Conformatonal analysis of n-cyclophanes by molecular mechanics. II. 5-, 6-, and 7-metacyclophane

The optimal geometries, gas phase thermodynamic functions, heats of formation, and strain energies of 5-, 6-, and 7-metacyclophane have been calculated using a molecular mechanical method developed by Boyd et al., and the results compared with available experimental data and with similar results previously obtained for the n-paracyclophane isomers. In general, strain energies in the meta series are some 12 kcal/mol less than in the para series, the strain energy of an n-metacyclophane being roughly that of an (n+1)-paracyclophane. The meta compounds may thus be said to be one degree more stable than the para compounds.