Knowledge Bank

A general theory of the diamagnetic susceptibilities of the alkanes is developed. It is found that the molecular susceptibilities are obtained as sums of contributions from the 1s electrons of the carbon atoms, from the various C-C and C-H bonds and from interactions between various pairs of adjacent C-C and C-H bonds. It is possible to express the theory in a semi-empirical form so that all susceptibilities of the alkane molecules are expressed in terms of three parameters. For the most reliable series of experimental data, the susceptibilities of 24 different hydrocarbons may be described by these parameters within an accuracy of 0.5%. Theoretical values of diamagnetic susceptibilities are given for 54 alkane molecules, namely for all isotopes up to and including octane, for the normal alkanes from nonane to hexadecane and for a few other molecules for which experimental data have been reported. The accuracy of the theoretical values is compatible with the accuracy of the measurements.