The vibrational spectrum of quinones. Part II. The infrared spectrum of 1,4-napthaquinone and 1,4-[2H6]naphthaquinone

Abstract

The absorption spectra of solution and powder samples of 1,4-naphthaquinone have been measured from 4000 to 33 cm.^–1; in the spectral region 4000–400 cm.^–1 the polarized spectra of the (100), (010), and (001) crystal planes have also been obtained. The dichroic behaviour of the absorption bands observed for the three different crystal planes is consistently interpretable by applying the oriented gas model. The validity of this assumption is further supported by the observed vapour-phase band envelope when it presents a clearly interpretable pattern and by the slightness of the crystal field effects. In this way it is possible to suggest a well supported vibrational assignment.

The investigation was extended to vapour, solution, and the (100) crystal plane of 1,4-[²H₆]naphthaquinone of high isotopic purity. The successful assignment achieved in this case adds substantial information to put the complete rationalization of the vibrational behaviour of this molecule on a firmer experimental base.