We comment briefly on the torsional potential around the C12-C13 bond shown in the lower panel of figure Figure . There are two unusual features. The GM has a zig-zag structure; the dihedral angle for such a structure is π. One might have thought that the "u"-or boat-shaped structure would be another minimum, but we find that it is actually a transition state (TS2) with a fairly high barrier, 2931 cm -1 , for the unrelaxed structure. The reason is that the hydrogen atoms interact with one another in an unfavorable way, so that the LM structures are more stable where the dihedral angles are not 0 and 2π but rather about 1.1 and 5.05 radians. The second feature of the potential is that TS1 is not, as might have been expected, at a θ dh of π/2 and 3π/2 but rather at about 2.05 and 4.1 radians.