Predominant role of basicity of leaving group in alpha-effect for nucleophilic ester cleavage.
It has been found that alpha-effects in nucleophilic reactions, unexpectedly large nucleophilicity due to adjacent unpaired electrons, are strongly dependent on the structure of substrate. The nucleophilic cleavages of 4-nitrobenzoate esters and 4-methylbenzoate esters by HOO- have been systematically investigated in detail. When the leaving groups of substrates are sufficiently good (aryl, 2,2,2-trifluoroethyl, and 2,2-dichloroethyl esters), alpha-effect is evident. However, this effect drastically decreases as the leaving group gets poorer, and is only marginal for the cleavages of 2-fluoroethyl and methyl esters. In the nucleophilic cleavages by salicylaldoxime and acetohydroxamic acid, alpha-effect is also notable only for the esters having good leaving groups. These enormous dependences of alpha-effects on the substrate-structure have been interpreted in terms of the difference in the position of transition-state in the reaction coordinate.
Nomura
Yasuo
Y
Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.
Kubozono
Takayasu
T
Hidaka
Makoto
M
Horibe
Mineko
M
Mizushima
Naoki
N
Yamamoto
Nobuyuki
N
Takahashi
Toshio
T
Komiyama
Makoto
M
D001565:Benzoates / Q000737:chemistry*; D004952:Esters / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry; D007700:Kinetics; D015394:Molecular Structure
D001565:Benzoates; D004952:Esters; D006861:Hydrogen Peroxide