Band Nomenclature for the Ultraviolet Spectra of Conjugated Organic Compounds

Several systems of band nomenclature for use in the ultraviolet region have been proposed by various authors, giving rise to confusion and, sometimes, ambiguity. For example, the main absorption band in the ultraviolet region is variously referred to as the first primary band, the C-band, the B-band, or as the K-band. This leads to difficulty in establishing relationships between structure and spectral property since it is frequently not immediately evident which band is referred to by a particular author. Band identification, even apart from the problem of different systems of band nomenclature, cannot always be carried out with certainty, and it is, therefore, not surprising that a number of incorrect assignments appear in the literature. The present paper gives examples of bands being given doubtful assignments, partly on account of the confusion of nomenclature, and summarizes the available methods of band identification. It is strongly recommended that in the future only one system of band nomenclature should be used, and in order to facilitate the choice of one particular system of band nomenclature the advantages and disadvantages of each of the presently used systems are discussed.