Infrared spectra of some aromatic compounds

A study was made of the effect of substituent groups on the infrared spectra of aromatic compounds. Particular attention was devoted to the out-of-plane vibrations which give rise to strong absorption bends between 650 and 900 cm-1 with frequencies characteristic of the number and position of substituent groups. Most substituent groups were found to affect the spectra in a manner dependent upon the mass of the atom attached to the ring, but nitro and carboxyl groups and salts and esters of carboxyl groups had the effect of abnormally light groups. In addition, these same groups sometimes caused a new absorption band to appear in this region. Possible reasons for the effect of these groups discussed, and a hydrogen bond between an electronegative atom of the substituent group and a hydrogen atom ortho to the group is found to be the most probable cause of the effect;Spectra in the region of the in-plane hydrogen bending vibrations and the C-H stretching vibrations were also studied in an effort to provide confirmation for the hydrogen bond hypothesis. No confirmation was found, but it is shown that the data do not disprove the hypothesis;A method was developed for the determination of the ratio of phenyl to para-tolyl groups in tetra-arylsilanes and hexa-aryldisilanes;Study of the spectra of benzyl chloride and phenyl acetate in that liquid and solid states showed the presence of at least two rotational isomers in benzyl chloride but no such isomerism in phenyl acetate;Study of the region between 15 and 25 microns indicated that it should be possible, for certain symmetries of substitution, to find correlations between the nature of the substituents and the frequency of absorption bands

Infrared spectra of some aromatic compounds

A study was made of the effect of substituent groups on the infrared spectra of aromatic compounds. Particular attention was devoted to the out-of-plane vibrations which give rise to strong absorption bends between 650 and 900 cm-1 with frequencies characteristic of the number and position of substituent groups. Most substituent groups were found to affect the spectra in a manner dependent upon the mass of the atom attached to the ring, but nitro and carboxyl groups and salts and esters of carboxyl groups had the effect of abnormally light groups. In addition, these same groups sometimes caused a new absorption band to appear in this region. Possible reasons for the effect of these groups discussed, and a hydrogen bond between an electronegative atom of the substituent group and a hydrogen atom ortho to the group is found to be the most probable cause of the effect;Spectra in the region of the in-plane hydrogen bending vibrations and the C-H stretching vibrations were also studied in an effort to provide confirmation for the hydrogen bond hypothesis. No confirmation was found, but it is shown that the data do not disprove the hypothesis;A method was developed for the determination of the ratio of phenyl to para-tolyl groups in tetra-arylsilanes and hexa-aryldisilanes;Study of the spectra of benzyl chloride and phenyl acetate in that liquid and solid states showed the presence of at least two rotational isomers in benzyl chloride but no such isomerism in phenyl acetate;Study of the region between 15 and 25 microns indicated that it should be possible, for certain symmetries of substitution, to find correlations between the nature of the substituents and the frequency of absorption bands.</p