Empirical force field calculations. Part 28. Conformations and pseudorotations of 1,3-dioxolane and some methyl-substituted derivatives

Article abstract of DOI:10.1002/recl.19871061202

The conformations and pseudorotations of 1,3-dioxolane(1), cis- and trans-4,5-dimethyl-1,3-dioxolane (2 and 3) and the corresponding 2,2-dimethyl derivatives (4, 5 and 6) have been studied with molecular mechanics using the MM2 force field.Free pseudorotation occurs in 1 and 4 (ΔE = 1.5 kJ/mol) and pseudolibration in 2, 3, 5 and 6 (ΔE = 6, 7, 11 and 14 kJ/mol, respectively).The steric energies of 3 and 6 are lower than those of 2 and 5 since the 4- and 5-methyl groups can both occupy a pseudo-equatorial position in the minimum energy conformation of the trans isomers.Estimates of ΔH⁰_f (25 deg C, gas, kJ/mol) are: 2, -376.1; 3, -380.5; 4, -387.2; 5, -464.4; 6, -470.1.Vicinal proton coupling constants were calculated from the appropriate torsion angles and averaged over the pseudorotation circuit. they are in good agreement with experimental values.The 1,3-dioxolanes can be used as model compounds for borate monoesters of vicinal diols.The 13C chemical shifts of C(2) in 1,3-dioxolanes correlate well with the 11B chemical shifts in the corresponding borate monoesters.