Question

What is the correct IUPAC name of the compound given below ?

• A. 5-ethylsulphohexanoic acid.
• B. 5-methyl-6-sulphohexanoic acid.
• C. 5-methyl-7-carboxysulphanoic acid.
• D. 7-carboxy-5-methylsulphanoic acid.

Answer 1

The correct option is B 5-methyl-6-sulphohexanoic acid.

According to functional group priority sequence
$-COOH>-S{O}_{3}H$
So carbon containing $-COOH$ will hold first priority.
Therefore Prefix: "sulpho" is used.
So , the correct IUPAC name of the compound is 5-methyl-6-sulphohexanoic acid.

Theory :
Functional group as suffix or prefix :
When an organic compound contains two or more different functional groups
1. Highest priority :
1.1 Use suffix
2. Other functional groups (act as a substituent) :
2.1 use as prefix
The choice of the principal functional group is made on the basis of the order of preferences.
Note :-
$-R,-C_6{H}_5,-X(F,Cl,Br,I),-NO,-N{O}_2,-OR\left(alkoxy\right)$ do not have any priority order and considered as alkyl substituents while numbering

Priority order of functional groups: (with first being the highest priority)

$\text{Functional Group}\text{Group}\text{Prefix}$
$\text{carboxylic acids}-COOH\text{-carboxy}$
$\text{Sulphonic acids}-S{O}_{3}H\text{-sulpho}$
$\text{Acid anhydride}-COOCOR\text{-}$
$\text{Esters}-COOR\text{-alkoxy carbonyl}$
$\text{Acid Halides}-COX\text{halo carbonyl}$
$\text{Amides}-CON{H}_2\text{-carbamoyl}$
$\text{Nitriles}-CN\text{-cyano}$
$\text{Isonitriles}-NC\text{-isocyano}$
$\text{Aldehydes}-CHO\text{-formyl/-oxo}$
$\text{Ketones}\text{>C}=O\text{-oxo/-keto}$
$\text{Alcohols}-OH\text{-hydroxy}$
$\text{Thiols}-SH\text{-mercapto}$
$\text{Amines}-N{H}_2,-NHR,-N{R}_2\text{-amino}$
$\text{Alkenes}-C=C-\text{-}$
$\text{Alkynes}-C\equiv C-\text{-}$