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Abstract

The rotational profiles and conformational minima of 2-chloro-2-fluoroacetaldehyde have been calculated using ab initio methods at the MP2/6-31G(d)//HF/6-31G(d) level of theory. Two minima could be located on the potential energy hypersurface. The transition state structures for the addition of CN⁻ to 2-chloro-2-fluoroacetaldehyde have been calculated to predict theoretically the π-facial stereoselection. -------------------------------------------------------------------------------- Quantum mechanical calculation of the transition states for CN⁻ addition to 2-chloro-2-fluoroacetaldehyde predict anti-Felkin-Anh diastereoselectivity for the addition reaction. Transition state 1^★a is 0.7 kcal mol⁻¹ (MP2/6-31G(d)//HF/6-31G(d) + ZPE) lower in energy than 1^★b, because the conformation of the substrate is more favorable in the former transition state than in the latter. The importance of the conformation of the substrate for the diastereoselectivity is emphasized.