The Diamagnetic Anisotropy of Large Aromatic Systems Parts I and II

Part I. A short discussion is given of the magnetic properties of large aromatic hydrocarbons and of the applicability of various wave-mechanical methods of calculating the diamagnetic susceptibility. The ultimate particles of most cokes and carbon blacks are not sufficiently large to be regarded as crystalline and must be treated as large molecules: calculations on certain simple types of molecule are to be carried out with a view to elucidating the effect of particle size and shape on the magnetic properties of such carbons. For systems of these dimensions the molecular orbital method should be valid and, in fact, appears to constitute the only feasible approach to the problem. Part II. The method of molecular orbitals is applied in a discussion of the diamagnetic anisotropy of the p-polyphenyls, which may be regarded as the simplest type of aromatic chain molecule. An almost perfectly linear relationship is predicted between diamagnetic anisotropy and chain length: in this case the molecular orbital method should be valid for chains of up to at least 2,000 rings. The results are discussed and the desirability of further accurate experimental work on these molecules is pointed out: this would make possible a stringent test of the whole theory.