IUPAC Nomenclature of
Hydrocarbons
I nternational
U nion of
P ure and
A pplied
C hemistry
Models Used to Represent
Structures
Model
Example
Empirical molecular formula
C7H16
Expanded molecular formula
CH3(CH2)5CH3
Structural formula
Condensed structural formula
Line structural formula
CH3-CH2-CH2-CH2-CH2-CH2-CH3
Naming Alkanes
• The IUPAC name of any organic compound
has three basic parts
Root- denotes number of carbon atoms in the
longest continuous chain of carbon atoms
Prefix- gives positions and names of any
branches
Suffix- indicates series to which the molecule
belongs (e.g. alkane, alkene alkyne)
Root and Side Group Names of
Alkanes
Number of
Carbon Atoms
Root Name
Prefix (Side
Group)
1
meth-
methyl-
2
eth-
ethyl-
3
prop-
propyl-
4
but-
butyl-
5
pent-
pentyl-
6
hex-
hexyl-
7
hept-
heptyl-
8
oct-
9
non-
10
dec-
The alkanes (CnH2n+2)
C
H
4
M
ethane
C
H
C
H
C
H
C
H
C
H
C
H
3
2
2
2
2
3
(C
H
4)
C
H
C
H
3
3
Ethane
(C
2H
6)
(C
3H
8)
(C
4H
10)
C
H
C
H
C
H
C
H
C
H
3
2
2
2
3
Pentane
H
eptane
(C
7H
16)
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
3
2
2
2
2
2
2
3
C
H
C
H
C
H
C
H
3
2
2
3
B
utane
(C
6H
14)
C
H
C
H
C
H
C
H
C
H
C
H
C
H
3
2
2
2
2
2
3
C
H
C
H
C
H
3
2
3
Propane
H
exane
(C
5H
12)
O
ctane
(C
8H
18)
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
3
2
2
2
2
2
2
2
3
N
onane
(C
9H
20)
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
3
2
2
2
2
2
2
2
2
3
D
ecane
(C
10H
22)
Steps for Naming Alkanes
1. Identify the root
• Identify the longest
continuous chain
• Find the root name for
the number of carbons
in the chain
2. Identify the suffix
• Longest chain has 6
carbon atoms
• Root name is hex• Compound is alkane
• Suffix is -ane
1. Identify the prefix
(name the branches)
• Identify the number of
carbon atoms in each
branch
• Determine the name of
each branch
• Number the C atoms on
the longest chain to
produce the lowest
number combinations
(or sum) for the
branches
• Two branches have one
carbon atom and 3rd branch
has 2 carbon atoms
• Methyl- and ethyl-
• Precede the name of
each branch with the
number of the carbon
atom to which it is
attached on the main
chain.
• For more than one of the
same branch use a
prefix: di = 2 ,tri = 3,
tetra = 4, penta = 5
• Separate numbers using
commas
• Separate numbers and
words using hyphens
• 3-ethyl
• 2,4-dimethyl
• Arrange branches
alphabetically (ignore
prefixes di, tri, etc…)
4. Name the compound
• Combine prefix, root,
and suffix to name the
compound
• Prefix: 3-ethyl-2,4dimethyl
• Root: hex• Suffix: -ane
• Name: 3-ethyl-2,4dimethylhexane
Finding the longest continuous chain
of carbon atoms is not always simple
all possibilites
must be examined
C-C
C-C-C-C-C-C-C-C-C
C
it won’t always be
the horizontal one
as shown here
9
try these also ……..
C-C
C-C
C- C-C-C-C-C-C-C-C
C
6
C-C-C- C-C-C-C-C-C
C
8
Name this alkane
4
3
2
1
C
H
C
H
C
H
C
H
3
2
3
C
H
3
2-methylbutane
Find the longest continuous
carbon chain
1
2
3
C
H
H
HC
H
3C
2C
3
C
H
C
H
2
3
4
3-methylpentane
5
Name the Following Compound
4
3
2
1
C
H
C
H
C
H
C
H
C
H
C
H
3 2
2 2 3
C
H
C
H
C
H
2 2 3
5
6
7
4-ethylheptane
Number from the end nearest
the first substituent
C
H
C
H
2
3
C
H
C
H
C
H
C
H
C
H
C
H
C
H
3
2
2
2
3
7
6
5
4
3
2
C
H
3
4-ethyl-3-methylheptane
1
Number from the end nearest
the first substituent
C
H
3
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
3 2 2
2
2 3
8
7
6
5
4
3
2
1
C
H
C
H
2 3
3-ethyl-5-methyloctane
Use “di-” with two substituents
CH3
CH3 CH CH CH3
1
2
3
4
CH3
2,3-dimethylbutane
Every substituent must get a
number
H
C
3
H
C
H
C
H
C
C
H
C
H
C
3
2
2
2
3
1
2
3
4
5
H
C
3
3,3-dimethylhexane
6
You need numbers, even though
it appears on the same carbon!
C
H
3
C
H
3
C
H
HC
H
H
3C
2C C
3
5
4
3
2
1
C
H
3
2,2,4-trimethylpentane
Name the following compound
C
H
3
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
3 2
2 2 2
2 3
1
2
3
4
C
H
3
5
6
7
8
9
C
H
3
3,4,8-trimethyldecane
10
Name the following compound
Dimethyl alphabetized as methyl, not dimethyl
C
H
3
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
3
2
2
2
3
1
2
3
4
C
H
3
5
6
7
8
C
H
C
H
2
3
6-ethyl-3,4-dimethyloctane
Drawing Alkanes
1. Identify the root
• Gives the number of
carbon atoms in the
main chain
1. Identify the suffix
• Indicates the type of
bond between carbon
atoms
3. Draw and number
main chain
e.g. draw
3-ethyl-3-methylpentane
root: pentsuffix: -ane
C-C-C-C-C
1 2 3 4 5
1. Identify the prefix
and draw the side
groups
2. Complete the
condensed structural
formula
Prefix: 3-ethyl-3methyl(ethyl and methyl
group on carbon 3)
Draw the structural diagram of 2methylheptane
Physical Properties of Alkanes
• Since alkanes are non-polar, they are not soluble
in water
Number of
carbon atoms
Boiling point
range(oC)
Uses
1 to 4
Below 30
(gases) Fuels to heat homes
and cook
5 to 16
30 to 275
(liquids) automotive, diesel
and jet engine fuels
16 to 22
Over 250
(heavy liquid) furnace oil
Over 18
Over 400
(Semi-solid) paraffin waxes to
make candles
Over 26
Over 500
(Solid residues) asphalts and
tars in paving
Naming Alkenes
1. Identify the root
• Identify longest chain
with a double bond.
• Assign root name
based on number of
carbons
1. Identify the suffix
• Number the main
chain by starting at
the end of the chain
nearest the double
bond.
Root: pentSuffix: -2-ene
• (indicate the number
of the carbon atom
that precedes the
double bond, only if
alkene has 4 or more
carbons)
1. Identify the prefix
• Name the side groups
on alkenes as you
would for alkanes
1. Name the compound. Root: pent• Combine the prefix, Prefix: 2,3-dimethylroot and suffix.
Suffix: -2-ene
Name:
2,3-dimethylpent-2-ene
C
H
H
2C
2
ethene
C
H
H
HC
H
3C
2C
2
but-1-ene
C
H
HC
H
3C
2
propene
C
H
HC
HC
H
3C
3
but-2-ene
CH3
C
CH CH3
CH3
2-methylbut-2-ene
H
C
3
H
H
H
H
H
H
H
C
C
C
C
C
C
C
3
2
2
3
6-methylhept-2-ene
C
H
3
C
H
H
HC
H
H
3C
2C
2C
2
C
C
H
H
H
3C
2C
2
H
C
C
H
3
trans-6-methyl-3-propyloct-2-ene
Drawing Alkenes
draw a structural formula for 2-methylbut-1-ene
• Identify the root
• Identify the suffix
• Draw and number the
main carbon chain
• Identify the prefix and
draw the branches
• Complete the
structural formula by
adding hydrogens
Root: but- (4 carbons)
Suffix: double bond between
c-1 and c-2
Prefix: methyl group on c-2
Naming Alkynes
1. Identify the root
• Identify longest chain
with a triple bond.
• Assign root name
based on number of
carbons
1. Identify the suffix
• Number the main
chain by starting at
the end of the chain
nearest the triple
bond.
Root: pentSuffix: -1-yne
• (indicate the number
of the carbon atom
that precedes the triple
bond, only if alkyne
has 4 or more carbons)
1. Identify the prefix
• Name the side groups
on alkynes as you
would for alkanes
1. Name the compound. Root: pent• Combine the prefix, Prefix: 3-methylroot and suffix.
Suffix: -1-yne
Name:3-methylpent-1yne
Drawing Alkynes
draw a structural formula for 3-ethyhex-1-yne
• Identify the root
• Identify the suffix
• Draw and number the
main chain
• Identify the prefix and
draw any side groups
• Add enough hydrogen
atoms to give each
carbon atom four
bonds.
• Root: hex- (6 carbons)
• Suffix: -1-yne (triple bond
between c1and c2
• Prefix: ethyl group on c3
H C C H
ethyne
“acetylene”
C
H
H
H
3C
2C C
but-1-yne
C
H
3C C H
propyne
C
H
H
3C C C
3
but-2-yne
ALKYNES
( -YNE )
The functional group has precedence in numbering.
CH3 C C CH2CH2CH3
Hex-2-yne
functional
group
CH3 C C CH CH3
CH3
4-methylpent-2-yne
The suffix has
precedence
over any
branches
nomenclature of halides and
nitro compounds
F
C
l
flu
o
ro
N
O
2
n
itro
c
h
lo
ro
B
r
b
ro
m
o
I
io
d
o
C
H
3
4-chloro-4-methylpent-2-yne
C
H
H
3C C C C
3
C
l
C
H
3
B
r
C
H
HC C C
HC
H
H
3C
2C
3
5-bromo-2-methylhept-3-yne
ene vs. yne: which one wins?
Number from the end closest to either the double bond
or the triple bond, whichever is closest to the end.
Compounds are named: en-yne.
8
7
6
CH3-CH2-C
5
4
3
2
1
C-CH2-CH=CH-CH3
oct-2-en-5-yne
cycloalkanes
• The names of the cycloalkanes always
contain the prefix cyclo
• Cycloalkanes have the general formula
CnH2n
Cyclic molecules
H H
C
H
C
H
2
H
C C
H
H
C
H
C
H
2
2
H
H
C
H
H
C
y
c
lo
p
ro
p
a
n
e
H H
H C C H
C
H
C
H
2
2
H C C H
C
H
C
H
2
2
H H
C
y
c
lo
b
u
ta
n
e
C
C
C C
H
H
H
H
H
H
H
H
H
C
C
C
H
C
H
2
2
C
y
c
lo
p
e
n
ta
n
e
H
C
C
C
H
H
H
H
C
H
2
C
H
C
H
2
2
C
H
2
C
H
C
H
2
2
H
H C
H
C
H
2
2
C
C
H
2
H
H
C
y
c
lo
h
e
x
a
n
e
Naming Cyclic Hydrocarbons
1. Identify the root
• Determine number of
carbon atoms in the
ring. Assign root
name
2. Identify the suffix
• Not necessary to
indicate location of
double or triple
bonds, always
between c1-c2
Root: pentSuffix: -1-yne
• (indicate the number
of the carbon atom
that precedes the triple
bond, only if alkyne
has 4 or more carbons)
Naming Cyclic Hydrocarbons
3. Identify the prefix.
• 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”!
• If there are two or more side groups, the numbering must
start with a side group and then proceed in the direction
that gives the lowest possible numbers to all the side
groups.
• If numbers are the same for two or more side groups, the
side group that comes first alphabetically is assigned as c1.
Naming Cyclic Hydrocarbons
• If the molecule is a cyclic alkene or cyclic alkyne,
the multiple bond takes highest priority. The
carbon atom on one side of the multiple bonds is
c-1 and one the other side is c-2. If there are
side groups, the numbering starts in the position
that will make the number of the carbon atoms
bonded to the side groups as small as possible.
4. Name the compound
• Combine the prefix, root, and suffix to name the
compound.
Naming Cyclic Hydrocarbons
1. Root: cyclopent
2. Suffix:-ene
3. Prefix:3,4-dimethyl
Name:
3,4-dimethylcyclopentene
CH3
CH3
1,1-dimethylcyclohexane
C
H
3
C
H
3
C
H
H
3 C
2
4-ethyl-1,1-dimethylcyclohexane
Some cycloalkanes
1,3-dimethylcyclopentane
CH3
1
2
3
CH3
CH3
CH3
Drawn
differently
but same
name.
1
=
2
3
CH3
CH3
4
3
1
2
1
CH2CH3
1-ethyl-4-methylcyclohexane
E before M
CH3CH2
3
CH3
2
3-ethyl-1,1-dimethylcyclobutane
The more substituted carbon
takes precedence even
though E comes before M.
Numbering starts at the most
highly-substituted carbon
Cl
CH3
CH3
2
1
3
7
4
6
5
CH3
2-chloro-1,1,6-trimethylcycloheptane
cycloalkyl groups
cyclopropyl
cyclopentyl
cyclobutyl
cyclohexyl
CH3 CH2 C
CH2 CH3
CH3
3-cyclobutyl-3-methylpentane
Another name of a group
o
r
o
rC
H
6
5
P
h
e
n
y
l
CH3
CH3 CH2 CH
CH
CH3
3-methyl-2-phenylpentane