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 co 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.