Transition state structure for peracid epoxidation. Secondary deuterium isotope effects
Kinetic deuterium isotope effects were measured for the epoxidation of p- phenylstyrene (3) and three deuterated derivatives ($alpha$-d (4); $beta$$,$$beta$- d$sub 2$ (5); $alpha$$,$$beta$,beta$sup -$ d$sub 3$ (6)) with m-chloroperbenzoic acid in 1,2-dicloroethane at 0$sup 0$. The isotope effects (k/sub H//k/sub D/) observed for 4,5, and 6 are 0.99, 0.82, and 0.82, respectively; for p- nitrostyrene and its $alpha$-d analog k/sub H//k/sub D/ at 25$sup 0$ was 0.98. The peracid isotope effect for epoxidation of 3 with m-ClC$sub 6$$H$$sub 4$COOOH(D) at 0$sup 0$ was k/sub H//k/ sub D/ = 1.17. These data suggest that in the transition state for epoxidation there is substantial C/sub beta/--O bond formation, but negligible change in the bonding or hybridization at C/sub alpha/ of the olefin. Epoxidation mechanisms suggested previously cannot accommodate these findings, thus an alternate transition state structure has been proposed. It is characterized by (1) sp$sup 2$ geometry and partial positive charge at C/ sub alpha/ of the olefin, (2) extensive C/sub beta/--O bond formation but with retention of some $pi$ bonding between C/sub alpha/ and C/sub beta/, (3) a nearly equal amount of partial negative charge on the peracid carboxylate, and (4) little change in the bonding of the peracid proton. (auth)
- Research Organization:
- Univ. of Kansas, Lawrence
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-33-004999
- OSTI ID:
- 4140412
- Journal Information:
- J. Am. Chem. Soc., v. 97, no. 18, pp. 5231-5237, Other Information: Orig. Receipt Date: 30-JUN-76
- Country of Publication:
- United States
- Language:
- English
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