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Priority of Functional Groups

Functional groups within molecules undergo characteristic chemical reactions regardless of molecule size. When compounds contain multiple functional groups, order of precedence determines which groups are named as substituents or as the parent name. Cations, carboxylic acids, and their derivatives have highest precedence, followed by aldehydes, ketones, alcohols, amines, ethers, alkenes, and alkynes in descending order.

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468 views1 page

Priority of Functional Groups

Functional groups within molecules undergo characteristic chemical reactions regardless of molecule size. When compounds contain multiple functional groups, order of precedence determines which groups are named as substituents or as the parent name. Cations, carboxylic acids, and their derivatives have highest precedence, followed by aldehydes, ketones, alcohols, amines, ethers, alkenes, and alkynes in descending order.

Uploaded by

Sumaira Rasool
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Order of Precedence of Functional Groups

In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the
characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar
chemical reaction(s) regardless of the size of the molecule it is a part of.

When compounds contain more than one functional group, the order of precedence determines which groups are
named with prefix – i.e. as substituents –, or suffix forms – i.e. as part of the parent name of the molecule. The
highest precedence group takes the suffix, with all others taking the prefix form. However, double and triple bonds
only take suffix form (-ene and -yne) and are used with other suffixes.

Prefixed substituents are ordered alphabetically (excluding any modifiers such as di-, tri-, etc.), e.g.
chlorofluoromethane, not fluorochloromethane. If there are multiple functional groups of the same type, either
prefixed or suffixed, the position numbers are ordered numerically (thus ethane-1,2-diol, not ethane-2,1-diol.)

Priority Functional group Formula Prefix Suffix


Cations -onio- -onium
1
e.g. Ammonium –NH4+ ammonio- -ammonium

2 Carboxylic acids –COOH carboxy- -oic acid

Carboxylic acid derivatives


3 Esters –COOR R-oxycarbonyl-
Amides –CONH2 carbamoyl- -amide

4 Aldehydes –CHO formyl- -al

5 Ketones >CO oxo- -one

Alcohols –OH hydroxy- -ol


6
Thiols –SH sulfanyl- -thiol

7 Amines –NH2 amino- -amine

Ethers –O– -oxy-


8
Thioethers –S– -thio-

Peroxides –OO– -peroxy-


9
Disulfides –SS– -disulfanyl-

Alkenes C=C -ene


10
Alkynes C≡C -yne

A final note: When the substituent names for side-chains contain the prefixes iso..., sec-..., tert-..., and neo (which
are commonly used for side-chains containing three to five carbons), the hyphenated prefixes (sec- and tert-) are
disregarded when alphabetizing.

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