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Updated: Jun 24, 2026

Retropinacol/Cross-pinacol Coupling Reactions - A Catalytic Access to 1,2-Unsymmetrical Diols
Published on: April 4, 2014
A mechanistic study of S(N)2 reaction in a diol solvent
Suk Im1, Sung-Woo Jang, Hye-Rim Kim
1College of Environmental Science and Applied Chemistry (BK 21), Kyunghee University, Kyungki 446-701, S. Korea.
Abstract:
We present calculations for the mechanism of S(N)2 reactions in ethylene glycol, focusing on the role of two protic functional groups (-OH) in the solvent molecule. We find that some hydroxyl groups act as Lewis base to interact with the cation, whereas others affect the reaction as Lewis acid to the nucleophile. We predict that the nucleophile (F-) reacts as an ion pair rather than as a solvent-separated ion when metal cation (Cs+) is used as a counterion. The overall influence of ethylene glycol manifests itself as the reaction barrier (E(double dagger) = 20.0, G(353K)(double dagger) = 21.5 kcal/mol) that is a bit smaller than that in tert-butyl alcohol, which proved to be a very efficient solvent for S(N)2 reactions [Kim, D. W., et al. J. Am. Chem. Soc. 2006, 128, 16394]. We therefore show that a small protic solvent such as ethylene glycol may be as efficient as a bulky alcohol for S(N)2 reactions.
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