Hydrogen atom abstraction

About: Hydrogen atom abstraction is a research topic. Over the lifetime, 7059 publications have been published within this topic receiving 151781 citations.

The electrostatic potential at atomic sites as a reactivity index in the hydrogen bond formation

Abstract: The paper reviews results from computational studies by molecular orbital and density functional theories on several series of hydrogen bonded complexes. These studies aim at quantifying the reactivity of molecules for the complexation process. Excellent linear relationships are found between the electrostatic potential values at the sites of the electron donor and electron accepting atoms and the energy of hydrogen bond formation (ΔE). The series studied are: (a) complexes of R–CHO and R–CN molecules with hydrogen fluoride; (b) complexes of mono-substituted acetylene derivatives with ammonia; (c) (HCN)n hydrogen bonded cluster for n=2–7. All 22 studied complexes of carbonyl and nitrile compounds with hydrogen fluoride fall in the same dependence between the energy of hydrogen bond formation and the electrostatic potential at the atomic site of the carbonyl oxygen and nitrile nitrogen atoms, with linear regression correlation coefficient r=0.979. In the case of complexes of mono-substituted acetylene and diacetylene derivatives with NH3, the correlation coefficient for the dependence between the electrostatic potential at the acidic hydrogen atom and ΔE equals 0.996. For the series of hydrogen bonded (HCN)n clusters, the correlation coefficient for the relationship between the electrostatic potential at the end nitrogen atom and ΔE is r=0.9996. Similarly, the analogous relationship with the electrostatic potential at the end hydrogen atom has a regression coefficient equal to 0.9994. The dependencies found are theoretically substantiated by applying the Morokuma energy decomposition scheme. The results show that the molecular electrostatic potential at atomic sites can be successfully used to predict the ability of molecules to form hydrogen bonds.

α-C−H Bond Strengths in Tetralin and THF: Application of Competition Experiments in Photoacoustic Calorimetry

Abstract: Photoacoustic Calorimetry is used to determine the α-C−H bond dissociation Energy (BDE) in 1,2,3,4-tetrahydronaphthalene (tetralin) in the neat liquid as well as in competition with hydrogen abstraction from tetrahydrofuran (THF) Also, the α-C−H BDE in THF was determined in the neat liquid The experiments with the mixtures of tetralin and THF and with the neat liquids lead to the same results BDEgas(tetralin) is found to be 829 ± 12 and BDEgas(THF) to be 921 ± 16 kcal mol-1 The revised global rate constant of hydrogen abstraction from THF is found to be 46 × 106 M-1 s-1 at 297 K

Density functional complete study of hydrogen bonding between the water molecule and the hydroxyl radical (H2O · HO)

Abstract: The hydrogen bonding complexes formed between the H2O and OH radical have been completely investigated for the first time in this study using density functional theory (DFT). A larger basis set 6-311++G(2d,2p) has been employed in conjunction with a hybrid density functional method, namely, UB3LYP/6-311++G(2d,2p). The two degenerate components of the OH radical 2Π ground electronic state give rise to independent states upon interaction with the water molecule, with hydrogen bonding occurring between the oxygen atom of H2O and the hydrogen atom of the OH radical. Another hydrogen bond occurs between one of the H atoms of H2O and the O atom of the OH radical. The extensive calculation reveals that there is still more hydrogen bonding form found first in this investigation, in which two or three hydrogen bonds occur at the same time. The optimized geometry parameter and interaction energy for various isomers at the present level of theory was estimated. The infrared (IR) spectrum frequencies, IR intensities, and vibrational frequency shifts are reported. The estimates of the H2O · OH complex's vibrational modes and predicted IR spectra for these structures are also made. It should be noted that a total of 10 stationary points have been confirmed to be genuine minima and transition states on the potential energy hypersurface of the H2O · HO system. Among them, four genuine minima were located. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Infrared chemiluminescence from water-forming reactions: Characterization of dynamics and mechanisms

Abstract: The formation of water molecules via hydrogen atom abstraction by hydroxyl radicals and their formation via unimolecular elimination from vibrationally excited alcohols and organic acids are important processes in a variety of gas-phase chemical environments. The nascent vibrational distributions of the water molecules produced by such reactions have been obtained by analysis of the infrared chemiluminescence from H 2 O, HOD and D 2 O. The analysis required computer simulation of the spectra obtained by recording emission from a fast-flow reactor at 298 K with a low-resolution Fourier transform spectrometer. By combining the information deduced from simulation of the H 2 O and HOD emission spectra from the reactions of OH and OD, the total vibrational energy released to the water molecule and the distribution between the stretch and bending modes have been assigned. The present report provides a summary of results from hydroxyl radicals reacting with inorganic hydride molecules, with the primary, secondar...

Rate constant calculations of H-atom abstraction reactions from ethers by HȮ2 radicals.

Abstract: In this work, we detail hydrogen atom abstraction reactions from six ethers by the hydroperoxyl radical, including dimethyl ether, ethyl methyl ether, propyl methyl ether, isopropyl methyl ether, butyl methyl ether, and isobutyl methyl ether, in order to test the effect of the functional group on the rate constant calculations. The Moller–Plesset (MP2) method with the 6-311G(d,p) basis set has been employed in the geometry optimizations and frequency calculations of all of the species involved in the above reaction systems. The connections between each transition state and the corresponding local minima have been determined by intrinsic reaction coordinate calculations. Energies are reported at the CCSD(T)/cc-pVTZ level of theory and include the zero-point energy corrections. As a benchmark in the electronic energy calculations, the CCSD(T)/CBS extrapolation was used for the reactions of dimethyl ether + HȮ2 radicals. A systematic calculation of the high-pressure limit rate constants has been performed us...