See image — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

Concept: E2 reaction rate depends on two main factors here: (1) the leaving group ability (Br- vs Cl-) and (2) the kinetic isotope effect (KIE) when C-H/C-D bonds are broken in the rate-determining step. Step 1 – Leaving group comparison (A vs C): Compound A is (CH3)3CBr and compound C is (CH3)3CCl. Both have the same carbon skeleton (tert-butyl) with normal hydrogen atoms. In E2, the leaving group departs in the rate-determining step. Bromide is a better leaving group than chloride (Br- is more stable, weaker base, lower pKa of HBr). Therefore, A reacts faster than C. Option (c) 'A is more reactive than C' is TRUE. Step 2 – Kinetic isotope effect comparison (B vs C): Compound B is (CD3)3CCl and compound C is (CH3)3CCl. Both have the same leaving group (Cl). In E2, a beta C-H (or C-D) bond is broken in the rate-determining step. Breaking a C-D bond is slower than breaking a C-H bond because the C-D bond has a lower zero-point energy, giving a higher activation energy. This is the primary kinetic isotope effect (kH/kD ≈ 2–7). Therefore, B (with C-D bonds) is less reactive than C (with C-H bonds). Option (d) 'B is less reactive than C' is TRUE. Step 3 – Comparing A vs B: A is (CH3)3CBr (better leaving group Br, normal H) and B is (CD3)3CCl (worse leaving group Cl, deuterium slows the reaction). Both factors—better leaving group in A and primary KIE disadvantage in B—make A more reactive than B. Option (a) 'A is more reactive than B' is TRUE. Step 4 – Evaluating option (b): Option (b) states 'B is more reactive than A.' This is the opposite of what we concluded in Step 3, so option (b) is FALSE. Overall reactivity order: A > C > B. - (a) A > B: TRUE - (b) B > A: FALSE - (c) A > C: TRUE - (d) B < C: TRUE Therefore, the correct answer is A,C,D.