Vibrational Spectra of Cyclic Organophosphorus Compounds and their Conformations in the Liquid and Solid States

Abstract

Abstract The Raman and IR spectra of 5,6-benzo-1,3,2-dloxaphos-phepines have been studied In the solld and liquld states, In solutions of dlfferent polarity, the temperature and concentration being varied. The asslgnments of the spectra have been made, The main spectral features that depend on molecular conformatlons are the Intense highly polarized lines of the symmetrlc vlbrations (“breathIng”) of the seven-membered ring In the 700–800 cm−1 region, νp=x(X=S, Se) ad 530–650cm−1, the vibrations of o-xylllenlc fragment in the regions of 1050–1070 cm−1 (δc=c-c) and 1200–1220 cm−1 (νc=c-c). The δc=c-c and νc=c-c vibrations appeared to be a reliable conformatlonal test for the Identification of the chair and twist forms, the frequencies being equal to ∼1050 and∼1220 cm−1 In the flrst case and ∼1070 and∼1200 cm−1 In the second. As for the equlllbrium of the chair-like forms the frequencies of the axlal P=X bonds are always lower than the equatorlal. For most of the compounds the complex three and even four-component equllibrlum of the chair-like and flexible (twist) forms have been found in liquids and solutlons. In the crystal phase only the chair form ls stable, the P=X bond orientation being dependent on the substltuents at phosphorus.