Comparative electronic analysis between hydrogen transfers in the CH4/CH3+, CH4/CH3•, and CH4/CH3- systems: on the electronic nature of the hydrogen (H-, H•, H+) being transferred. II. Analysis of electron-pair interactions from intracule and extracule densities

Abstract

The nature of the hydrogen transferred in the CH3/CH4+, CH3/CH4·, and CH3/CH4- systems is investigated by analyzing the topology of the contracted intracule and extracule electron-pair densities and their respective Laplacians. The CH3/CH4+, CH3/CH4·, and CH3/CH4- systems are taken as simple models for the study of hydride (H-), hydrogen (H·), and proton (H+) transfer reactions, respectively, under a constrained C-C distance. The study is focused on the comparison of the intracule and extracule densities at the intermediate structures for the three H-transfer reactions, complementing a previous investigation of the same model reactions based on the analysis of one-electron densities. The results obtained by analyzing the contracted electron-pair densities are consistent with those obtained from the analysis of one-electron densities. The electronic nature of the H atom being transferred in the three systems can be differentiated by the topologies of the corresponding intracule and extracule densities. However, the analysis underlies also the difficulties to interpretation of the topologies of contracted electron-pair densities, as different electron-electron interactions may contribute to the same point in the intracule or extracule spaces. In particular, for the systems studied, the contribution of the electron-electron interaction associated to the probability of having two electrons on the H being transferred is not reflected separately neither in the intracule nor in the extracule distributions. Nevertheless, the nature of the H being transferred can still be studied by comparing the importance of the electron-electron interactions associated to the probability of having one electron in C and one in the transferring H. The effects of inclusion of electron correlation are also discussed by means of (HF-CISD//HF) intracule and extracule density difference maps.Key words: hydrogen transfer, electron-pair density, intracule density, extracule density, topological density analyisis.