Diamagnetic anisotropy of organic molecules

Source abstract

Abstract The large positive value of the magnetic birefringence (Cotton-Mouton effect) of aromatic compounds led (Raman and Krishnan 1927) to the deduction, subsequently verified, that these compounds must possess pronounced molecular diamagnetic anisotropy, in addition to their already well-known optical anisotropy. The sign of the magnetic birefringence is very significant (Bhagavantam 1929). The positive sign indicates that, for uniaxial or approximately uniaxial molecules, the direction of maximum diamagnetic susceptibility is one of minimum optical polarizability, that is, of least refractive index. This is strikingly true of aromatic compounds, but must also be true of other classes of compound which show positive magnetic birefringence, such as ketones, fatty acids, esters of fatty acids and unsaturated alcohols. Very little information is as yet available concerning the magnetic anisotropy of these classes of organic molecule, measurements having been confined almost entirely to the aromatic compounds.