The structural features which influences the chemical reactions due to bulky substituents is known as stearic effect.         When the bulkier groups hinder the reaction it is called stearic hindrance wich may be due to 1) the sheer bulk of the substituents causing the approach of the reagent more difficult or may be due to 2) electronic factor i e., promoting or inhabiting the electron availabilityat a particular site!!  eg:- carboxylic groups with highly substituted alpha carbon are esterified with difficulty due to steric effect.