The ultraviolet absorption spectra of some substituted acetophenones

Mueller, William A. (1956) The ultraviolet absorption spectra of some substituted acetophenones. Masters thesis, Memorial University of Newfoundland.

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Abstract

In order to investigate more fully the steric influences in the B-band of the ultraviolet spectrum, several acetophenones were prepared, giving molecules in which the angle between the planes of the electron rich centers varied. It was found that the light absorption maximum moved to shorter wavelengths as the amount of hindrance about the carbonyl group was increased, (i.e., as the interplanar angle was increased), and that steric hindrance increased in the order hydrogen atom <. ortho-methylene group of the cyclopentyl ring ( ortho-methyl group z orthomethylene group of tbe cyclohexyl ring ( an orthomethyl group ''buttressed'' by a methyl group in the adjacent meta-position. The carbonyl group becomes less readily accessible as steric interference is increased, as shown by the inability of the highly hindered ketones to form the ordinary ketone derivatives. In the highly hindered ketones, conjugation is inhibited to such an extent that the main peaks closely correspond to those of the substituted benzenoid hydrocarbons. The spatial orientation of the compounds is discussed by interpreting the spectra in terms of the electronic and steric effects of the substituents. The 2,4-dinitrophenylhydrazones of the unsubstituted compounds, and some of the substituted aompounds are included, and it was found that the amount of steric hindrance c,an sometimes be estimated by color, 1.e., as conjugation increases, the colors tend from yellow to red. A recent example from the literature on the spectra of substituted hydroxybenzoic acids is included, and it was found possible to correlate nicely the observed spectra by means of the theories of ster.ic and el1ectronic effects. In the experimental part, the syntheses of the ketones are described, along with the reaction of β-chloropropionyl chloride with tetralin, and an attempt to prepare 2,3,5,6-tetraethylbenzene.

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