Theoretical Studies on the Base-Catalyzed Deprotonation of Sulfonyl-Activated Carbon Acids

摘要

Theoretical AM1 MO studies are reported on the gas-phase deprotonations of N-methyl 4-((Y-phenylsulfonyl)pyridinium cations (コ) and N-(Y-benzyl) 4-((phenylsulfonyl)methyl pyridinium cations (ゴ) using NH3 as a base. Bronsted メ values for deprotonation of コ and ゴ are 0.18 and 0.17, respectively. Bronsted モ value of 0.53 is found for the deprotonation of コ and ゴ by substituted aniline bases. The negative transition state (TS) imbalances, グ(=メ-モ) < 0, are rationalized by the negative distance factor, ツd (=dp-dTS) < 0, where dp and dTS are the distance between anionic charge center and substituents in the product and in the TS, respectively. The inability of d-pヰ-conjugation in コ, where instead n-ヲ* type sigma delocalization occurs, causes very little lag in the structural reorganization in the TS.