X-ray and vibrational studies of the complex between N-tert-butoxycarbonyl-L-phenylalanine and pyridine. Isotope effect

✍ Scribed by L. Van Meervelt; C. Bruyneel; H. Morisse; Th. Zeegers-Huyskens

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 216 KB
• Volume: 10
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(199711)10:11<825::aid-pca949>3.0.co;2-7

✦ Synopsis

The x-ray structure of the complex between N-tert-butoxycarbonyl-L-phenylalanine and pyridine shows that the crystals are held together by short hydrogen bonds between the OH group and the N atom of the pyridine ring [R O(H)• • •N = 2•574(3) Å]. Deuteration of the OH and NH groups results in a small expansion of the unit cell associated with an elongation of the O• • •N distance [R O(D)• • •N = 2•610(3) Å]. The infrared spectra show very broad stretching protonic bands in the range 2750-600 cm Ϫ 1 . The isotopic ratio (OH• • •H)/(OD• • •N) of nearly unity suggests a double minimum potential with a low barrier for the hydrogen bridge. The Raman and near-infrared spectra are discussed. The perturbation of the fundamental modes and of the overtones of pyridine suggests that the complex is not of the proton transfer type. The broad absorptions of the hydrogen bridge disappear in the near-infrared region. The perturbation of the pyridine overtones is discussed.