An investigation on the reaction mechanism of the F2+Cl2→2ClF using the B3LYP method

The reaction mechanism of F₂+Cl₂→2ClF has been investigated with the density functional theory at the B3LYP/6‐311G* level. Six transition states have been found for the three possible reaction paths and verified by the normal mode vibrational and IRC analyses. Ab initio MP2/6‐311G* geometry optimizations and CCSD(T)/6‐311G(2df)//MP2/6‐311G* single‐point energy calculations have been performed for comparison. It is found that when the F₂ (or Cl₂) molecule decomposes into atoms first and then the F (or Cl) atom reacts with the molecule Cl₂ (or F₂) nearly along the molecular axis, the energy barrier is very low. The calculated energy barrier of F attacking Cl₂ is zero and that of Cl attacking F₂ is only 15.57 kJ?mol^?1 at the B3LYP level. However, the calculated dissociation energies of F₂ and Cl₂ are as high as 145.40 and 192.48 kJ?mol^?1, respectively. When the reaction proceeds through a bimolecular reaction mechanism, two four‐center transition states are obtained and the lower energy barrier is 218.69 kJ?mol^?1. Therefore, the title reaction F₂+Cl₂→2ClF is most probably initiated from the atomization of the F₂ molecule and terminated by the reaction of F attacking Cl₂ nearly along the Cl? Cl bond. MP2 calculations lead to the same conclusion, but the geometry of TS and the energy barrier are somewhat different. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002     

Ab Initio energetics of Si?O bond cleavage

A multilevel approach that combines high‐level ab initio quantum chemical methods applied to a molecular model of a single, strain‐free Si O Si bridge has been used to derive accurate energetics for Si O bond cleavage. The calculated Si O bond dissociation energy and the activation energy for water‐assisted Si O bond cleavage of 624 and 163 kJ mol⁻¹, respectively, are in excellent agreement with values derived recently from experimental data. In addition, the activation energy for H₂O‐assisted Si O bond cleavage is found virtually independent of the amount of water molecules in the vicinity of the reaction site. The estimated reaction energy for this process including zero‐point vibrational contribution is in the range of −5 to 19 kJ mol⁻¹. © 2017 Wiley Periodicals, Inc.     

Mechanistic investigation inspired “on water” reaction for hydrobromic acid‐catalyzed Friedel–Crafts–type reaction of β‐naphthol and formaldehyde

The mechanism of the HBr‐catalyzed Friedel‐Crafts‐type reaction between β‐naphthol and HCHO was investigated by DFT to improve this reaction. The HBr‐H₂O co‐catalyzed the preferential pathway undergoes the concerted nucleophilic addition and hydrogen shift, stepwise followed by H₂O elimination and the C C bond formation. The origin of the high catalytic activity of HBr is ascribed to C H···Br⁻ and O H···Br⁻ interactions, which suggest that the active species is Br⁻. Moreover, water molecules efficiently assist in improving the activity of Br⁻. The computational results show that solvent polarity profoundly affects the activation barriers. To our delight, the activation barrier of the rate‐determining step for the favored pathway in water is comparable (0.6 kcal/mol difference) with that in acetonitrile. The experimental observation further confirmed our results and demonstrated that the title reaction can be successfully achieved “on water.” Therefore, we open a new efficient and green strategy for the synthesis of biphenol derivatives. © 2017 Wiley Periodicals, Inc.     

HNgBeF3 (Ng = Ar‐Rn): Superhalogen‐supported noble gas insertion compounds

Ab initio and density functional theory‐based calculations are performed to study the structure, stability, and nature of bonding of superhalogen‐supported noble gas (Ng) compounds of the type HNgY where (Ng = Ar‐Rn; Y = BeF₃). Here, BeF₃ acts as the superhalogen. Calculations show that the HNgBeF₃ spontaneously dissociates into product following the dissociation channels: HNgBeF₃ → HBeF₃ + Ng and HNgBeF₃ → Ng + HF + BeF₂. The transition states are optimized and the energy barriers are computed to show the metastable behavior of HNgBeF₃. HNgBeF₃ molecules are kinetically stable with respect to the first dissociation process having energy barriers of 1.0, 5.0, 10.6, and 13.9 kcal/mol for Ar, Kr, Xe, and Rn analogues, respectively, at CCSD(T)/Aug‐cc‐pVTZ level. These calculations suggest that the HXeBeF₃ and HRnBeF₃ can be shown to be stable up to ∼100 K temperature with a half‐life of ∼10² seconds. The nature of H Ng and two different types of Ng F bonds in HNgBeF₃ molecules is explored through the natural bond orbital and electron density analyses. The large Wiberg bond index (WBI) values for the H Ng bond indicate the formation of almost a single bond in between H‐atoms and Ng‐atoms, whereas small WBI values for the two Ng F bonds indicate a noncovalent interaction in between them. The electron density analysis further supports the covalency of the H Ng bond and noncovalent interaction in the two Ng F bonds in HNgBeF₃.     

PathOpt—A global transition state search approach: Outline of algorithm

We propose a new algorithm to determine reaction paths and test its capability for Ar₁₂ and Ar₁₃ clusters. Its main ingredient is a search for the local minima on a (n?1) dimensional hyperplane (n = dimension of the complete system in Cartesian coordinates) lying perpendicular to the straight line connection between initial and final states. These minima are part of possible reaction paths and are, hence, used as starting points for an uphill search to the next transition state. First, path fragments are obtained from subsequent relaxations starting from these transition states. They can be combined with information from the straight line connection procedure to obtain complete paths. Our test computations for Ar₁₂ and Ar₁₃ clusters prove that PathOpt delivers several reaction paths in one round. © 2013 Wiley Periodicals, Inc.     

Quantum chemical topology: The electronic structure of the alkaline nitrites MONO (M = Li,Na, K) studied by means of topological analysis of the electron localization function

In the search of the protocovalent bonding, previously recognized in the nitrous acid (HONO), a nature of the chemical bonds in the alkaline nitrites MONO (M = Li, Na, K) has been studied by means of the topological analysis of the Electron Localization Function (ELF) and Electron Localizability Indicator (ELI‐D). Calculations carried out with the B3LYP and MP2(full) methods, in conjunction with the aug‐cc‐pVTZ and 6‐311++G(3df,3pd) basis sets, revealed the cis (C_2v, more stable) and trans (C_s) isomers as minima on PES. Alkaline nitrites consist of the alkali metal cation M^δ+ interacting, mainly via electrostatic forces, with the nitrite anion [ONO]^δ− (δ ≈ 1e). The covalent N O bonds are characterized by disynaptic basins V(N,O) with the basin populations: 1.58÷1.62e for cis‐M^δ+[ONO]^δ− but 1.39÷1.49e for single N O bond and 1.81÷1.87e for formally double NO bond in trans M^δ+[O NO]^δ−. The protocovalent nitrogen–oxygen bond has not been observed. The N O bonds are slightly polarized towards the nitrogen atom with the polarity index p_NO ≤ 0.12. Two different sets of the hybrid (Lewis) structures are compared leading to different pictures of the bonding. According to NBO data there is a delocalization between the single N O and double NO type bonds, meanwhile results of the ELF analysis emphasize an electron delocalization between the single N O and ionic O⁻N⁺ hybrids. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Isomerization study of C5H5NO molecules

The complex potential energy surface (PES) for the isomerization of C₅H₅NO species, including 18 isomers and 23 interconversion transition states, is probed theoretically at the B3LYP/6‐311++G(d,p) and MP2//B3LYP/6‐311++G(d,p) levels of theory. The geometries and relative energies for various stationary points were determined. The zero‐point vibrational energy (ZPVE) corrections have been made to calculate the reliable energy. We predicted a six‐membered ring structure as a global minima isomer I, which is 118.49 and 131.48 kcal · mol^?1 more stable than the least stable, four‐ and three‐membered ring isomer VIII at B3LYP and MP2//B3LYP levels of theory, respectively. The isomers and interconversion transition states have verified by frequency calculation. The intrinsic reaction coordinates (IRC) calculations have been performed to confirm that each transition state is linked by the desired reactants and products. The isomer stability has been studied using relative energies, chemical hardness, and chemical potential. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Electronic Effects of para‐Substitution on the Melting Points of TAAILs

Owing to numerous new applications, the interest in “task‐specific” ionic liquids increased significantly over the last decade. But, unfortunately, the imidazolium‐based ionic liquids (by far the most frequently used cations) have serious limitations when it comes to modifications of their properties. The new generation of ionic liquids, called tunable aryl–alkyl ionic liquids (TAAILs), replaces one of the two alkyl chains on the imidazolium ring with an aryl ring which allows a large degree of functionalization. Inductive, mesomeric, and steric effects as well as potentially also π π and π π⁺ interactions provide a wide range of possibilities to tune this new class of ILs. We investigated the influence of electron‐withdrawing and ‐donating substituents at the para‐position of the aryl ring (NO₂, Cl, Br, EtO(CO), H, Me, OEt, OMe) by studying the changes in the melting points of the corresponding bromide and bis(trifluoromethanesulfonyl)imide, (N(Tf)₂⁻), salts. In addition, we calculated (B3LYP/6‐311++G(d,p)) the different charge distributions of substituted 1‐aryl‐3‐propyl‐imidazolium cations to understand the experimentally observed effects. The results indicated that the presence of electron‐donating and ‐withdrawing groups leads to strong polarization effects in the cations.     

Theoretical study on the kinetics and branching ratios of the gas phase reactions of 1, 1-Dichlorodimethylether (DCDME) with Cl atom

Quantum mechanical calculations are carried out on the reactions of CH₃OCHCl₂ (DCDME) with Cl atom by means of DFT and couple cluster methods. The geometries of the reactants, products, and transition states involved in the reaction pathways are optimized at BHandHLYP level of theory using 6-311G(d,p) basis set. Transition states are searched on the potential energy surface involved during the reaction channels, and each of the transition states is characterized by the presence of only one imaginary frequency. The existence of transition states on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate calculation. Single point energy calculations are performed at CCSD(T) level using the same basis set. The hydrogen abstraction rate constant for the title reaction is calculated at 298 K and atmospheric pressure using the canonical transition state theory including tunneling correction. The calculated value for rate constant as 1.204 × 10^?12 cm³ molecule^?1 s^?1 is found to be in very good agreement with the recent experimental data. The percentage contributions of both reaction channels are also reported at 298 K.     

Efficient Aerobic Oxidative Synthesis of Benzimidazoles with Fe(III) based PEG1000 Dicationic Imidazolium Ionic Liquid/toluene Temperature‐dependent Biphasic System

A green protocol for the synthesis of benzimidazoles with Fe(III) based PEG1000 dicationic imidazolium ionic liquid ([PEG₁₀₀₀mim₂][FeCl₄]₂)/toluene temperature‐dependent biphasic system was described. Conformed by IR analysis, FeCl₄⁻ is the dominating anion species. It could be seen that aldehydes aryla mines and aromatic aldehydes bearing electron‐deficient group ( Cl,  Br,  NO₂) and electron‐rich groups ( OH,  N(CH₃)₂) on the aromatic rings gave good yields (78–96 %). Moreover, the Fe(III) based PEG1000 dicationic imidazolium ionic liquid could be recycled and reused without significant loss of catalytic activity after seven runs.     

Influence of solvent structure on the aquation of K‐chloro(diethylenetriamine)(ethylenediamine) cobalt(III) ion in water and mixed aqueous solvents

The aquation of K‐[Co(dien)(en)Cl]²⁺ was followed spectrophotometrically within the temperature range (40–60°C) in water, water–isopropyl alcohol, and water–tert‐butyl alcohol media of varying solvent composition up to 50 and 60 vol% of the organic solvent component respectively. The nonlinear plot of log k vs. D^?1_s was attributed to the differential solvation of the initial and transition states. The variation of ΔH^≠, ΔS^≠, and ΔG^≠ with the mole fraction of the organic component was analyzed and discussed. The isokinetic temperatures were found to be 330 and 317 K for water–isopropyl alcohol and water–tert‐butly alcohol mixtures respectively, indicating that the aquation reaction is entropy controlled. The application of free energy cycle at 25°C for the aquation reaction in both co‐solvents suggests that the transition state is more stable than the initial one. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 1–6, 2002     

Singlet methylene insertion into polar O?H and N?H bonds of water and ammonia—Ab initio and DFT study

Correlated ab initio molecular orbital, DFT, QCISD, G3MP2, and QCISD(T) calculations have been used to investigate the geometries, energetics, and mechanisms governing the insertion reactions of ¹CH₂ into O H and N H bonds of water and ammonia, respectively, in gas phase adopting 6‐311++g(d, p) basis set. It is found that ¹CH₂ reacts with water and ammonia to produce the ylide‐like intermediates H₂C OH₂ and H₂C NH₃, which in turn undergo 1,2‐hydrogen shift to produce methanol and methylamine, respectively. Results obtained indicate that in the gas phase, the ylides and the transition states are located below the reactants' energy levels. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Comparison of collision‐ versus electron‐induced dissociation of sodium chloride cluster cations

The collision‐induced dissociation (CID) and electron‐induced dissociation (EID) spectra of the [(NaCl)_m(Na)_n]ⁿ⁺ clusters of sodium chloride have been examined in a hybrid linear ion trap Fourier transform ion cyclotron resonance mass spectrometer. For singly charged cluster ions (n = 1), mass spectra for CID and EID of the precursor exhibit clear differences, which become more pronounced for the larger cluster ions. Whereas CID yields fewer product ions, EID produces all possible [(NaCl)_xNa]⁺ product ions. In the case of doubly charged cluster ions, EID again leads to a larger variety of product ions. In addition, doubly charged product ions have been observed due to loss of neutral NaCl unit(s). For example, EID of [(NaCl)₁₁(Na)₂]²⁺ leads to formation of [(NaCl)₁₀(Na)₂]²⁺, which appears to be the smallest doubly charged cluster of sodium chloride observed experimentally to date. The most abundant product ions in EID spectra are predominantly magic number cluster ions. Finally, [(NaCl)_m(Na)₂]^{+ .} radical cations, formed via capture of low‐energy electrons, fragment via the loss of [(NaCl)_n(Na)] ^. radical neutrals. Copyright © 2008 John Wiley & Sons, Ltd.     

Structure and Bonding in [Sb@In8Sb12]3− and [Sb@In8Sb12]5−

We report the characterization of the compound [K([2.2.2]crypt)]₄[In₈Sb₁₃], which proves to contain a 1:1 mixture of [Sb@In₈Sb₁₂]^3? and [Sb@In₈Sb₁₂]^5?. The tri‐anion displays perfect T_h symmetry, the first completely inorganic molecule to do so, and contains eight equivalent In³⁺ centers in a cube. The gas‐phase potential energy surface of the penta‐anion has eight equivalent minima where the extra pair of electrons is localized on one In⁺ center, and these minima are linked by low‐lying transition states where the electron pair is delocalized over two adjacent centers. The best fit to the electron density is obtained from a model where the structure of the 5? cluster lies close to the gas‐phase transition state.     

Kinetics and products of propargyl (C3H3) radical self‐reactions and propargyl‐methyl cross‐combination reactions

Propargyl (HCC CH₂) and methyl radicals were produced through the 193‐nm excimer laser photolysis of mixtures of C₃H₃Cl/He and CH₃N₂CH₃/He, respectively. Gas chromatographic and mass spectrometric (GC/MS) product analyses were employed to characterize and quantify the major reaction products. The rate constants for propargyl radical self‐reactions and propargyl‐methyl cross‐combination reactions were determined through kinetic modeling and comparative rate determination methods. The major products of the propargyl radical combination reaction, at room temperature and total pressure of about 6.7 kPa (50 Torr) consisted of three C₆H₆ isomers with 1,5‐hexadiyne(CHC CH₂ CH₂ CCH, about 60%); 1,2‐hexadiene‐5yne (CH₂CC CH₂ CCH, about 25%); and a third isomer of C₆H₆ (∼15%), which has not yet been, with certainty, identified as being the major products. The rate constant determination in the propargyl‐methyl mixed radical system yielded a value of (4.0 ± 0.4) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for propargyl radical combination reactions and a rate constant of (1.5 ± 0.3) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ for propargyl‐methyl cross‐combination reactions. The products of the methyl‐propargyl cross‐combination reactions were two isomers of C₄H₆, 1‐butyne (about 60%) and 1,2‐butadiene (about 40%). © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 118–124, 2000     

Understanding the Mechanisms of Unusually Fast HH,CH,and CC Bond Reductive Eliminations from Gold(III) Complexes

Carbon–carbon bond reductive elimination from gold(III) complexes are known to be very slow and require high temperatures. Recently, Toste and co‐workers have demonstrated extremely rapid C?C reductive elimination from cis‐[AuPPh₃(4‐F‐C₆H₄)₂Cl] even at low temperatures. We have performed DFT calculations to understand the mechanistic pathway for these novel reductive elimination reactions. Direct dynamics calculations inclusive of quantum mechanical tunneling showed significant contribution of heavy‐atom tunneling (>25 %) at the experimental reaction temperatures. In the absence of any competing side reactions, such as phosphine exchange/dissociation, the complex cis‐[Au(PPh₃)₂(4‐F‐C₆H₄)₂]⁺ was shown to undergo ultrafast reductive elimination. Calculations also revealed very facile, concerted mechanisms for H?H, C?H, and C?C bond reductive elimination from a range of neutral and cationic gold(III) centers, except for the coupling of sp³ carbon atoms. Metal–carbon bond strengths in the transition states that originate from attractive orbital interactions control the feasibility of a concerted reductive elimination mechanism. Calculations for the formation of methane from complex cis‐[AuPPh₃(H)CH₃]⁺ predict that at ?52 °C, about 82 % of the reaction occurs by hydrogen‐atom tunneling. Tunneling leads to subtle effects on the reaction rates, such as large primary kinetic isotope effects (KIE) and a strong violation of the rule of the geometric mean of the primary and secondary KIEs.     

A CAS study on S‐loss and O‐loss dissociation mechanisms of the SO2+ ion in the C,D, and E states

In the present work, we mainly study dissociation of the C ²B₁, D²A₁, and E²B₂ states of the SO₂⁺ ion using the complete active‐space self‐consistent field (CASSCF) and multiconfiguration second‐order perturbation theory (CASPT2) methods. We first performed CASPT2 potential energy curve (PEC) calculations for S‐ and O‐loss dissociation from the X, A, B, C, D, and E primarily ionization states and many quartet states. For studying S‐loss predissociation of the C, D, and E states by the quartet states to the first, second, and third S‐loss dissociation limits, the CASSCF minimum energy crossing point (MECP) calculations for the doublet/quartet state pairs were performed, and then the CASPT2 energies and CASSCF spin‐orbit couplings were calculated at the MECPs. Our calculations predict eight S‐loss predissociation processes (via MECPs and transition states) for the C, D, and E states and the energetics for these processes are reported. This study indicates that the C and D states can adiabatically dissociate to the first O‐loss dissociation limit. Our calculations (PEC and MECP) predict a predissociation process for the E state to the first O‐loss limit. Our calculations also predict that the E²B₂ state could dissociate to the first S‐ and O‐loss limits via the A²B₂ ← E²B₂ transition. On the basis of the 13 predicted processes, we discussed the S‐ and O‐loss dissociation mechanisms of the C, D, and E states proposed in the previous experimental studies. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

A Theoretical Investigation on the Reaction Mechanism of the C8H10+· Side‐Chain Decomposition Processes

The dissociation of ethylbenzene cation C₈H₁₀^+· served as a prototype to investigate the decompasition mechanisms of alkylbenzene cations. The reactions of C₈H₁₀^+· decomposition reaction system have been studied extensively at the B3LYP/6‐311++G?? ?? level with Gaussion 98 package. The chain reaction of C₈H₁₀^+· dissociation is initiated by C–H bond rupture. All reaction channels were fully investigated with the vibrational mode analysis to confirm the transition states and reveal the reaction mechanism. The energetically most favorable pathway is C₈H₁₀^+·→TS4→P2+H· and the channel leading to C₈H₁₀^+· and C₂H₄ is also competitive.     

Possible mechanism of BN fullerene formation from a boron cluster: Density‐functional tight‐binding molecular dynamics simulations

We simulate the formation of a BN fullerene from an amorphous B cluster at 2000 K by quantum mechanical molecular dynamics based on the density‐functional tight‐binding method. We run 30 trajectories 200 ps in length, where N atoms are supplied around the target cluster, which is initially an amorphous B₃₆ cluster. Most of the incident N atoms are promptly incorporated into the target cluster to form B‐N‐B bridges or NB₃ pyramidal local substructures. BN fullerene formation is initiated by alternating BN ring condensation. Spontaneous atomic rearrangement and N₂ dissociation lead to the construction of an sp² single‐shelled structure, during which the BN cluster undergoes a transition from a liquid‐like to a solid‐like state. Continual atomic rearrangement and sporadic N₂ dissociation decrease the number of defective rings in the BN cluster and increase the number of six‐membered rings, forming a more regular shell structure. The number of four‐membered rings tends to remain constant, and contributes to more ordered isolated‐tetragon‐rule ring placement. © 2016 Wiley Periodicals, Inc.