on the spatial structure of methyl 6,7-endo, sin-dibrom-7-anti-(PHENYLSULFONYL) BICYCLO[3.1.1]HEPTANE-6-EXO-CARBOXYLATE
V. A. Vasin, P. S. Petrov, A. M. Genaev, V. A. Gindin, V. V. Razin
Keywords: tricyclo[4.1.0.02, 7]heptane, bicyclo[3.1.1]heptane, norpinane, single crystal X-ray analysis, 1H and 13C NMR spectra, donor-acceptor interaction, hindered rotation, coalescence, quantum chemical calculation, DF
Pages: 982-988
Abstract
In the 1H and 13C NMR spectra of methyl 6,7-endo,sin-dibromo-7-anti-(phenylsulfonyl)bicycle-
[3.1.1]heptane-6-exo-carboxylate, H(1) and H(5) protons as well as C(1) and C(5) carbon atoms show their chemical inequivalence determined by the hindered rotation of sulfonyl and ester groups about simple C-S and C-C bonds due to the existence of donor-acceptor interaction between the carbonyl C atom and the oxygen atom of the SO2Ph group. This interaction is indicated by the single crystal X-ray diffraction study detecting the shortened intramolecular contacts (2.49 Å with the sum of the C…O van der Waals radii of 3.00 Å). Other features of the norpinane skeleton conformation and the spatial orientation of substituents in the single crystal are discussed. By 1H NMR methods, the parameters of the dependence of molecular conformations on the temperature of DMSO-d6 solution and the activation free energy = 80.1 kJ/mol of conformational transitions are determined. By a quantum chemical DFT calculation of the potential energy surface it is revealed that the hindered rotation of the ester group makes the main contribution to the barrier of conformational transitions.
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