High-accuracy theoretical thermochemistry of atmospherically important nitrogen oxide derivatives

High-accuracy quantum chemical calculations were performed for several atmospherically important nitrogen oxide derivatives, such as HOONO, HOONO(2), NH(2)NO(2), FNO, FNO(2), FONO, FONO(2), ClNO, ClONO, ClONO(2), and ClOONO. The stable conformers of the molecules were identified, and the corresponding heats of formation (Δ(f)H(0)° and Δ(f)H(298)°) and entropy values (S(298)°) were computed. On the basis of the thermodynamic functions, equilibrium constants were also calculated for a couple of reactions with importance in the chemistry of the atmosphere. In a number of cases this study provides more reliable estimates for the investigated thermodynamic properties than those can be collected from previous reports.     

High-accuracy theoretical thermochemistry of atmospherically important sulfur-containing molecules

In this study, several sulfur-containing molecules with atmospherical importance were investigated by means of high-accuracy quantum chemical calculations including: HSO, HOS, HOSO2, HSNO, SH, CH2SO, CH2SH, S2COH, and SCSOH. After identifying the stable conformers of the molecules, a coupled-cluster-based composite model chemistry, which includes contributions up to quadruple excitations as well as corrections beyond the nonrelativistic and Born–Oppenheimer approximations, was applied to calculate the corresponding heat of formation (Δ(f)H(0)° and Δ(f)H(298)°) and entropy (S(298)°) values. In most of the cases, this study delivers more reliable estimates for the investigated thermodynamic properties than those reported in previous investigations. Our data also suggest that the experimental heats of formation associated with the HSO molecule are very likely to belong to its structural isomer, HOS. It is also confirmed by the calculated thermodynamic properties including standard reaction entropies, enthalpies, and equilibrium constants that, in the reaction CS2 + OH CS2OH, the SCSOH structural isomer is produced. It is also noted that the currently accepted Δ(f)H(0)°(S(gas)) = 274.73 ± 0.3 kJ/mol value is in need of revision, and based on a recent measurement, which is also confirmed by our computations, it is advised to update it to Δ(f)H(0)°(S(gas)) = 277.25 ± 0.3 kJ/mol.     

High-accuracy thermochemistry of atmospherically important fluorinated and chlorinated methane derivatives

High-precision quantum chemical calculations have been performed for atmospherically important halomethane derivatives including CF, CF(3), CHF(2), CH(2)F, CF(2), CF(4), CHF, CHF(3), CH(3)F, CH(2)F(2), CCl, CCl(3), CHCl(2), CH(2)Cl, CCl(2), CCl(4), CHCl, CHCl(3), CH(3)Cl, CH(2)Cl(2), CHFCl, CF(2)Cl, CFCl(2), CFCl, CFCl(3), CF(2)Cl(2), CF(3)Cl, CHFCl(2), CHF(2)Cl, and CH(2)FCl. Theoretical estimates for the standard enthalpy of formation at 0 and 298.15 K as well as for the entropy at 298.15 K are presented. The determined values are mostly within the experimental uncertainty where accurate experimental results are available, while for the majority of the considered heat of formation and entropy values the present results represent the best available estimates.     

High-accuracy extrapolated ab initio thermochemistry of vinyl chloride

Applying a modified "high accuracy extrapolated ab initio thermochemistry" (HEAT) scheme, the standard heat of formation of vinyl chloride at 0 K is computed to be 29.79 +/- 1 kJ/mol and at 298.15 K to be 20.9 +/- 2 kJ/mol, thus resolving earlier discrepancies among the available experimental values, which span a range from 21 up to 38 kJ/mol. The enthalpies of the reactions C2H4 + Cl2 --> CH2CHCl + HCl and C2H2 + HCl --> CH2CHCl at 298.15 K are determined to be -123.0 and -113.9 +/- 2 kJ/mol, respectively.     

Anharmonic thermochemistry of cyclopentadiene derivatives

This paper focuses on the thermochemistry of some derivatives of cyclopenta‐1,3‐diene, namely, 5‐methylcyclopenta‐1,3‐diene, 5‐ethylcyclopenta‐1,3‐diene, 5‐formylcyclopenta‐1,3‐diene, 5‐methylcyclopenta‐1,3‐diene‐1‐yl radical, 5‐ethylcyclopenta‐1,3‐diene‐1‐yl radical, 5‐carbonylcyclopenta‐1,3‐diene radical, 1‐formylcyclopenta‐2,4‐diene‐1‐yl radical, 5‐methylenecyclopenta‐1,3‐diene radical, 5‐ethylidenecyclopenta‐1,3‐diene radical, and 3,6‐dimethylenecyclohexa‐1,4‐diene. Several different chemistries of these compounds are of interest in combustion modeling. Here, we present gas‐phase thermochemical properties for the above cited species, which are, except for 3,6‐dimethylenecyclohexa‐1,4‐diene, previously unknown. These were obtained from corrected (using bond additivity corrections) high‐level ab initio quantum chemistry calculations validated with well‐known compounds including cyclopentane, cyclopentene, cyclopenta‐1,3‐diene, and cyclopentadienyl radical. Heat capacities and entropies have been corrected for anharmonic molecular motions, in particular for internal rotations. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 453–463, 2003     

High-accuracy extrapolated ab initio thermochemistry of the vinyl, allyl, and vinoxy radicals

Enthalpies of formation at both 0 and 298 K were calculated according to the HEAT (High-accuracy Extrapolated Ab initio Thermochemistry) protocol for the title molecules, all of which play important roles in combustion chemistry. At the HEAT345-(Q) level of theory, recommended enthalpies of formation at 0 K are 301.5 ± 1.3, 180.3 ± 1.8, and 23.4 ± 1.5 kJ mol(-1) for vinyl, allyl, and vinoxy, respectively. At 298 K, the corresponding values are 297.3, 168.6, and 16.1 kJ mol(-1), with the same uncertainties. The calculated values for the three radicals are in excellent agreement with the corresponding experimental values, but the uncertainties associated with the HEAT values for vinoxy are considerably smaller than those based on experimental studies.     

A theoretical study on the water-mediated asynchronous addition between urea and formaldehyde

The reaction between urea and formaldehyde in water solution was theoretically investigated by using B3LYP and MP2 methods.It was found that the addition of the nitrogen atom in urea to the carbonyl group in formaldehyde precedes the proton transfer and the proton migration from water to the carbonyl group occurs before the proton abstraction from the nitrogen.With one or two water molecules involved in the TS.the activation energy barrier is lowered compared to the TS of the mechanism with no water participation.The energy change along the reaction coordinate clearly shows that a zwitterionic-like intermediate does not exist on the PES.The reaction between urea and formaldehyde occurs in a concerted mechanism but with asynchronous characters.This is different from the stepwise mechanism recently found for the amination reactions of formaldehyde.     

A calorimetric and computational study of the thermochemistry of halogenated 1-phenylpyrrole derivatives

The standard molar enthalpies of formation, in the crystalline phase, of three halogenated 1-phenylpyrrole derivatives, namely 1-(4-fluorophenyl)pyrrole, 1-(4-chlorophenyl)pyrrole, and 1-(4-iodophenyl)pyrrole were derived from the respective enthalpies of combustion, measured by rotating-bomb combustion calorimetry. Their enthalpies of sublimation, at T = 298.15 K, were obtained from the Knudsen mass-loss effusion technique. From these two experimental parameters, the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of 1-(4-fluorophenyl)pyrrole, 1-(4-chlorophenyl)pyrrole, and 1-(4-iodophenyl)pyrrole were calculated, respectively, as (26.2 ± 2.4) kJ · mol⁻¹, (196.2 ± 2.5) kJ · mol⁻¹, and (311.5 ± 2.4) kJ · mol⁻¹.The gas-phase enthalpies of formation of both fluorine and chlorine compounds were estimated by G3(MP2)//B3LYP computations. For the iodine compound, the B3LYP/6-311G(d):ECP46MDF approach was employed. Additionally, the DFT calculations were extended to estimate the enthalpy of formation of the bromine derivative, 1-(4-bromophenyl)pyrrole, performed at the B3LYP/6-311G(d) level of theory.     

Gaussian-3 study of the thermochemistry of the germane and its fluoro chloro derivatives

The thermochemistry of all fluoro and chloro substituted germane molecules have been theoretically studied. Computed G3//B3LYP standard enthalpies of formation at 298 K obtained from isodesmic reaction schemes were compared with values derived via total atomization energies. Bond dissociation energies and energy barriers for the lowest dissociation pathways were estimated at 0 K. From these data, the most probable dissociation products at 0 K were predicted for the thermal decomposition reactions of the gaseous species. Calculated results are compared with experimental determinations as well as other theoretical data when available. The following isodesmic enthalpies of formation in kcal x mol(-1) were calculated for 10 new germane species simultaneously substituted with fluoro and chloro atoms, for which no previously available computations were found in the literature: GeHFCl2, -125.8; GeCl2F, -104.3; GeHFCl, -67.5; GeF2Cl2, -186.3; GeF3Cl, -242.9; GeH2FCl, -89.7; GeCl3F, -159.6; GeHClF2, -168.0; GeF2Cl, -144.3; GeFCl, -81.1.     

DFT theoretical studies of anions of aniline and its several derivatives

Detailed studies of the molecular and electronic structures, vibrational frequencies, and infrared intensities of [M ⁻] and [M-H ⁻] anions of aniline and its derivatives (2-, 3-, 4-fluoroanilines, N-[(2E)-1-methylbut-2-en-1-yl]aniline, (2-cyclopent-2-en-1-ylphenyl)amine, N-[(2E)-1-methylbut-2-en-1-yl]aniline, and N-cyclopent-2-en-1-ylaniline) have been carried out using the density functional method with UB3LYP functional and 6-31G** basis set augmented with sp diffuse functions on nitrogen, fluorine, and three carbon atoms of benzene ring (in 2, 4, and 6 positions). For comparison, similar calculations were carried out for the closed-shell neutral molecules ([M]). The studies have provided detailed insight into the structure changes that take place in negative ions of aniline and its derivatives.     

A theoretical study of the protonation of methylindole derivatives

Ab initio calculations on indole and all its mono-substituted methyl derivatives, using an STO-3G minimal basis set, show that the most basic site is C3. Protonation at the nitrogen atom cannot compete with protonation at C3; and C2 is the less basic site in all cases. The basicity increases with methyl substitution, with the only exception of 3-methyl indole. A good linear correlation exists between calculated and corresponding thermodynamics pK values. 2-Aminoindole is a much stronger base than methylindoles and its high pK value can be explained by the strong interactions with the solvent through tautomeric forms which accumulate positive charge at the NH₂ group. Intramolecular quenching of the fluorescence of some indole derivatives involves intramolecular proton transfer to C4 rather than C2. Reasons why ring nitrogens can behave as either π-acceptors or π-donors in this series are discussed.     

A DFT theoretical study of the condensation of aggregates of sp2 organolithium compounds on formaldehyde

[Chemical reaction: See text] The interaction between three different sp2 organolithium compounds (vinyllithium, 2-methoxyvinyllithium and phenyllithium) and formaldehyde has been investigated using DFT theoretical methods. The unsolvated monomers and dimers have been considered and compared to the 1:1 mixed aggregates formed with lithium dimethylamide. In all cases, the separate entities, their docking complexes, the transition states, and the condensation products have been characterized and compared to the corresponding situations involving methyllithium, taken as a prototypic sp3 nucleophile. Regarding the monomers, this study shows that, in the three cases considered, formaldehyde forms a pretransition state complex in which the oxygen of the carbonyl interacts with the lithium cation along one of its lone pair. A small energy barrier (< or =2.1 kcal.mol(-1)) brings to the transition state, then to the lithium alcoholate resulting from the largely exothermic condensation (approximately 40 kcal.mol(-1)). The structure of the homogeneous dimers considered in a second step has been optimized and lead to arrangements in which a planar quadrilateral C-Li-C-Li is always obtained. In the presence of formaldehyde, these entities provide complexes exhibiting lithium-oxygen interaction similar to those occurring with the monomers. For the dimers, the geometry at the TS evokes a pi-complex between the C=O and the lithium cation, particularly pronounced in the case of phenyllithium. The resulting alcoholates are obtained following a larger exothermic reaction (approximately 55 kcal.mol(-1)). The heterogeneous dimers with lithium dimethylamide have been finally examined. In these cases, the aldehyde can orientate toward either the carbon or the nitrogen, leading to the expected lithium alcoholate or alpha-amino alcoholate, respectively. Whatever the orientation, the complexes present characteristics close to those calculated for the homogeneous dimer complexes. These similarities are conserved at the transition state.     

Toward accurate theoretical thermochemistry of first row transition metal complexes

The recently developed correlation consistent Composite Approach for transition metals (ccCA-TM) was utilized to compute the thermochemical properties for a collection of 225 inorganic molecules containing first row (3d) transition metals, ranging from the monohydrides to larger organometallics such as Sc(C(5)H(5))(3) and clusters such as (CrO(3))(3). Ostentatiously large deviations of ccCA-TM predictions stem mainly from aging and unreliable experimental data. For a subset of 70 molecules with reported experimental uncertainties less than or equal to 2.0 kcal mol(-1), regardless of the presence of moderate multireference character in some molecules, ccCA-TM achieves transition metal chemical accuracy of ±3.0 kcal mol(-1) as defined in our earlier work [J. Phys. Chem. A2007, 111, 11269-11277] by giving a mean absolute deviation of 2.90 kcal mol(-1) and a root-mean-square deviation of 3.91 kcal mol(-1). As subsets are constructed with decreasing upper limits of reported experimental uncertainties (5.0, 4.0, 3.0, 2.0, and 1.0 kcal mol(-1)), the ccCA-TM mean absolute deviations were observed to monotonically drop off from 4.35 to 2.37 kcal mol(-1). In contrast, such a trend is missing for DFT methods as exemplified by B3LYP and M06 with mean absolute deviations in the range 12.9-14.1 and 10.5-11.0 kcal mol(-1), respectively. Salient multireference character, as demonstrated by the T(1)/D(1) diagnostics and the weights (C(0)(2)) of leading electron configuration in the complete active self-consistent field wave function, was found in a significant amount of molecules, which can still be accurately described by the single reference ccCA-TM. The ccCA-TM algorithm has been demonstrated as an accurate, robust, and widely applicable model chemistry for 3d transition metal-containing species with versatile bonding features.     

Experimental and computational study on the thermochemistry of ethylpiperidines

The standard (p^∘ = 0.1 MPa) massic energies of combustion in oxygen of 1-ethylpiperidine and 2-ethylpiperidine, both in the liquid phase, were measured at T = 298.15 K by static bomb calorimetry. These values were used to derive the standard molar enthalpies of combustion and the standard molar enthalpies of formation, in the condensed phase, for these compounds. Further, the standard molar enthalpies of vaporization, at T = 298.15 K, of these two ethylpiperidine isomers were determined by Calvet microcalorimetry. The combustion calorimetry results together with those from the Calvet microcalorimetry, were used to derive the standard molar enthalpies of formation, at T = 298.15 K, in the gaseous phase.     

18.

Concerted dihydrogen exchange between methanol and formaldehyde: a theoretical study     

McKee ML  Shevlin PB  Rzepa HS 《Journal of the American Chemical Society》1986,108(19):5793-5798

     

19.

Comparative theoretical study of formaldehyde decomposition on PdZn, Cu, and Pd surfaces     

Lim KH  Chen ZX  Neyman KM  Rösch N 《The journal of physical chemistry. B》2006,110(30):14890-14897

Methanol steam reforming, catalyzed by Pd/ZnO (PdZn alloy), is a potential source of hydrogen for on-board fuel cells. CO has been reported to be a minor side product of methanol decomposition that occurs in parallel to methanol steam reforming on PdZn catalysts. However, fuel cells currently used in vehicles are very sensitive to CO poisoning. To contribute to the understanding of pertinent reaction mechanisms, we employed density functional slab model calculations to study the decomposition of formaldehyde, a key intermediate in methanol decomposition and steam reforming reactions, on planar surfaces of Pd, Cu, and PdZn as well as on a stepped surface of PdZn. The calculated activation energies indicate that dehydrogenation of formaldehyde is favorable on Pd(111), but unfavorable on Cu(111) and PdZn(111). On the stepped PdZn(221) surface, the dehydrogenation process was calculated to be more competitive to formaldehyde desorption than on PdZn(111). Thus, we ascribe the experimentally observed small amount of CO, formed during steam reforming of methanol on the Pd/ZnO catalyst, to occur at metallic Pd species of the catalyst or at defect sites of PdZn alloy.     

20.

A theoretical study on keto-enol tautomerization involving simple carbonyl derivatives     

Doyoung Lee  Chang Kon Kim  Bon-Su Lee  Ikchoon Lee  Byung Choon Lee 《Journal of computational chemistry》1997,18(1):56-69

     

Comparative theoretical study of formaldehyde decomposition on PdZn, Cu, and Pd surfaces

Methanol steam reforming, catalyzed by Pd/ZnO (PdZn alloy), is a potential source of hydrogen for on-board fuel cells. CO has been reported to be a minor side product of methanol decomposition that occurs in parallel to methanol steam reforming on PdZn catalysts. However, fuel cells currently used in vehicles are very sensitive to CO poisoning. To contribute to the understanding of pertinent reaction mechanisms, we employed density functional slab model calculations to study the decomposition of formaldehyde, a key intermediate in methanol decomposition and steam reforming reactions, on planar surfaces of Pd, Cu, and PdZn as well as on a stepped surface of PdZn. The calculated activation energies indicate that dehydrogenation of formaldehyde is favorable on Pd(111), but unfavorable on Cu(111) and PdZn(111). On the stepped PdZn(221) surface, the dehydrogenation process was calculated to be more competitive to formaldehyde desorption than on PdZn(111). Thus, we ascribe the experimentally observed small amount of CO, formed during steam reforming of methanol on the Pd/ZnO catalyst, to occur at metallic Pd species of the catalyst or at defect sites of PdZn alloy.