Binary Complexes of Ammonia with Phenylacetylenes: A Combined Experimental and Computational Approach to Explore Multiple Minima on Intermolecular Potentials

Abstract

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-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-H···π and C-H···N hydrogen bonds, wherein the π-electron density of the acetylenic C≡C bond acts as an acceptor to the N-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.

The propargylbenzene dimer: C–H⋯π assisted π–π stacking

“…We have recently shown that under similar experimental conditions only the structures which are within 1 kJ mol À1 of the global minimum are populated. 31 Therefore it is reasonable to neglect all the structures which are above 2 kJ mol À1 . Consequently, only structures P1, P3 and P4 are considered.…”

Spectroscopic and Ab Initio Investigation of C−H⋅⋅⋅N Hydrogen‐Bonded Complexes of Fluorophenylacetylenes: Frequency Shifts and Correlations

“…The IR spectra in the acetylenic C−H stretching region for the five ammonia complexes with PHA, 4‐FPHA, 2‐FPHA, 3FPHA, and 2,6‐DFPHA, along with the corresponding monomers, are shown in Figure . The IR spectra of PHA, 4FPHA, and 2,6‐DFPHA monomers shows multiple bands in the 3330 cm −1 region, which have been attributed to the Fermi resonance and other higher‐order couplings .…”

“…The IR spectra in the acetylenic CÀHs tretching region for the five ammonia complexes with PHA, 4-FPHA, 2-FPHA, 3FPHA, and 2,6-DFPHA, along with the corresponding monomers, are shown in Figure 1. [22,41] The IR spectra of PHA, 4FPHA, and 2,6-DFPHA monomers shows multiple bands in the 3330 cm À1 region, which have been attributed to the Fermi resonance and other higher-order couplings. [42][43][44] These spectra can be analyzed to identify the unperturbed acetylenic CÀHo scillator, which places the CÀHs tretching frequencies of PHA, 4FPHA, and 2,6-DFPHA at 3334, 3338, and3 338 cm À1 ,r espectively.…”

The CH‥O H-Bond as a Determining Factor in Molecular Structure

“…Calculations [80,87,[115][116][117][118][119][120][121][122] have shown that N serves an equivalent purpose. In fact, due its greater basicity, CH··N HBs tend to be stronger than CH··O [123].…”