Electronic structure of monomeric methyl-lithium

Abstract

In order to investigate the nature of the C—Li bond in alkyl-lithium compounds, ab initio calculations have been performed for the monomeric CH₃Li molecule using spin-coupled theory. The eight singly occupied non-orthogonal valence orbitals have been fully optimized without symmetry constraints, and the complete spin space of 14 singlet spin functions has been employed. We found essentially four distorted sp³ hybrids on the carbon atom and three 1s orbitals on the hydrogen atoms. The eighth orbital can be described as the superposition of an s-type orbital on lithium and a p-type orbital on carbon, and it also has some amplitude on the hydrogen atoms. When compared with the situation expected for a normal covalent bond, the build-up of ‘overlap charge’ in the C—Li bond region appears to be quite limited. However, an examination of the valence contribution to the total electron density shown a residual peak on lithium. In this sense, the C—Li bond can be described as essentially ionic, although it does not correspond to the transfer of a whole electron.