取代锂卡宾正离子的电子效应及稳定性的理论研究

Theoretical Studies on the Electronic Effect and Stabitityof Substituted Lithium Carbene Cations

以从头算法研究了取代的锂卡宾正离子的构型及稳定能．讨论了它们的共轭效应、超共轭效应以及σ诱导效应对稳定性、旋转能垒以及键长的影响．取代基Ｘ的２ｐｚ和２ｐｚ（Ｃ）、２ｐｚ（Ｌｉ：）之间的π型交盖产生的二电子三中心（或多中心）的共轭分子轨道，是取代基Ｘ稳定ＣＨ２Ｌｉ＋的最主要原因，同时导致Ｙ—Ｃ键长比相应中性化合物缩短，而Ｈ—Ｙ键长增加．

The geometries and the stabilization energies of substituted lithium carbene cations were calculated by ab initio molecular orbital theory. The conjugation, hyperconjugation, σ inductive effect and their effect on the stability, rotation barries, bond length have been discussed. The π charge transfer from X to 2p(C) and 2p(Li) would be equal to the population of 2p(C) and 2p(Li) orbital (Table 2.). The σ change transfer from X to C and Li were calculated by subtracting the net π charge transfer from the total charge on X (Table 2.). The order of substituents X stabilizing CH2Li+ is:NH2>OH>C6H5>CH2=CH>CH≡C>CH3>Cl. The π-type overlap between the 2pz(C), 2pz(Li) and the p-orbitals of substituent products the two-electron three-center(or multi-center) conjugation orbitals. It is the principal cause to stabilize the CH2Li+. It also results in that the Y—C bonds length of XCHLi+ become longer and H—Y bonds shorter than those of corresponding neutral molecule.