H−π Landscape of the Phenylacetylene–HCl System: Does This Provide the Gateway to the Markovnikov Addition?

Dominance of unique Pπ phosphorus bonding with π donors: evidence using matrix isolation infrared spectroscopy and computational methodology

Albeit the first account of hypervalentπ interactions has been reported with halogenπ interactions, the feasibility of their extension to other hypervalent atoms as possible Lewis acids is still open. In this work, the role of phosphorus as an acceptor from the π electron cloud (Pπ pnicogen or phosphorus bonding) in PCl3-C2H2 and PCl3-C2H4 heterodimers is explored, by combining matrix isolation infrared spectroscopy with ab initio and DFT computational methodologies. The respective potential energy surfaces of the PCl3-C2H2 and PCl3-C2H4 heterodimers reveal unique minima stabilized by a concert of reasonably strong to weak interactions, of which Pπ phosphorus bonding was energetically dominant. Heterodimers, trimers and tetramers bound primarily by this unique phosphorus bond were generated at low temperatures. The dominance of phosphorus bonding in the PCl3-C2H2 and PCl3-C2H4 heterodimers over other interactions (such as Hπ, HCl, HP, Clπ and lone pair-π interactions) was confirmed and substantiated using extended quantum theory of atoms in molecules, natural bond orbital, electrostatic potential mapping and energy decomposition analyses. The following inferences in correlation with results from non-covalent-interaction analysis offer a complete understanding of the nature of the Pπ phosphorus bonding interactions. The significance of electrostatic forces kinetically favoring the formation of phosphorus bonded heterodimers, in addition to thermodynamic stabilization, is demonstrated experimentally.

Phenylacetylene as a gas phase sliding balance for solvating alcohols

Phenylacetylene offers two similarly attractive π binding sites to OH containing solvent molecules, the phenyl ring and the acetylenic triple bond. By systematically varying the solvent molecule and by methylating aromatic or acetylenic CH groups, the docking preference can be controlled. It ranges from almost exclusive acetylene docking to predominant phenyl docking, depending on how electron density is deposited into the conjugated system and how large the London dispersion interaction is. FTIR spectroscopy of supersonic jet expansions is used to observe the competitive docking preferences in phenylacetylene and some of its methylated derivatives. A new data evaluation procedure that estimates band strength uncertainties based on a Monte Carlo approach is introduced. We test how well two density functionals (B3LYP-D3 and M06-2X) in combination with a def2-TZVP basis set are able to describe the docking switch. B3LYP-D3 is slightly biased towards acetylenic hydrogen bond docking and M06-2X is strongly biased towards phenyl hydrogen bond docking. More accurate theoretical predictions are invited and some previous experimental assignments are questioned.

Structures and Spectroscopic Properties of F-(H2O) n with n = 1-10 Clusters from a Global Search Based On Density Functional Theory

Using a genetic algorithm incorporated in density functional theory, we explore the ground state structures of fluoride anion-water clusters F^-(H₂O) _n with n = 1-10. The F^-(H₂O) _n clusters prefer structures in which the F^- anion remains at the surface of the structure and coordinates with four water molecules, as the F^-(H₂O) _n clusters have strong F^--H₂O interactions as well as strong hydrogen bonds between H₂O molecules. The strong interaction between the F^- anion and adjacent H₂O molecule leads to a longer O-H distance in the adjacent molecule than in an individual water molecule. The simulated infrared (IR) spectra of the F^-(H₂O)_1-5 clusters obtained via second-order vibrational perturbation theory (VPT2) and including anharmonic effects reproduce the experimental results quite well. The strong interaction between the F^- anion and water molecules results in a large redshift (600-2300 cm^-1) of the adjacent O-H stretching mode. Natural bond orbital (NBO) analysis of the lowest-energy structures of the F^-(H₂O)_1-10 clusters illustrates that charge transfer from the lone pair electron orbital of F^- to the antibonding orbital of the adjacent O-H is mainly responsible for the strong interaction between the F^- anion and water molecules, which leads to distinctly different geometric and vibrational properties compared with neutral water clusters.