CBSE Class 11-science Answered

E2 mechanism is second order elimination reaction.

Element effect means that if element is changed in the reactant, the rate of reaction will change.

For example: with ethoxide ion, the rate of reaction of 2-phenyl ethyl halides is as follows:

C₆H₅CH₂CH₂I > C₆H₅CH₂CH₂Br > C₆H₅CH₂CH₂Cl > C₆H₅CH₂CH₂F

This is because the transition state involves the cleavage of carbon halogen bond.

Since carbon iodide bond is the weakest, the rate of reaction for C₆H₅CH₂CH₂I will be the highest.