JEE Main levelSingle correct optionDifficulty 2 of 3o4124
Assertion (A): E1 elimination of 2-bromo-2-methylbutane shows no significant primary deuterium kinetic isotope effect on the rate when the beta-hydrogens are replaced by deuterium.
Reason (R): The C-H bond is not broken in the rate-determining step of E1.
ABoth A and R are true, but R is not the correct explanation of A.
BA is true, but R is false.
CBoth A and R are true, and R is the correct explanation of A.
DA is false, but R is true.
Answer: C
In E1 the slow step is ionisation of the C-Br bond, and the beta C-H bond is broken only in the fast second step. Hence deuteration of the beta positions does not change the rate appreciably (kH/kD is close to 1). R directly explains A.