AMPLIFIED SECTOR RULE FOR ELECTRIC DIPOLE-ALLOWED TRANSITIONS

A sector rule based on electron correlation or “dynamic coupling” between the chromophore and bonds of a molecule is developed for electric dipole-allowed transitions. In its simplest form, the development corresponds to a quantum model of rotatory strength arising from coupled electric dipole oscillators. With the rule, the sign and magnitude of transition rotatory strength can be estimated by examining a molecular model. Only knowledge of the transition wavelength and direction of polarization is required. Unlike most sector rules, it is necessary to observe carefully the orientation as well as the location of bonds placed dissymmetrically with respect to the chromophore. A number of illustrations are given for the butadiene 260-nm, the ketone 190-nm, and the ethylene 190-nm transitions. It appears that a “resonance” of the carbon-carbon bond polarizability perpendicular to the usually dominant polarizability along the bond occurs somewhere between 260 and 200 nm. © 1979, American Chemical Society. All rights reserved.