IR STUDY ON CH2X2 DOUBLE HYDROGEN-BONDING

Study on double hydrogen bond formed between CH2Cl2, CH2Br2 and CH2I2 with electron donor organic solvents is performed using IR spectroscopy. The analysis of IR spectra is based mainly on intensity changes of the nu1 (symmetric) and the nu6 (antisymmetric) CH stretching vibration bands of the CH2X2 molecules. The significant (even more than ten times) increase of the intensities of both stretching CH vibration bands in electron donor media strongly suggest that the hydrogen bond is formed. Changes of the band maxima positions and the bandwidths confirm this fact but those parameters are not as sensitive as the intensities. Based on the nu1 to nu6 intensity ratio we show that CH2X2 molecule in complex with electron donor solvent molecules preserves its C2v symmetry. Thus the hydrogen bond in such complexes is double. In so called inert solvents, CH2Br2 and CH2I2 preserve their C2v symmetry too. On the contrary, dichloromethane molecule looses its C2v symmetry. This conclusion results from observation of inversion Of nu1 to nu6 intensity ratio. We explain this fact by dimerisation of CH2Cl2 (or CH2D2) molecules in the inert media. The comparison of behavior of CH2X2 molecules in both electron donor and inert media is presented.