Phase Effects on Conformational Equilibria. Nuclear Magnetic Resonance Studies of Methyl Nitrite

Article abstract of DOI:10.1021/j100232a033

Gas-phase 1H NMR spectra of methyl nitrite are consistent with the following thermodynamic parameters for the syn <*> anti conformational equilibrium: ΔH_anti-syn, 998 (50) cal mol^-1; ΔG_anti-syn, 520 (5) cal mol^-1 (at 205 K); and ΔS_anti-syn 2.3(3) eu.These results agree well with values obtained from a statistical mechanical calculation.The large entropy difference between the conformers is due to a very low methyl top internal rotation barrier for the anti conformer.Neat liquid methyl nitrite and 1 percent solutions of methyl nitrite is carbon disulfide, acetone-d6, and n-pentane all produce temperature-dependent NMR spectra which are consistent with the following ranges of thermodynamic parameters: ΔH_anti-syn, 803-866 cal mol_-1; ΔG_anti-syn, 440-460 cal mol^-1 (at 205 K); ΔS_anti-syn, 1.8-2.0 eu, demonstrating that in liquids the anti/syn partition function ratio is smaller and the equilibrium constant between the conformers is closer to 1.