Understanding the Nature of the CH路路路HC Interactions in Alkanes

详细信息    查看全文

• 作者：David Danovich ; Sason Shaik ; Frank Neese ; Jorge Echeverr铆a ; Gabriel Aull贸n ; Santiago Alvarez
• 刊名：Journal of Chemical Theory and Computation
• 出版年：2013
• 出版时间：April 9, 2013
• 年：2013
• 卷：9
• 期：4
• 页码：1977-1991
• 全文大小：614K
• 年卷期：v.9,no.4(April 9, 2013)
• ISSN：1549-9626

文摘

To understand the dispersion stabilization of hydrocarbons in solids and of encumbered molecules, wherein CH路路路HC interactions act as sticky fingers, we developed here a valence bond (VB) model and applied it to analyze the H路路路H interactions in dimers of H₂ and alkanes. The VB analysis revealed two distinct mechanisms of 鈥渄ispersion.鈥?In the dimers of small molecules like H鈥揌路路路H鈥揌 and H₃CH路路路HCH₃, the stabilization arises primarily due to the increased importance of the VB structures which possess charge alternation, e.g., C⁺H^{鈥?/sup>路路路H+C鈥?/sup> and C鈥?/sup>H+路路路H鈥?/sup>C+, and hence bring about electrostatic stabilization that holds the dimer. This is consistent with the classical mechanism of oscillating dipoles as the source of dispersion interactions. However, in larger alkanes, this mechanism is insufficient to glue the two molecules together. Here, the 鈥渄ispersion鈥?interaction comes about through perturbational mixing of VB structures, which reorganize the bonding electrons of the two interacting CH bonds via recoupling of these electrons to H路路路H, C路路路C, and C路路路H 鈥渂onds.鈥?Finally, an attempt is made to create a bridge from VB to molecular orbital (MO) and local pair natural-orbital coupled electron pair approximation (LPNO-CEPA/1) analyses of the interactions, which bring about CH路路路HC binding.}