The Absorption Spectra of Naphthalene Sulfonic Acid Derivatives

1) The absorption spectra of some naphthalene sulfonic acid derivatives have been determined in various pH solutions.2) The remarkable spectral change revealed by the variation in pH value can be interpreted in terms of the process of the proton association and dissociation of the functional groups.3) The pH region in which the process takes place is characteristic of the kinds, –NH2, –OH, and the number of the functional groups and their locations on the naphthalene skeleton.4) The relative pH regions have been explained in outline by taking into account the effects of the sulfonic group, the intramolecular hydrogen bond formed between the functional groups, and the resonance of the functional group to the link.5) The band assignment concerning the transition direction of the derivatives has been decided; the first and the second band correspond, respectively, to the 1Laand 1Bbof naphthalene.6) The order of the magnitude of the substitution effect has been clarified as –NH3+< –OH<–NH2<–O-.