Density functional study on phenol derivative-ammonia complexes in the gas phase

Ab initio calculations with the DFT/BLYP level of theory and the 6-31G(d,p) basis set were performed on the hydrogen-bonded phenol derivative-ammonia complexes. Phenol and its following four derivatives with growing acidity, p-nitrophenol, pentafluorophenol 2,6-difluoro-4-nitrophenol, and 2-fluoro-4,6-dinitrophenol, were considered. The parameters sensitive to hydrogen bonding as well as their changes due to complex formation were studied. The calculated frequencies of phenol-ammonia complex showed good overall agreement with the recently reported experimental data, Thus, it is concluded that, infrared spectra predicted for the other complexes studied in this work, at the same theory level are also correct. The OH stretch vibrations of the phenol derivative moieties have showed large red shifts from that of isolated phenol, whereas the OH torsion vibrations have shifted toward higher wavenumbers. Despite the growing acidity of investigated phenols, no proton transfer toward ammonia was observed.