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

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, 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, symmetry. The variable temperature H-1 NMR study indicates a population increase of the more stable conformer as the temperature is decreased to -65 degreesC. Lowering the temperature to -80 degreesC allows the detection of the relevant coupling constants. The theoretical results are complementary and consistent with the experimental ones. (C) 2002 Elsevier Science B.V. All rights reserved.