Empirical Relationships of the Minor Bands in the Absorption Spectra of Polyenes.

Abstract

A study of published electronic absorption spectra of polyenes has led to the simple rule that all minor bands at short wave lengths correspond in location with the main band of shorter chromophores of lengths equal to integral fractions of the chromophore considered. The relative intensities of these ''overtone" bands are shown to be influenced by stereochemical factors (compare Zechmeister's cis-peak). Some new ideas, pertaining to the distribution of extinction value on the various bands, are developed and applied in a discussion of poly-cis carotenoids and Karrer's sterically hindered cis-compounds. The spectra of retro-polyenes and vitamins A1 and A8 are also discussed, · and an explanation of the difference between "retro" and "normal" spectra is proposed. The more general validity of the principles established is demonstrated by the spectra of diphenylpolyenes, symmetrical azines, polyazobenzenes, and polyphenyls .