Chemistry Classification of Alcohols, Phenols and Ethers

### Topics Covered :

● Introduction
● Classification of Alcohols and Phenols
● Classification of Ethers

### Introduction :

=> Alcohols and phenols are formed when a hydrogen atom in a hydrocarbon, aliphatic and aromatic respectively, is replaced by color{red}(–OH) group.

=> These classes of compounds find wide applications in industry as well as in day-to-day life.

● Ordinary spirit used for polishing wooden furniture is chiefly a compound containing hydroxyl group, ethanol.

● The sugar we eat, the cotton used for fabrics, the paper we use for writing, are all made up of compounds containing color{red}(–OH) groups.

=> An alcohol contains one or more hydroxyl color{red}(OH) group(s) directly attached to carbon atom(s), of an aliphatic system color{red}(CH_3OH) while a phenol contains color{red}(–OH) group(s) directly attached to carbon atom(s) of an aromatic system color{red}(C_6H_5OH).

=> The subsitution of a hydrogen atom in a hydrocarbon by an alkoxy or aryloxy group (color{red}(R–O //Ar–O)) yields another class of compounds known as ‘ethers’, for example, color{red}(CH_3OCH_3) (dimethyl ether).

=> You may also visualise ethers as compounds formed by substituting the hydrogen atom of hydroxyl group of an alcohol or phenol by an alkyl or aryl group.

### Classification :

The classification of compounds makes their study systematic and hence simpler.

### Classification of Alcohols and Phenols :

text(Mono, Di, Tri or Polyhydric Compounds :) Alcohols and phenols may be classified as mono–, di–, tri- or polyhydric compounds depending on whether they contain one, two, three or many hydroxyl groups respectively in their structures as given below : See fig.1.

=> Monohydric alcohols may be further classified according to the hybridisation of the carbon atom to which the hydroxyl group is attached.

(i) color{green}("Compounds containing" C_(sp^3) - OH "bond ") : In this class of alcohols, the color{red}(–OH) group is attached to an color{red}(sp^3) hybridised carbon atom of an alkyl group. They are further classified as follows :

● color{green}("Primary, Secondary and Tertiary Alcohols" ) : In these three types of alcohols, the color{red}(–OH) group is attached to primary, secondary and tertiary carbon atom, respectively as shown in fig.2.

● color{green}("Allylic Alcohols ") : In these alcohols, the color{red}(—OH) group is attached to a color{red}(sp^3) hybridised carbon next to the carbon-carbon double bond, that is to an allylic carbon. For example : See fig.3.

● color{green}("Benzylic Alcohols ") : In these alcohols, the color{red}(—OH) group is attached to a color{red}(sp^3)—hybridised carbon atom next to an aromatic ring. For example : See fig.4.

(ii) color{green}("Compounds containing" C_(sp^2)− OH "bond" ) : These alcohols contain color{red}(—OH) group bonded to a carbon-carbon double bond i.e., to a vinylic carbon or to an aryl carbon. These alcohols are also known as vinylic alcohols.

Vinylic alcohol : color{red}(CH_2 = CH – OH)

Phenols : See fig.5.

### Ethers :

Ethers are classified as :

(i) color{green}("Simple or Symmetrical ") : If the alkyl or aryl groups attached to the oxygen atom are the same. Example : Diethyl ether, color{red}(C_2H_5OC_2H_5).

(ii) color{green}("Mixed or Unsymmetrical ") : If the two groups are different. Example : color{red}(C_2H_5OCH_3) and color{red}(C_2H_5OC_6H_5) are unsymmetrical ethers.