有机锂化合物中化学键的性质——反式1,2-二锂代乙烷、1,2-二锂代乙烯和1,2-二锂代乙炔分子中化学键的abinitio研究

The Nature of Chemical Bonds in Organolithium Compounds——An ab Initio Study on the Chemical Bonding in the Trans-forms of 1, 2-Dilithioethane, 1, 2-Dilithioethylene and 1, 2-Dilithioacetylene

用从头计算法计算了电荷密度图和各价分子轨道的键强参数.结果表明,三个标题化合物的稳定构型都存在双桥式四中心键.追其原因是:这种构型有利于Li的2p轨道的吸电子效应,这种效应可使C—Li键增强.此外,也发现这三个化合物中C—C键的强度大于C=C键,而后者又比C≡C键为强.本文亦讨论了这种“反常”的原因.

On basis of ab initio calculations by means of electron density contour maps and BSP's of individual valence MO's, we have found that all the stable configurationa of the three title compounds have a double bridge 4-center bond. The reason for that is found to be: Such a configuration is in favor of the electron drawing effect of the Li 2p-orbitals, which may strengthen the C—Li bonds. We have found also that within these three compounds C—C is stronger than C=C, the latter is stronger than C≡C. This seems to be somewhat abnormal. The reason of such an 'abnormality' has been discussed.