Mitoraj Mariusz, Michalak Artur
Department of Theoretical Chemistry, Faculty of Chemistry, Jagiellonian University, R. Ingardena 3, 30-060, Kracow, Poland.
J Mol Model. 2008 Aug;14(8):681-7. doi: 10.1007/s00894-008-0276-1. Epub 2008 Feb 16.
Natural orbitals for chemical valence (NOCV) were used to describe bonding in conjugated pi-electron molecules. The 'single' C-C bond in trans-1,3-butadiene, 1,3-butadiene-1,1,4,4-tetra-carboxilic acid, 1,3,5,7-octatetraene, and 11-cis-retinal was characterized. In the NOCV framework, the formation of the sigma-bond appears as the sum of two complementary charge transfer processes from each vinyl fragment to the bond region, and partially to the other fragment. The formation of the pi-component of the bond is described by two pairs of NOCV representing the transfer of charge density from the neighboring 'double' C-C bonds. The NOCV eigenvalues and the related fragment-fragment bond multiplicities were used as quantitative measures of the sigma- and pi- contributions. The sigma-component of the 'single' C-C bonds appears to be practically constant in the systems analyzed, whereas the pi-contributions increase from butadiene (ca. 7.5%) to retinal (ca. 14%).
化学价自然轨道（NOCV）被用于描述共轭π电子分子中的键合。对反式-1,3-丁二烯、1,3-丁二烯-1,1,4,4-四羧酸、1,3,5,7-辛四烯和11-顺式视黄醛中的“单”C-C键进行了表征。在NOCV框架中，σ键的形成表现为从每个乙烯基片段到键区域，部分到另一个片段的两个互补电荷转移过程的总和。键的π成分的形成由两对NOCV描述，代表电荷密度从相邻的“双”C-C键转移。NOCV本征值和相关的片段-片段键级被用作σ和π贡献的定量度量。在所分析的体系中，“单”C-C键的σ成分似乎实际上是恒定的，而π贡献从丁二烯（约7.5%）增加到视黄醛（约14%）。
