Conformational Studies of α-Substituted Carbonyl Compounds by I. R. Spectroscopy. II. α-Heterosubstituted N, N-Diethylacetamides

Abstract

The α-heterosubstituted N, N−diethylacetamides(1–8) cis/gauche conformations population ratio have been estimated through the analysis of the carbonyl group stretching vibration in the carbon tetrachloride and in chloroform. The substituent steric properties determine the cis/gauche ratio which decreases as the substituent size increases. For most of the studied amides, the gauche rotamer carbonyl band exhibits larger shifts to lower frequencies than in the corresponding α-heterosubstituted propanones¹, but for the α-chloro-(4) and for the α-bromo-N,N−diethylacetamide(5) a reverse trend is observed. This behavior can be related to changes in the πC=O C—X Dihedral angle, an hyperconjugative effect being sugges ted to explain the frequency shifts of the gauche rotamers.

Key Words:

• Conformational studies
• I. R. spectroscopy
• α-heterosubstituted N,N-diethylacetamides.