17264-86-7Relevant articles and documents
Studies of the Borderline between Concerted and Stepwise Mechanisms of Elimination : E1cB Elimination of Fluoren-9-ylmethyl Carboxylate Esters
O'Ferrall, Rory A. More,Larkin, Finbar,Walsh, Peter
, p. 1573 - 1580 (2007/10/02)
Rates of β-elimination of carboxylate leaving groups from fluoren-9-ylmethyl carboxylate esters in methanolic sodium methoxide at 25 deg C are reported.An E1cB mechanism with rate-determining formation of a carbanion intermediate is assigned on the basis of near identity of measured elimination rates and rates of carbanion formation predicted from a Taft correlation, and the similarity with elimination of 1-(1-acetoxy-1-methylethyl)indene for which the mechanism has been established by Ahlberg and Thibblin.Values of ρ=0.42 and βlg=0.27 measured for substituted benzoate leaving groups are a little larger than expected (ca. 0.24 and 0.18, respectively) and the discrepancy is tentatively ascribed to conformational enhancement of remote substituent effects, rather than to a contribution of E2 elimination.The effects of alkyl and aryl substitution α to the leaving group are discussed, especially in relation to the borderline between concerted and stepwise mechanisms.The measurements fail to confirm an earlier inference that the borderline shows a discontinuity in transition-state structure at the point of mechanistic change.
