I. The properties of certain strained hydrocarbons

Summary A detailed account is given of a quantum-mechanical treatment of the lower cycloparaffins, cyclobutadiene and ethylene. It is found that strained bonds (in the original sense of Baeyer) are to be described as bent. Strain energies comparable with those derived from thermochemical data are calculated; the properties of strained systems are discussed; and, in particular, a detailed description of the bonds in cyclopropane is given. The stability of cyclobutadiene has been considered with respect to that of the related molecules benzene, cyclooctatetraene and diphenylene; and hybridization in ethylene has been re-examined. The pairing approximation is used throughout, but an Appendix is added, in which the molecular orbital method is applied qualitatively to cyclopropane.