AN INVESTIGATION OF HYDROGEN-BONDING BETWEEN HCL AND VINYLACETYLENE - A MOLECULE WITH 2 DIFFERENT PI-ACCEPTOR SITES

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 script A sign0, ℬ0, script C sign0, 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⋯ H 35Cl, CH2 CHCCH⋯H37Cl, and CH 2CHCCH⋯D35Cl. These spectroscopic constants have been interpreted in terms of a dimer in which the HCl subunit forms a hydrogen bond to the C≡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°. © 1990 American Institute of Physics.