Quantum‐Chemical Investigation of Hydrogen Bonds in Porphin

Abstract

Using the DFT Becke–Lee–Yang–Parr exchange‐correlation three‐parametric functional (B3LYP), we have calculated the geometry, the electron density distribution, and the vibration frequencies for pyrrole, porphin, and their 13 analogs with a regularly varying structure. It is shown that the determining role in the change in the frequencies of stretching and out‐of‐plane deformation vibrations of porphin compared to pyrrole is played by intramolecular hydrogen bonds at the porphyrin macroring center. We have separately considered and compared with the data for porphin complexes of pyrrole with different intermolecular hydrogen bonds: with an aromatic ring (NH···π cluster formed by the pyrrole self‐aggregation in the liquid state) and an unshared electron pair (NH···OH2‐ and NH···NC4H4 clusters). The degree of participation of the NH group in the hydrogen bonds increases in the series NH···π cluster, porphin, NH···OH2‐ and NH···NC4H4 clusters.