Gauche effect. Stereochemical consequences of adjacent electron pairs and polar bonds

Structures of chloralide, d-lactic acid chloralide, malic acid chloralide and citric acid chloralide

The gauche/trans conformational equilibria of 2,2'-bi-1,3-dioxanyl (1), 2,2'-dimethyl-2,2'-bi-1,3-dioxanyl (2), 2,2'-bi-1,3-dithianyl (3), and 2,2'-dimethyl-2,2'-bi-1,3-dithianyl (4) dissolved in carbon tetrachloride and benzene are studied through dipole moment determination. Analyses of the relative permittivity data show that the dioxa system favors the trans form at 25 °C. Replacement of the oxygen atoms in 1 with sulfur completely reverses the gauche/trans equilibrium in carbon tetrachloride such that 3 exists predominantly in the gauche form. However, 4 exists mainly in the trans conformation in carbon tetrachloride solution and both 3 and 4 favor the trans form in benzene. X-ray crystallographic determination revealed that 1-4 favored the trans conformation in the solid state. Ab initio and DFT calculations were performed to examine the structural features of 1-4 and study the effects of solvent on these molecules. The calculated gauche/trans equilibria of 3 in different media are in excellent accord with the experimental findings. The observed difference in conformational preference of 3 in CCl 4 and benzene can be explained in terms of the specific solvation effect of benzene. CH...X (X = O or S) are important to understand the structures and relative energies of these 1,3-diheteroane systems.

Gauche/Trans Equilibria of 2,2`-Bi-1,3-dioxanyl, 2,2`-Dimethyl-2,2`-bi-1,3-dioxanyl, 2,2`-Bi-1,3-dithianyl, and 2,2`-Dimethyl-2,2`-bi-1,3-dithianyl in Different Media. Theory and Experiment

The gauche/trans conformational equilibria of 2,2‘-bi-1,3-dioxepanyl 1 and 2,2‘-bi-1,3-dithiepanyl 2 dissolved in carbon tetrachloride and benzene are studied through dipole moment determination. Analyses of the relative permittivity data show that both 1 and 2 favor the gauche form at 25 °C. However, X-ray crystallographic determination revealed that 1 and 2 favored the trans conformation in the solid state. Ab initio and DFT calculations were performed to examine the structural features of 1 and 2 and study the effects of solvent on these molecules. The calculated gauche/trans equilibria of 1 and 2 in different media are in good agreement with the experimental findings. CH···X (X = O or S) interactions are important to understand the structures and relative energies of these 1,3-diheteroane systems.

Gauche/Trans Equilibria of 2,2‘-Bi-1,3-dioxepanyl and 2,2‘-Bi-1,3-dithiepanyl in Different MediaTheory and Experiment

The gauche/trans conformational equilibria of 2,2‘-bi-1,3-dioxanyl (1), 2,2‘-dimethyl-2,2‘-bi-1,3-dioxanyl (2), 2,2‘-bi-1,3-dithianyl (3), and 2,2‘-dimethyl-2,2‘-bi-1,3-dithianyl (4) dissolved in carbon tetrachloride and benzene are studied through dipole moment determination. Analyses of the relative permittivity data show that the dioxa system favors the trans form at 25 °C. Replacement of the oxygen atoms in 1 with sulfur completely reverses the gauche/trans equilibrium in carbon tetrachloride such that 3 exists predominantly in the gauche form. However, 4 exists mainly in the trans conformation in carbon tetrachloride solution and both 3 and 4 favor the trans form in benzene. X-ray crystallographic determination revealed that 1−4 favored the trans conformation in the solid state. Ab initio and DFT calculations were performed to examine the structural features of 1−4 and study the effects of solvent on these molecules. The calculated gauche/trans equilibria of 3 in different media are in excellent acco...

Gauche/trans equilibria of 2,2′-bi-1,3-dioxolanyl, 2,2′-dimethyl-2,2′-bi-1,3-dioxolanyl, 2,2′-bi-1,3-dithiolanyl and 2,2′-dimethyl-2,2′-bi-1,3-dithiolanyl in different media—theory and experiment

Dipole moment and molar Kerr constant (×1012) values at 25° are recorded for 2,3-dicyano-2,3-dimethylbutane as a solute in carbon tetrachloride (2·13 D, +61) The electric moments have also been determined at 45°(2·30 D) and at 7°(1·98 D) Conformational analysis shows that the results at 25° indicate an equilibrium mixture of 82% of the trans-rotamer and 18% of the gauche-rotamer of the 2,3-dicyano-2,3-dimethylbutane molecule in which the dihedral angle is 85° The temperature-dependence of the dipole moment in carbon tetrachloride solution yields an apparent internal energy difference between the two rotational isomers of 1·31 kcal/mole

H. H. Huang

Papers

Conformation of 2,3-dicyano-2,3-dimethylbutane by electric dipole moment and Kerr effect measurements