The B–C and C–C bonds as preferred electron source for H-bond and Li-bond interactions in complex pairing of C<Subscript>4</Subscript>B<Subscript>2</Subscript>H<Subscript>6</Subscript> with HF and LiH molecules

Ab initio calculations were used to analyze the interaction of C₄B₂H₆ with HF and LiH molecules at the mp2/6-311++g(2d,2p) computational level. Interaction of C₄B₂H₆ with HF results to H–F···H–C and C–B···H–F, C–C···H–F hydrogen bond as well as B–H···H–F dihydrogen bond complexes. Also interaction of C₄B₂H₆ with LiH results to B–C···LiH, C–C···LiH and B–H···LiH lithium bond as well as C–H···H–Li dihydrogen complexes. In the both cases, complexes involving interaction of HF or LiH with peripheral B–C and C–C bonds of the C₄B₂H₆ backbone have greater stabilities. The structures of complexes have been analyzed using AIM and NBO methodologies.     

Characterization of the N?H···ON and N?H···NO H‐bonds in nitrosamine dimers

Ab initio molecular orbital and DFT calculations have been carried out for three most stable dimers of parent nitrosamine (NA) in order to elucidate the structures and energetics of the dimers. The structures were optimized using HF, B3LYP, and MP2 methods with 6‐311+G(d,p) and 6‐311++G(2d,2p) basis sets. At the optimized geometries obtained at MP2/6‐311++G(2d,2p) level of theory, the energies were evaluated at QCISD/aug‐cc‐pVDZ and CCSD/aug‐cc‐pVDZ levels. The most stable dimer has two N? H···O?N hydrogen bonds and the least stable dimer has two N? H···N?O hydrogen bonds. The natural bond orbital analysis showed that the lpO(N) → BD*(N? N) and lpO(N) → BD*(N? H_b) interactions play a decisive role in the stabilization of the NH···O(N) hydrogen bonds in dimers. The atoms in molecules results reveal that the intermolecular N? H···O(N) H‐bonds in dimers have electrostatic character. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

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.     

Frequency shifts and interaction strength of model hydrogen-bonded systems: new NBO and QTAIM characteristics

An innovative theoretical study of intermolecular properties of standard hydrogen-bonded complexes of H₂O···HCF₃, NH₃···HCF₃, H₂O···HF, and NH₃···HF is presented in this work. Several computational strategies were used, so initially the MP2/6-311++G(d,p) level of theory was applied to determine the optimized geometries by which the structural parameters, electronic properties, and the stretch vibration modes of these systems were examined. By taking into account the infrared spectrum analysis, the frequency shifted either to the red- or blue-region is the principal interpretation upon formation of intermolecular complexes. Due to this, the analysis of the interaction strengths corroborates with these vibration behaviors, and besides, the Natural Bond Orbital calculations revealed systematic changes in the percentage of the s and p orbitals, by which the stretch deformations on the proton donors (HF and HCF₃) could be understood. In advance, it was quoted the appearing of intermolecular covalence in these complexes, and this event could be theoretically discovered through the topological computations based on the Bader's Quantum Theory of Atoms in Molecules.     

A theoretical analysis of topography and molecular parameters of the CFCl3···O3 complex: Linear and bifurcate halogen‐oxygen bonding interactions

A theoretical analysis of linear and bifurcate halogen‐oxygen bonds is presented in this work. B3LYP/6‐311++G(d,p) and MP2/6‐311++G(d,p) calculations were used to determine the optimized geometries of intermolecular systems formed by CFCl₃ and O₃. Molecular properties often analyzed in hydrogen‐bonded complexes were used here to describe the interaction between chlorine (CFCl₃) and oxygen (O₃). The halogen‐oxygen bond in the CFCl₃···O₃ complex was characterized using the topological parameters derived from the quantum theory of atoms in molecules. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

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.     

Can the substituent in the para position of anilide ion influence the N−···H–F → N–H···F− switching: a quantum chemical study

The effect of substituents in the para position of anilide ion (An) on the N^?···H–F → N–H···F^? switching in X–An–HF (X = H, Me, CHO, CN, NO, F, NO₂, OH and OMe) complexes was investigated by means of B3LYP and MP2 quantum chemical methods. To delve into the mechanistic details of the proton transfer process, potential energy curve and further geometrical parameters involved in H-bonding during the course of the proton transfer process were evaluated at the MP2/6-311++G(2d,2p) level of theory. The changes in H-bond strength because of variation of substituents were well accompanied by changes in formation energy of complexes, structural parameter, electron density, natural charge and charge transfer between subunits. For X = H, Me, CHO, CN, NO, F and NO₂ substituents, our results at MP2/6-311++G(2d,2p) level showed that the minimum energy structures correspond to the N···HF H-bonded complexes without proton transfer occurring. On the other hand, for electron-donating substituents OH and OMe, proton is transferred from HF to anilide ion and the minimum energy structures are HNH···F^? H-bonded complexes. The nature of HN^?···HF and HN–H···F^? interactions in complexes was characterized by means of atoms in molecules and natural bond orbital analyses.     

A B3LYP and QTAIM study of a new proton donor for dihydrogen bonds: the case of the C2H5 +···nBeH2 complexes (n = 1 or 2)

B3LYP/6-311++G(d,p) calculations and molecular integrations from the quantum theory of atoms in molecules (QTAIM) were performed for the purposes of studying a new class of dihydrogen-bonded hyperconjugation complexes formed by C₂H₅ ⁺···n(BeH₂), when n = 1 (bimolecular) or n = 2 (trimolecular). Whether bimolecular or trimolecular, when the hyperconjugation on the ethyl cation (C₂H₅ ⁺) is taken into account, this enables the earth alkaline hydride, BeH₂, to interact efficiently with the nonlocalized hydrogen (H⁺) of the C₂H₅ ⁺ . In addition to computation of QTAIM topological parameters, analysis of the infrared harmonic spectrum at the B3LYP/6-311++G(d,p) level of theory revealed the existence of red-shifts on BeH₂, and this effect is explained by means of the atomic charges derived from the ChelpG approach. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

复合物HNO···H2O2内N-H···O蓝移氢键的理论研究

A theoretical study on the blue-shifted H-bond N-H…O and red-shifted H-bond O-H…O in the complexHNO…H_2O_2 was conducted by employment of both standard and counterpoise-corrected methods to calculate thegeometric structures and vibrational frequencies at the MP2/6-31G(d),MP2/6-31 G(d,p),MP2/6-311 q G(d,p),B3LYP/6-31G(d),B3LYP/6-31 G(d,p) and B3LYP/6-311 G(d,p) levels.In the H-bond N-H…O,the calcu-lated blue shift of N-H stretching frequency is in the vicinity of 120 cm~(-1) and this is indeed the largest theoreticalestimate of a blue shift in the X-H…Y H-bond ever reported in the literature.From the natural bond orbital analy-sis,the red-shifted H-bond O-H…O can be explained on the basis of the dominant role of the hyperconjugation.For the blue-shifted H-bond N-H…O,the hyperconjugation was inhibited due to the existence of significant elec-tron density redistribution effect,and the large blue shift of the N-H stretching frequency was prominently due tothe rehybridization of sp~n N-H hybrid orbital.     

Density functional theory and topological analysis on the hydrogen bonds in cysteine–propanoic acid complexes

The complexes formed via hydrogen bonding interactions between cysteine and propanoic acid have been studied at the density three-parameter hybrid functional DFT-B3LYP/6-311++G(d,p) level regarding their geometries, energies, vibrational frequencies, and topological features of the electron density. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis was employed to elucidate the interaction characteristics in cysteine–propanoic acid (Cys–Prop) complexes. More than 10 kinds of hydrogen bonds (H-bonds) including intra- and inter-molecular H-bonds have been found in Cys–Prop complexes. The results show that both the strength of H-bonds and the deformation are important factors for the stability of Cys–Prop complexes. The strongest H-bonds (O2H^A···O1^B and O2H^A···O1^B) exist in the most stable Cys–Prop complex. The stronger H-bonds formed between hydroxyl and O (or N) atom usually stronger than those involve C (or S) atom. Relationships between the electron density (ρ) of BCP and H-bond length as well as the Fock matrix element (F _ij) has also been investigated and used to study the nature of H-bonds. Moreover, the results show that the change of the bond length linearly correlates with the corresponding frequency shift.     

Conformation preference and related intramolecular noncovalent interaction of selected short chain chlorinated paraffins

Short chain chlorinated paraffins(SCCPs) are not only research focus of environmental issues but also interesting model molecules for organic chemistry which exhibit diverse conformation preference and intramolecular noncovalent interactions(NCIs). A systematic study was conducted to reveal the conformation preference and the related intramolecular NCIs in two C_(10)-isomers of SCCPs, 5,5,6,6-tetrachlorodecane and 4,4,6,6-tetrachlorodecane. The overall conformation profile was determined on the basis of relative energies calculated at the MP2/6-311++G(d,p) level with the geometries optimized by B3LYP/6-311++G(d,p) method. Then, quantum theory of atoms in molecules(QTAIM) has been adopted to identify the NCIs in the selected conformers of the model molecules at both B3LYP/6-311++G(d,p) and M06-2X/aug-cc-pvdz level. Different chlorine substitution modes result in varied conformation preference. No obvious gauche effect can be observed for the SCCPs with chlorination on adjacent carbon atoms. The most stable conformer of 5,5,6,6-tetrachlorodecane(t Tt) has its three dihedral angles in the T configuration, and there is no intramolecular NCIs found in this molecule. On the contrary, the chlorination on interval carbon atoms favors the adoption of gauche configuration for the H–C–C–Cl axis. Not only intramolecular H···Cl contacts but also H···H interactions have been identified as driving forces to compensate the instability from steric crowding of the gauche configuration. The gggg and g′g′g′g′ conformers are the most popular ones, while the populations of tggg and tg′g′g′ conformer are second to those of the gggg and g′g′g′g′ conformers. Meanwhile, the M06-2X method with large basis sets is preferred for identification of subtle intramolecular NCIs in large molecules like SCCPs.     

Theoretical study of bifurcated bent blue-shifted hydrogen bonds CH<Subscript>2</Subscript>···Y

Ab initio quantum chemistry methods were applied to study the bifurcated bent hydrogen bonds Y··· H₂CZ (Z = O, S, Se) and Y···H₂CZ₂ (Z = F, Cl, Br) (Y = Cl⁻, Br⁻) at the MP2/6-311++G(d,p) and MP2/6-311++G(2df,2p) levels. The results show that in each complex there are two equivalent blue-shifted H-bonds Y···H-C, and that the interaction energies and blue shifts are large, the energy of each Y···H-C H-bond is 15–27 kJ/mol, and Δr(CH) = −0.1 − −0.5 pm and Δv(CH) = 30 − 80 cm⁻¹. The natural bond orbital analysis shows that these blue-shifted H-bonds are caused by three factors: large rehybridization; small direct intermolecular hyperconjugation and larger indirect intermolecular hyperconjugation; large decrease of intramolecular hyperconjugation. The topological analysis of electron density shows that in each complex there are three intermolecular critical points: there is one bond critical point between the acceptor atom Y and each hydrogen, and there is a ring critical point inside the tetragon YHCH, so these interactions are exactly H-bonding.     

Theoretical study on the M-H···π interactions between metal hydrides and inorganic benzene B3X3H3(X = O,S, Se)

In this work, we conducted ab initio calculations to evaluate the properties of M-H···π interactions between the metal hydrides MH (M?=?Li, Na, MgH, CaH, NiH, CuH, ZnH) and inorganic benzenes B₃X₃H₃ (X?=?O, S, Se). Unlike benzene, inorganic benzene B₃X₃H₃ (X?=?O, S, Se) supports a large area of positive molecular electrostatic potential above and below the molecule, which acts as a Lewis acid and interacts with the H atom of metal hydride. MP2/6–311++G(d, p) results show that these intermolecular interactions exhibit the characteristics of close shell noncovalent interactions. The electrostatic interaction significantly contributes to stabilizing the complexes. The M-H···π interaction’s strength is associated with the property of group VI atom and metal hydride. X’s atomic number decreasing and the H of MH becoming more negative facilitate stronger interaction. Furthermore, the addition of substituent on the B₃O₃Y₃ (Y?=?F, Cl, CN, OH, and CH₃) significantly impacts the π-hole of inorganic benzene and thus modulates these M-H···π interactions. More elongation and blueshift of the MH bonds upon complexation were found for electron-withdrawing substituents. Analysis of σ and π orbital separation indicates that the π-attractor’s position relative to the B atom in the inorganic benzene changes with different substituents. The M-H···π interaction’s strength is primarily dependent on the π-electron density, not σ-electron density.

     

Theoretical study on reaction mechanism of sulfuric acid and ammonia and hydration of (NH4)2SO4

In order to understand the mechanism of nucleation of (NH₄)₂SO₄ aerosol, the reaction between sulfuric acid and ammonia in the absence of water molecule is performed at M06/6-311++G(d,p) level. The results show that the (NH₄)₂SO₄ and NH₄HSO₄ units may exist instantaneously in gas phase without water molecule, which is a theoretical prediction that needs detection by further experiment. To further study the growth of the primary nuclei, the geometries, energies, and harmonic frequencies of (NH₄)₂SO₄ · (H₂O) _n (n = 0–9) are calculated both at M06/6-311++G(d,p) and B3LYP/6-311++G(d,p) levels. The tendency of the theoretical vibration frequencies is in accordance with the experimental results. The influence of the water molecule on the properties of (NH₄)₂SO₄ is also analyzed. Our results indicate that M06 is more accurate than B3LYP for this kind of system. Moreover, the first principle molecular dynamics method is used to simulate the structural transformation for two representative isomers whose energies are close, to understand the relationship between solvent-shared ion pairs and contact ion pairs.     

Computational study of tautomerism and aromaticity in mono‐ and dithio‐substituted tropolone

Keto‐enol tautomerism in mono‐ and dithio‐substituted analogs of tropolone was investigated using electronic structure computations. Seven structural isomers of C₇H₆OS and four of C₇H₆S₂ were optimized fully in gas phase at HF and B3LYP theoretical levels in combination with the 6‐311++g** basis set, as well as with the CBS‐QB3 and G3 methods. To examine the effects of an aqueous solvent on tautomeric equilibrium constants, each species was optimized in water using the self‐consistent reaction field polarizable continuum model at HF/6‐311++g** and B3LYP/6‐311++g** model chemistries. In both phases it was found that the enol forms were significantly more stable with respect to electronic energy and Gibbs free energy compared to the keto isomers, and outnumbered the keto species by several orders of magnitude. This was understood on the basis of elementary Hückel theory and the 4n + 2 rule, and supported by nucleus independent chemical shifts computations of NMR chemical shifts in these seven membered cyclic systems. © 2012 Wiley Periodicals, Inc.     

Fluorines in tetrafluoromethane as halogen bond donors: Revisiting address the nature of the fluorine's σhole

It has been demonstrated in several instances that the 0.001 a.u. (electrons per bohr³) isodensity mapped electrostatic surface potentials on the fluorines along the outermost extensions of the C? F covalent bonds in tetrafluoromethane (CF₄) are entirely negative, they are thereby unable to engage in σ_hole bonding interactions with the negative sites on another molecules. In this study, we have attempted at resolving this controversy by performing various high‐level electronic structure calculations with Quadratic Configuration Integrals of Singles and Doubles QCISD(full), second‐order Møller–Plesset MP2(full), and 12 other Density Functional Theory (DFT) based functionals with and without dispersion corrections, all in conjunction with the 6–311++G(2d,2p) basis set. The results achieved with all the levels of theory utilized suggest that the fluorine's σ_holes in CF₄ are positive regardless of the 0.001‐, 0.0015‐, and 0.002‐a.u. isodensity mapped electrostatic surfaces examined. Because of this specific quality, the fluorines in CF₄ have displayed their capacities to form not only 1:1 clusters with the Lewis bases such as water (H₂O), ammonia (NH₃), formaldehyde (H₂C?O), hydrogen fluoride (HF), and hydrogen cyanide (HCN), but also 1:2, 1:3, and 1:4 clusters with the latter three randomly chosen Lewis bases. Various topological and nontopological features obtained from applications of atoms in molecules, noncovalent interaction reduced‐density‐gradient and natural bond orbital analytical tools reveal that the N···F, O···F, and F···F long‐ranged interactions developed between the interacting monomers in H₃N···FCF₃, H₂O···FCF₃, and (Y? D)_n=1–4···F₄C (Y? D = H₂C?O, HCN, and HF) are reminiscent of halogen bonding. The nonadditive cooperative and anticooperative energetic effects emerged on cluster formations are discussed in detail. © 2015 Wiley Periodicals, Inc.     

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     

Self-assembly of DMF with chloromethane and their structures: a theoretical study

The stability of hydrogen-bonded complexes, DMF–H _n CCl_4−n (n = 1–3), has been investigated by several theoretical methods including the MP2 level of ab initio theory at various basis sets from 6-31+G* to 6-311++G**. Two stable configurations (respectively a and b) were obtained for each complex with no imaginary frequencies. The minimum energy structure of these complexes has also been analyzed by means of the atoms in molecule theory at MP2/6-311++G** level. It is found that C–H···O hydrogen bonding exists in these systems and that the intensity of HB interaction gradually increases with successive chlorination. Computed results indicate that these complexes automatically assemble into different stable configurations. For the complexes under consideration, their stabilities can be mainly ascribed to the intermolecular HB interaction. The present work is helpful to clearly understand the interaction mechanism of these complexes in theory.     

Density functional investigations on the (H2O)n·CCH and (H2O)n·HCC complexes (n=1–3)

The electronic structures and energies of (H₂O)_n·CCH and (H₂O)_n·HCC complexes (n=1–3) between CCH and water have been theoretically investigated at the UB3LYP/6-311++G(2df,p)//UB3LYP/6-311G(d,p) level. The complexes with n=2–3 are cyclic structures with homodromic hydrogen-bond chain. The (H₂O)_n·CCH (n=1–3) complexes show increasing stabilities towards CCH- or H₂O-eliminations of 2.3, 5.8 and 7.6 kcal/mol and are energetically more stable than the corresponding (H₂O)_n·HCC complexes by 0.8, 2.7 and 3.4 kcal/mol, respectively, due to the charge-separation-enhanced hydrogen bonds within (H₂O)_n·CCH (n=2,3). Strong interactions between CCH and (H₂O)₂ and (H₂O)₃ clusters suggest special solvent effects of water on the chemical behavior of unsaturated radicals.     

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.