Logo : organicmystery.com Online Organic Chemistry Tutorial

Nomenclature of Compounds containing Polyfunctional Groups

«Previous Next »

Polyfunctional Compounds

Organic compounds that contain two or more functional groups are called polyfunctional compounds. Some examples of organic compounds with polyfunctional groups are given below :

Organic compounds containing polyfunctional groups examples

Polyfunctional compounds example : 3-Oxobutan-1-oic acid

3-Oxobutan-1-oic acid

Examples of polyfunctinal group : 4-Cyano-3-methoxybutan-1-al

4-Chloro-3-methoxybutan-1-al

organic compound containing polyfunctional group example : 4-Aminopentan-2-ol

4-Aminopentan-2-ol

polyfunctional compounds example : 2-Amino-5-formyl-3-hydroxypentan-1-oic acid

2-Amino-5-formyl-3-hydroxypentan-1-oic acid

Let us now study how such compounds are named :

Principal functional group

In a polyfunctional compound, one of the functional groups is selected as the principal functional group while all other functional groups are treated as substituents.

Functional groups according to their priorities are listed in the priority table in decreasing order i.e., Carboxylic acid with the highest priority is placed at the top while alkyne being the least in priority is placed at the bottom. The functional group which has the highest priority among all the functional groups present in an organic compound is selected as the principle functional group.

PRIORITY TABLE   [HIGHER to LOWER]
COMPOUND NAME FORMULA
Carboxylic acid -COOH
Sulphonic acid -SO3H
Ester -COOR
Acid chloride -COCl
Acid amides -CONH2
Nitrile -CN
Aldehyde -CHO
Ketone >C=O
Alcohol -OH
Phenol -C6H6O
Thiols -SH
Amines -NH2
Ether -OR
Alkene >C=C<
Alkyne -C≡C-

All functional groups other than the principal functional group present in an organic compound are called substituents.

In the following example, COOH being highest in priority is selected as the principal functional group while all others are treated as substituents.

 Nomenclature of compounds containing functional groups  : Principal functional group selection

Some of the substituents with their prefixes are given below :

Substituents
SECONDARY FUNCTIONAL GROUP PREFIX
-X (F,Cl,Br,I) Halo (fluoro, chloro, bromo, iodo )
-OH Hydroxy
-SH Mercapto
-OR Alkoxy
-NH2 Amino
-CHO Formyl or alkanoyl
-C=O Keto or oxo
-COOH Carboxy
-COOR Alkoxycarbonyl or carbalkoxy
-COCl Halocarbonyl or haloalkanoyl
-CN Cyano
-CONH2 Carbamoyl or Carboxamido

It's time you answered a question.

Can you identify the principal functional group :

IUPAC nomenclature : Question

Numbering the principal chain

The principal chain present in a polyfunctional compound must be numbered in such a way that the principal functional group gets the lowest possible number followed by double bond, triple bond and substituents.

Order of priority : Principle functional group > double bond > triple bond > substituents.

IUPAC Nomenclature of compounds containing more than one
 functional groups example : 4-Chlorobut-1-en-1,4-diene

4-Chlorobut-1-ene-1,4-diol (not 1-Chlorobut-3-ene-1,4-diol)

Name the following compound by doing the correct numbering :

IUPAC nomenclature : Question

Remember, some groups like Cl, F, NO2 are always considered as substituents even when no other functional group is present (already discussed in nomenclature introduction ).

IUPAC nomenclature : 2-Chloropropane

Alphabetical order

If two groups of the same priority occupy identical positions from either end of the parent chain, the lowest number must be assigned to the group whose prefix comes first in the alphabetical order.

IUPAC Nomenclature of compounds containing more than one functional groups example : 1-Bromo-4-chlorobutane

More than two occurrence

When the same carbon containing functional group appears more than two times in a chain, the carbons of that functional group are not included while numbering the chain. Further, secondary suffix used in these cases is different from what we have learnt so far.

Compare :

COOH appears two times

IUPAC Nomenclature example : Pentane-1,5-dioic acid

COOH appears three times (i.e., more than two times)

IUPAC nomenclature : Propane-1,3,5-tricarboxylic acid

Notice that the secondary suffix used in the above example is tricarboxylic acid (not trioic acid).

Secondary suffixes of different functional groups used in these cases are given below :

FUNCTIONAL GROUPPREFIXSUFFIX
-CHOFormylCarbaldehyde
-COOHCarboxyCarboxylic acid
-COX (X=F,Cl,Br,I)HalocarbonylCarbonyl halide
-COORAlkoxycarbonyl or CarbalkoxyAlkyl carboxylate
-CONH2CarbamoylCarboxamide
-CNCyanoCarbonitrile

However, these rules are not applicable if the occurrence is not more than two times in a single chain.

Compare :

IUPAC nomenclature : But-1,2,4-tricarbonitrile

In the above example, all the three occurrences of CN are the part of the same chain. Notice that the secondary suffix carbonitrile is used.

IUPAC nomenclature : 3-(Cyanomethyl)hexane-1,6-dinitrile

In the above example, one of the CN groups is considered as a substituent because it is not directly attached to the parent chain. Notice that the secondary suffix nitrile is used.

Name the following compound :

IUPAC nomenclature : Question

Some complicated namings

The naming of some functional groups like esters, amines is somewhat complicated; hence they are discussed below separately.

Esters (R-COOR')

In case of esters, alkyl group R' comes at the beginning of the name.

Example : 1

H-COOCH3 : Methyl methanoate

Example : 2

CH3-COOCH3 : Methyl ethanoate

Amines

In secondary and tertiary amines, the prefix N-alkyl is used to denote alkyl groups.

Example : 1

CH3CH2NHCH3 : N-Methylethanamine

Example : 2

(CH3)3N : N,N-Dimethylmethanamine

More examples on compounds containing more than one functional groups.
«Previous Next »