Study of the Cis and Trans Conformers of 2-Halophenols Using Coherent Anti-Stokes Raman Spectroscopic and Quantum Chemical Methods

The OH stretching wavenumbers of the cis and trans conformers of 2-halophenols were studied in the gas phase by using coherent anti-Stokes Raman spectroscopy and quantum chemical calculations. The wavenumber differences between the two isomers of 2-fluoro-, 2-chloro- and 2-bromophenol were found to be 20, 71 and 102 cm^-1, respectively. These results are in good agreement with quantum chemical calculations based on the use of the density function theory. However, the calculated energy differences between two isomers decrease in the order Cl > Br > F. These results indicate that the vibrational wavenumber shift is not directly correlated with the strength of the intramolecular hydrogen bonding in 2-halophenols.