An INDO-LMO and 13C NMR spectroscopic study of the C-H bonds in tetracyclo[3.2.0.02,7.04,6]heptane (quadricyclane) and tricyclo[3.1.0.02,4]hexane |
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Authors: | HP Figeys P Geerlings P Raeymaekers G Van Lommen N Defay |
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Institution: | Department of Organic Chemistry, Faculty of Science, Free University Brussels, 50, Av. F.D. Roosevelt, B-1050 Brussels, Belgium |
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Abstract: | Using an INDO approximation to Von Niessen's charge density localization method, the percent s character of the C atom hybrid orbitals engaged in C-H bonds is computed for a series of open-chain and cyclic saturated and unsaturated hydrocarbons. A semi-empirical linear relationship is found between these quantities and the experimental nuclear spin-spin coupling constants JCH (standard deviation 4·98 Hz). The experimental values of JCH were measured for quadricyclane (1) and tricyclo3.1.0.02,4]hexane (2) and were shown to be in fair agreement with the theoretical predictions. An analogous relationship is also established between the percent s character of the involved C atom hybrid orbital and the C-H bond distance, the standard deviation being 0·0040Å. This relation is used in order to predict the different C-H bond lengths in the vibrational ground state of 1 and 2, for which equal CH distances were assumed in the analysis of electron diffraction experiments. The results indicate that molecular geometries can be refined with the use of semi-empirical correlations of the above mentioned type. |
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Keywords: | Author to whom inquiries should be addressed |
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