Some remarks on the interpretation of natural and magnetically induced optical activity data

Abstract

1. Introduction—A classification for optically active chromophores One of the most useful concepts that emerges from the perturbation approach to the theory of natural optical activity is that of the ‘rotational strength’ of a transition (Condon 1937). This signed quantity conveniently and effectively measures how strongly a particular transition contributes to both the dispersive and absorp­tive aspects of the optical activity of a molecule (Moscowitz 1962); it is obtainable experimentally from either the pertinent partial optical rotatory dispersion curve or the partial circular dichroism curve (Djerassi 1960), and it is amenable to theo­retical calculation for homogeneous isotropic media as the following scalar product (Condon 1937; Moscowitz 1962; Djerassi 1960; Rosenfield 1928). R ba = I {( a | μ e | b ). ( b | μ m | a )}. Here ( a | μ e | b ) and ( b | μ m | a ) are the electric and magnetic dipole transition moments, respectively, connecting the ground state a and the excited state b , and I means imaginary part. Accessible as such to both theory and experiment, the rotational strength provides one of the most suitable foundations on which to build quanti­tative correlations between optical activity data and molecular structure.