AbstractThe K‐bands in the ultraviolet absorption spectra ofmetaandparasubstituted biphenylamines, dissolved in acidic media, appear to be essentially identical with each other and with that of their parent compound, biphenyl. Apparently the electronic interaction of the two aromatic rings is not markedly disturbed by the mere presence of positively charged ammonium groups, provided the molecules are able to assume a planar structure. As can be expected, however, appreciable hypsochromic shifts of the K‐bands become manifest when one or more of these groups are located at theorthopositions. Moreover, a buttressing effect is observed in the case where ammonium groups are present simultaneously in adjoiningmetapositions.A discussion of results takes into account both steric and electrostatic factors operating between the groups invol