• ab initio calculations;
  • ammonia;
  • hydrogen bonds;
  • phenylacetylene;
  • substituent effect


The hydrogen-bonded complexes of phenylacetylene, 4-fluorophenylacetylene, 2-fluorophenylacetylene, and 2,6-difluorophenylacetylene with ammonia are investigated using IR–UV double resonance spectroscopy in combination with high-level ab initio calculations at the CCSD(T)/CBS level of theory. The C[BOND]H⋅⋅⋅N hydrogen-bonded complex, which involves an interaction of ammonia with the acetylenic CH group is the global minimum and is observed in all four cases investigated. In addition, phenylacetylene and 4-fluorophenylacetylene form a quasi-planar cyclic complexes with ammonia incorporating N[BOND]H⋅⋅⋅π and C[BOND]H⋅⋅⋅N hydrogen bonds, wherein the π-electron density of the acetylenic C[TRIPLE BOND]C bond acts as an acceptor to the N[BOND]H group of ammonia. A third ammonia complex is observed for 4-fluorophenylacetylene in which ammonia interacts with the fluorine atom once again, leading to the formation of a quasi-planar cyclic complex. The substitution of the fluorine atom on the phenyl ring of phenylacetylene modulates the intermolecular potentials, which are dependent on the position of the substitution.