呋喃和苯多烯醛分子中的共轭效应和共轭基干  

The Conjugation and Conjugated Stem in Furyl and Phenyl-Polyenal

作　　者：虞忠衡[1] 蒋明谦[1] 戴萃辰[1] 褚文华[1] 

机构地区：[1]中国科学院化学研究所

出　　处：《化学学报》1990年第10期993-999,共7页Acta Chimica Sinica

摘　　要：呋喃和苯多烯醛系列的CNDO/2和微扰分子轨道法的计算表明,共轭效应与共轭基干是两个不同的概念,共轭效应包括了共轭基团之间的作用对分子性能全面的影响,而共轭基干仅仅反映了共轭基团间的作用对前沿分子轨道的影响。这意味着,相互之间有共轭作用的基团不一定属于同一个基于,属于同一个共轭基干的基团之间。必定有共轭作用。共轭基干更确切地反映了共轭基团间的作用对分子结构的依赖。The interaction of methoxyl group with formyl polyenio group is so strong that the every MO, especially HOMO and LUMO, of ω-methoxyl-polyenal molecule is very different from the corresponding MO of polyenal molecule. The interaction contributes to the lowering of HOMO-LUMO energy gap of formyl polyenic fragment and to the raising of the π bond order between the oxygen atom in methoxyl group and the carbon atom bound to it in the first excited state. The methoxyl group and formyl polyenic group belong to the same conjugated stem. In ω-furyl-polyenal molecule the interaction of oxygen lone pair with the higher occupied orbital, especially, with the HOMO, of formyl polyenic fragment is very weak, there is no appreciable difference in the energy and component of the orbital between the ω-furyl-polyenal and the polyenal having same number of carbons. The oxygen lone pair slightly affects HOMO-LUMO energy gap of formyl polyenic fragment; the π bond order between the oxygen atom in furyl group and the carbon atoms bound to it in ground state is greater than that in the first excited state. The oxygen in furyl group and formyl polyenie group do not belong to same conjugated stem. Based on the effect of interactions of the π MO's in ethyl fragment with the π MO's in formyl polyenio fragment on the HOMO-LUMO energy gap and on the difference in π bond order between the ground and first excited state, it is concluded that they do not belong to the same conjugated stem, although there is a p-π conjugation between the two group. CNDO/2 and PMO computation on above three series of substituted polyenal make a distinction between conjugation and conjugated stem, that is, the conjugation includes overall change of molecular properties resulted from the interaction among conjugated groups, on the other hand, the conjugated stem only reflects the effect of the interaction on the frontal MO's.

关 键 词：呋喃 苯多烯醛 共轭效应 共轭基干 

分 类 号：O621.13[理学—有机化学]