IR study of the dimerization and the proton acceptor ability of N-tertio-butoxycarbonyl-L-phenylalanine

In this work, the dimerization and proton acceptor ability of N-tertiobutox ycarbonyl-L-phenylalanine are investigated in carbon tetrachloride by infra red spectrometry. A preliminary theoretical study carried out at the PM3 le vel shows that in the gaseous state, the trans conformation of the urethane group is slightly preferred over the cis one. The FTIR spectra are studied in nu(OH), nu(NH) and nu(C=O) regions. In solution, homodimers between two carboxylic groups and heterodimers between the carboxylic group of one mol ecule and the urethane group of another molecule are formed. Complex format ion with phenol derivatives (pK(a) = 10.3-8.1) takes place on the urethane carbonyl group. The stability constants at 298 K range between 22 and 82 dm (3) mol(-1) and the enthalpies of complex formation from 13 to 18 kJ mol(-1 ). (C) 1999 Elsevier Science B.V. All rights reserved.