Theoretical Study on the Molecular Distortions in [2.2]Paracyclophane and Cyclobutane

Unrestricted geometry optimizations on [2.2]paracyclophane and cyclobutane at the MP2/6-31G(d) level led to significant ring distortions in agreement with experimental results. The MP2 method proved most successful in the study of the ring puckering of cyclobutane where various theoretical methods and basis sets were compared. Frequency calculations on [2.2]paracyclophane at the D 2 minimum and at the D 2 h saddle point demonstrate the influence of the molecular twist on the vibrational spectra. The two distorted minima are separated by a C 2 h symmetric barrier of 2.5 kJ/mol. Possible causes for the ring deformation in [2.2]paracyclophane are discussed.