Vermeeren Pascal, van Zeist Willem-Jan, Hamlin Trevor A, Fonseca Guerra Célia, Bickelhaupt F Matthias
Department of Theoretical Chemistry, Amsterdam Institute of, Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale, Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV, Amsterdam, The Netherlands.
Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, Einsteinweg 55, 2333 CC, Leiden, The Netherlands.
Chemistry. 2021 Apr 26;27(24):7074-7079. doi: 10.1002/chem.202004653. Epub 2021 Mar 3.
A fundamental and ubiquitous phenomenon in chemistry is the contraction of both C-H and C-C bonds as the carbon atoms involved vary, in s-p hybridization, along sp to sp to sp. Our quantum chemical bonding analyses based on Kohn-Sham molecular orbital theory show that the generally accepted rationale behind this trend is incorrect. Inspection of the molecular orbitals and their corresponding orbital overlaps reveals that the above-mentioned shortening in C-H and C-C bonds is not determined by an increasing amount of s-character at the carbon atom in these bonds. Instead, we establish that this structural trend is caused by a diminishing steric (Pauli) repulsion between substituents around the pertinent carbon atom, as the coordination number decreases along sp to sp to sp.
化学中一个基本且普遍存在的现象是，随着所涉及的碳原子在s-p杂化过程中从sp变化到sp再到sp，C-H键和C-C键都会收缩。我们基于科恩-沈分子轨道理论进行的量子化学键分析表明，这一趋势背后普遍接受的基本原理是不正确的。对分子轨道及其相应的轨道重叠进行检查后发现，上述C-H键和C-C键的缩短并非由这些键中碳原子处s轨道成分的增加所决定。相反，我们确定这种结构趋势是由相关碳原子周围取代基之间的空间（泡利）排斥力减小所导致的，因为配位数沿着sp到sp再到sp逐渐降低。
