naming organic chemicals

B11CC3B17CA

A comprehensive set of nomenclature rules has been devised by the International Union of Pure and

Applied Chemistry (IUPAC). This sheet explains basic chemical nomenclature.

Naming Alkanes

Straight chain alkanes are named with a stem to indicate the number of carbons in the chain followed

by the ending -ane.

For branched alkanes choose the longest chain as the parent chain for the name and include the side

chains as substituent prefixes: methyl-, ethyl-, propyl-, butyl- etc.

Use numbers (locants) to indicate the position of the side chains. Always start numbering from the

end of the parent chain that will give the lowest locant to the substituent. So the example above is 4-

methyloctane NOT 5-methyloctane.

For multibranched alkanes introduce all the side chains as prefixes in alphabetical order. When

more than one of the same substituent is present use multipliers (di-, tri- tetra- etc) to indicate the

number of these present:

CH4

CH3CH3

CH3CH2CH3

CH3CH2CH2CH3

CH3CH2CH2CH2CH3

CH3CH2CH2CH2CH2CH3

CH3CH2CH2CH2CH2CH2CH3

CH3CH2CH2CH2CH2CH2CH2CH3

CH3CH2CH2CH2CH2CH2CH2CH2CH3

CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

methane

ethane

propane

butane

pentane

hexane

heptane

octane

nonane

decane

CH3CH2CH2CHCH3

4-methyloctaneCH2CH2CH2CH31

4

85

CH3CHCHCH2CCH3

3-ethyl-2,5-dimethyl-5-propylnonane

1

9

CH3 e m p alphabetical order

hyphens to separate locants from name

NO spaces between locants & hyphensNO spaces between locants & namesNO spaces between locants & commas

CH2CH2CH3

CH2CH2CH2CH3CH3CH2

Naming Organic Chemicals

Principles of Chemistry • B17CA! 1

B17CA

Naming Alkenes

Alkenes are named in the same way that alkanes are named except that you use -ene as the stem

ending.

The parent chain for the name is the longest chain containing the alkene group.

Use a locant to indicate the position of the alkene and number from the end of the chain that gives

the lowest value to this locant.

Notice that the locant indicating the position of the double bond is located BEFORE the ending

‘-ene’. So the name of the above alkene is 5-methyloct-2-ene.

Naming Alkyl Halides

Alkyl halides are named using prefixes (fluoro-, chloro-, bromo-, iodo-) to indicate the presence of

halogen atoms. Use locants as usual to designate the position of the halogen atom in the molecule.

As before, number the main carbon chain from the end that gives the lowest locant numbers to the

attached groups!

stem ending -ene

4-methyloctane

5-methyloct-2-ene

ALKANE

ALKENE

locant indicates position of double bond

CH3CH2CH2CHCH3

CH2CH2CH2CH31

4

85

CH3CH2CH2CHCH3

CH2CH CHCH38

5

85 23

CH3CHCH2CH2CH3

Br

2-bromopentane not 4-bromopentane

CH3CH2CH2CCH3 2-chloro-2-methylpentane

Cl

CH3

not 4-chloro-4-methylpentane

CH3CH2CH2CH2CH2CHCH2 1,2-dibromoheptane not 6,7-dibromoheptane

Br Br



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Naming Alcohols

Alcohols are named using a suffix -ol to indicate the presence of the functional group. Choose the

longest chain containing the functional group and number the chain from the end that gives the low-

est locant to the carbon attached to the OH group.

Naming Aldehydes and Ketones

Ketones and aldehydes are molecules that contain a C=O group. They are named respectively using

-one and -al suffixes. Note that an aldehyde group is always at the end of a carbon chain so no locant

is necessary because it will always be in position-1. Ketones require a locant to indicate where the

C=O group is located in the carbon chain.

CH3CH2OH ethanol

CH3CH2CH2

OH

CH3CHCH3

OH

propan-1-ol propan-2-ol

Suffix -ol added to hydrocarbon chain indicates alcohol group.

Locant indicates position of OH group. Locant should be BEFORE the ending -ol.

CH3CCH3

OH

2-methylpropan-2-ol Substituents are named as normal with prefixes e.g. 2-methyl

CH3

Remove e from stem ending -ane because suffix begins with vowel.So name is ethanol NOT ethaneol

CH3CHCH2CHCHCH3

CH3 OH OH

5-methylhexane-2,3-diol

When 2 alcohol groups are present the compound is named as a -diol like this.

CH3CH2CH2CH2CH

O

pentanal

No locant necessary for the aldehyde group as it's ALWAYS at the end of the chain. Notice that the name is

based on pentane for a chain of 5 carbons; this includes the carbon which is part of the aldehyde functional group.

C

O

R R C

O

R H

KETONE ALDEHYDE

Note you will often see the aldehyde functional group

written as CHO without explicitly showing the C=O;

pentanal would be written: CH3CH2CH2CH2CHO



B17CA

Other substituents go into the name as prefixes. It’s the position of the aldehyde or ketone group that

controls which end of the chain you number from.

Naming Alkenes Containing Functional Groups

When no alcohol, aldehyde or ketone is present, it’s the position of the alkene that controls which end

of the chain you number from:

When an alcohol, aldehyde or ketone is present, it’s the position of the functional group NOT the al-

kene that controls which end of the chain you number from:

In the above example the name is based on pentene (the longest carbon chain). Take off the end ‘e’

and add ‘-2-ol’ for the alcohol (numbering from the end of the chain that gives the lowest number for

the OH position): penten-2-ol. Add the number ‘-4-’ to indicate the location of the alkene double bond:

pent-4-en-2-ol. Finally add in the extra methyl branch at the front of the name: 2-methylpent-4-en-2-ol.

Ketones require a locant to indicate where the C=O group is located in the chain. Place the locant BEFORE the -one.

CH3CH2CH2CCH3 pentan-2-one

O

CH3CH2CCH2CH3 pentan-3-one

O

CH3CHCH2CCH3

OCl

4-chloropentan-2-one CH3CH2CHCCH3 3-methylpentan-2-one

CH3

O

CH3CH2CHCH2CH

O

Br

3-bromopentanal

CH2=CHCH2CCH3 4-chloro-4-methylpent-1-ene

Cl

CH3

position-1

indicates position of double bond

CH2=CHCH2CCH3

OH

CH3

2-methylpent-4-en-2-ol

indicates position of alcohol functional group

position-4



naming organic chemicals

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