An investigation of hydrogen bonding between HCl and vinylacetylene: A molecule with two different π-acceptor sites

Abstract

The ground state rotational spectrum of a hydrogen-bonded dimer formed by vinylacetylene and hydrogen chloride has been detected by the pulsed-nozzle, Fourier-transform microwave technique. Vinylacetylene has been chosen as a prototype acceptor molecule containing two different π-acceptor sites. Rotational constants 𝒜0, ℬ0, 𝒞0, centrifugal distortion constants ΔJ, ΔJK, δJ, δK, and three components χaa, χbb−χcc, and χab of the Cl nuclear quadrupole coupling tensor have been determined for each of the three isotopomers CH2CHCCH⋅⋅⋅ H35Cl, CH2CHCCH⋅⋅⋅H37Cl, and CH2CHCCH⋅⋅⋅D35Cl. These spectroscopic constants have been interpreted in terms of a dimer in which the HCl subunit forms a hydrogen bond to the C 3/4 C triple bond in a T-shape configuration, but is displaced from the center of the triple bond by d=0.04 Å towards the inner C atom, and makes an angle φ=34° with the vinylacetylene plane. The experimental angular geometry is in excellent agreement with that predicted by the Buckingham–Fowler electrostatic model which gives φ=27°.