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Detailed studies on the infrared spectra of organic molecules are particularly useful since they often contribute significantly to a better knowledge of the molecular parameters. Owing to our particular interest in this field, a systematic investigation concerning the vibrational behaviour of different classes of organic compounds has been carried out in the last years (1–3).

Although the vibrational spectrum of benzophenone has been analysed to some extent (1,2), and an attempt to calculate the normal vibrations was also made (3), a full systematization of the fundamentals of this molecule is not reached yet.

As a part of a continuing research program on the relationship between vibrational properties and molecular structure of -phenones (aceto- (1,2), and benzo- (3)) developed in this Laboratory, the results of i.r. measurements and assignments for a number of m-halogen benzophenones are presented here. The presence of rotational isomers has been deduced in the molecules examined and the observed features arising from their existence have been elucidated in the interpretation of the infrared spectra.

Systematic studies on the vibrational behaviour of organic molecules are of considerable interest since a good knowledge of the intramolecular vibrations often helps to establish spectra-structure correlations. In continuation of previous investigations on different classes of organic compounds (1–3), a vibrational analysis concerning a group of phenyl selenocyanates has been undertaken here.

Investigations on the vibrational behaviour of organic molecules in the low infrared region are of considerable interest since they often provide helpful results for a better knowledge of the molecular parameters. Although the vibrational features of simple benzene derivatives have been extensively investigated in the past years (1–3), the spectral analysis of more complex and less symmetrical molecules still appears rather difficult, mainly because in such systems strong coupling effects may occur. In the previous paper of this series (4) a vibrational analysis on a number of acetophenones was presented. Results for a group of methyl-phenyl-sulfoxides also including some deuterated derivatives are reported in the present work. It may be pointed out that a number of differences in the spectra of the two classes of compounds was observed.

The i,r. spectrum of CH2BrCl between 4000 and 200 cm−1 has been investigated in the liquid phase. All the absorptions, except few features, have been identified and more than 50 bands including fundamentals, overtone and combination bands have been assigned. Anharmonicity constants from the characterized vibrational levels have been also determined. Data from liquid phase spectra are needed to correctly interpret the rather complex vapor phase features whose investigation is in progress now.

Normal coordinate calculations are widely used by spectroscopists either to check the assignment of the fundamental vibrations or to derive a potential function representing the observational data of the molecules investigated.

Although various structural properties can be determined by investigating the far-infrared, the lack of systematic results for most classes of organic molecules seems to hinder a number of workers from undertaking studies in this region. As a part of an extensive investigation in this field (1), we report here the data and our interpretation for a group of acetophenones.

The infrared characteristics of aromatic-N-oxides and their correlations with other structural properties have been investigated in some details in monocyclic compounds, especially pyridine-N-oxides. However the amount of infrared observational data available in more complex systems is rather limited and its interpretation still mostly tentative (1).

As known, the hydrogen bond can be described as an interaction between a proton-donor group (A-H) and a proton–acceptor group (B) with the formation of a complex of the type (A-H··B).

In a previous work, the far-infrared spectra of pyridines were investigated and the hydrogen bonding stretching frequencies of their complexes with phenol were correlated with the electronic proper...