Ab initio study of conformational energy surface of spiro [cyclohexane-1,2′-(1′,3′-dioxep-5′-ene)

Abstract

The gas phase conformational properties of spiro [cyclohexane-1,2′-(1′,3′-dioxep-5′-ene)], 1, in which the C-2′ atom of the dioxepin ring and the C 1 atom of the cyclohexane ring are bonded in a spiro form, are investigated by semiempirical and ab initio methods at the Hartree–Fock (HF), the second-order Moller–Plesset perturbation (MP2) and DFT(B3LYP) levels of theory with 6-31G ∗ and 6-311++G ∗∗ basis sets. Eight energy-minima and seven maxima are found for 1. All conformers appear to have C 1 symmetry. The variable temperature 1H NMR study indicates a population increase of the more stable conformer as the temperature is decreased to −65 °C. Lowering the temperature to −80 °C allows the detection of the relevant coupling constants. The theoretical results are complementary and consistent with the experimental ones.