The selectivity of charged phenyl radicals in hydrogen atom abstraction reactions with isopropanol

The vertical electron affinity is demonstrated to be a key factor in controlling the selectivity of charged phenyl radicals in hydrogen atom abstraction from isopropanol in the gas phase. The measurement of the total reaction efficiencies (hydrogen and/or deuterium atom abstraction) for unlabeled and partially deuterium-labeled isopropanol, and the branching ratios of hydrogen and deuterium atom abstraction, by using a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer, allowed the determination of the selectivity for each site in the unlabeled isopropanol. Examination of hydrogen atom abstraction from isopropanol by eight structurally different radicals revealed that the preferred site is the CH group. The selectivity of the charged phenyl radicals correlates with the radical's vertical electron affinity and the reaction efficiency. The smaller the vertical electron affinity of a radical, the lower its reactivity, and the greater the preference for the thermodynamically favored CH group over the CH3 group or the OH group. As the vertical electron affinity increases from 4.87 to 6.28 eV, the primary kinetic isotope effects decrease from 2.9 to 1.3 for the CD group, and the mixture of primary and alpha-secondary kinetic isotopes decreases from 6.0 to 2.4 for the CD3 group.     

Investigation of methylene group hydrogen atom reactivity in some azolidines

UV specttoscopy is used to investigate the kinetics of formation of arylidenerhodanines from rhodanine and various aromatic aldehydes whose benzene ring substitutents differ in nature and position. Hammett's equation is used to determine quantitatively the reactivities of the substituted aldehydes. The order of effect of substituent on reaction velocity is p-NO₂ > p-Cl > H > p-N(CH₃)₂, corresponding to a positive value of ρ in the Hammett equation. The position sequence is p-NO₂ > m-NO₂ > o-NO₂, and for chloro derivatives m-Cl > p-Cl, in agreement with views on transmission of inductive and conjugation effects through a benzene ring to a reaction center.     

Quantum mechanical reaction dynamics in collisions of chlorine atom with hydrogen molecule

We report the accurate determinations of quantum mechanical state-to-state probabilities tor reactions Cl H2 - HCl H and H' HCl - H'Cl H by the generalized Newton variational principle, on the most accurate available potential energy surface. We compare the results for three versions of realistic potential energy surfaces, and to those from hyperspherical close-coupling calculations.     

Quantitative determination of the selectivities of five different phenyl radicals in hydrogen atom abstraction from ethanol

An experimental method is described for obtaining quantitative selectivity information for H-atom abstraction by organic radicals from different sites of a substrate in the gas phase. The method is used to determine the selectivities of five different phenyl radicals toward the three different types of hydrogen atoms in ethanol. This experimental method involves studying the reactivities and selectivities of derivatives of the radicals that contain a chemically inert, charged group (distonic ions), which allows them to be manipulated in a Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer.     

Stable nitroxyl radicals with a hydrogen atom at α-carbon atom of nitroxyl group

Nitroxyl radicals containing the diphenylmethyl group as one of the substituents at the nitroxyl group are stable compounds that can be isolated in an individual state.N-(2-Hydroxy-3-methyl-2-phenylcyclohexyl)-N-diphenylmethylnitroxyl was characterized by X-ray diffraction analysis for the first time.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 400–408, February, 1996.     

Modeling of hydrogen and hydroxyl group migration on graphene

Density functional calculations of optimized geometries for the migration of single hydrogen and hydroxyl groups on graphene are performed. It is shown that the migration energy barrier for the hydroxyl group is three times larger than for hydrogen. The crucial role of supercell size for the values of the migration barriers is discussed. The paired migration of hydrogen and hydroxyl groups has also been examined. It could be concluded that hydroxyl group based magnetism is rather stable in contrast with unstable hydrogen based magnetism of functionalized graphene. The role of water in the migration of hydroxyl groups is also discussed, with the results of the calculations predicting that the presence of water weakens the covalent bonds and makes these groups more fluid. Increasing the number of water molecules associated with hydroxyl groups provides an increase of the migration energy.     

Theoretical study of hydrogen atom migration models in cyclic conformation of 1-pentene

Migration of hydrogen atoms in the cyclic conformation of 1-pentene is assumed. Four migration models are proposed and their relative stability studied by semiempirical methods. According to the results obtained by the MINDO/2 method all model structures assumed are more stable than the original cyclic conformation, whereas by CNDO/2 only one structure is relatively stable. From the results achieved the cyclic conformation of 1-pentene appears as a barrier structure behind which there are other relatively stable structures.     

Polarity of the transition state controls the reactivity of related charged phenyl radicals toward atom and group donors

Polar effects are demonstrated to be a key factor in controlling the reactivities of related charged phenyl radicals in different exothermic atom and group abstraction reactions in the gas phase. The effects of various meta substituents on the phenyl radicals' reactivity were probed via the measurement of bimolecular reaction rate constants by using Fourier transform ion cyclotron resonance mass spectrometry. This approach requires an additional, charged substituent to be present in the phenyl radical to allow mass spectrometric manipulation. The m-pyridinium group was chosen for this purpose. The substrates studied were allyl iodide, dimethyl disulfide, and tert-butyl isocyanide. Two of the reactions of interest, *I and *SCH(3) transfer, are thought to occur by concerted bimolecular homolytic substitution (S(H)2), and the third one, *CN transfer, by an addition/elimination mechanism. For all three substrates, the reaction rate was found to increase in the following order for the differently substituted phenyl radicals: CH(3) approximately H < Br approximately Cl approximately COOH < NO(2) approximately CN. This trend does not arise from differences in reaction exothermicities or bond dissociation energies but via lowering the reaction barrier by electronic effects. The stabilization of the transition state is attributed to its increased polar character. A semiquantitative measure of the barrier lowering effect for each substituent is obtained from its influence on the electron affinity of the charged radical, as the calculated (B3LYP/6-31+G(d)) adiabatic electron affinities of the radical model systems (ammonium instead of pyridinium charge site) follow the same trend as the reactivities.     

Quantum-chemical analysis of the nucleophilic substitution of the bromine atom by the cyano group at the sp-hybridized carbon atom in the methylbromoacetylene molecule

This paper reports on our quantum-chemical analysis of the nucleophilic substitution of the bromine atom by the cyano group in the reaction of methylbromoacetylene with copper cyanide. According to calculations, the reaction can form a four-membered ring containing a copper atom.     

氟原子与氢分子共线反应几率的量子散射计算

基于最新的6SEC势能面,用邓从豪等提出的LCAC-SW方法计算得到了共线反应F+H~2(v=0)→HF(v')+H的态-态反应几率,计算结果准确地反映出势能面的特点,进一步证明LCAC-SW方法是一成功的量子散射方法。     

Initiation of the internal-conversion process in the phenyl benzoate molecule

The INDO and CNDO/S methods were used to calculate changes in the energy of the ground state and the energy of the first singlet-singlet transition of phenyl benzoate permitted with respect to its multiplet nature with consistent rotation of phenyl groups of the molecule in the cis conformation. It was found that in the lowest excited singlet state of the phenyl benzoate molecule an adiabatic photoreaction can occur, as a result of which the energy of the S₀-S₁ electron transition decreases to values of 2 eV. With motion of the molecular system along the coordinate of the photoreaction, an internal-conversion process is initiated, which leads to the experimentally observed absence of luminescence of phenyl benzoate solutions.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 21, No. 3, pp. 365–367, May–June, 1985.     

Variation of the polarizability of the hydrogen molecule ion and the hydrogen molecule with internuclear separation

The variation of the polarizability of H and H₂ with internuclear separation R = 1.6 – R = 2.4 a.u. for H and R = 1.0 – R = 2.0 a.u. for H₂ is determined using a variational method suggested by Das and Bersohn. From these data, values of 〈α〉_0,J for which nuclear motion due to zero point vibration and centrifugal stretching is taken into account, are calculated at 300°K. The relative percent increases of the motion averaged values compared to the equilibrium values are as follows: 10.50% for H and 6.52% for H₂.     

Reactions of hydrogen atom with hydrogen peroxide

Rate coefficients are calculated using canonical variational transition state theory with multidimensional tunneling (CVT/SCT) for the reactions H + H2O2 --> H2O + OH (1a) and H + H2O2 --> HO2 + H2 (1b). Reaction barrier heights are determined using two theoretical approaches: (i) comparison of parametrized rate coefficient calculations employing CVT/SCT to experiment and (ii) high-level ab initio methods. The evaluated experimental data reveal considerable variations of the barrier height for the first reaction: although the zero-point-exclusive barrier for (1a) derived from the data by Klemm et al. (First Int. Chem. Kinet. Symposium 1975, 61) is 4.6 kcal/mol, other available measurements result in a higher barrier of 6.2 kcal/mol. The empirically derived zero-point-exclusive barrier for (1b) is 10.4 kcal/mol. The electronic structure of the system at transition state geometries in both reactions was found to have "multireference" character; therefore special care was taken when analyzing electronic structure calculations. Transition state geometries are optimized by multireference perturbation theory (MRMP2) with a variety of one-electron basis sets, and by a multireference coupled cluster (MR-AQCCSD) method. A variety of single-reference benchmark-level calculations have also been carried out; included among them are BMC-CCSD, G3SX(MP3), G3SX, G3, G2, MCG3, CBS-APNO, CBS-Q, CBS-QB3, and CCSD(T). Our data obtained at the MRMP2 level are the most complete; the barrier height for (1a) using MRMP2 at the infinite basis set limit is 4.8 kcal/mol. Results are also obtained with midlevel single-reference multicoefficient correlation methods, such as MC3BB, MC3MPW, MC-QCISD/3, and MC-QCISD-MPWB, and with a variety of hybrid density functional methods, which are compared with high-level theory. On the basis of the evaluated experimental values and the benchmark calculations, two possible recommended values are given for the rate coefficients.     

A theoretical study on the effect of intercalating sulfur atom and doping boron atom on the adsorption of hydrogen molecule on (10,0) single-walled carbon nanotubes

Adsorption of molecular hydrogen on single-walled carbon nanotube (SWCNT), sulfur-intercalated SWCNT (S-SWCNT), and boron-doped SWCNT (BSWCNT), have been studied by means of density functional theory (DFT). Two methods KMLYP and local density approximation (LDA) were used to calculate the binding energies. The most stable configuration of H₂ on the surface of pristine SWCNT was found to be on the top of a hexagonal at a distance of 3.54 Å in good agreement with the value of 3.44 Å reported by Han and Lee (Carbon, 2004, 42, 2169). KMLYP binding energies for the most stable configurations in cases of pristine SWCNT, S-SWCNT, and BSWCNT were found to be ?2.2 kJ mol^?1, ?3.5 kJ mol^?1, and ?3.5 kJ mol^?1, respectively, while LDA binding energies were found to be ?8.8 kJ mol^?1, ?9.7 kJ mol^?1, and ?4.1 kJ mol^?1, respectively. Increasing the polarizability of hydrogen molecule due to the presence of sulfur in sulfur intercalated SWCNT caused changes in the character of its bonding to sulfur atom and affected the binding energy. In H₂-BSWCNT system, stronger charge transfer caused stronger interaction between H₂ and BSWCNT to result a higher binding energy relative to the binding energy for H₂-SWCNT.     

Chemical bonding in the hydrogen molecule

The chemical bond in the hydrogen molecule is examined using the electron density and the generalized overlap amplitudes. Logarithmic derivatives of the electron density provide a clear picture of its behavior in the bonding region as well as in the outer region. The GOA expansion of the density is used to examine the dependence of the rate of decay of the density on the GOA ionization potentials. The increase in the electron density at the nuclei and in the bonding region coincides with the higher ionization potential of H₂ over the H atom. The density in the bonding region along the internuclear axis does not decay exponentially, but its shape is very nearly an inverted Gaussian. © 1996 John Wiley & Sons, Inc.     

Dynamic changing features of the molecular face for interaction of a rare gas atom with a hydrogen molecule

We perform a systematical investigation on the dynamic changing feature of the molecular shape and size and electron density distribution in the process of a rare‐gas atom (He, Ne, Ar, and Kr) approaching a hydrogen molecule by an ab initio method. In terms of the molecular face (MF) theory, the polarization effect in the above processes is vividly demonstrated. There is a good linear correlation between our average variation rate (S_aver) of molecular intrinsic characteristic radius at the contacting point and the experimental polarizability of the rare‐gas atoms. This indicates that the MF theory can well represent the intermolecular polarization effect. Interestingly, the pictures of shape changing, charge‐flow, and exchange repulsion processes especially on the reacting active areas have been clearly observed. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Some remarks on the hydrogen atom

The path integral for the Green's function involving the Coulomb potential in combination with the Kustaanheimo-Stiefel transformation is used to generate the atomic orbitals of the nonrelativistic hydrogen atom as various combinations of the product of one-dimensional isotropic harmonic oscillator wave functions. The use of the transformation is justified, by connecting the homogeneous space with the quotient space in the Feynman quantization formalism.     

Information theoretical analysis of the hydrogen atom

This is an analysis of the statistical nature of the time-independent Schrödinger equation through the use of the information entropy concept. We first study the Schrödinger equation in a general way and then by actually computing entropies of various states of the hydrogen atom for a re-examination of the problem. It is found that there exists a variational procedure involving maximizing entropy for obtaining all solutions once one solution is known. Based on certain observations of the particular single system, some general conclusions can be deduced. First of all, we can safely say that the Schrödinger equation, among many other interpretations, is but the consequence of a principle of minimum potential energy expectation with certain proper constraints imposed. In addition, the ensemble concept in statistical thermodynamics is also useful in understanding microscopic quantum systems and many quantum mechanical concepts such as energy quantization and wave nodal properties can be discussed in the light of information theory and statistics in general.