Infrared spectra of N-tert-butoxycarbonyl-amino acids at different temperatures

The IR spectra of N-tert-butoxycarbonyl-amino acids and of the complex betw een N-tert-butoxycarbonyl-L-phenylalanine and pyridine are investigated at temperatures ranging from 25 to -180 degrees C. A decrease of the temperatu re results in a contraction of the nN ... O or OH ... O hydrogen bonds. In this temperature range, linear correlations between the v(NK) and v(OH) str etching vibrations and the temperature are established. The slope of these correlations decreases with the R(O ... O) or R(N ... O) distances previous ly determined by X-ray diffraction. (C) 2000 Elsevier Science B.V. All righ ts reserved.