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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 18, Number 4
BKCSDE 18(4)
April 20, 1997 

 
Title
Theoretical Studies on the Gas-Phase Wolff Rearrangement of α-Ketocarbenes
Author
Chan Kyung Kim, Ikchoon Lee
Keywords
Abstract
The substituent effects in the gas-phase rearrangement of carbenes to ketenes involved in the Wolff reaction have been investigated theoretically using the AM1 method. In the initial state, carbene, there is a relatively strong vicinal n-σ* interaction between the lone pair (n) and carbonyl group (σ*). In the bridged transition state (TS), electronic charge is transferred from the migrating ring (Z-ring) toward the nonmigrating ring (Y-ring). The carbenes are stabilized by an electron donor Y (δ σY < 0) whereas the TS is stabilized by an electron acceptor Y (δσY > 0). Multiple regression analysis of log (kYZ/kHH)(=-δΔG≠ /2.3RT) leads to a relatively large negative cross-interaction constant, ρYZ=-0.53, log (kYZ/kHH)=2.96 σY--1.40 σZ-0.53 σY-σZ reflecting an extensive structural change in the transition state due to the stabilization of the initial state by the vicinal n-σ* overlap. When the solvent (water) effects are accounted for by the SM2.1 model of the Cramer and Truhlar method, the magnitude of all the selectivity parameters, ρY-, ρZ and ρYZ (=-0.66) are increased.
Page
395 - 401
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