作者:S. Ranganathan、D. Ranganathan、P.V. Ramachandran、M.K. Mahanty、S. Bamezai
DOI:10.1016/0040-4020(81)85008-9
日期:1981.1
A variety of reactions, whilst predicted to be symmetry allowed, are not observed experimentally. Several such non-observed yet allowed reactions have been studied in order to understand them and to possibly bring about, with suitably modified substrates, their observation. For example, although ozone adds to π-bonds, the isoelectronic nitro group does not, due to a high activation energy barrier.
虽然预计不会出现对称反应,但无法通过实验观察到各种反应。为了理解它们并可能通过适当修饰的底物进行观察,已研究了几种此类未观察到但允许的反应。例如,尽管臭氧加成了π键,但是由于高的活化能垒,因此等电子硝基没有。该反应的类型为A→B→C。一系列1,3-偶极子物种的分子轨道计算表明,在[4 + 2]加成中π键顺序与其有效性相关。基于此,硝基和臭氧都应视为不良的偶极试剂。异常高的ΔH ˚F °臭氧的(+ 34.00千卡摩尔-1)与硝基苯(+3.8 kcal mol -1)相比,可能可以解释前者的反应性。这反映在-45.5千卡mol的估计ΔH°值-1的乙烯-臭氧加成与+ 7.5千卡摩尔比-1的非存在的乙烯-硝基苯加成。热化学计算表明,与作为1,3-偶极试剂相比,硝基更容易以2π伴侣形式加成。