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Samples of propyne trapped in solid parahydrogen show multiple peak structures in their infrared spectra. These structures are attributed to molecules in two distinct kinds of matrix sites. The most intense lines are assigned to propyne molecules executing a slightly hindered methyl rotation, as was extensively studied in our earlier publication from our two groups, and the other set of peaks to propyne trapped in a secondary site where the methyl rotation is quenched and replaced by methyl torsion within the matrix site. The assignment of the various rovibrational transitions is made possible by the observation of nuclear spin conversion (NSC) within the methyl group at long timescales. The NSC rate depends on the site and is much slower in the sites where the methyl rotation is quenched. [ABSTRACT FROM AUTHOR]

Context: Allene (H2C = C = CH2) and propyne (CH3-C≡CH) are important compounds in the combustion chemistry. They can be created from the reaction of proparyl radicals with water. In this study, therefore, a computational study into the C3H3 + H2O potential energy landscape has been carefully conducted. The computed results indicate that the reaction paths forming the products (allene: CH2CCH2 + •OH) and (propyne: HCCCH3 + •OH) prevail under the 300–2000 K temperature range, where the latter is much more predominant compared to the former. However, these two products are not easily formed under ambient conditions due to the high energy barriers. In the 300 – 2000 K temperature range, the branching ratio for the propyne + •OH product declines from 100 to 86%, whereas the allene + •OH product shows an increase, reaching 14% at 2000 K. The overall bimolecular rate constant of the title reaction can be presented by the modified Arrhenius expression of ktotal = 1.94 × 10–12 T0.14 exp[(-30.55 kcal.mol−1)/RT] cm3 molecule−1 s−1. The total rate constant at the ambient conditions in this work, 2.37 × 10–34 cm3 molecule−1 s−1, was found to be over five orders of magnitude lower than the total rate constant of the C3H3 + NH3 reaction, 7.98 × 10–29 cm3 molecule−1 s−1, calculated by Hue et al. (Int. J. Chem. Kinet. 2020, 4(2), 84–91). The results in this study contribute to elucidating the mechanism of allene and propylene formation from the C3H3 + H2O reaction, and they can be used for modeling C3H3-related systems under atmospheric and combustion conditions. Methods: All the geometric structures of the C3H3 + H2O system were optimized by the B3LYP method in conjunction with the 6–311 + + G(3df,2p) basis set. Single-point energies of these species were calculated at the CCSD(T)/6–311 + + G(3df,2p) level of theory. The CCSD(T)/CBS level has also been used to compute single-point energies for the two major reaction channels (C3H3 + H2O → allene + •OH and C3H3 + H2O → propyne + •OH). Rate constants and branching ratios of the key reaction channels were calculated in the 300–2000 K temperature interval using the Chemrate software based on the transition state theory (TST) with Eckart tunneling corrections. [ABSTRACT FROM AUTHOR]

A novel kind of ionic porous polymer that integrated stable structure and well-tuned pore microenvironment was presented as an efficient adsorbent for challenging C 3 H 4 /C 3 H 6 separation with the highest polymer-grade C 3 H 6 productivity among porous organic polymers. [Display omitted] • A novel ionic porous polymer was designed for propyne/propylene separation. • P(Ph4Im-Br-DVB) features abuntant micrporosity, high ionic content and stability. • The polymer exhibits excellent selectivity (43) and boosted diffusion performance. • Highest polymer-grade propylene productivity among POPs (5.7 mol/kg) was achieved. Developing highly selective and stable adsorbents for capturing trace propyne from propylene to produce polymer-grade propylene is of great significance but challenging. Porous organic polymers with high stability are promising for propyne removal, but display trade-off effect between capacity and selectivity. Here, we report a novel ionic porous polymer with stable structure and well-tuned pore microenvironment featured abundant microporosity and inorganic anions, which realized efficient propyne/propylene separation. Gas adsorption experiments demonstrate excellent propyne/propylene selectivity (43) and boosted diffusion performance. Meanwhile, polymer-grade propylene (≥99.5 %) could be obtained with the highest productivity (5.7 mol kg−1) among porous organic polymers. Molecular simulations reveal the high-density anions in P(Ph4Im-Br-DVB) enable effective discrimination of propyne from propylene with hydrogen-bonding like interactions. This work highlights how pore microenvironment tuning in porous organic polymers can realize the efficient gas separation. [ABSTRACT FROM AUTHOR]