Rotational barriers in five related amides

Interest in the low carbonyl IR frequency of 2-hydroxy-N,N-bis(2-hydroxyethyl)acetamide (2) initially prompted our interest in the amide rotational barrier of this molecule and four related amides that present a variety of hydrogen-bonding possibilities. In the course of this study, a previously incorrect structural assignment was established as N,N-bis[2-(acetyloxy)ethyl]-acetamide (6). In acetonitrile-d3, the carbonyl IR frequencies of the five amides were all essentially normal amide frequencies. Despite very different hydrogen-bonding possibilities in the five amides, no clear trends emerged in the comparison of the rotational barriers (ΔG‡), and the rotational barriers were essentially normal for amides. The rotational barrier of 2 did not vary over one order of magnitude difference in concentration.