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:


(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.