di-, tri-, tetra-, penta-, hexa-,
and so on. A comma is used to separate position
numbers;

4. If there are two or more different substituents,
list them in alphabetical order, and number the chain
from the end that gives the lower number to the
substituent encountered first. If there are different
substituents in equivalent positions on opposite
ends of the parent chain, the substituent of lower
alphabetical order is given the lower number;
5.The prefixes di-, tri-, tetra-, and so on are not
included in alphabetizing. Neither are the
hyphenated prefixes sec- and tert-. “Iso,” as in
isopropyl, is included in alphabetizing. Alphabetize
the names of the substituents first, and then insert
the prefix. In the following example, the alphabetizing
parts are ethyl and methyl, not ethyl and dimethyl.

Commercial Significance:
Alkanes are the principal constituents of gasoline and
lubricating oils. They are also widely used in organic
chemistry, although pure alkanes (such as hexanes)
are mainly employed as solvents.
Saturated Hydrocarbons:
Alkanes are the simplest and least reactive
hydrocarbons. Their lack of unsaturation (double or
triple bonds) makes them relatively uninteresting but
crucial in various applications1.

Energy Content:
The carbon-carbon and carbon-hydrogen bonds in
alkanes contain high energy. Their rapid oxidation
produces a significant amount of heat, often in the
form of fire1.
Raw Materials:
Alkanes serve as raw materials in the chemical
industry for the synthesis of various compounds.
Natural Gas:
Natural gas primarily contains methane and ethane
(both alkanes) and is used for heating, cooking, and
power utilities (gas turbines).

A hydrocarbon that contains carbon atoms
joined to form a ring is called a cyclic
hydrocarbon. When all carbons of the ring are
saturated, we call the hydrocarbon a
cycloalkane.
Cycloalkanes of ring sizes ranging from 3 to over
30 abound in nature, and, in principle, there is no
limit to ring size.

Five-membered (cyclopentane)
and six-membered
(cyclohexane) rings are
especially abundant in nature
and have received special
attention.
Cycloalkanes have molecular formula
C₂H₂, and contain carbon atoms
arranged is a ring.

To name a cycloalkane, prefix the
name of the corresponding open-
chain hydrocarbon with cyclo-, and
name each substituent on the ring. If
there is only one substituent, there is
no need to give it a number.

If there are two substituents, number
the ring by beginning with the
substituent of lower alphabetical order.
If there are three or more substituents,
number the ring so as to give them the
lowest set of numbers, and then list the
substituents in alphabetical order.

1. For a monosubstituted cycloalkane
the ring supplies the root name (table
above) and the substituent group is
named as usual. A location number is
unnecessary.
2. If the alkyl substituent is large and/or
complex, the ring may be named as a
substituent group on an alkane.

3. If two different substituents are present on
the ring, they are listed in alphabetical order,
and the first cited substituent is assigned to
carbon #1. The numbering of ring carbons
then continues in a direction (clockwise or
counter-clockwise) that affords the second
substituent the lower possible location
number.

4. If several substituents are present on the
ring, they are listed in alphabetical order.
Location numbers are assigned to the
substituents so that one of them is at carbon
#1 and the other locations have the lowest
possible numbers, counting in either a
clockwise or counter-clockwise direction.

5. The name is assembled, listing groups
in alphabetical order and giving each group
(if there are two or more) a location
number. The prefixes di, tri, tetra etc., used
to designate several groups of the same
kind, are not considered when
alphabetizing.

This can still happen in the presence of light - but
you will get substitution reactions as well. The
ring is broken because cyclopropane suffers
badly from ring strain. The bond angles in the ring
are 60° rather than the normal value of about
109.5° when the carbon makes four single bonds.
The overlap between the atomic orbitals in
forming the carbon-carbon bonds is less good
than it is normally, and there is considerable
repulsion between the bonding pairs. The system
becomes more stable if the ring is broken.

The reactions of the cycloalkanes are generally
just the same as the alkanes, with the exception
of the very small ones - particularly
cyclopropane. In the presence of UV light,
cyclopropane will undergo substitution reactions
with chlorine or bromine just like a non-cyclic
alkane. However, it also has the ability to react in
the dark. In the absence of UV light, cyclopropane
can undergo addition reactions in which the ring
is broken. For example, with bromine,
cyclopropane gives 1,3-dibromopropane.

Medical Use
Cyclopropane, a cycloalkane, is
used as an an aesthetic agent.
Cancer Treatment
Carboplatin, derived from
cyclobutene, is used to treat
cancers.

Petroleum Industry
Cycloalkanes find applications in the
petroleum industry.
Pigmentation and Fragrances
Certain classes of cycloalkanes are
used for pigmentation and in
perfume manufacturing.

Food
Cycloalkanes are important
components of food, such as fats, oils,
and waxes. For example, cyclopentane
is found in mint oil, which is used as a
flavoring agent. Cyclohexane is found
in carotene, which is a pigment that
gives carrots and other vegetables
their orange color.

Pharmaceuticals
Cycloalkanes are used as an organic
solvent in the production of drugs, such
as aspirin, ibuprofen, and
acetaminophen. Cyclopropane, a type of
cycloalkane, is used as an anaesthetic
agent in the medical field. Carboplatin,
which is derived from cyclobutane, is
used to treat cancers.

Cosmetics
Cycloalkanes are used in the
manufacture of hair products, such as
shampoos, conditioners, and styling
gels. Cycloalkanes help to moisturize,
protect, and smooth the hair.
Cycloalkanes are also used in
perfumes, as they can enhance the
fragrance and stability of the product.

Alkanes and Cycloalkanes chemistry.pptx

Alkanes and Cycloalkanes chemistry.pptx

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