Consider the following carboxylic acids: (I) Formic acid (II) Acetic acid (III) Isobutyric acid (IV) Pivalic acid The correct decreasing order of their reactivity towards esterification with ethanol is:

Step-by-step solution

Esterification of carboxylic acids with alcohols is a nucleophilic acyl substitution reaction. The rate of this reaction is highly sensitive to steric hindrance around the carbonyl carbon of the carboxylic acid. As the size and number of alkyl groups attached to the -carbon increase, the steric crowding around the carbonyl carbon increases, making the nucleophilic attack by the alcohol more difficult. This leads to a decrease in the rate of esterification. The structures of the given acids are: (I) Formic acid: HCO