Chemistry Nomenclature and Structure of Alcohols, Phenols and Ethers

### Topics Covered :

● Nomenclature of Alcohols
● Nomenclature of Phenols
● Nomenclature of Ethers
● Structure of Alcohols, Phenols and Ethers

### Nomenclature :

Nomenclature of alcohols, phenols and ethers is given as follows :

### Alcohols :

color{green}("Common Name ") : The common name of an alcohol is derived from the common name of the alkyl group and adding the word alcohol to it.

● For example, color{red}(CH_3OH) is methyl alcohol.

color{green}("IUPAC Name ") : According to IUPAC system, 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 ‘color{red}(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 color{red}(–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 ‘color{red}(ol)’ is added.

● The number of color{red}(–OH) groups is indicated by adding the multiplicative prefix, di, tri, etc., before ‘color{red}(ol)’.

● The positions of color{red}(–OH) groups are indicated by appropriate locants e.g., color{red}(HO–CH_2–CH_2–OH) is named as ethane–1, 2-diol.

● Table 11.1 gives common and IUPAC names of a few alcohols as examples.

● Cyclic alcohols are named using the prefix cyclo and considering the color{red}(—OH) group attached to color{red}(C–1). See image.

### 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. See fig.1.

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

### Ethers :

=> If both the alkyl groups are the same, the prefix ‘di’ is added before the alkyl group.

● For example, color{red}(C_2H_5OC_2H_5) is diethyl ether.

=> According to IUPAC system of nomenclature, ethers are regarded as hydrocarbon derivatives in which a hydrogen atom is replaced by an color{red}(–OR) or color{red}(–OAr) group, where color{red}(R) and color{red}(Ar) represent alkyl and aryl groups, respectively.

=> The larger (color{red}(R)) group is chosen as the parent hydrocarbon. The names of a few ethers are given as examples in Table 11.2.
Q 3022856731

Give IUPAC names of the following compounds:

Solution:

(i) 4-Chloro-2,3-dimethylpentan-1-ol
(ii) 2-Ethoxypropane
(iii) 2,6-Dimethylphenol
(iv) 1-Ethoxy-2-nitrocyclohexane

### Structures of Functional Groups :

=> In alcohols, the oxygen of the color{red}(–OH) group is attached to carbon by a sigma color{red}(σ ) bond formed by the overlap of a color{red}(sp^3) hybridised orbital of carbon with a color{red}(sp^3) hybridised orbital of oxygen. Fig. 11.1 depicts structural aspects of methanol, phenol and methoxymethane.

=> The bond angle in alcohols is slightly less than the tetrahedral angle (109°-28′).

● It is due to the repulsion between the unshared electron pairs of oxygen.

=> In phenols, the color{red}(–OH) group is attached to color{red}(sp^2) hybridised carbon of an aromatic ring.

● The carbon– oxygen bond length (136 pm) in phenol is slightly less than that in methanol.

● This is due to (i) partial double bond character on account of the conjugation of unshared electron pair of oxygen with the aromatic ring and (ii) color{red}(sp^2) hybridised state of carbon to which oxygen is attached.

=> In ethers, the four electron pairs, i.e., the two bond pairs and two lone pairs of electrons on oxygen are arranged approximately in a tetrahedral arrangement.

● The bond angle is slightly greater than the tetrahedral angle due to the repulsive interaction between the two bulky color{red}(–R) groups.

● The color{red}(C–O) bond length (141 pm) is almost the same as in alcohols.