Rotational Isomers of N-Alkyl-N-(o-acylphenyl)acetamides

Rotational Isomers of N-Alkyl-N-(o-acylphenyl)acetamides

  We have studied molecular structure of N-alkyl-N-(o-acylphenyl)acetamides 1？3 by <SUP>1</SUP>H NMR spectroscopy. The <SUP>1</SUP>H NMR spectra clearly displayed that two rotational isomers are present in solution and two geminal N？CH₂ protons are magnetically nonequivalent. This was explained by restricted rotations about both the amide N？CO bond and the aryl-nitrogen bond. The ratios of exo (benzene ring trans to carbonyl) and endo rotamers were estimated to be 6？8:1 from the <SUP>1</SUP>H NMR spectra. The X-ray analysis of N-ethyl-N-(o-benzoylphenyl) acetamide 1 showed that the crystal has exo-form. The rotations about both the amide N？CO bond and the aryl-nitrogen bond were slower on the NMR time scale.