Magnitudes of Barriers in Intramolecular Rotation

By applying symmetry considerations to intramolecular torsional barriers the over-all barriers are resolved into contributions from the interactions of individual change distributions (i and k). This makes it possible to classify internal potential barriers and calculate their heights and shapes if the Fourier coefficients Cvik are known. Some figures, mainly C3ik values, were obtained from experimental barriers others can be estimated by theoretical methods. The Lennard-Jones potential with n = 12 and m = 6 appears to be altogether unsuitable for describing barriers of internal rotation, but a simple repulsive potential V = anR-n with n∼5 furnishes a reasonable approximation.