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

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 Lennard-Jones−Pike analysis of the dipole moment data in benzene gives a Δ G value of 5.31 kJ mol -1 and μ g of 3.62 D. From eq 2, the composition of gauche form in benzene solution was found to be 19% at 25 °C. These values in benzene compare well with the results obtained from carbon tetrachloride solution, which indicate that, unlike 2,2‘-bi-1,3-dioxolanyl, there is minimal conformational change in the molecule on passing into different solutions.…”

“…Application of the Lennard-Jones−Pike analysis to our dipole moment data yields Δ G value of −5.26 kJ mol -1 and μ g of 2.74 D. From eq 2, the percentage gauche population at 25 °C was found to be 81%. These results contrast with those for 2,2‘-diphenyl-2,2‘-bi-1,3-dithianyl, 1 , 2 , and 4 , which favor the trans conformer when the compounds are in carbon tetrachloride. Because 3 exists in the trans conformation in the solid state (as shown by our X-ray data), the preference for the gauche conformer in carbon tetrachloride may plausibly be attributed to the greater solvent stabilization of the polar conformer in 3 so as to reverse the gauche / trans equilibrium.…”

“…In our previous study on bi-1,3-dioxolanyl and bi-1,3-dithiolanyl systems, we have shown that the noncovalent CH···X (X = O or S) interaction plays an important role in governing their rotational equilibria . In these systems, the gauche form is stabilized by two favorable CH···X interactions between the X atom of one five-membered ring and the methylene hydrogen of the adjacent five-membered ring.…”

“…To this end, we have examined the solvent effects of the rotational equilibria of 1 − 4 using the reaction field methods (SCRF and SCIPCM). In our recent study, we showed that the quadrupole moments of bi-1,3-diheteroanes play a significant role in stabilizing the solute in a dielectric medium. In other words, it is not straightforward to predict the solvent effect based simply on the dipole moment alone.…”

“…In recent years, much attention has also been paid to the interactions involving CH groups and electronegative atoms X. , These interactions have been found to contribute an important role in the stabilization of particular conformations of isolated single molecules. , To elucidate the effect of solvents on CH····X interactions, we have studied the conformations of 2,2‘-bi-1,3-dioxolanyl, 2,2‘-dimethyl-2,2‘-bi-1,3-dioxolanyl, 2,2‘-1,3-dithiolanyl, and 2,2‘-dimethyl-2,2‘-1,3-dithiolanyl by dipole moment determination, X-ray crystallography, and density functional calculations. In these studies, we have shown that these compounds, except 2,2‘-1,3-dithiolanyl, prefer the gauche conformer in the gas phase due to favorable CH····X (X = O, S) interactions.…”