Conformational Influences on Electronic Spectra and Structure. Polymorphs of N-(p-Chlorobenzylidene)-p-chloroaniline

Conformational polymorphism, in which a molecule adopts significantly different conformations in different crystal polymorphs, is exhibited by N-(p-chlorobenzylidene)-p-chloroaniline (1). Conformations observed in the two solids also differ somewhat from the most likely one in solution. Normal incidence reflection spectra and Kramers-Kronig transforms are reported for both crystal forms. Differences in electronic structure due to variations in conformation are manifested in the spectra and provide direct evidence for conformational influences on electronic structure and spectra. Bands in the Kramers-Kronig derived absorption spectra show a very good correspondence with the π electronic energy levels for nonplanar benzylideneaniline (BA) and a planar analogue as determined by previously reported photoelectron spectra.