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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 18, Number 2
BKCSDE 18(2)
February 20, 1997 

Theoretical Studies on the Base-Catalyzed Deprotonation of Sulfonyl-Activated Carbon Acids
Wang Ki Kim, Wang Sun Ryu, Chang Kook Sohn, Bon-Su Lee, Chang Kon Kim, Ikchoon Lee
Theoretical AM1 MO studies are reported on the gas-phase deprotonations of N-methyl 4-((Y-phenylsulfonyl)pyridinium cations (Ⅳ) and N-(Y-benzyl) 4-((phenylsulfonyl)methyl pyridinium cations (Ⅴ) using NH3 as a base. Bronsted α values for deprotonation of Ⅳ and Ⅴ are 0.18 and 0.17, respectively. Bronsted β value of 0.53 is found for the deprotonation of Ⅳ and Ⅴ by substituted aniline bases. The negative transition state (TS) imbalances, Ⅰ(=α-β) < 0, are rationalized by the negative distance factor, Δd (=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-pπ-conjugation in Ⅳ, where instead n-σ* type sigma delocalization occurs, causes very little lag in the structural reorganization in the TS.
208 - 212
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