Gas- and liquid-phase ¹h NMR study of syn⇌anti conformational exchange of n-propyl, n-butyl, and isobutyl nitrite

Gas-phase free activation energies, ΔG^‡₂₉₈, for syn⇌anti conformational exchange in n-propyl, n-butyl, and isobutyl nitrite are 11.3 (0.2), 11.4 (0.2) and 11.3 (0.2) kcal mol^-1, respectively. For 1 mol% solutions in CS₂, ΔG^‡₂₉₈ values are 11.6 (0.2), 11.6 (0.2), and 11.5 (0.1) kcal mol^-1, respectively. The gas-phase values are about 1 kcal mol^-1 lower than the previously obtained ΔG^‡₂₉₈ for syn⇌anti conformational exchange in methyl nitrite and similar to those obtained for ethyl and neopentyl nitrite. The observed trends may reflect steric destabilization of the syn conformer in the larger nitrites. Solvent effects on the kinetic parameters of these three nitrites are similar in direction and magnitude to those observed for the previously studied nitrites, again implying a balance between steric and dielectric effects on the conformational dynamics of these systems.