Ab Initio calculation of the equilibrium structure and coplanar decomposition of cyclobutane
American Chemical Society Journal , Volume 94 - Issue 2 p. 322- 329
Using a minimum basis set of Slater-type orbitals, the equilibrium structure of cyclobutane is determined. The calculated structure has C-C and C-H bond distances and HCH bond angles, which are within the limits of error for the experimentally measured values. The importance of methylene rocking in the puckered structure, shown in an earlier semiempirical calculation, is verified by the ab initio results. However, only a very small double minimum puckering potential is found. Force constants calculated for some of the important normal modes of vibration are too large by a factor of two. The crbitai energies obtained agree very well with the measured photoelectron spectrum of cyclobutane. A potential surface for the coplanar (2s + 2s) rectangular decomposition of cyclobutane to form two ethylenes shows a potential barrier of 156 kcal/mol. The properties of this surface are discussed with reference to the Woodward-Hoffmann predictions.