title: The ultraviolet absorption spectra of some chlorinated biphenyls.
abstract: The UV  spectra of 29 chlorobiphenyls have been examined. With increasing chloro substitution in which there are less than two chlorine groups ortho to the Ph-Ph bond the lambdamax values for the K band (attributed to the conjugation between the two phenyl rings) are shifted to longer wavelengths and for the more highly substituted chlorobiphenyls there is also a bathochromic shift of the main band (due to the benzenoid skeleton). Introduction of two or more chlorine atoms ortho to the Ph-Ph bond results in a hipsochromic shift of K band and diminished xi value due to steric inhibition of resonance between the two phenyl rings. The sterically hindered chlorobiphenyls and the more highly chlorinated Aroclors also exhibit a series of low-intensity fine-structured absorption maxima between 268-302 nm. The UV spectra of chlor-biphenyls are particularly diagnostic with respect to the degree of substitution at the 2, 2', 6 and 6' positions and can be used in the structural analysis of separated chlorobiphenyls. The data may also aid in correlating the photochemical reactivities.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D011078:Polychlorinated Biphenyls / Q000032:analysis*; D013056:Spectrophotometry, Ultraviolet; D013329:Structure-Activity Relationship
chemical_list: D011078:Polychlorinated Biphenyls