Match each step with the description of its transition state according to the Hammond postulate. Column I: (P) Cl^. + secondary C-H (C-H 98, H-Cl 103 kcal/mol); (Q) Br^. + secondary C-H (H-Br 88 kcal/mol); (R) ionisation (CH3)3C-Cl -> (CH3)3C+ + Cl- in solution (strongly endothermic); (S) CH3^. + CH3^. -> C2H6 (highly exothermic). Column II: (1) early transition state, resembles reactants; (2) late transition state, resembles products.

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Match each step with the description of its transition state according to the Hammond postulate. Column I: (P) $Cl X^{∙}$ + secondary C-H ( $C - H$ 98, $H - Cl$ 103 kcal/mol); (Q) $Br X^{∙}$ + secondary C-H ( $H - Br$ 88 kcal/mol); (R) ionisation $(CH X_{3}) X_{3} C - Cl (CH X_{3}) X_{3} C X^{+} + Cl X^{-}$ in solution (strongly endothermic); (S) $CH X_{3} X^{∙} + CH X_{3} X^{∙} \to C X_{2} H X_{6}$ (highly exothermic). Column II: (1) early transition state, resembles reactants; (2) late transition state, resembles products.

AP-1, Q-2, R-2, S-1
BP-2, Q-1, R-1, S-2
CP-2, Q-2, R-1, S-1
DP-1, Q-1, R-2, S-2

Answer: A

(P):

Δ H = 98 - 103 = - 5

kcal/mol, exothermic, early. (Q):

Δ H = 98 - 88 = + 10

, endothermic, late. (R): strongly endothermic, so the transition state is late and ion-pair-like. (S): about 90 kcal/mol is released and the barrier is essentially zero, so it is very early. P-1, Q-2, R-2, S-1.

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