11.2 Nomenclature

 According to IUPAC system (Unit 12, Class XI), the name of an alcohol is derived from the name of the alkane from which the alcohol is derived, by substituting ‘e’ of alkane with the suffix ‘ol’. The position of substituents are indicated by numerals. For this, the longest carbon chain (parent chain) is numbered starting at the end nearest to the hydroxyl group. The positions of the –OH group and other substituents are indicated by using the numbers of carbon atoms to which these are attached.  For naming polyhydric alcohols, the ‘e’ of alkane is retained and the ending ‘ol’ is added. The number of –OH groups is indicated by adding the multiplicative prefix, di, tri, etc., before ‘ol’. The positions of –OH groups are indicated by appropriate locants, e.g., HO–CH2–CH2–OH is named as ethane–1, 2-diol. Table 11.1 gives common and IUPAC names of a few alcohols as examples.

 Table 11.1: Common and IUPAC Names of Some Alcohols

 Cyclic alcohols are named using the prefix cyclo and considering the —OH group attached to C–1.

 (b) Phenols: The simplest hydroxy derivative of benzene is phenol. It is its common name and also an accepted IUPAC name. As structure of phenol involves a benzene ring, in its substituted compounds the terms ortho (1,2- disubstituted), meta (1,3-disubstituted) and para (1,4-disubstituted) are often used in the common names.

Common name IUPAC name

 

Dihydroxy derivatives of benzene are known as 1, 2-, 1, 3- and 1, 4-benzenediol.

 (c) Ethers: Common names of ethers are derived from the names of alkyl/aryl groups written as separate words in alphabetical order and adding the word ‘ether’ at the end. For example, CH3OC2H5 is ethylmethyl ether.

 

 Example 11.1

 Give IUPAC names of the following compounds:

(i) 

(ii)

(iii)

(iv)

 

Solution

(i) 4-Chloro-2,3-dimethylpentan-1-ol 

(ii) 2-Ethoxypropane

(iii) 2,6-Dimethylphenol

(iv) 1-Ethoxy-2-nitrocyclohexane

According to IUPAC system of nomenclature, ethers are regarded as hydrocarbon derivatives in which a hydrogen atom is replaced by an –OR or –OAr group, where R and Ar represent alkyl and aryl groups, respectively. The larger (R) group is chosen as the parent hydrocarbon. The names of a few ethers are given as examples in Table 11.2.

Intext Question

11.3 Name the following compounds according to IUPAC system. 

(i)

(ii)

(iii)

(iv) 

(v)