Water Vapor Does Not Catalyze the Reaction between Methanol and OH Radicals

Recent reports [Jara‐Toro et al., Angew. Chem. Int. Ed. 2017 , 56, 2166 and PCCP 2018 , 20, 27885] suggest that the rate coefficient of OH reactions with alcohols would increase by up to two times in going from dry to high humidity. This finding would have an impact on the budget of alcohols in the atmosphere and it may explain differences in measured and modeled methanol concentrations. The results were based on a relative technique carried out in a small Teflon bag, which might suffer from wall reactions. The effect was reinvestigated using a direct fluorescence probe of OH radicals, and no catalytic effect of H₂O could be found. Experiments in a Teflon bag were also carried out, but the results of Jara‐Toro et al. were not reproducible. Further theoretical calculations show that the water‐mediated reactions have negligible rates compared to the bare reaction and that even though water molecules can lower the barriers of reactions, they cannot make up for the entropy cost.     

A comprehensive kinetic mechanism for CO,CH2O,and CH3OH combustion

New experimental profiles of stable species concentrations are reported for formaldehyde oxidation in a variable pressure flow reactor at initial temperatures of 850–950 K and at constant pressures ranging from 1.5 to 6.0 atm. These data, along with other data published in the literature and a previous comprehensive chemical kinetic model for methanol oxidation, are used to hierarchically develop an updated mechanism for CO/H₂O/H₂/O₂, CH₂O, and CH₃OH oxidation. Important modifications include recent revisions for the hydrogen–oxygen submechanism (Li et al., Int J Chem Kinet 2004, 36, 565), an updated submechanism for methanol reactions, and kinetic and thermochemical parameter modifications based upon recently published information. New rate constant correlations are recommended for CO + OH = CO₂ + H ( R23 ) and HCO + M = H + CO + M ( R24 ), motivated by a new identification of the temperatures over which these rate constants most affect laminar flame speed predictions (Zhao et al., Int J Chem Kinet 2005, 37, 282). The new weighted least‐squares fit of literature experimental data for ( R23 ) yields k₂₃ = 2.23 × 10⁵T^1.89exp(583/T) cm³/mol/s and reflects significantly lower rate constant values at low and intermediate temperatures in comparison to another recently recommended correlation and theoretical predictions. The weighted least‐squares fit of literature results for ( R24 ) yields k₂₄ = 4.75 × 10¹¹T^0.66exp(?7485/T) cm³/mol/s, which predicts values within uncertainties of both prior and new (Friedrichs et al., Phys Chem Chem Phys 2002, 4, 5778; DeSain et al., Chem Phys Lett 2001, 347, 79) measurements. Use of either of the data correlations reported in Friedrichs et al. (2002) and DeSain et al. (2001) for this reaction significantly degrades laminar flame speed predictions for oxygenated fuels as well as for other hydrocarbons. The present C₁/O₂ mechanism compares favorably against a wide range of experimental conditions for laminar premixed flame speed, shock tube ignition delay, and flow reactor species time history data at each level of hierarchical development. Very good agreement of the model predictions with all of the experimental measurements is demonstrated. © 2007 Wiley Periodicals, Inc. 39: 109–136, 2007     

Quantum Chemical Study of the Pressure-dependent Phosphorescence of [Cr(ddpd)2]3+ in the Solid State

The chromium(III) complex [Cr(ddpd)₂][BF₄]₃ shows two spin-flip emission bands in the near-infrared spectral region. These bands shift bathochromically by −14.1 and −7.7 cm⁻¹ kbar⁻¹ under hydrostatic pressure (Angew. Chem. Int. Ed. 2018 , 57, 11069). The present study elucidates the structural changes of the chromium(III) cations under pressure using density functional theory with periodic boundary conditions and the resulting effects on the excited state energies using high-level CASSCF-NEVPT2 calculations. The differences of the bands in pressure sensitivity are traced back to a different orbital occupation of the intraconfigurational excited states.     

Muon‐Substituted Malonaldehyde: Transforming a Transition State into a Stable Structure by Isotope Substitution

Isotope substitutions are usually conceived to play a marginal role on the structure and bonding pattern of molecules. However, a recent study [Angew. Chem. Int. Ed. 2014 , 53, 13706–13709; Angew. Chem. 2014, 126, 13925–13929 ] further demonstrates that upon replacing a proton with a positively charged muon, as the lightest radioisotope of hydrogen, radical changes in the nature of the structure and bonding of certain species may take place. The present report is a primary attempt to introduce another example of structural transformation on the basis of the malonaldehyde system. Accordingly, upon replacing the proton between the two oxygen atoms of malonaldehyde with the positively charged muon a serious structural transformation is observed. By using the ab initio nuclear‐electronic orbital non‐Born–Oppenheimer procedure, the nuclear configuration of the muon‐substituted species is derived. The resulting nuclear configuration is much more similar to the transition state of the proton transfer in malonaldehyde rather than to the stable configuration of malonaldehyde. The comparison of the “atoms in molecules” (AIM) structure of the muon‐substituted malonaldehyde and the AIM structure of the stable and the transition‐state configurations of malonaldehyde also unequivocally demonstrates substantial similarities of the muon‐substituted malonaldehyde to the transition state.     

Alpha-Carbonic Acid Revisited: Carbonic Acid Monomethyl Ester as a Solid and its Conformational Isomerism in the Gas Phase

In this work, earlier studies reporting α-H₂CO₃ are revised. The cryo-technique pioneered by Hage, Hallbrucker, and Mayer (HHM) is adapted to supposedly prepare carbonic acid from KHCO₃. In methanolic solution, methylation of the salt is found, which upon acidification transforms to the monomethyl ester of carbonic acid (CAME, HO-CO-OCH₃). Infrared spectroscopy data both of the solid at 210 K and of the evaporated molecules trapped and isolated in argon matrix at 10 K are presented. The interpretation of the observed bands on the basis of carbonic acid [as suggested originally by HHM in their publications from 1993–1997 and taken over by Winkel et al., J. Am. Chem. Soc. 2007 and Bernard et al., Angew. Chem. Int. Ed. 2011] is inferior compared with the interpretation on the basis of CAME. The assignment relies on isotope substitution experiments, including deuteration of the OH- and CH₃- groups as well as ¹²C and ¹³C isotope exchange and on variation of the solvents in both preparation steps. The interpretation of the single molecule spectroscopy experiments is aided by a comprehensive calculation of high-level ab initio frequencies for gas-phase molecules and clusters in the harmonic approximation. This analysis provides evidence for the existence of not only single CAME molecules but also CAME dimers and water complexes in the argon matrix. Furthermore, different conformational CAME isomers are identified, where conformational isomerism is triggered in experiments through UV irradiation. In contrast to earlier studies, this analysis allows explanation of almost every single band of the complex spectra in the range between 4000 and 600 cm⁻¹.     

A Shock Tube Study of H2 + OH → H2O + H Using OH Laser Absorption

The rate constant for the reaction of hydroxyl radicals (OH) with molecular hydrogen (H₂) was measured behind reflected shock waves using UV laser absorption of OH radicals near 306.69 nm. Test gas mixtures of H₂ and tert‐butyl hydroperoxide (TBHP) diluted in argon were shock‐heated to temperatures ranging from 902 to 1518 K at pressures of 1.15–1.52 atm. OH radicals were produced by rapid thermal decomposition of TBHP at high temperatures. The rate constant for the title reaction was inferred by best fitting the measured OH time histories with the simulated profiles from the comprehensive reaction mechanism of Wang et al. (USC‐Mech v2.0) (2007). The measured values can be expressed in the Arrhenius equation as k₁(T) = 4.38 × 10¹³ exp(–3518/T) cm³ mol^?1 s^?1 over the temperature range studied. A detailed error analysis was performed to estimate the overall uncertainty of the title reaction, and the estimated (2 – σ) uncertainties were found to be ±17% at 972 and 1228 K. The present measurements are in excellent agreement with the previous experimental studies from Frank and Just (Ber Bunsen‐Ges Phys Chem 1985, 89, 181–187), Michael and Sutherland (J Phys Chem 1988, 92, 3853–3857), Davidson et al. (Symp (Int) Combust 1988, 22, 1877–1885), Oldenborg et al. (J Phys Chem 1992, 96, 8426–8430), and Krasnoperov and Michael (J Phys Chem A 2004, 108, 5643–5648).In addition, the measured rate constant is in close accord with the non‐Arrhenius expression from GRI‐Mech 3.0 ( http://www.me.berkeley.edu/gri_mech/ ) and the theoretical calculation using semiclassical transition state theory from Nguyen et al. (Chem Phys Lett 2010, 499, 9–15).     

Dynamics of the CH3 + OH reaction

We study dynamics of the CH₃ + OH reaction over the temperature range of 300–2500 K using a quasiclassical method for the potential energy composed of explicit forms of short‐range and long‐range interactions. The explicit potential energy used in the study gives minimum energy paths on potential energy surfaces showing barrier heights, channel energies, and van der Waals well, which are consistent with ab initio calculations. Approximately, 20% of CH₃ + OH collisions undergo OH dissociation in a direct‐mode mechanism on a subpicosecond scale (<50 fs) with the rate coefficient as high as ～10^?10 cm³ molecule^?1 s^?1. Less than 10% leads to the formation of excited intermediates CH₃OH? with excess vibrational energies in CO and OH bonds. CH₃OH? stabilizes to CH₃OH, redissociates back to reactants, or forms one of various products after intramolecular energy redistribution via bond dissociation and formation on the time scale of 50–200 fs. The principal product is ¹CH₂ (k being ～10^?11), whereas ks for CH₂OH, CH₂O, and CH₃O are ～10^?12. The minor products are HCOH and CH₄ (k～10^?13). The total rate coefficient for CH₃ + OH → CH₃OH? → products is ～10^?11 and is weakly dependent on temperature. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 455–466, 2011     

DFT study on the role of methanol solvent in Morita–Baylis–Hillman reaction

B3LYP/6‐311++G** calculations have been carried out to study the role of methanol solvent in the trimethylamine‐catalyzed Morita‐Baylis‐Hillman reaction between acraldehyde and formaldehyde with CPCM solvent method and supramolecular model with one explicit CH₃OH solvent molecule, respectively. The optimized geometries and energies of the reactant complexes, intermediates, transition states, and products of the two reaction channels (corresponding to the scenarios of syn‐ and anti‐acraldehyde, respectively) were obtained, and the relative energy profiles were completed. The results reveal that CH₃OH solvent molecules can stabilize the zwitterionic intermediates and largely reduce the barrier of H transfer process by taking part in the formation of the transition state in this process. C? C bond formation step is the rate‐determining step of the whole reaction cycle. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Multidisciplinary Team of Chemists and Geneticists Working to Reclaim Value Embedded in Plastics

This invited Team Profile was created by Clay C. C. Wang. He and his collaborators recently published an article on the conversion of polyethylenes to fungal secondary metabolites. First, the team employs an oxidative catalytic process, highly tolerant of impurities, to degrade post-consumer polyethylenes to carboxylic diacids. Then, they utilize engineered strains of the fungus Aspergillus nidulans to convert these diacids to structurally diverse and pharmacologically active secondary metabolites. “Conversion of Polyethylenes into Fungal Secondary Metabolites”, C. Rabot, Y. Chen, S. Bijlani, Y.-M. Chiang, C. E. Oakley, B. R. Oakley, T. J. Williams, C. C. C. Wang, Angew. Chem. Int. Ed. 2023, e202214609 ; Angew. Chem. 2023, e202214609 .     

Vibrational mode analysis for the multichannel reaction of CH3Cl + OH

The recently presented ab initio calculations for the reaction system of CH₃Cl + OH (Dehestani and Shojaie, Int J Quantum Chem, in press) are applied to the vibrational mode analysis. Extending previous work, we use the vibrational mode analysis to elucidate the relationships of the reactants, the transition state, the intermediates (IM), and the products. The extensive investigation shows that the reaction mechanism is reliable. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical Investigation of the Topology of Spiroborate-Linked Ionic Covalent Organic Frameworks (ICOFs)

A novel type of ionic covalent organic framework (ICOF) with a spiroborate linkage has been recently designed and synthesized by Zhang and co-workers (Ionic Covalent Organic Frameworks with Spiroborate Linkage, Angew. Chem. Int. Ed. 2016 , 55, 1737–1741). The spiroborate-linked ICOFs exhibit high Brunauer–Emmett–Teller (BET) surface areas and significant amounts of H₂ and CH₄ uptakes, combined with excellent thermal and chemical stabilities. Inspired by the novel properties of ICOFs, with the aim of gaining better understanding of the structure of such spiroborate-linked ICOFs, a series of potential 3D network configurations of ICOFs connected with tetrahedral [BO₄]⁻ nodes were proposed, assuming the [BO₄]⁻ node in spiroborate segments takes a tetrahedral configuration. These ICOFs, in terms of 2D and 3D topology through torsional energy of the [BO₄]⁻ fragment, pore-size distribution, total energy of the framework, and gas adsorption properties were compared and systematically investigated by density functional theory calculations, molecular mechanics, and well-established Grand canonical Monte Carlo simulations. The results indicate that spiroborate-linked ICOFs are likely a mixture of various topologies. Among these architectures, the five-fold interpenetrating model shows the lowest energy and reasonable gas uptakes, therefore, it is considered to be the most possible structure. More importantly, the five-fold interpenetrating model, showing high CH₄ uptakes compared with several classic porous materials, represents a promising CH₄ storage material.     

The Moores Lab & ACRD-Advanced Biomaterials and Chemical Synthesis Team

This invited Team Profile was created by the Moores Lab at the Centre in Green Chemistry and Catalysis at McGill University and the Advanced Biomaterials and Chemical Synthesis (ABCS) team of the Aquatic and Crop Resource Development (ACRD) research centre of the National Research Council of Canada in Montréal. They recently published an article on the first solvent-free method for the synthesis of cellulose and chitin nanocrystals. “High-Humidity Shaker Aging to Access Chitin and Cellulose Nanocrystals”, T. Jin, T. Liu, F. Hajiali, M. Santos, Y. Liu, D. Kurdyla, S. Régnier, S. Hrapovic, E. Lam, A. Moores, Angew. Chem. Int. Ed. 2022, e202207006 ; Angew. Chem. 2022, e202207006 .     

Theoretical study on the formation mechanism of iso‐CH2I‐Cl

The dissociation and isomerization reaction mechanism on the ground‐state potential energy surface for CH₂ClI are investigated by ab initio calculations. It is found that the isomer iso‐CH₂I‐Cl can be produced from either the recombination of the photodissociation fragments or the isomerization reaction of CH₂ClI, rather than from isomerization reaction of iso‐CH₂Cl‐I. Further explanations of experimental results are also presented. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Clam‐like Cyclotricatechylene‐based Capsules: Identifying the Roles of Protonation State and Guests as well as the Drivers for Stability and (Anti‐)Cooperativity

Cyclotricatechylene (ctcH₆) is a bowl‐shaped macrocyclic compound that can be used as a building block for self‐assembled capsules. ctcH₆ and its derivatives in various protonation states – here collectively labeled as CTC – form dimers that resemble the shape of a clam. These clam‐shaped entities have been studied experimentally by Abrahams, Robson, and co‐workers [B. F. Abrahams, N. J. FitzGerald, T. A. Hudson, R. Robson and T. Waters, Angew. Chem. Int. Ed. 2009 , 48, 3129–3132] where the capsules acted as an excellent host for large alkali‐metal cations. In this study, we present a detailed analysis based on accurate dispersion‐corrected Density Functional Theory approaches that reveals the factors that stabilise such CTC‐based capsules at different protonation states and their interaction with various encapsulated guests. Our results show that the capsules’ overall stability results as an interplay of hydrogen bonding, London dispersion, and electrostatic effects. The most stable capsules with group‐1 and group‐2 cations as guests contain only six phenolic hydrogens, as opposed to the maximum possible number of twelve. Inclusion of larger alkali‐metal cations is favoured due to larger London‐dispersion contributions. Cations are favoured as guests over isoelectronic neutral species, as the resulting host‐guest complexes experience additional stability due to cooperative effects. In fact, using the latter to drive the formation of specific capsules could be used in future strategies aimed at synthesising similar aggregates; our results provide an insightful understanding and useful guidance for such future endeavours.     

Multichannel RRKM study on the mechanism and kinetics of the CH3Cl + OH reaction

The kinetics and mechanism of the reaction of OH with CH₃Cl have been theoretically studied. The potential energy surface for each possible pathway has been investigated by the G2MP2 method. The rate constants for channels leading to several products have been calculated by multichannel‐Rice‐Ramsperger‐Kassel‐Marcus (RRKM) theory over a temperature range 200–2000 K. The results show the major channel is hydrogen abstraction mechanism. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Theoretical study of thermal rearrangements of α‐silylalcohols: Effects of substituents attached to the silicon atom on the reactions

To investigate the effects of substituents attached to the silicon atom on the thermal rearrangement reactions of α‐silyl alcohols, the thermal rearrangement reactions of dimethylsilyl methanol (CH₃)₂SiHCH₂OH and vinylsilyl methanol CH₂?CHSiH₂CH₂OH were studied by ab initio calculations at the G3 level. Geometries of various stationary points were fully optimized at the MP2(full)/6‐31G(d) and MP2(full)/6‐311G(d,p) levels, and harmonic vibrational frequencies were calculated at the same levels. The reaction paths were investigated and confirmed by intrinsic reaction coordinate (IRC) calculations at the MP2(full)/6‐31G(d) level. The results show that two dyotropic reactions could occur when (CH₃)₂SiHCH₂OH or CH₂?CHSiH₂CH₂OH is heated. One is Brook rearrangement reaction (reaction A), and the dimethylsilyl or vinylsilyl groups migrates from carbon atom to oxygen atom coupled with a simultaneous migration of a hydrogen atom from oxygen atom to carbon atom passing through a double three‐membered ring transition state, forming dimethylmethoxylsilane (CH₃)₂SiHOCH₃ or methoxylvinylsilane CH₂?CHSiH₂OCH₃; the other is a hydroxyl group migration (reaction B) from carbon atom to silicon atom, coupled with a simultaneous migration of a hydrogen atom from silicon atom to carbon atom, via a double three‐membered ring transition state, forming trimethylsilanol (CH₃)₃SiOH or methylvinylsilanol CH₃SiH(OH)CH?CH₂. The G3 barriers of the reactions A and B were computed to be 312.8 and 241.4 kJ/mol for (CH₃)₂SiHCH₂OH, and 317.6 and 233.7 kJ/mol for CH₂?CHSiH₂CH₂OH, respectively. On the basis of the MP2(full)/6‐31G(d) optimized parameters, vibrational frequencies, and G3 energies, the reaction rate constants k(T) and equilibrium constants K(T) were calculated using canonical variational transition state theory (CVT) with centrifugal‐dominant small‐curvature tunneling (SCT) approximation over a temperature range of 400–1800 K. The influences of methyl and vinyl groups attached to the silicon atom on reactions are discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

The hydroxyl radical reaction rate constant and products of 3,5‐dimethyl‐1‐hexyn‐3‐ol

A bimolecular rate constant,k_DHO, of (29 ± 9) × 10^?12 cm³ molecule^?1 s^?1 was measured using the relative rate technique for the reaction of the hydroxyl radical (OH) with 3,5‐dimethyl‐1‐hexyn‐3‐ol (DHO, HC?CC(OH)(CH₃)CH₂CH(CH₃)₂) at (297 ± 3) K and 1 atm total pressure. To more clearly define DHO's indoor environment degradation mechanism, the products of the DHO + OH reaction were also investigated. The positively identified DHO/OH reaction products were acetone ((CH₃)₂C?O), 3‐butyne‐2‐one (3B2O, HC?CC(?O)(CH₃)), 2‐methyl‐propanal (2MP, H(O?)CCH(CH₃)₂), 4‐methyl‐2‐pentanone (MIBK, CH₃C(?O)CH₂CH(CH₃)₂), ethanedial (GLY, HC(?O)C(?O)H), 2‐oxopropanal (MGLY, CH₃C(?O)C(?O)H), and 2,3‐butanedione (23BD, CH₃C(?O)C(?O)CH₃). The yields of 3B2O and MIBK from the DHO/OH reaction were (8.4 ± 0.3) and (26 ± 2)%, respectively. The use of derivatizing agents O‐(2,3,4,5,6‐pentalfluorobenzyl)hydroxylamine (PFBHA) and N,O‐bis(trimethylsilyl)trifluoroacetamide (BSTFA) clearly indicated that several other reaction products were formed. The elucidation of these other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible DHO/OH reaction mechanisms based on previously published volatile organic compound/OH gas‐phase reaction mechanisms. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 534–544, 2004     

Supramolecular Materials Chemistry in the MacLachlan Group

This invited Team Profile was created by the MacLachlan group at the University of British Columbia . They recently published an article on the uniform growth of a metal–organic framework, ZIF-8, on the surface of individual cellulose nanocrystals (CNCs). After the ZIF-8/CNC fibers had been coated with a microporous organic polymer, the ZIF-8 was removed to leave a microporous polymer with CNCs encapsulated in a ship-in-a-bottle architecture. This material proved to be effective for CO₂ fixation. “Uniform Growth of Nanocrystalline ZIF-8 on Cellulose Nanocrystals: Useful Template for Microporous Organic Polymers”, K. Cho, L. J. Andrew, M. J. MacLachlan, Angew. Chem. Int. Ed. 2023 , e202300960 .