MCD behavior of benzene and its derivatives

A general method for correlating data from CD and MCD spectra is formulated. The origin dependence of the MCD terms is resolved by minimization of appropriate terms in the Lagrangian density expression. Approximate summation techniques are developed for magnetic and natural optical activity. The salient features of the MCD spectra of benzene derivatives are analyzed. The observed opposite signed magnetic rotational strengths of (o,p)‐ and m‐directors is accounted for by a variation calculation which includes electron donor and acceptor wavefunctions based on occupied and unoccupied substituent orbitals. The uniqueness of the alternating signed benzene spectrum as compared with most hexasubstituted derivatives of D_6h symmetry is rationalized on the basis of the vibrational modes of E_2g symmetry for carbon‐carbon bond stretching and bending. The importance of comparable vibronic and electronic effects is emphasized in the anomalous behavior of the $B_{2_u}$ and $B_{1_u}$ bands for low symmetry derivatives.