The electronic absorption spectra of a number of N-acylimidazoles have been investigated with special emphasis on the type and extent of interaction across the carbonyl group. Quantitative discussion of substituent and solvent effects is presented, based on the results of MO computation and energy partitioning analysis. The results of the present analysis enabled a quantitative definition of the classical and frequently used terminology of cross- and linear conjugation.
Rifaat Hilal, Sulaiman Basahel, and Saadullah Aziz, "On the Electronic Structure of Azolides. Part II: Electronic Absorption Spectra of N-Acylimidazoles. A MO Approach to Cross- and Linear Conjugation," Appl. Spectrosc. 40, 556-562 (1986)