Ab initio Study of the Keto-Enol Equilibriumof Malonaldehyde |
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Authors: | Vassil B Delchev and Georgi S Nikolov |
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Institution: | (1) School of chemistry of chemical engineering, Southwest China Normal University, Chongqing, 400715, Peoples Republic of China;(2) College of Chemistry, Sichuan University, Chengdu, 610064, Peoples Republic of China;(3) Department of Biology and Chemistry, City University of Hong Kong, Kowloon, Hong Kong |
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Abstract: | The mechanism of the keto-enol tautomerism of malonaldehyde was studied by ab initio methods using 6-21G** and 6-311G** basis functions at the HF level. Two separate mechanisms were examined: through-space proton transfer in the ω-shaped form and through-space proton transfer in a sickle-shaped form obtained from the ω form by rotation. The transition state structure of the ω form is non-planar, whereas that of the sickle form is planar. The sickle form is connected with a 2nd order saddle, indicating that there should exist a lower energy barrier, i.e. that the through-bond mechanism may be preferred. The calculated energy barriers of keto-enol tautomerism for the sickle form is twice as high as those for the omega form. |
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