THE PROTON RESONANCE SPECTRA OF BENZYL ACETONE

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Abstract
The proton resonance spectra of benzyl acetone (4-phenyl-2-butanone) are reported in a variety of solvents at 23 °C. A marked solvent dependence is noted for the CH3 group and the methylene protons adjacent to the keto group. The shifts to high field in aromatic solvents are interpreted in terms of a specific dipole-induced interaction with solvent molecules.The signals for the two non-equivalent pairs of methylene protons show changes in coupling constant with temperature. From this it is concluded that rapid rotation occurs about the C—C bond in the temperature range investigated with an increase in population of the trans conformation at low temperature. Significant changes in relative chemical shifts are also noted with temperature change for the two pairs of methylene protons and are attributed to the formation of weak molecular complexes in aromatic solvents.