Alkyl Hydrogen Atoms Research Articles

Alkyl hydrogen atom abstraction reactions of the CN radical with ethanol.

We present a study of the abstraction of alkyl hydrogen atoms from the β and α positions of ethanol by the CN radical in solution using the Empirical Valence Bond (EVB) method. We have built separate 2 × 2 EVB models for the Hβ and Hα reactions, where the atom transfer is parameterized using ab initio calculations. The intra- and intermolecular potentials of the reactant and product molecules were modelled with the General AMBER Force Field, with some modifications. We have carried out the dynamics in water and chloroform, which are solvents of contrasting polarity. We have computed the potential of mean force for both abstractions in each of the solvents. They are found to have a small and early barrier along the reaction coordinate with a large energy release. Analyzing the solvent structure around the reaction system, we have found two solvents to have little effect on either reaction. Simulating the dynamics from the transition state, we also study the fate of the energies in the HCN vibrational modes. The HCN molecule is born vibrationally hot in the CH stretch in both reactions and additionally in the HCN bends for the Hα abstraction reaction. In the early stage of the dynamics, we find that the CN stretch mode gains energy at the expense of the energy in CH stretch mode.

Local Structure in Terms of Nearest-Neighbor Approach in 1-Butyl-3-methylimidazolium-Based Ionic Liquids: MD Simulations.

Description of the local microscopic structure in ionic liquids (ILs) is a prerequisite to obtain a comprehensive understanding of the influence of the nature of ions on the properties of ILs. The local structure is mainly determined by the spatial arrangement of the nearest neighboring ions. Therefore, the main interaction patterns in ILs, such as cation-anion H-bond-like motifs, cation-cation alkyl tail aggregation, and ring stacking, were considered within the framework of the nearest-neighbor approach with respect to each particular interaction site. We employed classical molecular dynamics (MD) simulations to study in detail the spatial, radial, and orientational relative distribution of ions in a set of imidazolium-based ILs, in which the 1-butyl-3-methylimidazolium (C4mim(+)) cation is coupled with the acetate (OAc(-)), chloride (Cl(-)), tetrafluoroborate (BF4(-)), hexafluorophosphate (PF6(-)), trifluoromethanesulfonate (TfO(-)), or bis(trifluoromethanesulfonyl)amide (TFSA(-)) anion. It was established that several structural properties are strongly anion-specific, while some can be treated as universally applicable to ILs, regardless of the nature of the anion. Namely, strongly basic anions, such as OAc(-) and Cl(-), prefer to be located in the imidazolium ring plane next to the C-H(2/4-5) sites. By contrast, the other four bulky and weakly coordinating anions tend to occupy positions above/below the plane. Similarly, the H-bond-like interactions involving the H(2) site are found to be particularly enhanced in comparison with the ones at H(4-5) in the case of asymmetric and/or more basic anions (C4mimOAc, C4mimCl, C4mimTfO, and C4mimTFSA), in accordance with recent spectroscopic and theoretical findings. Other IL-specific details related to the multiple H-bond-like binding and cation stacking issues are also discussed in this paper. The secondary H-bonding of anions with the alkyl hydrogen atoms of cations as well as the cation-cation alkyl chain aggregation turned out to be poorly sensitive to the nature of the anion.

SO2 Solvation in the 1-Ethyl-3-Methylimidazolium Thiocyanate Ionic Liquid by Incorporation into the Extended Cation-Anion Network.

We have carried out an ab initio molecular dynamics study on the sulfur dioxide (SO2) solvation in 1-ethyl-3-methylimidazolium thiocyanate for which we have observed that both cations and anions play an essential role in the solvation of SO2. Whereas, the anions tend to form a thiocyanate- and much less often an isothiocyanate-SO2 adduct, the cations create a “cage” around SO2 with those groups of atoms that donate weak interactions like the alkyl hydrogen atoms as well as the heavy atoms of the pi -system. Despite these similarities between the solvation of SO2 and CO2 in ionic liquids, an essential difference was observed with respect to the acidic protons. Whereas CO2 avoids accepting hydrogen bonds form the acidic hydrogen atoms of the cations, SO2 can from O(SO2)–H(cation) hydrogen bonds and thus together with the strong anion-adduct it actively integrates in the hydrogen bond network of this particular ionic liquid. The fact that SO2 acts in this way was termed a linker effect by us, because the SO2 can be situated between cation and anion operating as a linker between them. The particular contacts are the H(cation)cdots O(SO2) hydrogen bond and a S(anion)–S(SO2) sulfur bridge. Clearly, this observation provides a possible explanation for the question of why the SO2 solubility in these ionic liquids is so high.Electronic supplementary materialThe online version of this article (doi:10.1007/s10953-015-0321-5) contains supplementary material, which is available to authorized users.

Reaction kinetics of the CN radical with primary alcohols

The kinetics of the reactions of CN radicals with several small primary alcohol molecules were studied by transient infrared laser absorption spectroscopy. Direct time-resolved detection of CN was used to determine total rate constants. In addition, HCN and DCN products were detected in order to estimate the branching ratios of the CN+CH3OH reaction. We find that abstraction of an alkyl hydrogen atom dominates the CN+CH3OH reaction, but a small, ∼8% yield of hydroxyl hydrogen abstraction is also observed.

The dynamic behavior of a liquid ethanol–water mixture: a perspective from quantum chemical topology

Quantum Chemical Topology (QCT) is used to reveal the dynamics of atom-atom interactions in a liquid. A molecular dynamics simulation was carried out on an ethanol-water liquid mixture at its azeotropic concentration (X(ethanol)=0.899), using high-rank multipolar electrostatics. A thousand (ethanol)(9)-water heterodecamers, respecting the water-ethanol ratio of the azeotropic mixture, were extracted from the simulation. Ab initio electron densities were computed at the B3LYP/6-31+G(d) level for these molecular clusters. A video shows the dynamical behavior of a pattern of bond critical points and atomic interaction lines, fluctuating over 1 ns. A bond critical point distribution revealed the fluctuating behavior of water and ethanol molecules in terms of O-H···O, C-H···O and H···H interactions. Interestingly, the water molecule formed one to six C-H···O and one to four O-H···O interactions as a proton acceptor. We found that the more localized a dynamical bond critical point distribution, the higher the average electron density at its bond critical points. The formation of multiple C-H···O interactions affected the shape of the oxygen basin of the water molecule, which is shown in three dimensions. The hydrogen atoms of water strongly preferred to form H···H interactions with ethanol's alkyl hydrogen atoms over its hydroxyl hydrogen.

The thermodynamic interaction of N-methyllactams with cyclohexane and methanol

The study deals with the dependence of thermodynamic interaction of the N-methylamine group in N-methyllactams with the acid hydrogen atom of methanol on the size of the lactam ring. The heats of mixing of N-methyl-4-butanelactam, N-methyl-6-hexanelactam, N-methyl-7-heptanelactam and N-methyl-8-octanelactam with methanol and cyclohexane were measured, and the data thus obtained were treated in terms of Barker’s quasichemical theory. In a series of N-methyllactam-cyclohexane systems the mixing is endothermic, and the heats of mixing decrease with increasing size of the lactam ring. On the contrary, the mixing of N-methyllactams with methanol proceeds exothermically; first, the heats of mixing decrease depending on the lactam ring size, but for N-methyl-8-octanelactam they are very close to values obtained for N-methyl-4-butanelactam. However, with increasing ring size the energy of interaction between the N-methylamide group and the acid hydrogen atom of methanol increases. Such apparent discrepancy may be explained, in particular, by an opposite effect of the interaction between this group and the alkyl hydrogen atom.

IR Spectra and the Aromaticities of Pyridine Extracts of Coals

Petroleum ether insoluble and chloroform soluble parts (γ2 fractions) of pyridine extracts of Australian Moura and Chinese Tatung coals were separated into 6 parts by solvent extractions and liquid chromatography, respectively. These parts were analyzed by 1H-, quantitative 13C-NMR and IR spectrometry.A linear relationship exists between the ratio of optical densities of 1, 600 to 2, 920 cm-1 bands in the IR spectrum, D1600/D2920, and the ratio of aromatic carbon atoms to alkyl hydrogen atoms in the average molecular structural parameters calculated from the 1H-and 13C-NMR spectra, *Ca/*Hal. Further, it has been found that this relationship applies in γ2 fractions of Japanese coals (Taiheiyo, Akabira, Yubari and Miike) and hydrogenated products of γ2 fraction of Nakayama lignite. Assuming that H/C molar ratio of alkyl groups is 2, the estimated values of aromaticities (fa) in original coals that are only slightly soluble in solvents can be calculated from the D1600/D2920 values and this linear relationship.These estimated aromaticities in the original coals agree fairly well with the values obtained by the other methods.

The crystal and molecular structure of a heptacoordinated molybdenum compound, mononitrosylmolybdenum tris(NN-di-n-butyldithiocarbamate)

The crystal structure of tris(N,N-di-n-butyldithiocarbamato) molybdenum(II) nitrosyl has been determined from the three dimensional X-ray data collected by precession methods and measured with a scanning microdensitometer. The material crystallizes in the space group P2 1/c with four molecules per unit cell, a = 15.078(9), b = 27.590(7), c = 9.502(4) Å, and β = 92.33(8)°. Anisotropic refinement of all non-hydrogen atoms by block diagonal least-squares methods led to final residuals of R 1 = 8.1% and R 2 = 10.3 per cent for 2185 non-zero reflections for which F⩾ 2σ. The structure consists of discrete monomers, each composed of three bidentate dithiocarbamato ligands and one nitrosyl group. The donor atoms surrounding the central metal are arranged in a pentagonal bipyramidal configuration which is somewhat distorted due to the small and rigid bite of the dithiocarbamato ligands, two of which occupy four of the basal plane positions while the third one spans an axial to equatorial pair of sites. The nitrosyl ligand coordinates through the nitrogen and ocupiecs the second axial position. The MoN and NO distances, 1.731(8) and 1.154(9) Å respectively, are relatively short and the MoNO angle is slightly bent (173.2(7)°). Adjacent S…S contacts in the equatorial plane are quite short, ranging from 2.809 to 3.080 Å, suggesting sizable non-bonded interactions. The molecule has the following mean bond lengths: MoS, 2.518; SC, 1.715; CN, 1.296 Å. the three S 2CNC 2 fragments are planar and the canonical from (—)S 2CN(+)R 2 makes an important contribution to the electronic structure of the dithiocarbamato ligands. There are weak intermolecular interactions between the nitrosyl oxygen atoms and alkyl hydrogen atoms.

Conformation of the esters of steroid hydroxyl groups by infrared spectroscopy

Infrared spectral studies show that the carbonyl group of the esters of steroid hydroxyl groups are stabilized near the adjacent alkyl hydrogen atoms; this energy of stabilization appears to be more than that of hydrogen bonding between the carbonyl and a nearby hydroxyl group.

Nickel-catalysed hydrogen exchange of aniline, phenol, and their alkylated derivatives with deuterium oxide

Selective exchange of hydrogen atoms ortho to amino or hydroxyl groups, together with benzylic hydrogen atoms in aniline, phenol, and their C- alkylated derivatives, was achieved by allowing these compounds to react with deuterium oxide over nickel on kieselguhr at 99�. In addition to the benzylic hydrogen atoms, alkyl hydrogen atoms farther from the aromatic ring underwent slower exchange. Hydrogen atoms ortho to methoxyl did not exchange. Mechanisms of the catalytic exchange reactions are discussed in the light of the results of deuterium distribution measurements and poisoning experiments with electron donors.