Effects of hydrogen bond formation on vibrations of pyridine, pyrazine, pyrimidine, and pyridazine

Abstract

Vibrational frequency shifts of pyridine, pyrazine, pyrimidine, and pyridazine have been studied in several hydrogen donor solvents, H 2O, D 2O, CH 3OH, C 2H 5OH, and CHCl 3. Shifts to higher frequencies of almost all the vibrations of these molecules have been observed. In particular, new bands, which clearly arise from hydrogen bonded species, have been detected for skeletal vibrations, ν 1, ν 6 a , and ν 8 a (nomenclature after Lord et al.), in pyridine and pyrimidine. From the shifts to higher frequencies, it is concluded that considerable changes of electron distribution which strengthen the chemical bonds in these molecules take place when they participate in hydrogen bonds.