Question

Which of the following reactions show secondary isotope effect?

• A. I, II
• B. II, III, IV
• C. III, IV, V
• D. I, III, IV

Answer 1

Answer: (C)

$I$ and $II$ shows $1^{\circ }$ isotope effect $III,IV$ and $V$ shows $2^{\circ }$ isotope effect.
(I) $(C-H)$ bond breaks
(II) $(C-D)$ bond breaks.
(III) No $(C-H)$ bond breaks in R.D.S.

(IV) No $(C-H)$ bond breaks in R.D.S. like in (III)
(V) No $(C-D)$ bond breaks in R.D.S. like in (III).