The phenyl vinyl ether–methanol complex: a model system for quantum chemistry benchmarking

Abstract

The structure of the isolated aggregate of phenyl vinyl ether and methanol is studied by combining a multi-spectroscopic approach and quantum-chemical calculations in order to investigate the delicate interplay of noncovalent interactions. The complementary results of vibrational and rotational spectroscopy applied in molecular beam experiments reveal the preference of a hydrogen bond of the methanol towards the ether oxygen (OH∙∙∙O) over the π-docking motifs via the phenyl and vinyl moieties, with an additional less populated OH∙∙∙P(phenyl)-bound isomer detected only by microwave spectroscopy. The correct prediction of the energetic order of the isomers using quantum-chemical calculations turns out to be challenging and succeeds with a sophisticated local coupled cluster method. The latter also yields a quantification as well as a visualization of London dispersion, which prove to be valuable tools for understanding the role of dispersion on the docking preferences. Beyond the structural analysis of the electronic ground state (S0), the electronically excited (S1) state is analyzed, in which a destabilization of the OH∙∙∙O structure compared to the S0 state is observed experimentally and theoretically.

Isomerism of the Aniline Trimer

“…Thebalance of weak non-covalent forces alternating between ring or chain structures has been observed before, [9] but the structural detail of the present rotational study is unprecedented for ac luster of this molecular size.I np articular, the reduced stability of the symmetric top aniline trimer compared to phenol questions whether this kind of regular geometries will be present for even weaker interactions, calling for additional experiments with lower electronegativity atoms.T he advantages of ad irect comparison between rotational data and computational calculations proves valuable to assess the performance of the DFT methods. [40] As previously observed in related clusters [24,29,30] the structural description of the B3LYP-D3(BJ) model is satisfactory for the present spectroscopic purposes,but the energetic description is unclear and the conformational search still pose considerable difficulties.I np articular, it is difficult to correlate energetic properties and jet populations,w hich might be kinetically controlled by multi-body collisions benefiting specific structures less stable thermodynamically. [41] Af ull description of the jet populations would require adescription of the conformational relaxation paths,aformidable task out of the scope of our experiment.…”

“…[27] Predictions using both ap arametrized functional (M06-2X [25] )and dispersion-corrected DFT energies (B3LYP-D3(BJ) [26] )w ill be evaluated. Ther esults will illustrate the balance of forces in the aniline trimers,s imultaneously revealing shortcomings of the DFT models.F inally,a nalysis of the reduced electron density will help describing the physical forces in the clusters.O ur model selection was justified by aprevious analysis of vibrational data using M06-2X [28] and the documented performance of D3 corrections in rotational [29] and vibrational [30] experiments. Thee xperiment probed aj et expansion of aniline,u sing neon as carrier gas.The rotational spectrum was measured in the region 2-8 GHz with broadband fast-passage microwave spectroscopy, [31] using different configurations (see Supporting Information, SI).…”

Phenylacetylene as a gas phase sliding balance for solvating alcohols

“…15 For others, only a single gas phase UV/IR study is currently available. 4 Here, we apply the intermolecular energy balance concept [21][22][23] to phenylacetylene and its meta-methylated derivative. Several examples of intermolecular balances have been described in a recent review.…”

“…24 The competition between these two sites of diphenylether-methanol complexes can essentially be tipped to either side by chemical substitution on the ether or the alcohol. 22,25,26 Aromatic ring methylation has been used before to tip the balance in anisole microsolvation experiments. 26 While we have included the case of water and ethanol solvation, the main focus of this work is on methanol and tert-butyl alcohol, which differ significantly in their secondary dispersion interaction.…”

“…26 While we have included the case of water and ethanol solvation, the main focus of this work is on methanol and tert-butyl alcohol, which differ significantly in their secondary dispersion interaction. Although phenylacetylene offers three docking sites, like the structurally somewhat related phenyl vinyl ether, 22 only two are competitive towards alcohols and water. Both involve phenylacetylene as a hydrogen bond acceptor, either via its acetylenic (Ac) or its phenyl (Ph) p cloud.…”