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环烯烃中双键吸收频率的红外光谱实验研究表明从六元环到四元环C=C键的吸收频率向低波数方向移动,但三元环vc=c频率却反常地增加。本文采用量子化学计算中的密度泛函理论,在B3LYP/6-31G基组水平上,对环烯烃CnH2n-2(n=3 -6)的几何结构、振动频率和Laplacian电子密度进行了研究。从电子结构水平的层次,这类化学键的特点分析了出现反常的真正成因结果表明,C=C键的伸缩振动频率出现反常的原因是由于三元环中弯键的存在,使C=C键长缩短所致。
The experimental study on the absorption frequency of double bond in cycloalkene shows that the absorption frequency of C = C bond from six-membered ring to four-membered ring shifts to the lower wave number, but the frequency of vc = c of the three-membered ring increases anomalously. In this paper, the geometrical structures, vibrational frequencies and Laplacian electron densities of CnH2n-2 (n = 3 -6) have been investigated at the B3LYP / 6-31G basis by density functional theory in quantum chemistry calculations. From the level of the electronic structure, the characteristics of such chemical bonds were analyzed to reveal the real causes of abnormalities. The results show that the abnormal vibrational frequency of C = C bonds is due to the existence of the bending bonds in the three-membered ring and the C = C bonds Shorten due to long.