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Nucleophilicity Parameters for Carbanions in Methanol
Author(s) -
Binh Phan Thanh,
Mayr Herbert
Publication year - 2006
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200500769
Subject(s) - chemistry , carbanion , nucleophile , methoxide , solvation , reaction rate constant , acetonitrile , medicinal chemistry , methanol , electrophile , conjugate acid , ion , organic chemistry , kinetics , catalysis , physics , quantum mechanics
Abstract The kinetics of the reactions between eleven carbanions 2a – k (nitronates and malonic acid derivatives) and benzhydrylium ions 1a – g were investigated photometrically in methanol/acetonitrile (91:9, v/v) at 20 °C. Since the competing reactions of the benzhydrylium ions with methanol and methoxide ions are generally slower, the second‐order rate constants of the reactions between the benzhydrylium ions 1a – g and the carbanions 2a – k can be determined with high precision. The second‐order rate constants (log k ) correlate linearly with the electrophilicity parameters E of the benzhydrylium ions, allowing us to determine the nucleophilicity parameters N and s of the carbanions in methanol/acetonitrile (91:9, v/v). The nucleophilic reactivities do not correlate with the acidity constants of the conjugate CH acids, and from the poor correlation of the reactivities of the substituted α‐nitrobenzyl anions 2d – h with Hammett’s σ – constants it can be inferred that the nucleophilic reactivities are strongly controlled by solvation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)