Complexation of Phenol and Thiophenol by Amine N‐Oxides: Isothermal Titration Calorimetry and ab Initio Calculations

To develop a new solvent‐impregnated resin (SIR) system for removal of phenols from water, the complex formation of dimethyldodecylamine N‐oxide (DMDAO), trioctylamine N‐oxide (TOAO), and tris(2‐ethylhexyl)amine N‐oxide (TEHAO) with phenol (PhOH) and thiophenol (PhSH) is studied. To this end we use isothermal titration calorimetry (ITC) and quantum chemical modeling (on B3LYP/6‐311G(d,p)‐optimized geometries: B3LYP/6‐311+G(d,p), B3LYP/6‐311++G(2d,2p), MP2/6‐311+G(d,p), and spin component scaled (SCS) MP2/6‐311+G(d,p); M06‐2X/6‐311+G(d,p)//M06‐2X/6‐311G(d,p), MP2 with an extrapolation to the complete basis set limit (MP2/CBS), as well as CBS‐Q). The complexes are analyzed in terms of structural (e.g., bond lengths) and electronic elements (e.g., charges). Furthermore, complexation and solvent effects (in benzene, toluene, and mesitylene) are investigated by ITC measurements, yielding binding constants K, enthalpies ΔH⁰, Gibbs fre energies ΔG⁰, and entropies ΔS⁰ of complex formation, and stoichiometry N. The ITC measurements revealed strong 1:1 complex formation between both DMDAO–PhOH and TOAO–PhOH. The binding constant (K=1.7–5.7×10⁴ M ^?1) drops markedly when water‐saturated toluene was used (K=5.8×10³ M ^?1), and π–π interaction with the solvent is shown to be relevant. Quantum mechanical modeling confirms formation of stable 1:1 complexes with linear hydrogen bonds that weaken on attachment of electron‐withdrawing groups to the amine N‐oxide moiety. Modeling also showed that complexes with PhSH are much weaker than those with PhOH, and in fact too weak for ITC determination. CBS‐Q incorrectly predicts equal or even higher binding enthalpies for PhSH than for PhOH, which invalidates it as a benchmark for other calculations. Data from the straightforward SCS‐MP2 method without counterpoise correction show very good agreement with the MP2/CBS values.     

Theoretical study of dihydrogen bonded clusters of water with tetrahydroborate

Ab initio calculations were used to analyze interactions of BH₄ ^? with 1?C4 molecules of H₂O at the MP2/6-311++G(d,p) and B3LYP/6-311++G(d,p) computational levels. The negative cooperativity for dihydrogen bond clusters containing H₂O···H₂O hydrogen bonds is more remarkable. The negative cooperativity is increased with increasing the size and also the number of hydrogen bonds in the cluster. The B?CH stretching frequencies show blue shifts with respect to cluster formation. Also greater blue shift of stretching frequencies where predicted for B?CH bonds which did not contribute in dihydrogen bonding with water molecules. The structures obtained have been analyzed with the Atoms in Molecules (AIM) methodology.     

Reactions of dichlorocarbene,dichlorosilylene, and dichlorogermylene with carboranes(12). A theoretical study

Insertion of CCl₂, SiCl₂, and GeCl₂ into the B-H and C-H bonds of the carborane(12) molecules as well as into the B-Hal, C-Hal bonds of some halogen-substituted ortho-carboranes are studied at the B3LYP/6-311+G(d,p) and M06-2X/6-311+G(d,p) levels of theory. Thermodynamic parameters of the reactions are calculated and their variation for the isomeric carboranes(12) and for a series of carbenoid species is shown. For several insertion reactions the energies of activation are calculated based on the model of three-center synchronous transition state. The energy barriers are regularly varied depending on the position of the B-H bond in the carborane molecule.     

Theoretical studies on the formation of N-nitrosodimethylamine

The mechanisms of the formation of N-nitrosodimethylamine (NDMA) were studied at the MP2/6-311+G(d,p)//B3LYP/6-311+G(d,p) level of theory. We focused on the formation of NDMA from the reactions of dimethylamine (DMA) with nitrous acid and nitrite anion. Our calculations show that the reaction of DMA with nitrous acid is predicted to proceed via two distinct pathways: a concerted or a stepwise mechanism. Moreover, the energy barrier for the stepwise mechanism is somewhat higher than that for the concerted mechanism. The difference in these barriers indicates that the reaction of DMA with nitrous acid via the concerted mechanism is much more favored than that via the stepwise mechanism. In the other situation, our results demonstrate that the reaction of DMA with nitrite anion becomes feasible in the presence of carbon dioxide. Furthermore, this reaction proceeds via a stepwise pathway, in which CO₂ first attacks DMA, the result of which then reacts with nitrite anion. It is noteworthy that carbon dioxide appears to be an active catalyst to promote the formation of NDMA. Additionally, the effects of aqueous solvation on the reactions of DMA with nitrous acid and nitrite anion were investigated.     

A theoretical study on the mechanism and thermodynamics of ozone-water gas phase reaction

Ozone water reaction including a complex was studied at the MP2/6-311++G(d,p) and CCSD/6-311++G(2df,2p)//MP2/6-311++G(d,p) levels of theory. The interaction between water oxygen and central oxygen of ozone produces stable H₂O-O₃ complex with no barrier. With decomposition of this complex through H-abstraction by O₃ and O-abstraction by H₂O, three possible product channels were found. Intrinsic reaction coordinate, topological analyses of atom in molecule, and vibrational frequency calculation have been used to confirm the preferred mechanism. Thermodynamic data at T = 298.15 K and atmospheric pressure have been calculated. The results show that the production of hydrogen peroxide is the main reaction channel with ΔG = ?21.112 kJ mol^-1.     

羰基化合物在Si(100)表面[2+2]环加成和α-H裂解反应的选择性

最近研究表明: 丙酮能与半导体Si(100)表面发生[2+2]环加成和α-H 裂解反应形成相应的Si―C键或Si―O键, 在半导体材料的合成方面具有重要意义. 为进一步弄清不同羰基化合物在Si(100)表面的反应机理,本文应用密度泛函理论方法在B3LYP/6-311++G(d,p)//6-31G(d)水平上较为系统地研究了一系列羰基化合物CH₃COR (R=CH₃, H, C₂H₅, C₆H₅)与Si(100)表面的反应. 研究结果表明: 不论是[2+2]环加成反应还是α-H 裂解反应都对应较低的反应势垒(小于25 kJ·mol^-1); 环加成反应的势垒比α-H 裂解反应的势垒略高; 羰基上的取代基对反应势垒的影响较少; α-H裂解反应产物为动力学和热力学控制产物; 对丁酮来说, 1-位和3-位H原子的裂解反应都比较容易, 势垒相差很小. 这些结果表明羰基化合物与Si(100)表面的反应将得到多种产物.     

Theoretical study on the gas phase reaction of dimethyl sulfoxide with atomic chlorine in the presence of water

We have investigated theoretically the gas phase reactions of dimethyl sulfoxide (DMSO) with atom Cl in the absence and presence of a single water molecule. The calculations of the potential energy surfaces in the water-free and water-assisted along the different channels are performed at the CCSD(T)/6-311++G(2df,2p)//MP2/6-31G(d) level. The calculated results show that energy barriers of the H_c-abstraction reaction are reduced due to one water molecule added. The computed rate constants of H_c-abstraction reaction indicate that the reaction with water is faster than the value of the naked reaction. However, H_a-abstraction reaction, path2, path3, and path4 are slower without water than hydrous channels.     

FT-IR, FT-Raman vibrational spectra and molecular structure investigation of 2-chloro-4-methylaniline: A combined experimental and theoretical study

In this work, the experimental and theoretical vibrational spectra of 2-chloro-4-methylaniline (2Cl4MA, C₇H₈NCl) were studied. FT-IR and FT-Raman spectra of 2Cl4MA in the liquid phase have been recorded in the region 4000–400 cm⁻¹ and 3500–50 cm⁻¹, respectively. The structural and spectroscopic data of the molecule in the ground state have been calculated by using Hartree-Fock (HF) and density functional method (B3LYP) with the 6-31G(d), 6-31G(d,p), 6-31+G(d,p), 6-31++G(d,p) and 6-311G(d), 6-311G(d,p), 6-311+G(d,p), 6-311++G(d,p) basis sets. The vibrational frequencies have been calculated and scaled values have been compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The DFT-B3LYP/6-311++G(d,p) calculations have been found more reliable than the ab initio HF/6-311++G(d,p) calculations for the vibrational study of 2Cl4MA. The optimized geometric parameters (bond lengths and bond angles) were compared with experimental values of aniline and p-methylaniline molecules.     

Ab initio molecular orbital analysis of acetaldehyde dimers.: Thermodynamic properties

The surface of the acetaldehyde dimer was studied by MP2/6-31+G^* ab initio calculations and some of the minima thus located were used in subsequent optimizations and single-point calculations at the B3-LYP/6-311+G(2d,p), MP2/6-311+G(2d,p), MP2/aug-cc-pDVZ and MP2/aug-cc-pTVZ levels. An overall of six minima in two distinct groups were detected, one group consisting of planar configurations and the other of more stable, non-planar (spatial) configurations of the two monomers. Some of the dimer thermodynamic properties were calculated from its harmonic frequencies and a comparison between the experimental values for the thermodynamic properties and the calculated values is discussed.     

Rate constants calculation of hydrogen abstraction reactions CH3CHBr + HBr and CH3CBr2 + HBr

Dual‐level direct dynamics method is used to study the kinetic properties of the hydrogen abstraction reactions of CH₃CHBr + HBr → CH₃CH₂Br + Br (R1) and CH₃CBr₂ + HBr → CH₃CHBr₂ + Br (R2). Optimized geometries and frequencies of all the stationary points and extra points along the minimum‐energy path are obtained at the MPW1K/6‐311+G(d,p), MPW1K/ma‐TZVP, and BMK/6‐311+G(d,p) levels. Two complexes with energies less than that of the reactants are located in the entrance of each reaction at the MPW1K/6‐311+G(d,p) and MPW1K/ma‐TZVP levels, respectively. The energy profiles are further refined with the interpolated single‐point energies method at the G2M(RCC5)//MPW1K/6‐311+G(d,p) level of theory. By the improved canonical variational transition‐state theory with the small‐curvature tunneling correction (SCT), the rate constants are evaluated over a wide temperature range of 200–2000 K. Our calculations have shown that the radical reactivity decreases from CH₃CHBr to CH₃CBr₂. Finally, the total rate constants are fitted by two modified Arrhenius expression. © 2012 Wiley Periodicals, Inc.     

三重态类硅烯HB＝SiLiF的结构及其与R—H(R=F,OH,NH_2)的插入反应

用密度泛函理论(DFT)和二次组态相互作用(QCISD)方法研究了三重态类硅烯HB=SiLiF的结构及其与RH(R=F,OH,NH2)的插入反应.计算结果表明,类硅烯HB=SiLiF有三种平衡构型,其中四元环构型能量最低,是其存在的主要构型.HB=SiLiF与HF,H2O和NH3发生插入反应的机理相同.QCISD/6-311++G(d,p)//B3LYP/6-311+G(d,p)计算的三个反应的势垒分别为124.85,140.67和148.16kJ·mol-1,反应热分别为-2.22,20.08和23.22kJ·mol-1.相同条件下发生插入反应时,反应活性都是H—FH—OHH—NH2.     

Gaseous reaction mechanism of C2F radical with water

The kinetic properties of the carbon-fluorine radicals are little understood except those of CFn (n =1-3). In this article, a detailed mechanistic study was reported on the gas-phase reaction between the simplest pi-bonded C2F radical and water as the first attempt to understand the chemical reactivity of the C2F radical. Various reaction channels are considered. The most kinetically competitive channel is the quasi-direct hydrogen-abstraction route forming P5 HCCF + OH. At the CCSD(T)/6-311+G(2d,2p)//B3LYP/6-311G(d,p)+ZPVE, CCSD(T)/6-311+G(3df,2p)//QCISD/6-311G(d,p)+ZPVE and Gaussian-3//B3LYP/6-31G(d) levels, the overall H-abstraction barriers (4.5, 4.7, and 4.2 kcal/mol) for the C2F + H2O reaction are comparable to the corresponding values (5.5, 3.7, and 5.7 kcal/mol) for the analogous C2H + H2O reaction. This suggests that C2F is a reactive radical like the extensively studied C2H, in contrast to the situation of the CF and CF2 radicals that have much lower reactivity than the corresponding hydrocarbon species. Thus, the C2F radical is expected to play an important role in the combustion processes of the carbon-fluorine chemistry. Furthermore, addition of a second H2O can catalyze the reaction with the H-abstraction barrier significantly reduced to a marginally zero value (0.5 kcal/mol). This is also indicative of the potential relevance of the title reactions in the low-temperature atmospheric chemistry.     

Theoretical study of hydrogen bonded clusters of water and cyanic acid: Hydrogen bonding in terms of the molecular structure

Ab initio and density functional calculations were used to analyze the interaction between a molecule of cyanic acid (HOCN) and up to 4 molecules of water at the B3LYP/6-311++G(d,p) and MP2/6-311++G(d,p) computational levels. The cooperative effect (CE) is increased with the increasing size of the studied clusters. Red shifts of the H–O stretching frequency for complexes involving HOCN as an H-donor were predicted. The strength of the hydrogen bonds in terms of molecular structures could be deduced from a comparison of HOCN–H₂O with HCNO–H₂O, HONC–H₂O and HNCO–H₂O HB clusters. The atom in molecules (AIM) method was used to analyze the cooperative effects on topological parameters.     

Molecular structure, barriers to internal rotation, and the enthalpy of formation of cumene hydroperoxide PhCMe2OOH: a DFT study

Conformational analysis of cumene hydroperoxide PhCMe₂OOH (1) has been carried out using the density functional methods B3LYP/6-31G(d,p) and B3LYP/6-311+G(3df,2p). Ignoring rotation of methyl groups, molecule 1 has seven conformers differing in orientation of the — CMe₂OOH fragment relative to the benzene ring and in mutual position of atoms in this fragment. The molecular structures, relative energies, and statistical distribution of the conformers were determined, and intramolecular rotational barriers were estimated. The enthalpies of formation of all conformers of molecule 1 were calculated using two approximations with inclusion of zero-point vibrational energy and temperature correction. Calculations using the isodesmic reaction (IDR) scheme made it possible to reduce the systematic error of the determination of the enthalpy of reactions. The total enthalpy of formation of compound 1 calculated with inclusion of statistical distribution of rotamers equals −19.7±3.6 kcal mol⁻¹. The combination of the B3LYP/6-31G(d,p) approximation and the IDR scheme gives fairly accurate results (relative error is ±0.4 kcal mol⁻¹) as compared to those obtained with the extended basis set 6-311+G(3df,2p). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1157–1164, June, 2008.     

Reaction mechanism between carbonyl oxide and hydroxyl radical: a theoretical study

The reaction mechanism of carbonyl oxide with hydroxyl radical was investigated by using CASSCF, B3LYP, QCISD, CASPT2, and CCSD(T) theoretical approaches with the 6-311+G(d,p), 6-311+G(2df, 2p), and aug-cc-pVTZ basis sets. This reaction involves the formation of H2CO + HO2 radical in a process that is computed to be exothermic by 57 kcal/mol. However, the reaction mechanism is very complex and begins with the formation of a pre-reactive hydrogen-bonded complex and follows by the addition of HO radical to the carbon atom of H2COO, forming the intermediate peroxy-radical H2C(OO)OH before producing formaldehyde and hydroperoxy radical. Our calculations predict that both the pre-reactive hydrogen-bonded complex and the transition state of the addition process lie energetically below the enthalpy of the separate reactants (DeltaH(298K) = -6.1 and -2.5 kcal/mol, respectively) and the formation of the H2C(OO)OH adduct is exothermic by about 74 kcal/mol. Beyond this addition process, further reaction mechanisms have also been investigated, which involve the abstraction of a hydrogen of carbonyl oxide by HO radical, but the computed activation barriers suggest that they will not contribute to the gas-phase reaction of H2COO + HO.     

Theoretical Study of Reactions between Oxygen‐Centered Radicals (•OH and SO4•—) and Vinyl Monomers in Aqueous Phase

In this work, reactions between industrially relevant monomers (methyl acrylate, ethyl acrylate, methyl methacrylate, vinyl acetate, and isopropenyl acetate) and oxygen‐centered radicals (^•OH and SO₄ ^•—) are studied using a combination of quantum mechanics and transition state theory. These reactions may have a strong influence on polymer structure and properties. Thus, computational methodologies able to estimate reliably coefficients for these reactions are needed to improve the understanding of emulsion polymerization processes. In the case of reactions involving ^•OH, the computational approach is based on the SMD‐water/M06‐2X/6‐311++G(3df, 2p)//B3LYP/6‐31+G(d, p) DFT scheme. All calculated and experimental Gibbs free energy barriers, , are within 1 kcal mol⁻¹. In the case of reactions involving SO₄^•—, the SMD‐water/M06‐2X/6‐311++G(3df, 2p)//CAM‐B3LYP/6‐31+G(d, p) DFT scheme is found to be more suitable than a similar scheme based on B3LYP. This proposed scheme works well for acrylates and methacrylates (errors within 1 kcal mol⁻¹), but it may overestimate the rate coefficients of acetates reacting with SO₄^{• —} .

     

Isomerizations of CH3SO2: Quantum Chemistry and Topological Study

The structures, stabilities and the isomerization reactions of CH₃SO₂ isomers in a doublet electronic state have been studied at B3LYP/6‐311+ +G (d,p), MP2/6‐311++G (d,p) and CCSD(T)/6‐311++G (d,p) levels. The three different levels of calculation give the similar results: thirteen minimum isomers were located and they were connected by eleven transition states. Among the thirteen isomers, cis‐CH₃OSO, trans‐CH₃OSO and CH₃SO₂ are the most stable species, and they should be detected easily in experiment. This is well consistent with the experimental result. These isomers could isomerize to each other by chemical bond vibration, chemical bond rotation and atom migration. The non‐planar ring structure transition state (STS), which was found in this paper, extended the concept of ring STS to the non‐planar systems.     

An ab initio evaluation of the role of p,π interaction: II. Molecules of the CH3COX series

The RHF/6-311G(d) and MP2/6-311G(d) calculations with full geometry optimization were performed for CH₃COX molecules (X = F, Cl, Br, CH₃). Variations in the populations of the p _y orbitals of their halogen and carbon atoms (orbitals whose symmetry axes are perpendicular to the molecular plane) from X = F to X = Cl, Br, and CH₃ are not associated with variations in the extent of the p,π conjugation between the lone electron pair of the halogen atom and the π-electron system of the carbonyl group. The bonding molecular orbitals formed by these atomic p _y orbitals are not determined by this interaction. The RHF/6-311G(d) and MP2/6-311G(d) calculations give similar results.     

Theoretical studies on the reaction of pentafulvenone with water in gas phase and aqueous solvent

In gas phase, the hydrations of pentafulvenone to generate three types of cyclopentadienyl carboxylic acids are studied theoretically at the MP2/6-311+G**//B3LYP/6-311+G** level. A water molecule attacking the C=O double bond of pentafulvenone can yield cyclopentadienyl carboxylic acids via the formation of fulvenediols, and attacking the C=C double bond of pentafulvenone can directly yield cyclopentadienyl carboxylic acid. The barriers of rate-determining transition states are 42.2 and 30.4 kcal mol⁻¹, respectively. The barriers of rate-determining transition states for two water molecules system are 20.2 and 19.6 kcal mol⁻¹, respectively. The products can isomerize to each other. In aqueous solvent, the hydrations of pentafulvenone are investigated using PCM-UAHF model at the MP2 (PCM)/6-311+G**// B3LYP (PCM)/6-311+G** and MP2 (PCM)/6-311+G**// B3LYP/6-311+G** levels. The barriers of all rate-determining transition states are decreased. The added water molecule acts as catalyst in both gas phase and aqueous solvent. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

DFT studies on the mechanism of the reaction of C2H5S with NO2

The mechanisms for the reaction of C₂H₅S with NO₂ are investigated at the QCISD(T)/6‐311++G(d, p)//B3LYP/6‐311++G(d, p) level on both single and triple potential energy surfaces. The geometries, vibrational frequencies and zero‐point energy (ZPE) corrections of all stationary points involved in the title reaction are calculated at the B3LYP/6‐311++G(d, p) level. The results show that the reaction is more predominant on the single potential energy surface, while it is negligible on the triple potential energy surface. Without barrier height in the whole process, the major channel is R → C₂H₅SONO (IM1 and IM2) → P1 (C₂H₅SO+NO). With much heat released in the formation of C₂H₅SNO₂ (IM3) and the transition state involved in the subsequent step more stable than reactants, P4 (CH₃CHS + t‐HONO) is subdominant product energetically. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007