A New Method For Detecting Intramolecular H-Bonds Of Aromatic Amides Based On The De-Shielding Effect Of Carbonyl Groups On Beta-Protons

Aromatic amide foldamers with highly predictable conformations possess potential for application in the fields of stereoselective recognition, charge transport and catalysis, whose conformations are commonly limited by the intramolecular hydrogen bonding between amide groups and hydrogen-bonding receptors. Herein, on the basis of the de-shielding effect of carbonyl groups on beta-protons, we develop a new method for detecting intramolecular hydrogen bonds of aromatic amide compounds. The solvent-related changes in the beta H chemical shifts (Delta(delta(beta H))) and NH chemical shifts (Delta(delta(NH))) of three kinds of amide compounds, which are frequently used as building blocks of aromatic amide foldamers, were recorded in chloroform, nitromethane, acetonitrile and DMSO. The Delta(delta(beta H)) method is found to be highly suitable for studying methoxy-benzamides and fluoro-benzamides in chloroform and DMSO. It is worth noting that a reference compound is not required for applying the Delta(delta(beta H)) method, which is an advantage over the Delta(delta(NH)) method. In addition, we extend the Delta(delta(NH)) method from methoxy-benzamides to pyridine-carboxamides and fluoro-benzamides in chloroform and DMSO, and propose that nitromethane and acetonitrile will be possible alternatives for the Delta(delta(NH)) method if a test compound is not soluble in chloroform.