Theoretical study of the trans-N 2H 2→ cis-N 2H 2 and F 2S 2→FSSF reactions in gas and solution phases (original) (raw)
Related papers
Effect of solvent polarity on the potential energy surface in the SN2 reaction of F− + CH3Cl
Computational and Theoretical Chemistry, 2019
The S N 2 reaction of F-+ CH 3 Cl covers a conducive energy domain described by its potential energy surface with varied F-C-Cl and C-F distance. Loci of the potential energy surface produce two reaction wells, one is due to nonconventional F•••H-C hydrogen bonding and the other is due to linear backside attack. The effect of solvent polarity on the PESs leads to (i) a significant increase in the energy barrier of the reaction with increase in the polarity of the solvent, (ii) disappearance of the transition state between the reaction complexes formed due to hydrogen bonding and direct attack on the carbon atom in the polar solvents, and (iii) the formation of reactant complex in cyclohexane due to direct attack of the nucleophile, while in toluene, the complex formation is due to hydrogen bond interaction.
Solvent Effect on the Potential Energy Surfaces of the F– + CH3CH2Br Reaction
The Journal of Physical Chemistry A, 2018
Although substantial works have been undertaken on reaction pathways involved in basepromoted elimination reactions and bimolecular nucleophilic substitution reaction of Fon CH CH 2 X (X=Cl, Br, I), the effect of solvents with varying dielectric constants on the stereochemistry of each of the reaction species involved across the reaction profile have not yet been clearly understood. The present investigation reports the effect of solvents on the potential energy surfaces (PES) and structures of the species appearing in the reaction pathway of Fwith bromoethane. The PESs in gas phase have been computed at MP2 level and CCSD(T) level. The performance of several hybrid density functional, such as B3LYP, M06, M06L, BHandH, X3LYP, M05, M05-2X, M06-2X have also been investigated towards describing the elimination and nucleophilic substitution reactions. With respect to MAE values and to make the computation cost effective, we have explored the implicit continuum solvent model, CPCM in solvents like cyclohexane, methanol acetonitrile, dimethyl sulphoxide and water. The reactant complexes proceed through the subsequent steps to produce fluoroethane as the substitution product and ethylene as one of the elimination products. For elimination reaction both syn and anti elimination have been explored. The calculated relatives energies values which are negative in gas phase are found to be positive in polar solvents since the point charge in the separated reactants are more stabilized than the dispersed charge in the transient complex, which has also been analysed through NBO analysis.
Journal of Molecular Structure: THEOCHEM, 2003
The molecular mechanism for the 1,3-dipolar cycloaddition of nitrone with sulfonylethene chlorides has been studied using ab initio and DFT methods at the HF, MP2 and B3LYP levels together with the 6-31G* basis set. Relative rates, stereo and regioselectivity, have been analysed and discussed. For this cycloaddition four reactive channels associated with the formation of two pairs of diastereoisomeric regioisomers have been characterized. Analysis of the geometries of the corresponding transition structures shows that the cycloaddition takes place along a concerted but asynchronous mechanism. Activation energies as asynchronicity are dependent on the computation level. Thus, while HF calculations gave large barriers, MP2 calculations tend to underestimate them. DFT calculations gave reasonable values. These 1,3-dipolar cycloadditions present an endo stereoselectivity while the meta regioselectivity depends on the computational level. Thus, while HF and DFT calculations predict meta path, in agreement with the experimental results, MP2 calculation predict ortho regioselectivity. The frontier molecular orbitals analysis shows that the reaction is controlled by the (HOMO dipole -LUMO dipolarophile ) interaction in agreement with the charge transfer analysis carried out at the transition structures. Inclusion of diffuse functions at the B3LYP/6-31 þ G* level increases the energy barriers about 4 kcal/mol, giving a similar endo/meta selectivity. Solvent effects have been taken into account, by means of self-consistent reaction field. q
The Journal of Physical Chemistry B, 1999
A quantum chemical investigation of the solvent effects on the competition between the Wolff transposition and 1,2-H-shift in-hydroxy-ketocarbenes in aqueous solution was carried out at the B3LYP/6-31G** level of theory. The inclusion of solvent effects by means of a continuum model was not able to reproduce the experimental yields. Then, a semidiscrete approach consisting of solute-solvent association complexes embedded in a dielectric continuum was used to estimate the solvent influence on the Gibbs activation energies. The calculated ∆G are 0.88 and 4.94 kcal/mol for the 1,2-H-shift and the Wolff transposition processes, respectively, thus rendering a 100% yield for the formation of the vinyl-ketone product in agreement with experiment. The TS for the 1,2-H-shift process is preferentially stabilized by solvent due to a H-bond between the migrating hydrogen and one of the water molecules in the association complex. This effect of solvent is analyzed by means of hybrid QM/MM calculations using a classical description of water molecules with the TIP3P model.
Steric, Quantum, and Electrostatic Effects on S N 2 Reaction Barriers in Gas Phase
The Journal of Physical Chemistry A, 2010
Biomolecular nucleophilic substitution reactions, S N 2, are fundamental and commonplace in chemistry. It is the well documented experimental finding in the literature that vicinal substitution with bulkier groups near the reaction center significantly slows the reaction due to steric hindrance, but theoretical understanding in the quantitative manner about factors dictating the S N 2 reaction barrier height is still controversial. In this work, employing the new quantification approach that we recently proposed for the steric effect from the density functional theory framework, we investigate the relative contribution of three independent effects, steric, electrostatic, and quantum, to the S N 2 barrier heights in gas phase for substituted methyl halide systems, R 1 R 2 R 3 CX, reacting with fluorine anion where R 1 , R 2 , and R 3 denote substituting groups and X=F or Cl. We found that in accordance with the experimental finding, for these systems the steric effect dominates the transition state barrier, contributing positively to barrier heights, but this contribution is largely compensated by the negative, stabilizing contribution from the quantum effect due to the exchange-correlation interactions. Moreover, we find that it is the component from the electrostatic effect that is linearly correlated with the S N 2 barrier height for the systems investigated in the present study. In addition, we compared our approach with the conventional method of energy decomposition in density functional theory, as well as examined the steric effect from the wavefunction theory for these systems via the natural bond orbital analysis.
Computational and Theoretical Chemistry, 2012
Density functional theory (DFT) based calculations on a series of double and single proton-transfer reactions e.g. formamide (FA), acetamide (AA) and trifluoro acetamide (TFA) dimmers are performed to understand the potential energy surfaces during proton transfer processes. Apart from using the N-H distances as proton transfer coordinate we have computed the variations in polarizations and chemical hardnesses of the species involved to locate the transition state structures during the double proton transfer reactions. The average polarizability (a av) and the chemical hardness (g) show their optimum value at the same N-H distance and it corresponds to the transition state for all the three titled complexes. The maximum polarizability and minimum chemical hardness at the transition state (TS) are due to maximal charge separation at TS. We observe that computation of maximum polarizability and minimum chemical hardness along the reaction coordinate are the easiest way to locate the transition state during the proton transfer processes.
Chemical Physics Letters, 1983
Minimum+znerg,y (ME) paths have been calculated for an intermolecular mechanism of the acid-catalysed rcarrangcmrtn of cr-acctylenic tertiary alcohols. Hydrogen-bonding along the reaction path is examined. A detailed clmmctcrizzlion of the saddle point has been obtained. Good ageement between calculated rind experimental activation cntbalpy is found. Tbc bypersurface obtained berc points out a possible major role of salvation alon tile hlE reaction path I_ Introduction lecular mechanism proposed by Edens et al. [S J_ These paths have been calculated with a STO-3G minimal basis set [6] _ The potential
International Journal of Quantum Chemistry, 2020
This study aims to investigate the efficiency and effectiveness of some of the intramolecular boron-nitrogen frustrated Lewis pairs (B/N-FLPs) as metal-free organocatalysts in CO 2 conversion. A two-step mechanism was considered for the catalytic reaction, including the hydrogen splitting by the FLPs (step 1) and reduction reaction by the hydrogenated FLPs (FLPH 2 s) (step 2). The boron atom in the studied FLPs is bonded to various substituents, which have substantial effects on the performance of the B atom as a Lewis acid. The studied FLPs are classified into two distinguished categories. The quantum theory of atoms in molecules method and natural bond orbital analyses showed that more occupation of the p orbital of boron by the substituted groups causes the reluctance of the boron atom in hydrogen splitting and acceptation of electron density of the hydride ion. However, molecular electrostatic potential at the nuclear positions was used as a novel descriptor in justification of the kinetic behavior of FLPs in hydrogen splitting and reduction reactions. Obtained ΔΔV n values in the donor-acceptor interacting system, as an outcome of the electrostatic potential concept, show a remarkable linear correlation with the calculated barrier energies (ΔG ≠) of hydrogen splitting and reduction reactions. This linear correlation can be observed for ΔΔV n values vs electron localization function and localized orbital locator of the developing bond at transition states 1 and 2. Finally, it is concluded that similar activation energies for hydrogen splitting and reduction reactions can be an appropriate criterion for the performance and efficacy of the studied FLPs in the overall reaction.
Chemical Physics Letters, 2007
CCSD(T) with a series of correlation consistent basis up to quintuple-zeta is used to investigate the structures, vibrational spectra, relative stability, heats of formation, and barrier to isomerization of S = SF 2 and FSSF. It represents the most accurate characterization of these molecules to date. Including corrections for relativistic and core-valence correlation effects, we found À78.87 (À76.77) kcal/mol for DH f (298.15 K) of S = SF 2 (FSSF). The accuracy of our results shows that the experimental NIST-JANAF value of À95.94 kcal/mol for S = SF 2 is much overestimated, and sets a reference for a better estimate of the error bar in their value of À80.41 kcal/mol for FSSF.