


Hydrocarbons are compounds containing only
and
Also known as saturated hydrocarbons – all C-C bonds are
Can be found in straight chain form, but also have rings and branches
STRAIGHT CHAIN ALKANES



Have the general formula: CnH2n+2
Bond angle between carbon based bonds in the chain are 109.5 (
arrangement)
The physical arrangement or configuration of a straight chain alkane is a zig-zag
Table 1: Straight Chain Alkanes from Methane to Decane
# of
Carbon
atoms
Chemical
Formula
1
CH4
Schematic
formula
Structural formula
3D View
Name
Boiling
Point
(oC)
methane
-162
ethane
-89
propane
-42
butane
0
pentane
36
hexane
69
heptane
98
octane
126
H
H C
H
H
2
3
4
5
6
7
8
C2H6
C3H8
C4H10
C5H12
C6H14
C7H16
C8H18
H
H
H C
C
H
H
H
H
H
H
H C
C
C
H
H
H
H
H
H
H
H
H C
C
C
C
H
H
H
H
H
H
H
H
H
H
H C
C
C
C
C
H
H
H
H
H
H
H
H
H
H
H
H
H C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
9
C9H20
nonane
151
10
C10H22
decane
174
STRUCTURAL ISOMERS AND BRANCHES
 Some hydrocarbons contain one or more hydrocarbon branches that are attached in the
main structure of the molecule. The branch is called an alkyl group. The naming of alkyl
groups usually contain a prefix (indicating the number of carbons in the branch) followed
by the –yl suffix.
 These branches (and others) that would normally replace a hydrogen in an organic
molecule are called substituent groups
 Structural isomers are compounds that contain the same molecular formula, but have a
different structure or arrangement of atoms.
2,2-dimethylpropane
CH3C(CH3)2CH3
2-methylbutane
CH3CH2CH(CH3)CH3
pentane
CH3CH2CH2CH2CH3
Table 2: Branches of Alkyl Groups
-CH3
Methyl
-CH2CH3
Ethyl
Propyl
-CH2CH2CH3
CH3
-CH
Isopropyl
CH3
OR
CH3CHCH3
Butyl
-CH2CH2CH2CH3
CH2CH3
-CH
Sec-Butyl
CH3
OR
CH3CHCH2CH3
NAMING ALKANES
1. Find and name the longest continuous carbon chain (parent chain). It does not have to be
straight. This gives the root name.
2. Identify and name groups attached to this chain (branches).
3. Number the chain consecutively, starting at the end nearest a substituent group (branching
alkyl- group).
4. Designate the location of each substituent group by an appropriate number and name.
5. Assemble the name, listing groups in alphabetical order. The prefixes di, tri, tetra etc.,
used to designate several groups of the same kind, are not considered when alphabetizing.
Example:
DRAWING ALKANES
Example 1: 2,3-dimethylhexane
1. Identify the root and suffix of the name –hexane. Hex- tells us 6 carbons and –ane tells us
that the compound is an alkane.
2. Draw the main chain in a straight line.
3. Choose one end of the chain to be carbon #1. Find the carbon atoms where branches should
be added. There is one methyl branch on carbon #2 and another methyl branch on carbon
#3.
4. Add the appropriate number of hydrogens beside each carbon. Each carbon has a valence of
4 and can form a maximum of 4 bonds.
Example 2: 4-ethyl-3,5-dimethylnonane
Example: 3: 7-ethyl-2-methyl-4-secbutyldecane
CYCLOALKANES





These are alkanes that are closed and have no ends – they are in a cyclic shape
The simplest cycloalkane is
– it looks like an equilateral triangle
(bond angle =
)
For drawing cycloalkanes, use can use line diagrams, where the bonds between carbons, are
shown as a straight lines
Each point between the lines is a carbon atoms, but hydrogen atoms are not shown
Here are four basic shapes:
cyclopropane
cyclobutane
cyclopentane
cyclohexane
NAMING CYCLOALKANES
1. The name of the ring is preceded by the “cyclo” and the prefix that indicates the number of
carbon atoms in the ring ending in -ane, -ene, -yne
2. A multiple bond gets priority for the lowest number
3. Alkyl groups are numbered so that each must have the lowest possible position number,
alphabetically. You can count in any direction around the ring.
Examples:
CH3
CH3
Here, since only one carbon has a branch attached to the ring, this is
considered carbon #1. THIS IS 1-methylcyclobutane
This is 1,2-dimethylcyclobutane
CH3
CH3
In the case of two or more branches, each should have the lowest position
number. 1-ethyl-1,2-dimethylcyclobutane
CH3
CH2
CH3
DRAWING CYCLOALKANES
Example: 1-ethyl-2-propylcyclobutane
PROPERTIES OF ALKANES
 Elements making up alkanes: carbon and hydrogen have
 The bonds are
 These molecules tend to be
 The predominant forces between alkanes are the very weak


Alkanes have low
The
boiling points
and
the chain of an alkane, the
the melting and
REACTIONS OF ALKANES
 Generally unreactive and are used as lubricating materials and structural materials
 Alkanes and other hydrocarbons undergo complete combustion – the product being a large
amount of energy,
and
C4H10(g) + O2(g)  CO2(g) + H2O(g) + thermal energy

Smaller alkanes are very flammable, because the temperature at which they vaporize is
much lower, and therefore they are easier to ignite
ALKYL HALIDES
 Named by writing the root of the halogen name first followed by the –o suffix
 When halogens are added to hydrocarbons they make the molecule more polar because of
their
 The polarity of the molecule increases the number of
 The melting points and boiling points of alkyl halides are
than
alkanes of similar structure
 Methane-like molecules with chlorine and fluorine are called
are damaging to the ozone layer, but have been used as collant fluids in fridges and air
conditioners
Alkyl halides are formed from substitution reactions
CH4 + Cl2  CH3Cl + HCl
CH3Cl + Cl2  CH2Cl2 + HCl
CH2Cl2 + HCl  CHCl3 + HCl
CHCl3 + HCl  CCl4 + HCl
Examples of Alkyl Halides
HOMEWORK: Read Pages 8-16 and do Practice #1-2 on Page 14 and
Questions #1-9 on Page 17 (Also Explain Fractional Distillation)