ELECTRON-DIFFRACTION STUDY OF ROTATIONAL ISOMERISM OF METHYL ETHYL KETONE

The rotational isomerism of methyl ethyl ketone in the vapor phase has been investigated by electron diffraction. Analyses of the radial distribution curves and the background functions (for small scattering angles, q = 8-20) have shown that the more stable isomer has the trans conformation with regard to the end C-C bonds, and that the relative compositions of this isomer and the less stable isomer (possibly in the gauche conformation) are 95 % : 5 % at room temperature with the limit of uncertainty of 3 %. This corresponds to a free energy difference of ΔG = 2.1 ± 0.4 kcal mol, in good agreement with the ΔH of 2.02 ± 0.1 kcal mol obtained by infrared spectroscopy. © 1969.