The preferred OH docking site in phenylacetylene can be controlled by chemical tuning between phenyl and acetylenic OH⋯π

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This study reports, for the first time, the experimental study of the hydrogen-bonded complexes of HO and MeOH with 1,3-dimethylimidazol-2-ylidene, which is a dimethyl-substituted N-heterocyclic carbene, using matrix isolation infrared spectroscopy. The hydrogen bond was found to be established between the carbene carbon and the hydrogen in the O-H group of HO or MeOH. The hydrogen-bonded complexes of N-heterocyclic carbenes are significantly stronger than many conventional hydrogen-bonded systems, as is evidenced by the large red shifts observed in the infrared frequencies of complexed HO and MeOH. The experimental results were corroborated by computations performed at MP2 and M06-2X levels of theory, using 6-311++G(d,p) and aug-cc-pVDZ basis sets, which indicated large interaction energies (∼9 kcal mol) for these complexes. Single-point calculations at the CCSD level of theory were also performed. Atoms-in-molecules (AIM), NBO, and LMOEDA analyses were also performed to understand the nature of the intermolecular interactions in these complexes. The dominant interaction was the electron delocalization from the carbene carbon to the σ* orbital of O-H of HO or MeOH.

Hydrogen-bonded complexes of phenylacetylene (PhAc) with methanol (MeOH) and diethylether (DEE) were studied using matrix isolation infrared spectroscopy. This study specifically searched for the ≡C-H⋯O hydrogen bonded complex in these systems, which manifest a n-σ* interaction and which is a local minimum on the PhAc-MeOH potential surface, as in the case of PhAc-H₂O heterodimer. This n-σ* local minimum eluded observation in gas phase studies and it was therefore thought interesting to look for this isomer in cryogenic matrices. While MeOH can interact with PhAc as both a proton donor (O-H⋯π complex) or a proton acceptor (n-σ* complex), DEE can only manifest the n-σ* isomer. A comparison of the spectral shifts observed in the features of PhAc-MeOH and PhAc-DEE would therefore independently confirm the existence or not of n-σ* complex in both these systems. In addition to the n-σ* complex observed in both the above systems, the O-H⋯π complex was also discerned in the PhAc-MeOH system. These complexes have stabilization energy in the range of 8-25 kJ /mol. The experimental results were corroborated by computations performed at MP2 and M06-2X, levels of theory, using 6-311++G(d,p) and aug-cc-pVDZ basis sets. Single point calculations at the CCSD level of theory were also performed. Atoms-in-molecules (AIM), NBO and LMOEDA analysis were also performed to understand the nature of the intermolecular interactions in these complexes