NOTE

C H E M I S T R Y

GENERAL ORGANIC CHEMISTRY

CLASH OF THE TITANS: IUPAC NAMING IN
COMPOUNDS WITH POLYFUNCTIONAL GROUPS

What you already know

• Nomenclature of cyclic hydrocarbons • Nomenclature of organic compounds with

• Functional groups functional groups

What you will learn

• Nomenclature of organic compounds with functional groups continued

• Nomenclature of compounds with polyfunctional groups
• Determining the priority order of functional groups
• Practice questions

BOARDS MAIN
Nomenclature of Organic Compounds
with Functional Groups (Continued)

Alcohols (−OH)

The alkanes containing the -OH groups are known as alkanols, i.e., replacing ‘e’ from the name of
the alkane by -ol.
Alkane (-e) + ol = Alkanol
Here, the suffix -ol is used.
While numbering, give the lowest possible number to the functional group.
Examples:
OH

1 2 3 4 2 1
H3C CH CH2 CH3 H3C CH2 OH
Butan-2-ol Ethanol

Thiols (−SH)

Here, the suffix −thiol is used.

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Examples:
SH

1 2 3 4 2 1
H3C CH CH2 CH3 H3C CH2 SH

Butane-2-thiol Ethanethiol
If the secondary suffix is starting with a vowel, then the e in the primary suffix will be dropped.

Amines (−NH2, −NHR, −NR2)

Amines may be regarded as the derivatives of ammonia (NH3) formed by the replacement of one
or more hydrogen atoms by the corresponding number of alkyl groups. Amines are classified as
primary (1°), secondary (2°), or tertiary (3°) depending on the number of alkyl groups attached to the
nitrogen atom.
Replace one H with -R group: Primary amine
Replace two H with -R groups: Secondary amine
Replace three H with -R groups: Tertiary amine
In the IUPAC system, the primary amines are named by replacing the final ‘-e’ in the parent alkane
by -amine (alkanamine). A number is added to indicate the position of the -NH2 group.

Examples:
1 NH2
CH2
2 2
H3C NH2 CH 3
1
H3C CH3
Ethanamine Propan-2-amine

Secondary or tertiary amines are named as N-substituted derivatives of primary amines. The larg-
est group attached to nitrogen is taken as the parent chain in secondary and tertiary amine.
Examples:
1 2
CH3 CH2 CH3
NH
H3C CH3 N N 1 2 3
H3C CH3 H3C CH2 CH2 CH3

N-Methylmethanamine N,N-dimethylmethanamine N-Ethyl-N-methylpropanamine

Ethers (R−O−R΄)

For ether, the prefix ‘alkoxy’ is used.

IUPAC name: Alkoxy alkane

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΄
R−O−R : Unsymmetrical ether
R−O−R: Symmetrical ether
In an unsymmetrical ether, the alkyl group that has less number of C atoms is added in the prefix.
Examples:
O 2
O CH3
H3C CH3 1
H3C CH2

Methoxymethane Methoxyethane

IUPAC nomenclature

Which of the following compounds has the wrong IUPAC name?

O

(a) H3C CH2 CH2 C O CH2 CH3 Ethylbutanoate

(b) H3C CH CH2 C H 3-Methylbutanal

CH3

(c) H3C CH CH CH3 2-Methyl-3-butanol

OH CH3

(d) H3C CH C CH2 CH3 2-Methyl-3-pentanone

CH3 O

Solution

In option (c) the functional group -OH should get the 1 2 3 4

lowest possible number, i.e., 2. So, the IUPAC name H3C CH CH CH3
should be 3-methyl-2-butanol. Hence, it has the wrong
IUPAC name. OH CH3
Thus, option (c) is the correct answer. 3-Methyl-2-butanol.

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IUPAC nomenclature

Choose the correct IUPAC name of the following compound.

O
(a) Butan-2-aldehyde
(b) 2-Methylbutanal
H3C CH C H
(c) 3-Methyl isobutyraldehyde
(d) 2-Ethylpropanal
CH2 CH3

Solution

The parent chain must contain the functional

group and it should be the longest chain. So, the O
parent chain contains four C-atoms. The functional
2 1
group is aldehyde. The suffix for aldehydes is ‘al’. H3C CH C H
Since aldehyde is a chain-terminating group, the
numbering starts from this carbon atom.
3 CH2 CH3
Therefore, the IUPAC name of the given molecule is 4
2-Methylbutanal.
2-Methylbutanal
Thus, option (b) is the correct answer.

BOARDS MAIN
Nomenclature of Polyfunctional Compounds

Determining the parent chain: Longest chain with maximum groups

Rule 1: Select the longest possible chain with the maximum number of functional groups and
maximum number of unsaturations, even if the prior rules are violated.
Example:
6
Here, if we select the straight chain, then CH2 O
unsaturation will not be included. So, 2 1 5 4 3 2 1
the longest chain rule is violated. So, the H3C CH2 C CH2 CH2 CH2 C OH
IUPAC name is 5-Ethylhex-5-en-1-oic acid.
5-Ethylhex-5-en-1-oic acid

Rule 2: If a functional group is present in a cyclic compound, then the chain containing the principal
functional group is taken as the parent chain.

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Example 1:
OH

1 1 3
2 2
Here, the cyclic ring contains the functional 6
group -OH. So, it is the parent chain. So, the
IUPAC name is 2-Propylcyclohexan-1-ol. 5 3
4

2-Propylcyclohexan-1-ol

Example 2:
6 1 3
1 2
5
Here, the open chain contains the functional
group -OH. So, it is the parent chain. So, the OH
4 2
IUPAC name is 1-Cyclohexylpropan-2-ol.
3
1-Cyclohexylpropan-2-ol

Rule 3: If the principal functional group is present in both the ring and the alkyl chain, then the
parent chain will be the one with the maximum number of carbon atoms.

Example: OH

1
The cyclic ring contains more C-atoms. So,
it is the parent chain. So, the IUPAC name is
2-(1-Hydroxyethyl)cyclopropanol. 2 2
3 1

OH
2-(1-Hydroxyethyl)cyclopropanol

Note

In the IUPAC name, the substituent -OH is termed as hydroxy in the prefix.

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Rule 4: When a chain-terminating functional group is directly attached to the ring, the ring is taken
as the parent chain.

Examples:
O O
O

2 2
1
1 H 3 O
3

4 6 1
4 6
5 2
5

Cyclohexanecarbaldehyde Ethyl-2-oxocyclohexane-1-carboxylate

Here, for the ester group, the suffix is used, and for the ketone group, the prefix is used. So, the
IUPAC name is Ethyl-2-oxocyclohexane-1-carboxylate.

Assigning locants

Rule 1: The numbering is done from the side of the chain which gives the lowest locant to the
principal functional group (will be discussed later in this session) followed by the multiple
bonds. The numbering of the parent chain follows the order:

Principal functional group > Multiple bond > Substituents

Example:

O
Here, the principal functional group
is ester. The parent chain must 3 2 1 3 2 1
CH2 CH2 CH2 CH CH2 C O C2H5
contain the primary functional group
and the double bond. So, the IUPAC 4 5
name is Ethyl-3-(3-hydroxypropyl) OH CH CH2
pent-4-enoate.
Ethyl-3-(3-hydroxypropyl)pent-4-enoate

Rule 2: When a chain-terminating functional group such as –CHO, –COOH, –COOR, –CONH2,
–COCl, –CN, etc., is present, it is always numbered as one.
Examples:

4 3 2 4 3 2
CH3 CH2 CH CH3 CH3 CH CH CH3

1C OH CI 1C OH

O O
2-Methylbutan-1-oic acid 3-Chloro-2-methylbutan-1-oic acid

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Note

Example:
If a compound contains two or more O O
like (similar) groups, then the numerical
1 2 3 4
prefixes di, tri, tetra, etc., are used. HO C CH2 CH2 C OH
Butan-1,4-dioic acid

Rule 3: More than one chain-terminating groups

If more than one chain-terminating
groups of the same type are present, 1 2 3 4 5
NC CH CH2 CH2 CN
then the principal chain is selected 5 4 3 2 1
including the functional groups. The
numbering is done from the side of the CH3
chain which gives the lowest locant to 2-Methylpentane-1,5-dinitrile
unsaturation and substituents.
Here, the numbering can be done from both the ways, but in the case of left to right, -CH3 is getting
position 2, while from right to left, -CH3 is getting position 4. So, the numbering should be done
from left to right because of the lowest locant rule. So, the IUPAC name is 2-Methylpentane-1,5-
dinitrile.

Note

Always remember to count the C atoms of the chain-terminating groups.

Note

Example:
O
If the organic molecule contains more 2 1
HO CH2 CH2 O
than one similar complex substituents,
CH C OH
then the numeral prefixes di, tri, tetra, 2 1
HO CH2 CH2 O 2 1
etc., are replaced by bis, tris, tetrakis,
etc., respectively.
2,2-Bis(2-hydroxyethoxy)ethanoic acid

BOARDS MAIN
Organic Compound Contains Two or More Different Functional Groups

In the case of polyfunctional compounds, one of the functional groups is chosen as the principal
functional group and the compound is then named on that basis. The remaining functional groups
that are subordinate functional groups are named as substituents using the appropriate prefixes.
The choice of principal functional group is made on the basis of the order of preference. The order

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of decreasing priority for some functional groups is as follows:

Carboxylic acids > Sulphonic acid > Acid anhydride > Esters > Acid halide > Amides > Nitriles >
Isonitriles > Aldehydes > Ketones > Alcohols > Thiols > Amines > Alkenes > Alkynes

Note

-R, -C6H5, -X (F, Cl, Br, I), -NO, -NO2, -OR (alkoxy) do not have any priority order and are considered
as alkyl substituents while numbering.

Functional group
Class of compounds IUPAC group suffix IUPAC group prefix
structure
−oic acid/carboxylic
Carboxylic acids −COOH carboxy
acid

Sulphonic acids −SO3H −sulphonic acid sulpho

Acid anhydride −COOCOR −oic anhydride

alkoxycarbonyl/
Esters −COOR −oate/carboxylate
alkanoyloxy
−oyl halide/carbonyl
Acyl halides −COX halocarbonyl
halide
−CONH2, −CONHR,
Amides −amide/carboxamide carbamoyl
and −CONR2

Nitriles −CN −nitrile/carbonitrile cyano

Isonitriles −NC −isonitrile isocyano

Aldehydes −CHO −al/carbaldehyde formyl/oxo

Ketones >C=O −one oxo / keto

Alcohols −OH −ol hydroxy

Thiols −SH −thiol mercapto/sulfanyl

Amines −NH2, −NHR, −NR2 −amine amino

Alkenes >C=C< −ene −

Alkynes −C≡C− −yne −

Table 1: IUPAC group suffix and prefix for various class of compounds

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NH2
Example:
5 4 3 2 1
Alcohol is the primary functional group. CH3 CH CH CH CH3
The primary functional group should
get number 1. So, the IUPAC name is
Cl OH
4-Amino-3-chloropentan-2-ol.
4-Amino-3-chloropentan-2-ol

Note

1 2
Cl CH CH3
When two or more prefixes consist of
identical roman letters, the priority for 1
citation is given to the group that contains the 6 2
lowest locant at the first point of difference.
The IUPAC name is 1-(1-Chloroethyl)-4-(2- 5 3
chloroethyl)cyclohexane. Parent chain: 4
Cyclic ring and substituents: 1-choroethyl
and 2-chloroethyl. Here, 1-chloroethyl get CH2 CH2 Cl
priority over 2-chloroethyl. 1 2
1-(1-Chloroethyl)-4-(2-chloroethyl)cyclohexane

BOARDS MAIN
Nomenclature of Polyfunctional Compounds

Carboxylic acids (−COOH) O

Suffix: −oic acid/carboxylic acid; Prefix: carboxy
Example: C OH
The carboxylic group present at the third
position is used as a substituent and the prefix O CH2 O
‘carboxy’ is used for it. So, the IUPAC name is
3-Carboxymethylpentane-1,5-dioic acid.
HO C CH2 CH CH2 C OH
1 2 3 4 5
3-Carboxymethylpentane-1,5-dioic acid

O
Sulphonic acids (−SO3H)
O 5 3 1
Suffix: −sulphonic acid; Prefix: sulpho
4 2
Example: S OH
Here, the carboxyl group is preferred over the
sulphonic group. Therefore, the prefix ‘sulpho’ HO O
and the suffix ‘-oic acid’ are used. So, the IUPAC
name is 5-Sulphopentanoic acid. 5-Sulphopentanoic acid

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Esters (−COOR)
Suffix: −oate/carboxylate; Prefix: alkoxy carbonyl OH
Examples:

O
The prefix ‘alkoxy carbonyl’ is used when -C=O 1
O
of ester is directly attached to the parent chain. H3C 2 4
3 5
Here, the carboxylic group is the principal O
functional group. Therefore, the suffix ‘-oic
acid’ and the prefix ‘alkoxy carbonyl’ are used. 2-(Methoxycarbonyl)pentanoic acid
So, the IUPAC name is 2-(Methoxycarbonyl)
pentanoic acid.
O

C OH
Here, -COOH is not a part of the parent 1
chain. So, the suffix ‘carboxylic acid’ is used.
So, the IUPAC name is 3-(Ethoxycarbonyl) 5 2
O
cyclopentanecarboxylic acid. 3
4 C O C2H5

3-(Ethoxycarbonyl)cyclopentanecarboxylic acid

The prefix ‘alkanoyloxy’ is used when the oxygen atom of ester is directly attached to the parent
chain.
Examples:

O
5 3 1
Here, the oxygen atom of ester is directly 4 2
6 OH
attached to the parent chain. So, the prefix
‘alkanoyloxy’ is used for ester. So, the O
CH3
IUPAC name is 4-Ethanoyloxyhexanoic acid
(Ethanoyloxy: 2 C atoms in ester substituent). O

4-Ethanoyloxyhexanoic acid
O

C OH
The oxygen atom of ester is directly attached
to the parent chain. So, the prefix ‘alkanoyloxy’ 1
is used for ester. So, the IUPAC name of the 5 2
compound is 3-(Propanoyloxy)cyclopentan- O
ecarboxylic acid. 4 3
O C C2H5

3-(Propanoyloxy)cyclopentanecarboxylic acid

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Acid halides (−COX) O O

Suffix: −halide/carbonyl halide; Prefix: halocarbonyl 1
Example: 2
HO CI
Here, -COOH is the principal functional
group. So, the suffix ‘-oic acid’ and the prefix 5 3
‘halocarbonyl’ are used. So, the IUPAC name 4
is 2-(Chlorocarbonyl)pentanoic acid.
2-(Chlorocarbonyl)pentanoic acid

Amides (−CONH2, −CONHR, −CONR2)

Suffix: −amide/carboxamide; Prefix: carbamoyl
Examples:
Here, -COOH is the principal functional. So, the suffix ‘-oic acid/carboxylic acid’ and the prefix
‘carbamoyl’ are used. So, the IUPAC name is 2-Carbamoylethanoic acid.

C OH
1
6 2
O O
3

O
5
1 C
HO 4
NH2
2 NH2
2-Carbamoylethanoic acid 3-Carbamoylcyclohexanecaboxylic acid

If nitrogen is directly attached to the parent chain, then the prefix ‘alkanoyl amino’ is used.
Example: O

C OH

Here, nitrogen is directly attached to the parent 1

chain. So, the prefix ‘alkanoyl amino’ is used 5 2
for it. So, the IUPAC name for given compound O
is 3-Ethanoylaminocyclopentanecarboxylic 4 3
acid. N C CH3
1 2
H
3-Ethanoylaminocyclopentanecarboxylic acid

Cyanide ( −C≡N )
Suffix: −nitrile/carbonitrile; Prefix: cyano N O
Example: C 3 1
Here, -COOH is the principal functional. So, 4 2
OH
the suffix ‘-oic acid’ and the prefix ‘cyano’ are
5
used. So, the IUPAC name is 4-Cyanopenta-
noic acid.
4-Cyanopentanoic acid

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Isocyanide (−NC)
Suffix: −isonitrile; Prefix: isocyano O 2 C
Example: 1 3 N
H3C
Here, ester is the principal functional group.
So, the suffix ‘-oate’ and the prefix ‘-isocyano’
O 4
are used. So, the IUPAC name is Methyl-3-iso-
cyanobutanoate. Methyl-3-isocyanobutanoate

Aldehydes (−CHO)
Suffix: −al/carbaldehyde; Prefix: formyl/oxo
‘Oxo’ is used as the prefix when ‘C’ of ‘CHO’ is included in the parent chain, else ‘formyl’ is used.
Examples:

H H
2 4 4 2
HO
1 3 5 5 3 OH
6 1

O
O

O
6 O
7
6-Oxohexanoic acid 5-Formylheptanoic acid
Ketones (>C=O)
Suffix: −one; Prefix: oxo/keto O
Example: 6
Here, -COOH is the principal functional group. 3
5 1
O

So, the suffix ‘-oic acid’ and the prefix ‘-oxo’ are 4 2 OH
used. So, the IUPAC name is 5-Oxohexanoic
acid. 5-Oxohexanoic acid

O
Alcohols (−OH)
Suffix: −ol; Prefix: hydroxy
Example: 3 C
2 1
Here, amide (-CONH2) is the primary function- NH2
al group. So, the suffix ‘-amide’ and the pre-
fix ‘-hydroxy’ are used. So, the IUPAC name is OH
2-Hydroxypropanamide. 2-Hydroxypropanamide

Amines (−NH2, −NHR, −NR2) O

Suffix: −amine; Prefix: amino
Examples: NH2
1
Here, the carboxylic group is the principal func- OH 2
tional group. So, the suffix ‘-oic acid’ and the
prefix ‘-amino’ are used. So, the IUPAC name 2-Aminoethanoic acid
is 2-Aminoethanoic acid.

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NH2

5
O 3 6 Br
5 3 4
6 1 4 2
4 2
OH 5 1
3
6 1

O
N C
2
H CH2CH3 OH OH

4-(N-Ethylamino)hexanoic acid 5-Amino-6-bromo-2-hydroxycyclohex-3-enecarboxylic acid

Red way: Position 4 to the double bond.
Green way: Position 3 to the double bond.
So, the green way is the correct way of numbering.
IUPAC name: 5-Amino-6-bromo-2-hydroxycyclohex-3-enecarboxylic acid

IUPAC name

What is the IUPAC name of the following compound?

(a) 4,4-Dimethyl-3-hydroxybutanoic acid O
(b) 2-Methyl-3-hydroxypentan-5-oic acid CH3 OH
(c) 3-Hydroxy-4-methylpentanoic acid
H3C CH CH CH2 C OH
(d) 4-Methyl-1,3-hydroxypentanoic acid

Solution

Here, the carboxylic acid (-COOH) is the primary O

functional group. So, the suffix ‘-oic acid’ and CH3 OH
the prefix ‘-hydroxy’ are used. Carboxylic carbon
should get number 1, so the numbering starts H3C CH CH CH2 C OH
from the carboxylic carbon. So, the IUPAC name 5 4 3 2 1
is 3-Hydroxy-4-methylpentanoic acid.
3-Hydroxy-4-methylpentanoic acid
Therefore, option (c) is the correct answer.

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IUPAC name

What is the IUPAC name of the following compound?

H3C CH3
(a) 3-Bromo-3-methyl-1,2-dimethylprop-1-ene
(b) 3-Bromo-1,2-dimethylbut-1-ene
(c) 2-Bromo-3-methylpent-3-ene
(d) 4-Bromo-3-methylpent-2-ene H H
H3C Br

Solution
1
H3C CH3
5
In the red way, the double bond gets number 3. However, 2 3
in the green way, the double bond gets number 2. So, the
4 3
green way is the correct way of numbering. So, the IUPAC
name is 4-Bromo-3-methylpent-2-ene. H 2 4 H
Therefore, option (d) is the correct answer. 1
H3C 5 Br

4-Bromo-3-methylpent-2-ene

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