Rotational Isomerism in 2-Methyl-1,2-dinitropropane

Abstract IR and Raman spectra of 2-methyl-1,2-dinitropropane in the solid and solution states are reported and assignment of frequencies is made. Comparison of the Raman and IR spectra in both the solid and solution states indicates that the compound exists in the polar gauche conformation in the solid state and as a rotameric mixture of the gauche and non-polar trans conformers in solution. Analysis of dipole moment data shows that in carbon tetrachloride at 25°C, the mixture contains approximately 12% trans and 88% polar gauche rotamers. In benzene solution, the gauche population is further enhanced. These experimental results are compared with those obtained from a semiempirical MO programme AMPCA (AM1) calculation.