Conformational analysis and dipole moments of tetra-O-methyl-(+)-catechin and tetra-O-methyl_(-)-epicatechin

Abstract

A conformational energy analysis has been performed for tetra-0-methyl-(+)-catechin and tetra-O-methyl-(-)-epicatechin. Rotation was permitted about five C-O bonds and about the single bond connecting two rings. Eighteen rotational isomers each were assigned for tetra-0-methyl-(-)-epicatechin. Relative populations of the rotational isomers are governed by short-range interactions which give rise to five weighting factors, one of which is common to tetra-0-methyl-(+)-catechin and tetra-0-methyl-(-)-epicatechin. The mean-square dipole moment is most sensitive to the weighting factor common to the two molecules studied. The calculated root-mean-square dipole moment of tetra-0-methyl-(-)-epicatechin at 300 K is in excellent agreement with the experimental value of 2.98 D obtained in p-dioxane. In the case of tetra-0-methyl-(+)-catechin, the calculated root-mean-square dipole moment is larger than the experimental result of 2.45 D if ring conformations in solution are the same as those found in the crystal. Good agreement between theory and experiment for tetra-0-methyl-(+)-catechin can be obtained if an alternative ring conformation is assumed. Temperature coefficients were calculated and found experimentally to be positive for both molecules.

Citation

Mattice, W.L.; Tobiason, F.L.; Houghlum, K.; Shanafelt, A. 1982. Conformational analysis and dipole moments of tetra-O-methyl-(+)-catechin and tetra-O-methyl_(-)-epicatechin. Journal of the American Chemical Society 104:3359-3362