Aliphatic organolithiums by fluorine-lithium exchange: n-octyllithium

The reaction of 1-fluorooctane (1) with an excess of lithium powder (4-10 equiv.) and DTBB (2-4 equiv.) in THP at 0°C for 5 min gives a solution of the corresponding 1-octyllithium (2), which reacts then with different electrophiles at 0°C (D₂O, MeSiCl, Bu^tCHO, Et₂CO), or −78°C [ClCO₂Me, (PhCH₂S)₂] or −40°C (CO₂) to room temperature to give, after hydrolysis, the expected products (3). The same process applied to 2-fluorooctane gives mainly octane as reaction product, independently on the electrophile used, resulting from a proton abstraction by 2-lithiooctane formed from the reaction medium before addition of the electrophilic reagent.     

Modeling the cyclopolymerization of diallyl ether and methyl α‐[(allyloxy)methyl]acrylate

The free‐radical cyclopolymerization of diallyl ether (1) and methyl α‐(allyloxymethyl)acrylate (2) has been modeled with the B3LYP/6‐31G* methodology, by making use of model compounds for the growing radicals. The cyclization of both monomers is exo, with activation barriers of 5.33 and 9.82 kcal/mol, respectively. To account for the polymerizabilities of these monomers, competing reactions have also been modeled. Although both monomers have a lower barrier for homopolymerization than for cyclization, cyclization dominates due to entropy. This explains the high cyclopolymerization vs. homopolymerization of monomer 2, although its monofunctional counterpart has been reported to homopolymerize well. It has also been shown that the degradative chain transfer by H‐abstraction from the allylic carbon is not effective with this monomer. Poor cyclopolymerization of the monomer 1 has been demonstrated by modeling the degradative chain transfer by H‐abstraction from the allylic carbon, which has been shown to compete very efficiently with polymerization reactions. Additionally, intermolecular propagation reaction has been shown to be facile due to cyclization, since the attacking monomer adopts a cyclic structure. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Theoretical study of hydrogen abstraction reactions CH4 + R → CH3 + HR,geometrical, energetical and kinetical aspects

Five hydrogen abstraction reactions, CH₄ + R CH₃ + HR have been studied usingab initio SCF and CI methods. R was successively chosen as H, CH₃, NH₂, OH and F. Geometries were fully optimized at SCF level and energies were computed at CI level for products, reactants and transition states. Quadratic hypersurfaces were fitted in the neighborhood of the most important points of the potential energy hypersurfaces and vibrational analysis were performed thereupon. Wigner's and Christov's approximations were used to obtain an idea of the importance of tunneling of H atoms through the reaction barrier, and this effect was shown to be non-negligible. Finally, rate constant calculation were carried out at different temperatures.Chercheur Qualifié au Fonds National Belge de la Recherche Scientifique.     

MCl4n− (AuCl4−, PtCl42−, or PdCl42−) anion extraction from NanMCl4 in water using a tetraimidazolium macrocyclic receptor

Highly effective exaction (up to 97%) of noble metal Au, Pt, or Pd as MCl₄^n? form (i.e., AuCl₄^?, PtCl₄^2?, or PdCl₄^2?) from Na_nMCl₄ aqueous solution have been achieved on the basis of the interactions between MCl₄^n? and cyclo[2](2,6-di(1H-imidazol-1-yl)pyridine)[2](2,6-bisbromomethyl)pyridine (1⁴⁺).     

Kinetics of isopropanol decomposition and reaction with H atoms from shock tube experiments and rate constant optimization using the method of uncertainty minimization using polynomial chaos expansions (MUM‐PCE)

We have used the single‐pulse shock tube technique with postshock GC/MS product analysis to investigate the mechanism and kinetics of the unimolecular decomposition of isopropanol, a potential biofuel, and of its reaction with H atoms at 918‐1212 K and 183‐484 kPa. Experiments employed dilute mixtures in argon of isopropanol, a radical scavenger, and, for H‐atom studies, two different thermal precursors of H. Without an added H source, isopropanol decomposes in our studies predominantly by molecular dehydration. Added H atoms significantly augment decomposition, mainly by abstraction of the tertiary and primary hydrogens, reactions that, respectively, lead to acetone and propene as stable organic products. Traces of acetaldehyde were observed in some experiments above ≈ 1100 K and establish branching limits for minor decomposition pathways. To quantitatively account for secondary chemistry and optimize rate constants of interest, we employed the method of uncertainty minimization using polynomial chaos expansions (MUM‐PCE) to carry out a unified analysis of all datasets using a chemical model–based originally on JetSurF 2.0. We find: k(isopropanol → propene + H₂O) = 10^{(13.87 ± 0.69)} exp(?(33 099 ± 979) K/ T) s^?1 at 979‐1212 K and 286‐484 kPa, with a factor of two uncertainty (2σ), including systematic errors. For H atom reactions, optimization yields: k(H + isopropanol → H₂ + p‐C₃H₆OH) = 10^{(6.25 ± 0.42)} T^2.54 exp(?(3993 ± 1028) K /T) cm³ mol^?1 s^?1 and k(H + isopropanol → H₂ + t‐C₃H₆OH) = 10^{(5.83 ± 0.37)} T^2.40 exp(?(1507 ± 957) K /T) cm³ mol^?1 s^?1 at 918‐1142 K and 183‐323 kPa. We compare our measured rate constants with estimates used in current combustion models and discuss how hydrocarbon functionalization with an OH group affects H abstraction rates.     

Theoretical studies on the hydrogen abstraction reactions of methyl esters with HO2 radical and the following β‐scission reactions

Unsaturated fatty acid methyl esters are ubiquitous in biodiesel fuels. The C = C double bond greatly affects the combustion characteristics of biodiesel, especially its ignition behavior at low temperatures. In this work, we report detailed theoretical study on the mechanism and kinetics of the hydrogen abstraction reactions of linear unsaturated C6 methyl esters with hydroperoxy radical (HO₂), which play a critical role in the low‐temperature combustion of biodiesel. Reaction profiles are obtained via intrinsic reaction coordinate (IRC) analysis including the formation of reactant complexes and product complexes at the entrance and exit channels, respectively. The potential energy surfaces are explored at the CBS‐QB3 level. The following β‐scission reactions of the forming radicals are also investigated at the same level of theory. The high‐pressure limit rate constants for all the reactions in the temperature range from 500 to 2000 K are calculated via conventional transition‐state theory with quantum tunneling effect and fitted to the modified Arrhenius expression.     

Product Vibrational State Distributions of F+CH3OH Reaction on Full-Dimensional Accurate Potential Energy Surface

The hydrogen abstraction reaction of methanol with fluorine atoms can produce HF and CH\begin{document}$ _3 $\end{document}O or CH\begin{document}$ _2 $\end{document}OH radicals, which are important in the environment, combustion, radiation, and interstellar chemistry. In this work, the dynamics of this typical reaction is investigated by the quasi-classical trajectory method based on a recently developed globally accurate full-dimensional potential energy surface. Particularly, the vibrational state distributions of the polyatomic products CH\begin{document}$ _3 $\end{document}O and CH\begin{document}$ _2 $\end{document}OH are determined by using the normal mode analysis method. It is found that CH\begin{document}$ _3 $\end{document}O and CH\begin{document}$ _2 $\end{document}OH are dominantly populated in the ground state when the reactants are at the ground ro-vibrational state. The OH stretching mode, torsional mode, H\begin{document}$ _2 $\end{document}CO out-of-plane bending mode and their combination bands in the CH\begin{document}$ _2 $\end{document}OH product can be effectively excited once the OH stretching mode of the reactant CH\begin{document}$ _3 $\end{document}OH is excited to the first vibrationally excited state. Most of the available energy flows into the HF vibrational energy and the translational energy in both channels, while the radical products, CH\begin{document}$ _3 $\end{document}O or CH\begin{document}$ _2 $\end{document}OH, receive a small amount of energy, consistent with experiment, which is an indication of its spectator nature.     

EPR studies on regio-selective H-abstraction by “magic blue” reagent from polymers

The radical reactions of polyolefin and olefin copolymers (4-9), polydienes and diene coplymers (10-15), and polysiloxane (16) with “magic blue” reagent containing H-abstracting agent-bis{perfluoro-1-[1-(2-fluorosulfonyl)ethoxy]ethyl}nitroxide [FSO₂CF₂CF₂OCF(CF₃)]₂N(O) (2)and spin trap-perfluoro-1-nitroso-[1-(2-fluoro-sulfonyl)ethoxy]ethane FSO₂CF₂CF₂OCF(CF₃)NO (3) were studied by EPR detection of the spin adducts of the corresponding polymeric radicals generated in the H-abstraction step to the spin trap 3, namely, the nitroxides FSO₂CF₂CF₂OCF(CF₃)N(O) (polymer-H) 17-29. EPR studies have provided information about the regio-selectivity of H-abstraction, the subsequent radical steps followed H-abstraction and grounded a possibility of employing “magic blue” reagent in polymer modification via H-abstraction-initiated grafting polymerization.     

Visualization of network structure by the application of hypernodes

In the literature several authors describe methods to construct simplified models of networks. These methods are motivated by the need to gain insight into the main properties of medium sized or large networks. The present paper contributes to this research by setting focus on weighted networks, the geographical component of networks and introducing a class of functions to model how the weights propagate from one level of abstraction to the next. Hierarchies of network models can be constructed from reordering of the adjacency matrix of the network; this is how “hypernodes” are derived in the present paper. The hypernode algorithm is explored and it is shown how it can be formulated to handle weighted networks. Weighted networks enable handling the uncertainty or the strength of the components which make up the network. The hypernode algorithm can be run in an iterative manner so that a hierarchy of simplified models of the network can be derived. Some case studies demonstrate the hypernode algorithm. In the first case the algorithm is compared with a similar implementation described in the literature. In the second case an airline dataset is analysed. This study shows that when networks are embedded in the geographical space hypernodes may relate to clusters in the spatial domain. The selection of the visual variables to illustrate the strength of the edges and nodes in a weighted network is discussed.