Hydrolysis of Ketene Catalyzed by Formic Acid: Modification of Reaction Mechanism, Energetics, and Kinetics with Organic Acid Catalysis

Intramolecular Catalytic Hydrogen Atom Transfer (CHAT)

Intramolecular catalysis (IntraCat) is the acceleration of a process at one site of a molecule catalyzed by a functional group in the same molecule; an external agent such as a solvent typically facilitates it. Here, we report a general first-principles-based IntraCat mechanism, which strictly occurs within a single molecule with no coreagent being involved─we call it intramolecular catalytic transfer of hydrogen atoms (CHAT). A reactive part of a molecule (chat catalyst moiety or chat agent, represented by -OOH, -COOH, -SH, -CH2OH, -HPO4, or another bifunctional H-donor/acceptor group) catalyzes an interconversion process, such as keto-enol or amino-imino tautomerization, and cyclization in the same molecule, while being regenerated in the process. It can thus be regarded as an intramolecular version of the intermolecular H atom transfer processes mediated by an external molecular catalyst, e.g., dihydrogen, water, or a carboxylic acid. Earlier, we proposed a general mechanistic systematization of intermolecular processes, illustrated in the simplest case of the H2-mediated reactions classified as dihydrogen catalysis [Asatryan, R.; et al. Catal. Rev.: Sci. Eng., 2014, 56, 403-475]. Following this systematization, the CHAT catalysis belongs to the category of relay transfer of H atoms, albeit in an intramolecular manner. A broader class of intramolecular processes includes all types of H-transfer reactions stimulated by an H-migration, which we call self-catalyzed H atom transfer (SC-HAT). The CHAT mechanism comprises a subset of SC-HAT in which the catalytic moiety is regenerated (i.e., acts as a true catalyst and not a reagent). We provide several characteristic examples of CHAT mechanism based on detailed analysis of the corresponding potential energy surfaces. All such cases showed a dramatically reduced activation barrier relative to the corresponding uncatalyzed H-transfer reactions. For example, we show that CHAT can facilitate long-range H-migration in larger molecules and can occur multiple times in one molecule with multiple interconverting groups. It also facilitates amino-imino tautomerization of unsaturated GABA-analogues and peptides, as well as intramolecular cyclization processes to form heterocycles, e.g., oxygenated rings. CHAT pathways may also explain the pH-dependent increase of mutarotation rate of glucose-6-phosphate demonstrated in pioneering experiments that introduced the classical IntraCat concept. In addition, we identify a ground electronic state CHAT pathway as an alternative to the UV-promoted long-range molecular crane keto-enol conversion with a remarkably low activation energy. To initially assess the possible impact of the new keto-enol conversion pathway on combustion of n-alkanes, we present a detailed kinetic analysis of isomerization and decomposition of pentane-2,4-ketohydroperoxide (2,4-KHP). The results are compared with key alternative reactions, including direct dissociation and Korcek channels (for which a new alkyl group migration channel is also identified), revealing the competitiveness of the CHAT pathway across a range of conditions. Taken together, this work provides insight into a general class of reaction pathways that has not previously being systematically considered and that may occur in a broad range of contexts from combustion to atmospheric chemistry to biochemistry.

Metal-free catalysis for the reaction of nitrogen dioxide dimer with phenol: An unexpected favorable source of nitrate and aerosol precursors in vehicle exhaust

Atmospheric reaction mechanism and dynamics of phenol with nitrogen dioxide dimer were explored by the density functional theory and high-level quantum chemistry combined with statistical kinetic calculations within 220-800 K. The nitric acid and phenyl nitrite, the typical aerosol precursors, are the preponderant products because of the low formation free energy barrier (∼8.7 kcal/mol) and fast rate constants (∼10^-15 cm³ molecule^-1 s^-1 at 298 K). Phenyl nitrate is the minor product and it would be also formed from the transformation of phenyl nitrite in NO₂-rich environment. More importantly, kinetic effects and catalytic mechanism of a series of metal-free catalysts (H₂O, NH₃, CH₃NH₂, CH₃NHCH₃, HCOOH, and CH₃COOH) on the title reaction were investigated at the same level. The results indicate that CH₃NH₂ and CH₃NHCH₃ can not only catalyze the title reaction by lowering the free energy barrier (about 1.4-6.5 kcal/mol) but also facilitate the production of organic ammonium nitrate via acting as a donor-acceptor of hydrogen. Conversely, the other species are non-catalytic upon the title reaction. The stabilization energies and donor-acceptor interactions in alkali-catalyzed product complexes were explored, which can provide new insights to the properties of aerosol precursors. Moreover, the lifetime of phenol determined by nitrogen dioxide dimer in the presence of dimethylamine may compete with that of determined by OH radicals, indicating that nitrogen dioxide dimer is responsible for the elimination of phenol in the polluted atmosphere. This work could help us thoroughly understand the removal of nitrogen oxides and phenol as well as new aerosol precursor aggregation in vehicle exhaust.

Possible atmospheric source of NH2SO3H: the hydrolysis of HNSO2 in the presence of neutral, basic, and acidic catalysts

NH₂SO₃H can directly participate in H₂SO₄-(CH₃)₂NH-based cluster formation, and thereby substantially enhance the cluster formation rate. Herein, the reaction mechanisms and kinetics for the formation of NH₂SO₃H from the hydrolysis of HNSO₂ without and with neutral (H₂O, (H₂O)₂, and (H₂O)₃), basic (NH₃ and CH₃NH₂), and acidic (HCOOH, H₂SO₄, H₂SO₄⋯H₂O, and (H₂SO₄)₂) catalysts were studied theoretically at the CCSD(T)-F12/cc-pVDZ-F12//M06-2X/6-311+G(2df,2pd) level. The calculated results showed that neutral, basic, and acidic catalysts decrease the energy barrier by over 18.1 kcal mol^-1; meanwhile, the product formation of NH₂SO₃H was more strongly bonded to neutral, basic, and acidic catalysts than to the reactants HNSO₂ and H₂O. This reveals that the reported neutral, basic, and acidic catalysts promote the formation of NH₂SO₃H from the hydrolysis of HNSO₂ both kinetically and thermodynamically. Kinetic calculations using the master equation showed that (H₂O)₂ (100% RH) dominate over the other catalysts within the range of 0-10 km altitudes and 230-320 K with its rate ratio larger by at least 2.98 times, whereas HCOOH (3.2 × 10⁹ molecules cm^-3) is the most favorable catalysts at 15 km altitude in the troposphere. Overall, the present results will provide a definitive example that neutral, basic, and acidic catalysts have important influences on atmospheric reactions.

Effect of Water and Formic Acid on ·OH + CH4 Reaction: An Ab Initio/DFT Study

In this work, we used ab initio/DFT method coupled with statistical rate theory to answer the question of whether or not formic acid (HCOOH) and water molecules can catalyze the most important atmospheric and combustion prototype reaction, i.e., ·OH (OH radical) + CH4. The potential energy surface for ·OH + CH4 and ·OH + CH4 (+X) (X = HCOOH, H2O) reactions were calculated using the combination of hybrid-density functional theory and coupled-cluster theory with Pople basis set [(CCSD(T)/ 6-311++G(3df,3pd)//M06-2X/6-311++G(3df,3pd)]. The results of this study show that the catalytic effect of HCOOH (FA) and water molecules on the ·OH + CH4 reaction has a major impact when the concentration of FA and H2O is not included. In this situation the rate constants for the CH4 + HO···HCOOH (3 × 10−9 cm3 molecule−1 s−1) reaction is ~105 times and for CH4 + H2O···HO reaction (3 × 10−14 cm3 molecule−1 s−1 at 300 K) is ~20 times higher than ·OH + CH4 (~6 × 10−15 cm3 molecule−1 s−1). However, the total effective rate constants, which include the concentration of both species in the kinetic calculation has no effect under atmospheric condition. As a result, the total effective reaction rate constants are smaller. The rate constants when taking the account of the FA and water for CH4 + HO···HCOOH (4.1 × 10−22 cm3 molecule−1 s−1) is at least seven orders magnitude and for the CH4 + H2O···HO (7.6 × 10−17 cm3 molecule−1 s−1) is two orders magnitude smaller than ·OH + CH4 reaction. These results are also consistent with previous experimental and theoretical studies on similar reaction systems. This study helps to understand how FA and water molecules change the reaction kinetic under atmospheric conditions for ·OH + CH4 reaction.

Effect of a single water molecule on ˙CH2OH + 3O2 reaction under atmospheric and combustion conditions

The hydroxymethyl (˙CH₂OH) radical is an important intermediate species in both atmosphere and combustion reaction systems. The rate coefficients for ˙CH₂OH + ³O₂ and (˙CH₂OH + ³O₂ (+H₂O)) reactions were calculated using the Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation (ME) simulation and canonical variational transition state theory (CVT) between the temperature range of 200 to 1500 K based on the potential energy surface constructed using CCSD(T)//ωB97XD/6-311++G(3df,3pd). The results show that ˙CH₂OH + ³O₂ leads to the formation of CH₂O and HO₂ at temperatures below 800 K, and goes back to reactants at high temperature (>1000 K). When a water molecule is added to the reaction, the formation of CH₂O and HO₂ is favored at all temperatures. The calculated rate coefficient for the ˙CH₂OH + ³O₂ (2.8 × 10^-11 cm³ molecule^-1 s^-1 at 298 K) is in good agreement with the previous experimental values (∼1 × 10^-11 cm³ molecule^-1 s^-1 at 298 K). The rate coefficients for the water-assisted reaction (2.4 × 10^-16 cm³ molecule^-1 s^-1 at 1000 K) is at least 3-4 orders of magnitude smaller than the water-free reaction (6.2 × 10^-12 cm³ molecule^-1 s^-1 at 1000 K). This result is consistent with the similar types of reaction system. Our calculations also predict that the effect of a single water molecule favors the formation of CH₂O in the combustion condition. However, the water-free reaction favors the formation of CH₂O in the atmospheric condition. The current study helps to understand how a single water molecule changes the reaction mechanism and chemical kinetic behaviour under atmospheric and combustion conditions.

Atmospheric Ring-Closure and Dehydration Reactions of 1,4-Hydroxycarbonyls in the Gas Phase: The Impact of Catalysts

1,4-Hydroxycarbonyls can potentially undergo sequential reactions involving cyclization followed by dehydration to form dihydrofurans. As dihydrofurans contain a double bond, they are highly reactive toward atmospheric oxidants such as OH, O₃, and NO₃. In the present study, we use ab initio calculations to examine the impact of various atmospheric catalysts on the energetics and kinetics of the gas-phase cyclization and dehydration reaction steps associated with 4-hydroxybutanal, a prototypical 1,4-hydroxycarbonyl molecule. The cyclization step transforms 4-hydroxybutanal into 2-hydroxytetrahydrofuran, which can subsequently undergo dehydration to form 2,3-dihydrofuran. As the barriers associated with the cyclization and dehydration steps for 4-hydroxybutanal are, respectively, 34.8 and 63.0 kcal/mol in the absence of a catalyst, both reaction steps are inaccessible under atmospheric conditions in the gas phase. However, the presence of a suitable catalyst can significantly reduce the reaction barriers, and we have examined the impact of a single molecule of H₂O, HO₂ radical, HC(O)OH, HNO₃, and H₂SO₄ on these reactions. We find that H₂SO₄ reduces the reaction barriers the greatest, with the barrier for the cyclization step being reduced to -13.1 kcal/mol and that for the dehydration step going down to 9.2 kcal/mol, measured relative to their respective separated starting reactants. Interestingly, our kinetic study shows that HNO₃ gives the fastest rate due to the combined effects of a larger atmospheric concentration and a reduced barrier. Thus, our study suggests that, with acid catalysis, the cyclization reaction step can readily occur for 1,4-hydroxycarbonyls in the gas phase. Because the dehydration step exhibits a significant barrier even with acid catalysis, the 2-hydroxytetrahydrofuran products, once formed, are likely lost through their reaction with OH radicals in the atmosphere. We have investigated the reaction pathways and the rate constant for this bimolecular reaction in the presence of excess molecular oxygen (³O₂), as it would occur under tropospheric conditions, using computational chemistry over the 200-300 K temperature range. We find that the main products from these OH-initiated oxidation reactions are succinaldehyde + HO₂ and 2,3-dihydro-2-furanol + HO₂.

Effect of ammonia and water molecule on OH + CH3OH reaction under tropospheric condition

The rate coefficients for OH + CH3OH and OH + CH3OH (+ X) (X = NH3, H2O) reactions were calculated using microcanonical, and canonical variational transition state theory (CVT) between 200 and 400 K based on potential energy surface constructed using CCSD(T)//M06-2X/6-311++G(3df,3pd). The results show that OH + CH3OH is dominated by the hydrogen atoms abstraction from CH3 position in both free and ammonia/water catalyzed ones. This result is in consistent with previous experimental and theoretical studies. The calculated rate coefficient for the OH + CH3OH (8.8 × 10-13 cm3 molecule-1 s-1), for OH + CH3OH (+ NH3) [1.9 × 10-21 cm3 molecule-1 s-1] and for OH + CH3OH (+ H2O) [8.1 × 10-16 cm3 molecule-1 s-1] at 300 K. The rate coefficient is at least 8 order magnitude [for OH + CH3OH(+ NH3) reaction] and 3 orders magnitude [OH + CH3OH (+ H2O)] are smaller than free OH + CH3OH reaction. Our calculations predict that the catalytic effect of single ammonia and water molecule on OH + CH3OH reaction has no effect under tropospheric conditions because the dominated ammonia and water-assisted reaction depends on ammonia and water concentration, respectively. As a result, the total effective reaction rate coefficients are smaller. The current study provides a comprehensive example of how basic and neutral catalysts effect the most important atmospheric prototype alcohol reactions.

Lactic Acid Spectroscopy: Intra- and Intermolecular Interactions

Lactic acid, a relevant molecule in biology and the environment, is an α-hydroxy acid with a high propensity to form hydrogen bonds, both internally and to other hydrogen-bond-accepting molecules. This work includes the novel recording of infrared spectra of gas-phase lactic acid using Fourier transform infrared spectroscopy, and the vibrational absorption features of lactic acid are assigned with the aid of computationally simulated vibrational spectra with anharmonic corrections. Theoretical chemistry methods are used to relate intramolecular hydrogen-bond strengths to the relative stability of lactic acid conformers. The formation of hydrogen-bonded lactic acid dimers and 1:1 water complexes is investigated by simulated vibrational spectra and calculated thermodynamic parameters for the lactic acid monomer and dimer and its water complex in the gas phase. The results of this study are discussed in the context of environmental chemistry with an emphasis on indoor environments.

Kinetic instability of sulfurous acid in the presence of ammonia and formic acid

In the present work, we have studied the effect of ammonia and formic acid on the kinetic stability of sulfurous acid using high level ab initio calculations. Our investigation reveals that the decomposition reaction of sulfurous acid becomes barrierless in the presence of both ammonia and formic acid. The half-life of the isolated sulfurous acid is estimated to be ∼20 days at room temperature, which becomes only ∼4.0 × 10^-3 s and ∼7.08 × 10² s in the presence of ammonia and formic acid, respectively. These results indicate that, in the presence of ammonia, the stability of sulfurous acid reduces substantially at room temperature. The temperature dependency of the rate constant values indicates that, in the presence of ammonia and formic acid, the reaction has a negative activation energy, while the uncatalyzed and water catalyzed channels have a positive activation energy. We have also studied the pressure dependency of the catalyzed reaction, which suggests that the ammonia catalyzed channel is most sensitive towards the pressure change, as the values of the bimolecular rate constant (k_bi) for this channel were found to be increased by an order of magnitude on going from 0.1 to 10 atm of pressure. Whereas, for the FA and WM catalyzed channels the changes in k_bi with pressure were negligible.

Computational studies on the gas phase reaction of methylenimine (CH2NH) with water molecules

In this work, we used quantum chemical methods and chemical kinetic models to answer the question of whether or not formaldehyde (CH2O) and ammonia (NH3) can be produced from gas phase hydration of methylenimine (CH2NH). The potential energy surfaces (PESs) of CH2NH + H2O → CH2O + NH3 and CH2NH + 2H2O → CH2O + NH3 + H2O reactions were computed using CCSD(T)/6-311++G(3d,3pd)//M06-2X/6-311++G(3d,3pd) level. The temperature-and pressure-dependent rate constants were calculated using variational transition state theory (VTST), microcanonical variational transition state theory [Formula: see text] and Rice-Ramsperger-Kassel-Marcus/master equation (RRKM/ME) simulations. The PES along the reaction path forming a weakly bound complex (CH2NH⋯H2O) was located using VTST and [Formula: see text]VTST, however, the PES along the tight transition state was characterized by VTST with small curvature tunneling (SCT) approach. The results show that the formation of CH2NH + H2O → CH2NH⋯H2O is pressure -and temperature-dependent. The calculated atmospheric lifetimes of CH2NH⋯H2O (~ 8 min) are too short to undergo secondary bimolecular reactions with other atmospheric species. Our results suggest that the formation of CH2O and NH3 likely to occur in the combustion of biomass burning but the rate of formation CH2O and NH3 is predicted to be negligible under atmospheric conditions. When a second water molecule is added to the reaction, the results suggest that the rates of formation of CH2O and NH3 remain negligible.

Oxidation of Alkynyl Boronates to Carboxylic Acids, Esters, and Amides

A general efficient protocol was developed for the synthesis of carboxylic acids, esters, and amides through oxidation of alkynyl boronates, generated directly from terminal alkynes. This protocol represents the first example of C(sp)-B bond oxidation. This approach displays a broad substrate scope, including aryl and alkyl alkynes, and exhibits excellent functional group tolerance. Water, primary and secondary alcohols, and amines are suitable nucleophiles for this transformation. Notably, amino acids and peptides can be used as nucleophiles, providing an efficient method for the synthesis and modification of peptides. The practicability of this methodology was further highlighted by the preparation of pharmaceutical molecules.

Hydrolysis of Formyl Fluoride Catalyzed by Sulfuric Acid and Formic Acid in the Atmosphere

Formyl fluoride (HFCO) is an important atmospheric molecule, and its reaction with the OH radical is an important pathway when degradation of HFCO is considered in earth's troposphere. Here, we study the hydrolysis of formyl fluoride (HFCO + H₂O) with sulfuric acid (H₂SO₄) and formic acid (HCOOH) acting as catalysts by utilizing M06-2X, CCSD(T)-F12a, and conventional transitional state theory with Eckart tunneling to explore the atmospheric impact of the above-said hydrolysis reactions. Our calculated results show that H₂SO₄ has a remarkably catalytic role in the gas-phase hydrolysis of HFCO, as the energy barriers of the HFCO + H₂O reaction are reduced from 39.22 and 41.19 to 0.26 and -0.63 kcal/mol with respect to the separate reactants, respectively. In addition, we also find that H₂SO₄ can significantly accelerate the decomposition of FCH(OH)₂ into hydrogen fluoride (HF) and HCOOH. This is because while the barrier height for the unimolecular decomposition of FCH(OH)₂ into HF and HCOOH is 31.63 kcal/mol, the barrier height for the FCH(OH)₂ + H₂SO₄ reaction is predicted to be -5.99 kcal/mol with respect to separate reactants. Nevertheless, the comparative relative rate analysis shows that the reaction between HFCO and the OH radical is still the most dominant pathway when the tropospheric degradation of HFCO is taken into account and that the gas-phase hydrolysis of HFCO may only occur with the help of H₂SO₄ when the atmospheric concentration of OH is about 10¹ molecules cm^-3 or less. Having an understanding from the present study that the gas-phase hydrolysis of HFCO in the presence of H₂SO₄ has very limited role possibly in the absence of sunlight, we also prefer here to emphasize that the HFCO + H₂O + H₂SO₄ reaction may occur on the surface of secondary organic aerosols for the formation of HCOOH.

Theoretical study of the cis-pinonic acid and its atmospheric hydrolysate participation in the atmospheric nucleation

cis-Pinonic acid (CPA), one of the major photooxidation products of α-pinene, is believed to contribute to the formation of aerosols formed over forested areas. In the current study, we implement quantum chemical calculation to investigate the interaction between sulfuric acid (SA) and CPA as well as the hydrolysate of CPA (HCPA) in the presence of water or ammonia in the atmosphere. The lowest free energy configurations, reactants, transition states, intermediates, and products were optimized at 298/278K and 1atm at the M06-2X/6-311+G(3df,3pd) level. Our results show that one CPA molecule might initially nucleate with SA molecules and subsequently participate in the formation and growth of the new particle in the form of HCPA. More than one HCPA molecule may be involved in the critical nuclei. Furthermore, the hydrolysis reaction of CPA can be effectively catalyzed by SA and nitric acid (NA) in presence of water, which significantly increases the HCPA content in the atmosphere and subsequently promotes the particle nucleation. Overall, the current study elucidates a new mechanism of atmospheric nucleation driven by CPA and its hydrolysate.

Photolytic Labeling and Its Applications in Protein Drug Discovery and Development

In this mini-review, the major types of photolytic labeling reagents are presented together with their reaction mechanisms. The applications of photolytic labeling in protein drug discovery and development are then discussed; these have expanded from studies of protein-protein interactions in vivo to protein-matrix interactions in lyophilized solids. The mini-review concludes with recommendations for further development of the approach, which include the need for new and more chemically diverse photo-reactive reagents and better understanding of the mechanisms of photolytic labeling reactions in various media.

Picosecond activation of the DEACM photocage unravelled by VIS-pump-IR-probe spectroscopy

The light-induced ultrafast uncaging process of the [7-(diethylamino)coumarin-4-yl]methyl (DEACM) cage is measured by time-resolved visible-pump-infrared-probe spectroscopy, and supported by steady-state absorption spectroscopy in the visible and infrared spectral regions. Understanding the uncaging process is important because its favorable properties make DEACM an interesting case for chemical and biological applications. It has a convenient absorption in the visible spectral range, and is relatively easily modified to carry leaving groups (LGs) such as nucleotides, substrates or inhibitors, which are inactive when bound and active when released. Previous work suggested a lower limit for the uncaging rate, which places it among the fastest available cages. Here, we determine the photodissociation directly to occur on the picosecond time scale by monitoring the appearance of the released LG in the infrared spectral region. In the present study, azide (N₃) is chosen as an LG to monitor photodissociation because its vibrational mode is spectrally isolated (hence easy to follow) and its absorption wavenumber is sensitive to local structural rearrangements. The uncaging process is recorded up to 3 nanoseconds and compared to the collected steady-state spectra. The free LG appears on a picosecond time scale, rendering this one of the fastest known cages. No evidence is found for a tight-ion pair (TIP) preceding the free LG. The uncaging mechanism is found to be slowed down upon the addition of water to acetonitrile.

Atmospheric chemistry of CH3CHO: the hydrolysis of CH3CHO catalyzed by H2SO4

We found the catalytic effect of H₂SO₄ on the hydrolysis of CH₃CHO in the atmosphere.

Ammonolysis of ketene as a potential source of acetamide in the troposphere: a quantum chemical investigation

Quantum chemical calculations at the CCSD(T)/CBS//MP2/aug-cc-pVTZ levels of theory have been carried out to investigate a potential new source of acetamide in Earth's atmosphere through the ammonolysis of the simplest ketene.

B, Lin KC. Catalytic effect of a single water molecule on the OH + CH2NH reaction

Effect of water molecule on atmospheric oxidation of imines.

Role of Double Hydrogen Atom Transfer Reactions in Atmospheric Chemistry

Hydrogen atom transfer (HAT) reactions are ubiquitous and play a crucial role in chemistries occurring in the atmosphere, biology, and industry. In the atmosphere, the most common and traditional HAT reaction is that associated with the OH radical abstracting a hydrogen atom from the plethora of organic molecules in the troposphere via R-H + OH → R + H2O. This reaction motif involves a single hydrogen transfer. More recently, in the literature, there is an emerging framework for a new class of HAT reactions that involves double hydrogen transfers. These reactions are broadly classified into four categories: (i) addition, (ii) elimination, (iii) substitution, and (iv) rearrangement. Hydration and dehydration are classic examples of addition and elimination reactions, respectively whereas tautomerization or isomerization belongs to a class of rearrangement reactions. Atmospheric acids and water typically mediate these reactions. Organic and inorganic acids are present in appreciable levels in the atmosphere and are capable of facilitating two-point hydrogen bonding interactions with oxygenates possessing an hydroxyl and/or carbonyl-type functionality. As a result, acids influence the reactivity of oxygenates and, thus, the energetics and kinetics of their HAT-based chemistries. The steric and electronic effects of acids play an important role in determining the efficacy of acid catalysis. Acids that reduce the steric strain of 1:1 substrate···acid complex are generally better catalysts. Among a family of monocarboxylic acids, the electronic effects become important; barrier to the catalyzed reaction correlates strongly with the pKa of the acid. Under acid catalysis, the hydration of carbonyl compounds leads to the barrierless formation of diols, which can serve as seed particles for atmospheric aerosol growth. The hydration of sulfur trioxide, which is the principle mechanism for atmospheric sulfuric acid formation, also becomes barrierless under acid catalysis. Rate calculations suggest that such acid catalysis play a key role in the formation of sulfuric acid in the Earth's stratosphere, Venusian atmosphere, and on heterogeneous surfaces. Over the past few years, theoretical calculations have shown that these acid-mediated double hydrogen atom transfers are important in the chemistry of Earth's atmosphere as well as that of other planets. This Account reviews and puts into perspective some of these atmospheric HAT reactions and their environmental significance.

Ammonia as an efficient catalyst for decomposition of carbonic acid: a quantum chemical investigation

Electronic structure calculations using M06-2X, MP2 and CCSD(T) methods have been employed to show ammonia as an efficient catalyst for decomposition of carbonic acid.

External control over tautomeric distribution and inter-conversion: new insights into the realm of catalyzed tautomerization

Relative stabilities of tautomers and tautomeric barriers are extensively modulated by use of carboxylic acids and amine bases.