I nternational U nion ofP ure andA ppliedC hemistry

IUPAC Nomenclature of Hydrocarbons

Models Used to Represent Structures

Model ExampleEmpirical molecular formula C7H16

Expanded molecular formula CH3(CH2)5CH3

Structural formula

Condensed structural formula CH3-CH2-CH2-CH2-CH2-CH2-CH3

Line structural formula

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)

Methane (CH4)

Ethane (C2H6)

Propane (C3H8)

Butane (C4H10)

Pentane (C5H12)

Hexane (C6H14)

Heptane (C7H16)

Octane (C8H18)

Nonane (C9H20)

Decane (C10H22)

CH4

CH3 CH3

CH3 CH2 CH3

CH3 CH2 CH2 CH3

CH3 CH2 CH2 CH2 CH3

CH3 CH2 CH2 CH2 CH2 CH3

CH3 CH2 CH2 CH2 CH2 CH2 CH3

CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH3

CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3

CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3

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-2,4-dimethyl

• Root: hex-• Suffix: -ane• Name: 3-ethyl-2,4-

dimethylhexane

Finding the longest continuous Finding the longest continuous chain chain of carbon atoms is not always of carbon atoms is not always simplesimple

C-C-C-C-C-C-C-C-CC-C-C-C-C-C-C-C-CC

C-C

C-C-CC-C-CC-CC-C

CC-C-C-C-C-CC- C-C-C-C-C-CC-C-C-C-C-C

C-CC-CC-C-C-

C

all possibilitesmust be examined

it won’t always bethe horizontal one as shown here

try these also ……..

99

66 88

CH3 CH2 CH CH3

CH3

Name this alkane

4 3 2 1

2-methylbutane

CH3 CH2 CH CH3

CH2 CH3

Find the longest continuouscarbon chain

1 2 3

4 5

3-methylpentane

CH3 CH2 CH CH2 CH2 CH3

CH2 CH2 CH3

Name the Following Compound

4 3 2 1

5 6 7

4-ethylheptane

CH3 CH2 CH2 CH CH CH2 CH3

CH3

CH2 CH3

Number from the end nearestthe first substituent

7 6 5 4 3 2 1

4-ethyl-3-methylheptane

CH3 CH2 CH2 CH CH2 CH CH2 CH3

CH2 CH3

CH3

Number from the end nearestthe first substituent

8 7 6 5 4 3 2 1

3-ethyl-5-methyloctane

CH3 CH CH CH3

CH3

CH3

Use “di-” with two substituents

1 2 3 4

2,3-dimethylbutane

CH3 CH2 C CH2 CH2 CH3

CH3

CH3

Every substituent must get a number

1 2 3 4 5 6

3,3-dimethylhexane

CH3 CH CH2 C CH3

CH3 CH3

CH3

You need numbers, even though it appears on the same carbon!

5 4 3 2 1

2,2,4-trimethylpentane

CH3 CH2 CH CH CH2 CH2 CH2 CH CH2 CH3

CH3

CH3

CH3

Name the following compound

1 2 3 4 5 6 7 8 9 10

3,4,8-trimethyldecane

CH3 CH2 CH CH CH2 CH CH2 CH3

CH3

CH3

CH2 CH3

Name the following compound Dimethyl alphabetized as methyl, not dimethyl

1 2 3 4 5 6 7 8

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: pent-suffix: -ane

C-C-C-C-C1 2 3 4 5

1. Identify the prefix and draw the side groups

2. Complete the condensed structural formula

Prefix: 3-ethyl-3-methyl-(ethyl and methyl group on carbon 3)

Draw the structural diagram of 2-methylheptane

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 Alkenes1. 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: pent-Suffix: -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.• Combine the prefix,

root and suffix.

Root: pent-Prefix: 2,3-dimethyl-Suffix: -2-ene

Name:2,3-dimethylpent-2-ene

CH2 CH2 CH3 CH CH2

CH3 CH2 CH CH2 CH3 CH CH CH3

ethene propene

but-1-ene but-2-ene

C CH CH3

CH3

CH3

2-methylbut-2-ene

CH3 CH CH2 CH2 CH CH CH3

CH3

6-methylhept-2-ene

C C

CH3

H

CH2

CH2

CH2CH3

CH2CHCH2

CH3

CH3

trans-6-methyl-3-propyloct-2-ene

Drawing Alkenesdraw 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-2Prefix: methyl group on c-2

Naming Alkynes1. 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: pent-Suffix: -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.• Combine the prefix,

root and suffix.

Root: pent-Prefix: 3-methyl-Suffix: -1-yne

Name:3-methylpent-1-yne

Drawing Alkynesdraw 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 CH3 C C H

CH3 CH2 C CH CH3 C C CH3

ethyne propyne

but-1-yne but-2-yne

“acetylene”

ALKYNES ( -YNE )ALKYNES ( -YNE )

C CCH3 CH2CH2CH3

CCH3 C CHCH3

CH3

Hex-2-yne

4-methylpent-2-yne

The suffix hasprecedenceover anybranches

The functional group has precedence in numbering.

functionalgroup

nomenclature of halides and nitro compounds

fluoro chloro bromo iodo

nitro

F Cl Br I

NO2

CH3 C C

CH3

Cl

C CH3

CH3 CH C

CH3

C CH CH2

Br

CH3

4-chloro-4-methylpent-2-yne

5-bromo-2-methylhept-3-yne

Number from the end closest to either the double bondor the triple bond, whichever is closest to the end.

ene vs. yne: which one wins?ene vs. yne: which one wins?

CH3-CH2-C C-CH2-CH=CH-CH3oct-2-en-5-yne

8 7 6 5 4 3 2 1

Compounds are named: en-yne.

cycloalkanes

• The names of the cycloalkanes always contain the prefix cyclo

• Cycloalkanes have the general formulaCnH2n

Cyclic molecules

Cyclopropane

Cyclobutane

Cyclopentane

Cyclohexane

CC

C

H H

H

H

H

H

CH2

CH2

CH2

C

C C

C

H

H

H

H

H

H

H

H

CH2

CH2 CH2

CH2

C

CC

C

C

H HH H

HH

HH

HHCH2

CH2

CH2CH2

CH2

C

CC

C

CC

H HH

H

H

H

HH

H

H

H

HCH2

CH2CH2

CH2

CH2

CH2

Naming Cyclic Hydrocarbons1. 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: pent-Suffix: -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 c-1.

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: cyclopent2. Suffix:-ene3. Prefix:3,4-dimethylName:3,4-dimethylcyclopentene

CH3

CH3

1,1-dimethylcyclohexane

CH3

CH3

CH2CH3

4-ethyl-1,1-dimethylcyclohexane

CH3

CH3

CH3

CH3CH3

CH2CH3

CH3

CH3

CH3CH2

1,3-dimethylcyclopentane

1-ethyl-4-methylcyclohexane3-ethyl-1,1-dimethylcyclobutane

Some cycloalkanesSome cycloalkanes

The more substituted carbontakes precedence even though E comes before M.

Drawndifferentlybut samename.=

E before M

1 23

12

3

1

2312

34

Numbering starts at the most highly-substituted carbon

Cl CH3

CH3

CH3

2 13 74 6 5

2-chloro-1,1,6-trimethylcycloheptane

cycloalkyl groups

cyclopropyl cyclobutyl

cyclopentyl cyclohexyl

C

CH3

CH2CH2CH3 CH3

3-cyclobutyl-3-methylpentane

Another name of a group

or

Phenyl

or C6H5

CH3 CH2 CH CH CH3

CH3

3-methyl-2-phenylpentane