Intra‐ and inter‐molecular interactions in non‐centrosymmetric and centrosymmetric phases of crystalline m‐nitrophenol as studied by polarized Raman and IR spectra. Comparison with internal vibrational spectra of m‐nitroaniline, m‐aminophenol and α‐resorcinol

Abstract

AbstractThe polarized Raman and IR spectra of m‐nitrophenol (mNPh) crystals in two modifications and of mNPh and its deuterated analogue powders in a KBr pellet, nujol mull and CCl4 solution have been measured in the region 200–4000 cm−1. The results are discussed and compared with earlier published data for α‐resorcinol, m‐nitroaniline and m‐aminophenol (mAPh). For the last compound new results, i.e. the IR spectra of the deuterated analogue, are presented, and reinterpretation of some previous assignments is proposed. The assignments of the bands in the mNPh spectra and the re‐examination of the mAPh spectra were facilitated by ordering the spectra of the four compounds into two classes exhibiting common features.It has been found that the differences between the spectra of two phases of the mNPh crystal are small and reflect the differences in interactions between the chains of molecules linked by hydrogen bonds. These interactions perturb particularly the NO2 group vibrations which cannot be treated using the oriented gas model. On the basis of INDO/CI calculations of electronic absorption spectra vibronic couplings in the IR and Raman spectra of the mNPh crystals have been proposed to account for many intensity enhancements.