CnH2n+2
Alkanes:
Methane, Ethane, and Propane
The Simplest Alkanes
Methane
Ethane
(C2H6)
Propane
bp -160°C
(CH4)
(C3H8)
bp -89°C
CH4
CH3CH3
CH3CH2CH3
bp -42°C
C4H10
Isomeric Alkanes: The Butanes
Butane
Isomer
CH3CH2CH2CH3
of butane (CH3)3CH
bp -0.4°C
bp -10.2°C
Higher Alkanes
CH3CH2CH2CH2CH3
Pentane
CH3CH2CH2CH2CH2CH3
Hexane
CH3CH2CH2CH2CH2CH2CH3
Heptane
The C5H12 Isomers
C5H12
(CH3)2CHCH2CH3
CH3CH2CH2CH2CH3
Isomer of pentane
Pentane
(CH3)4C
Neopentane
How many isomers?
The number of isomeric alkanes increases as
the number of carbons increase.
There is no simple way to predict how many
isomers there are for a particular molecular
formula.
Number of Constitutionally
Isomeric Alkanes
 CH4
 C2H6
 C3H8
 C4H10
 C5H12
 C6H14
 C7H16
1
1
1
2
3
5
9
 C8H18
 C9H20
 C10H22
 C15H32
 C20H42
 C40H82
18
35
75
4,347
366,319
62,491,178,805,831
Systematic Nomenclature

International Union of Pure and Applied
Chemistry
 IUPAC
 Committee on Organic Nomenclature
The alkanes
CH4
CH3 CH2 CH2 CH2 CH2 CH3
Methane
(CH4)
CH3 CH3
Ethane
(C2H6)
(C3H8)
CH3 CH2 CH2 CH3
Butane
(C4H10)
CH3 CH2 CH2 CH2 CH3
Pentane
(C6H14)
CH3 CH2 CH2 CH2 CH2 CH2 CH3
CH3 CH2 CH3
Propane
Hexane
(C5H12)
Heptane
(C7H16)
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH3
Octane (C8H18)
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3
Nonane (C9H20)
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3
Decane
(C10H22)
Nomenclature of the Alkanes

Alkanes always have the ending -ane.
 Side chains (substituents) are named as
alkyl groups.
Common alkyl groups
(C1 through C4)
CH3
CH3 CH2 CH2 CH2
Methyl
Butyl
CH3
Isobutyl
CH3 CH2
(2-Methylpropyl)
Ethyl
CH3 CH2 CH2
Propyl
CH3 CH
CH3
Isopropyl
(1-Methylethyl)
CH3 CH CH2
CH3
CH3 CH2 CH
CH3
CH3 C
CH3
sec-Butyl
tert-Butyl
(1-Methylpropyl)
(1,1-Dimethylethyl)
IUPAC nomenclature of alkanes






identify the longest chain -- parent
number from the end closest to first branch
Name the groups attached to the chain, using the
carbon number as the locator.
Alphabetize substituents.
Use di-, tri-, etc., for multiples of same substituent
combine number and name of substituent with
parent name, separating with hyphen
Longest Chain
The number of carbons in the longest chain
determines the base name: ethane, hexane.
 If there are two possible chains with the
same number of carbons, use the chain with
the most substituents.

H3C
CH CH2
CH3
CH3
H3C CH2
C
CH3
CH
CH2
CH2
CH3
=>
Number the Carbons
Start at the end closest to the first attached
group.
 If two substituents are equidistant, look for
the next closest group.

1
CH3
3
4
H3C CH CH CH2
2
CH2CH3
5
CH2
CH3
CH CH3
6
7
Organic nomenclature
4
3
2
1
CH3 CH2 CH CH3
CH3
2-methylbutane
Find the longest continuous
carbon chain
1
2
3
CH3 CH2 CH CH3
CH2 CH3
4
3-methylpentane
5
You must choose the longest
continuous carbon chain
4
3
2
1
CH3 CH2 CH CH2 CH2 CH3
CH2 CH2 CH3
5
6
7
4-ethylheptane
IUPAC rules
1. Find the longest straight chain = parent chain
2. Number the parent chain in the direction that gives the lowest number
to the substituents at the first point of difference.
CH2
CH3
CH2
CH2
CH2
CH3
CH CH3
Longest chain is 7 .(not 6).
This is 3-methylheptane.
3. Two or more identical groups are indicated by di, tri, tetra, etc.
2,3,6-trimethylheptane
(not 2,5,6-trimethyl heptane)
2,2,6,6,7-pentamethyloctane
(not 2,3,3,7,7-pentamethyloctane)
IUPAC rules
4. Different groups are listed in alphabetical order (di, tri, tetra, etc.
don’t count; n, sec, tert don’t count; iso does).
6-ethyl-5-isopropyl-2,2-dimethyloctane
5. If the numbering is the same in both directions, choose the
numbering to follow the alphabetical order.
5-ethyl-6-methyldecane
IUPAC rules
6. When two or more chains compete for the longest, the choice goes to
the one with the greater number of side groups.
2,4,6-trimethyl-5-propyloctane
Number from the end nearest
the first substituent
CH2 CH3
CH3 CH2 CH2 CH CH CH2 CH3
7
6
5
4
3
2
CH3
4-ethyl-3-methylheptane
1
Number from the end nearest
the first substituent
CH3
CH3 CH2 CH2 CH CH2 CH CH2 CH3
8
7
6
5
4
3
2
CH2 CH3
3-ethyl-5-methyloctane
1
Use “di-” with two substituents
CH3
CH3 CH CH CH3
1
2
3
4
CH3
2,3-dimethylbutane
Every substituent must get a number
CH3
CH3 CH2 C
CH2 CH2 CH3
1
4
2
3
5
CH3
3,3-dimethylhexane
6
Number from the end nearest
first substituent
CH3
CH3 CH2 CH CH CH2 CH2 CH2 CH2 CH CH3
10
9
8
7
6
5
4
3
CH3
2,7,8-trimethyldecane
2
CH3
1
Number from the end which has
the “first difference”
CH3
CH3 CH2 CH CH CH2 CH2 CH2 CH CH2 CH3
1
2
3
4
5
6
7
CH3
3,4,8-trimethyldecane
8
CH3
9
10
A More-Highly-Substituted
Carbon Takes Precedence
CH3
CH3
CH3 CH CH2 C
5
4
3
2
CH3
1
CH3
2,2,4-Trimethylpentane
Which end do we number from?
CH3 CH2 CH CH2 CH2 CH CH2 CH3
8
7
6
CH3
5
4
3
2
CH2 CH3
3-ethyl-6-methyloctane
1
IUPAC rules
Name the following compounds.
6-ethyl-2,2,5,7-tetramethylnonane
(not 6,7-diethyl-2,2,5-trimethyloctane.
7-tert-butyl-8-isobutyl-4-isopropyldodecane
(hyphenated words aren’t alphabetized).
OR
7-(1,1-dimethylethyl)-4-(1-methylethyl)8-(2-methylpropyl)dodecane
Good Luck!
CH3
CH3 C
CH3
CH2
CH3
CH
CH2
CH2
CH2
CH2
C
CH2
CH2
CH2
CH2
CH3
CH2
CH2
CH3
CH3
7-(1,1-Dimethylbutyl)-3-ethyl-7-methyldodecane
Branched Substituents
H3C
CH CH3
isopropyl
CH3
H3C
CH CH2
sec-butyl
CH3
H2C
CH3
CH CH3
isobutyl
CH3
H3C
C
CH3
CH2
neo-pentyl
H3C
C
CH3
tert-butyl
(t-butyl)
Halogens and other side groups





Flouro –F
Chloro –Cl
Bromo –Br
Iodo –I
Nitro –NO2
O
N
O
CH 3 CH 2 Br
Bromoethane
“Ethyl bromide”
CH3
CH3 C
Cl
CH3
2-Chloro-2-methylpropane
“tert-Butyl chloride”
CH 3 CH
Br
CH
CH 2 CH 3
CH 3
2-Bromo-3-methylpentane
Complex Substituents
If the branch has a branch, number the
carbons from the point of attachment.
 Name the branch off the branch using a
locator number.
 Parentheses are used around the complex
branch name.

1
2
3
1-methyl-3-(1,2-dimethylpropyl)cyclohexane
=>
The isopropyl group can be named
as a “complex” substituent
CH3
CH3 CH
2
1
1-methylethyl
If you can name this,
you can name almost anything!
CH3
CH3
CH3 CH CH2 CH CH2 C
1
2
3
4
CH3 CH
CH3
5
6
CH3
CH2
7
CH2 CH3
8
9
4-isopropyl-2,6,6-trimethylnonane
Now, rename the isopropyl group.
Notice the alphabetical order!
CH3
CH3
CH3 CH CH2 CH CH2 C
1
2
3
4
CH3 CH
CH3
5
6
CH3
CH2
7
CH2 CH3
8
9
2,6,6-trimethyl-4-(1-methylethyl)nonane
Naming complex substituents -this one is alphabetized under d
CH3
CH3
CH3 CH CH2 CH
4
3
2
1
1,3-dimethylbutyl
deciding on alphabetical order
for complex groups

Complex groups are alphabetized under the
first letter of the name
 (1,3-dimethylbutyl)
= d
 (1,1,2-trimethylpropyl) = t
 (1-ethyl-1,2-dimethylbutyl) = e
Naming complex substituents
CH3 CH2 CH3
CH3 C
1
CH CH2 CH3
2
3
4
2-ethyl-1,1-dimethylbutyl
This Should Be Fun
CH3
CH3 CH2 C
CH3 CH2 CH2 CH2
1
2
3
4
C
5
1
CH2 CH3
2
3
CH2 CH2 CH2 CH3
6
7
8
9
CH2 CH2 CH3
5-(1-Ethyl-1-methylpropyl)-5-propylnonane
name this two ways -- (the complex group)
CH3
CH3 C
CH2
CH3
CH
CH2
CH2
CH3
CH2
CH2
C
CH3
CH2
CH3
CH2
CH3
7-(1,1-dimethylethyl)-3-ethyl-7-methyldecane
7-tert-butyl-3-ethyl-7-methyldecane
Common Nomenclature
Pitfalls

Did not find the longest carbon chain
 Numbered chain from the wrong end
 Forgot to repeat number for each identical
substituent; forgot to use di- tri- tetra-, etc.
 Used “iso”, “sec”, or “tert” as part of a
parent name
 Confusing propyl / isopropyl, etc.
 Writing the name as more than one word
 Incorrect punctuation
degree of substitution
CH3 R
primary (1°)
R CH2 R
secondary (2°)
R
R
R
CH R
R
C
R
R
tertiary (3°)
quaternary (4°)
Degree of Substitution
CH
3
1°
CH
3
1°
CH3
CH3 CH CH2 CH CH2 C
1°
3°
2°
1°
3°
2°
CH3 CH
3°
4°
1°
CH2
2°
CH3
CH2 CH3
1°
2°
1°
Block diagram for
nomenclature
LOCANT
PREFIX
N
STEM
SUFFIX
numbers
substituents
number
-ALK(AN)-
ending
cyclic molecules
H
H
H
H
C
H
H
CH2 CH2
H
H
C
C
H
CH2 CH2
H
C
C
H
CH2 CH2
H
Cyclobutane
H
H
C
C
H
H
HH
C
H
H
H
H
C
C
C
C
C
H
CH2
Cyclopentane
C
H
CH2
CH2 CH2
H
H
H
H
CH2
C
C
Cyclopropane
H
H
H
CH2
C
C
H
H
H
CH2
H
H
CH2
CH2
CH2
CH2
CH2
Cyclohexane
Nomenclature for Cyclic Alkanes

For compounds with a single ring, add the
prefix “cyclo-” to the root name for the
alkane comprising the ring.
Nomenclature of the Substituted
Cycloalkanes





If there is only one substituent, do not use the “1”.
If there is more than one substituent, you must use all
numbers, including “1”!
Number around the ring in a direction to get from the first
substituent to the second substituent by the shorter path.
For equivalent degrees of substitution, number in a
direction that follows the alphabetical sequence.
A carbon with greater substitution has precedence in
numbering.
Br
Bromocyclopropane
CH3
CH3
1,1-Dimethylcyclohexane
CH3
CH3
CH3 CH2
4-Ethyl-1,1-dimethylcyclohexane
Two ways of naming this
CH3
CH
CH3
CH3
1-isopropyl-2-methylcyclohexane
1-methyl-2-(1-methylethyl)cyclohexane
Numbering Starts at the Most
Highly-Substituted Carbon
Cl
CH3
2
CH3
1
3
7
4
5
6
CH3
2-Chloro-1,1,6-trimethylcycloheptane
cycloalkyl groups
Cyclopropyl
Cyclopentyl
Cyclobutyl
Cyclohexyl
CH3 CH2 C
CH2 CH3
CH3
3-Cyclobutyl-3-methylpentane
CH3 CH2 CH
CH3
2-Cyclobutylbutane
sec-Butylcyclobutane
IUPAC rules
Name the following cycloalkanes. Check your answers by clicking on
the arrow.
1,1,2-trimethycyclohexane
4-cyclopentyl-2,3-dimethylhexane
1,2-dicyclopropylethane