A sector rule is developed for optically active lactones and lactams through the application of perturbation theory. The sign and qualitative magnitude of the 220 nm circular dichroism can be predicted by observing the placement of polarizable nonpolar substituents about the chromophore group. The perturbation treatment shows the effect on a sector rule of adding electric dipole allowedness to the zerohyphen;order electric quadrupole allowedness of the carboxylate ion chromophore from which the lactone or lactam derives. The observed difference in sign of circular dichroism between similar lactams and lactones has significant implications for the theoretical assignment of the long wavelengthnndash;pgr;ast; transition(s) in peptides. The peptide (lactam) transition is concluded to resemble most nearly the1A2larr;1A1(nndash;pgr;ast;) transition of the carboxylate ion. A transition resembling1B1larr;1A1(nndash;pgr;ast;) in carboxylate ion is expected at only slightly shorter wavelengths. A reversed order in wavelength is expected for the corresponding transitions in lactones.
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