1. Hydrocarbons
Objectives
Describe the bonding in hydrocarbons.
Distinguish between straight-chain alkane
and branched-chain alkane.
2. Organic Chemistry
• Includes the Chemistry of • Carbon compounds number
virtually all carbon more than a million, with
compounds, regardless of many valuable properties:
their origin.
• One main reason is carbon´s
• Before scientists believed unique bonding ability.
that organic compounds
could only be sinthesized by • The simplest of the organic
organisms, but Friedrich compounds are the
Wöhler(1800-1882) refuted Hydrocarbons .
that theory in 1828.
3. Basic Principle of Carbon Bonding:
• Carbon has four (4)
valence
electrons, therefore will
always form four
covalent carbon-
hydrogen bonds.
Note:
Remembering this will
help you complete and
correct structures for
organic molecules.
4. Types of Formulas:
• Structural Formulas:
Convenient to write.
Two-dimensional
representations of
three-dimensional
molecules
6. Carbon has the ability to make stable
carbon-carbon bonds and to form
chains. This is the main reason for
the numerous carbon compounds.
Carbon + Hydrogen→ Methane
C + H2 CH4
7. Straight-Chain Alkanes:
• Contain any number of carbon atoms, one after the
other, in a chain
• They always end in –ane
• To draw the structural formula for a straight-chain
alkane, write the symbol for carbon as many times as
necessary to get the proper chain length.
• Then, fill in with hydrogens and lines representing
covalent bonds.
– Each covalent bond is equivalent to two electrons.
9. Homologous Series:
The straight chain of alkanes are an example of
a homologous series.
A group of compounds form a homologous series if
there is a constant increase/increment of change in
molecular structure from one compound in the
series to the next.
The -CH2- group is the increment of change in
straight –chain alkanes.
As the number of carbons in the straight-chain
alkane increases, so does the boiling point and
their melting point.
10. • Molecular Formula:
• CH4 Methane
• Complete Structural
Formulas:
• Show all the atoms and
bonds in a molecule.
Complete Structural Formula
• Condensed Structural
Formulas:
• Leave out some bonds
and/or atoms from the
structural formula.
Although they do not
appear, you must
understand that these
bonds and atoms are
Condensed Structural Formula
there.
11. Nomenclature/ Naming System:
IUPAC: International Union of Pure and Applied
Chemistry.
All the names end in –ane.
The root part of an alkane´s name indicates how many carbon
atoms it contains.
Scientists also rely on a combination of systematic,
semisystematic, and common names to identify organic
compounds.
Some organic compounds are best known for their
common names.
13. Branched-Chain Alkanes
• An alkane with one or more
alkyl groups
– An alkyl group is a
hydrocarbon substituent
• Substituent: an atom or group
of atoms that can take the
place of a hydrogen atom on a
parent hydrocarbon molecule.
– An alkyl group consists on an
alkane with one hydrogen
removed.
– Sometimes referred to as
radicals.
– Change the suffix –ane from
the parent structure to -yl
14. Rules for Naming Branched-Chain Alkanes:
1. Find the longest chain of carbons in the molecule. We consider this
the parent structure.
2. Number the carbons in the main chain sequence. Start at the end that
will give the groups attached to the chain the smallest numbers.
3. Add numbers to the names of the substituent groups to identify their
positions on the chain. These numbers become prefixes to the name of
the parent alkane.
4. Use prefixes to indicate the appearance of a group more than once in
the structure. Ex. Di-, tri-, tetra-; penta-, etc.
5. List the names of the alkyl substituents in alphabetical order.
6. Use proper punctuation. Commas( ,) are used to separate numbers,
hyphens(-) are used to separate numbers and words. The entire name is
written without spaces.
16. To draw the formula when given the name:
• With an alkane name and knowledge of the
IUPAC rules, it is easy to reconstruct the
structural formula.
• Steps:
1. Find the root word(ending in –ane) in the
hydrocarbon name.
2. Number the carbons on this parent chain.
3. Identify the substituent groups. Attach the
substituents to the numbered parent chain at
the proper positions.
4. Add hydrogens as needed.
18. Other Properties of Alkanes:
-They are non-polar
-Hydrocarbons of low molar mass tend to be
gases or low-boiling liquids.
-Non-polar organic molecules are insoluble in
water.
-Rule: “Like dissolves like”
-Polar dissolves polar and non-polar dissolves
non-polar.
- Non-polar will never mix with a polar.
21. Unsaturated Hydrocarbons:
Objectives:
• Explain the difference between unsaturated
and saturated hydrocarbons.
• Differentiate between the structures of
alkenes and alkynes.
22. Alkenes
• Alkanes are said to be saturated compounds
because they contain a maximum number of
hydrogens.
• Alkenes and alkynes, on the other
hand, contain double and triple bonds
respectively.
• They are said to be unsaturated compounds
because they contain fewer number of
hydrogens in their structure.
23. IUPAC Naming System for Alkenes:
1. Find the longest chain in the molecule that
contains the double bond. This is the parent
alkene. As a base, you use the base name of
alkanes and change the suffix –ane to –ene.
2. The chain is numbered in the same way that
alkanes, except that the carbon atoms of the
double bond get the lowest possible numbers.
3. Substituents on the chain are named and
numbered in the same way they are for alkanes.
Ethene and propene are the simplest alkenes.
26. Alkynes:
• Are hydrocarbons
containing carbon-
carbon triple covalent
bonds
• They are unsaturated
compounds
• They are not plentiful in
nature
• The simplest alkynes
are:
ethyne, propyne, butyn
e
• Ethyne is commonly called
acetylene.
