Match the following:
Column I
(A) on treatment with alc. KOH gives as a major product.
(B) reacts faster than .
(C) on treatment with gives as the major product.
(D) and react with same rate.
Column II
(P) E1 reaction
(Q) E2 reaction
(R) E1cb reaction
(S) First order reaction
Column I
(A) on treatment with alc. KOH gives as a major product.
(B) reacts faster than .
(C) on treatment with gives as the major product.
(D) and react with same rate.
Column II
(P) E1 reaction
(Q) E2 reaction
(R) E1cb reaction
(S) First order reaction
Answer: A → II, B → II, C → III, C → IV, D → I, D → IV
Solution
(A) Isotope effect on product distribution: The C-D bonds are stronger than C-H bonds. In E2 elimination, the base preferentially abstracts the weaker C-H proton, giving the observed product. This is characteristic of E2 mechanism. Matches Q (E2 reaction).
(B) Primary kinetic isotope effect: The faster reaction of the non-deuterated compound indicates C-H bond breaking in the rate-determining step, characteristic of E2 where β-hydrogen abstraction is concerted with C-Br bond breaking. Matches Q (E2 reaction).
(C) Deuterium incorporation from solvent: The product contains deuterium from the solvent (EtOD), indicating the carbanion intermediate abstracts a proton from solvent. This is characteristic of E1cb mechanism where carbanion formation precedes elimination. E1cb is also first-order in substrate. Matches R (E1cb reaction) and S (First order reaction).
(D) No isotope effect: Same rate for deuterated and non-deuterated substrates indicates C-H/C-D bond breaking is not in the rate-determining step. This is characteristic of E1 mechanism where ionization (first-order) is rate-determining, followed by fast proton loss. Matches P (E1 reaction) and S (First order reaction).
Answer: A→Q; B→Q; C→R,S; D→P,S
(B) Primary kinetic isotope effect: The faster reaction of the non-deuterated compound indicates C-H bond breaking in the rate-determining step, characteristic of E2 where β-hydrogen abstraction is concerted with C-Br bond breaking. Matches Q (E2 reaction).
(C) Deuterium incorporation from solvent: The product contains deuterium from the solvent (EtOD), indicating the carbanion intermediate abstracts a proton from solvent. This is characteristic of E1cb mechanism where carbanion formation precedes elimination. E1cb is also first-order in substrate. Matches R (E1cb reaction) and S (First order reaction).
(D) No isotope effect: Same rate for deuterated and non-deuterated substrates indicates C-H/C-D bond breaking is not in the rate-determining step. This is characteristic of E1 mechanism where ionization (first-order) is rate-determining, followed by fast proton loss. Matches P (E1 reaction) and S (First order reaction).
Answer: A→Q; B→Q; C→R,S; D→P,S
JEE Advanced · 2006 · 09 Apr 2006 · Match the columns