Intermolecular structure on binary complexes of water with phenylacetylene and its substituted analogs: a combined spectroscopic and ab initio investigation

Abstract

The hydrogen-bonded complexes of phenylacetylene, 4-fluorophenylacetylene, 2-fluorophenylacetylene and 4-cyanophenylacetylene with water were investigated using IR-UV double resonance spectroscopy. Phenylacetylene, 4-fluorophenylacetylene, 2-fluorophenylacetylene and 4-cyanophenylacetylene form quasi-planar cyclic complexes with water incorporating C–H···O and O–H···π hydrogen bonds. In the case of phenylacetylene, 4-fluorophenylacetylene and 2-fluorophenylacetylene complexes the π electron density of the acetylenic C≡C bond acts as an acceptor to the O–H···π hydrogen bond, while in the case of 4-cyanophenylacetylene complex it’s the π electron density of the C≡N bond is the acceptor. A second water complex was also observed for 2-fluorophenylacetylene in which water interacts with fluorine atom and acetylenic C≡C bond rendering a double donor motif for the water molecule. One of the most interesting features of water complexes of 4-fluorophenylacetylene and 2-fluorophenylacetylene is the preference of π hydrogen bond over σ hydrogen bond.