NMR isotope shift and perturbational MO study of conformation and hyperconjugation in cyclopentyl cations
作者:James H. Botkin、David A. Forsyth、Dennis J. Sardella
DOI:10.1021/ja00271a001
日期:1986.5
possible in the twist conformation. The 1-(4-fluorophenyl)cyclopentyl cation also exists in the twist conformation. The ratio of ..beta..-CD/sub 2/ to ..beta..-CD/sub 3/ effects in these and other cations indicates that hyperconjugation is stronger for endocyclic methylene bonds than for exocyclic methyl bonds. A theoretical model, based on MINDO/3 calculations and a perturbational approach, provides a possible
1-甲基环戊基阳离子通过由..β..-氘化引起的C/sup +/ 处NMR同位素位移的可加性特征显示具有扭曲构象。trans-2,5-d/sub 2/ 同位素异构体的同位素位移小于基于可加性的预期。这种小的同位素偏移是由于同位素对构象平衡的影响,而这种影响仅在扭曲构象中才有可能。1-(4-氟苯基)环戊基阳离子也存在于扭曲构象中。在这些和其他阳离子中 ..beta..-CD/sub 2/ 与..beta..-CD/sub 3/ 效应的比率表明内环亚甲基键的超共轭比环外甲基键更强。基于 MINDO/3 计算和扰动方法的理论模型,