IR study of the proton acceptor ability of N-t-butoxycarbonylproline N′-methylamide

Hydrogen bonding between N-t-butoxycarbonylproline N′-methylamide and phenol derivatives (pK_a = 10.20–7.75) are investigated by ir and Fourier transform ir spectrometry. The thermodynamic parameters determined in carbon tetrachloride solution show that the complexes are of medium strength, the stability constants at 298 K range from 80 to 1530 L mol^?1, and the enthalpies of complex formation range from – 30 to –34 kJ mol^?1. The study of the ir spectra in the ν_OH, ν_NH, and ν_c?o regions shows that complex formation occurs at the oxygen atom of the amide carbonyl. Hydrogen-bond formation at this site strengthens the intramolecular hydrogen bond of the seven-membered ring. © 1993 John Wiley & Sons, Inc.