In the present study, we quantify the local electric field produced by Chorismate Mutase and calculated the reactivity of the enzyme in presence of oriented electric field using hybrid QM/MM calculations. Chorismate Mutase is an enzyme formally known to catalyse the Claisen rearrangement where (-) chorismate is converted into prephenate as shown in Scheme 1, and hence presents a rare example of enzyme catalysed pericyclic process .