Frequencies and absorption intensities of fundamentals and overtones of NH stretching vibrations of pyrrole and pyrrole-pyridine complex studied by near-infrared/infrared spectroscopy and density-functional-theory calculations

摘要

Near-infrared (NIR)/IR spectra were measured for pyrrole, pyridine and pyrrole-pyridine complex in CCl4 solutions. The first-overtone of the NH stretching vibration of free pyrrole was observed at 6856 cm(-1), but that of pyrrole-pyridine complex was missing or barely detectable. Theoretical calculations of the molecular vibrational potentials and the dipole moment functions of the NH stretching modes of free pyrrole and pyrrole-pyridine complex revealed that the transition dipole moment is significantly decreased upon formation of the complex, resulting in the remarkably weak intensity of the overtone mode of the hydrogen-bonded NH group.