Fluorobenzene⋯water and difluorobenzene⋯water systems: An ab initio investigation

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Abstract
Recently, Brutschy and co-workers have reported the spectra of (substituted benzene)⋯ ( H 2 O ) n systems. To investigate the possibility of these systems exhibiting a π–H kind of bonding interaction as observed in benzene⋯ ( H 2 O ) n systems, we have carried out extensive ab initio calculations on different conformations of the fluorobenzene⋯ ( H 2 O ) and p- difluorobenzene⋯(H 2 O) systems using various basis sets. Our results indicate that unlike the π interaction observed in benzene⋯ ( H 2 O ) n , the O–H of the water molecule is involved in the formation of a six-membered ring system with the F–C–C–H of the aromatic ring. This six-membered ring which results from the formation of two H-bonds (water hydrogen and fluorine, water oxygen and benzene hydrogen), is extensively stabilized by electrostatic interactions. The strength of this σ-bonding interaction of water to fluorobenzene in C 6 H 5 F⋯H 2 O is nearly equal to the corresponding π-bonding interaction of water to benzene in C 6 H 6 ⋯H 2 O . However the σ interaction of water to difluorobenzene in p- C 6 H 4 F 2 ⋯H 2 O is somewhat higher than the π interaction in C 6 H 6 ⋯H 2 O and slightly higher than the corresponding interaction in C 6 H 5 F⋯H 2 O . The frequency shifts of the predicted OH stretching modes are in reasonable agreement with the experimental vibrational frequency shifts for both C 6 H 5 F⋯H 2 O and p- C 6 H 4 F 2 ⋯H 2 O .

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