Theoretical studies on the transition-state imbalance in malononitrile anion-forming reactions in the gas phase and in water

✍ Scribed by Ikchoon Lee; Chang Kon Kim; Bon-Su Lee; Chan Kyung Kim; Hai Whang Lee; In Suk Han

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 122 KB
• Volume: 10
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(199712)10:12<908::aid-poc961>3.0.co;2-c

✦ Synopsis

Semiempirical MO theoretical studies were carried out on the nucleophilic addition of phenoxide nucleophiles to 1,1-dicyano-2-arylethenes in the gas phase and in water using the AM1 method and the Cramer-Truhlar solvation model SM2.1. The gas-phase ␣ n and ␤ n values are 0•81 and 0•65, respectively, leading to the positive imbalance of I = 0•16; the electric polarization and dispersion interactions of water incorporated in the SM2.1 model reduce both the ␣ n and ␤ n values to 0•61 and 0•36, giving I = 0•25. The two Brønsted coefficients obtained theoretically in water agree satisfactorily with the experimental values (␣ n corr = 0•55 and ␤ n = 0•35) obtained with amine bases. The small imbalance found both theoretically (I = 0•25) and experimentally (I ≈ 0•20) can be ascribed to (i) a near-zero distance factor, ⌬d = d p Ϫ d TS ≈ 0 and (ii) the small extent of negative charge localization by strucutral reorganization in the transition state.