SHIFTS IN THE CHARACTERISTIC CARBONYL WAVELENGTH

Abstract

The infrared spectra of complexes formed between twelve benzoylic compounds (benzoyl bromide, benzoyl chloride, phenyl benzoate, methyl benzoate, ethyl benzoate, benzaldehyde, benzoic anahydride, benzoic acid, acetophenone, propiophenone, benzamide, and benzophenone) and six metal halides ($SbBr_{3}, SbCl_{3}, FeCl_{3}, AlI_{3}, AlCl_{3}$, and $SbCl_{5}$) together with the $SnCl_{4}$, $HCl_{4}$, and $AlBr_{3}$ complexes of benzaldehyde have been studied in the 5.0 to 7.5 $\mu$ carbonyl region. A shift in the characteristic carbonyl wavelength of each benzoylic compound has been taken as prima-facie evidence of complex formation. The decreasing order of these metal halides to effect a shift in the characteristic carbonyl wavelength is: $SbCl_{5}$, $AlCl_{3}$, $AlBr_{3}$, $AlI_{3}$, $FeCl_{3}$,$TlCl_{4}$, $SnCl_{4}$, $SbCl_{3}$, $SbBr_{3}$. No wavelength shifts were observed with either $SnI_{4}$ or $SbI_{3}$. This order bears a striking resemblance to the catalytic effectiveness of these metal halides in a Friedel-Crafts reaction. The investigation has further shown the existence of a straight-line relationship between the amount of shift in the characteristic carbonyl wavelength and the bond energy of the complex (1, 2) provided the comparison be made for complexes of a single benzoylic compound and halides of metals in the same valence state.