INTRAMOLECULAR HYDROGEN-BONDS AND FERMI RESONANCE IN N-SUBSTITUTED N'-(2-FLUOROBENZOYL)THIOUREA DERIVATIVES

The presence of intramolecular NH...O=C bonds was proved in N-substitu ted N'-(2-fluorobenzoyl)-thiourea derivatives by analysis of their inf rared spectra. The intramolecular vibrational effects bring about a sh ift of the nu(NH) vibrational band to lower frequencies to the extent that the band gets into a vicinity to the delta(NH) overtone and Fermi resonance occurs between them. In addition, the nu(NH) vibration is a lso affected by Fermi resonance with the nu(CO) + delta(NH) combinatio n. Double absorption bands were observed in the nu(CO) region for some of the derivatives. Based on perturbation theory applied to three-lev el interactions and using the Langseth and Lord equations, the band fr equencies corrected for Fermi resonance were calculated and the hydrog en bond strength was examined in the compounds studied.