Temperature Dependence of Optical Rotation: α-Pinene, β-Pinene Pinane, Camphene, Camphor and Fenchone

The temperature dependence of the specific rotations of α-pinene, β-pinene, pinane, camphene, camphor, and fenchone were measured in ethylcyclohexane solutions from 0 to 100 °C, and at several wavelengths. The rotations for α-pinene and camphene have only a very small temperature dependence. In contrast, the specific rotations of β-pinene and pinane decrease significantly with increasing temperature. This does not appear to be a result of a complex between pinane and the solvent, since changing to di-n-butyl ether leads to essentially the same temperature dependence. The specific rotations of camphor and fenchone are temperature sensitive, but in opposite directions. The observed temperature dependence of the specific rotations of these compounds has important consequences for variable temperature studies of chiral compounds having two or more conformers with similar energies.