The increasing order of reactivity towards esterification is as follows:
Tertiary alcohol: Tertiary alcohols are the least reactive towards esterification. This is because the carbon atom to which the hydroxyl group (-OH) is attached has three alkyl groups bonded to it, making it sterically hindered. This hindrance restricts the approach of the carboxylic acid, reducing the likelihood of the esterification reaction taking place.
Secondary alcohol: Secondary alcohols are more reactive than tertiary alcohols but less reactive than primary alcohols in esterification reactions. The presence of two alkyl groups on the carbon bearing the -OH group provides some steric hindrance, which affects the reaction rate.
Primary alcohol: Primary alcohols are the most reactive towards esterification. In these alcohols, the carbon atom with the -OH group is only bonded to one alkyl group, which means there is less steric hindrance. Consequently, primary alcohols can more easily react with carboxylic acids to form esters.
In summary, the order of increasing reactivity towards esterification is: tertiary alcohol < secondary alcohol < primary alcohol.