Comparative electronic analysis between hydrogen transfers in the CH4/CH3+, CH4/CH3o, and CH4/CH3- systems: on the electronic nature of the hydrogen (H-, H-o, H+) being transferred. II. Analysis of electron-pair interactionsfrom intracule and extracule densities

The nature of the hydrogen transferred in the CH3/CH4+, CH3/CH4., and CH3/C H4- systems is investigated by analyzing the topology of the contracted int racule and extracule electron-pair densities and their respective Laplacian s. 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 rea ctions, respectively, under a constrained C-C distance. The study is focuse d on the comparison of the intracule and extracule densities at the interme diate structures for the three H-transfer reactions, complementing a previo us investigation of the same model reactions based on the analysis of one-e lectron densities. The results obtained by analyzing the contracted electro n-pair densities are consistent with those obtained from the analysis of on e-electron densities. The electronic nature of the H atom being transferred in the three systems can be differentiated by the topologies of the corres ponding intracule and extracule densities. However, the analysis underlies also the difficulties to interpretation of the topologies of contracted ele ctron-pair densities, as different electron-electron interactions may contr ibute to the same point in the intracule or extracule spaces. In particular , for the systems studied, the contribution of the electron-electron intera ction 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 transferr ed can still be studied by comparing the importance of the electron-electro n interactions associated to the probability of having one electron in C an d one in the transferring H. The effects of inclusion of electron correlati on are also discussed by means of (HF-CISD//HF) intracule and extracule den sity difference maps.