Alkanes theoretical study

Olivella, S. Sole, A. McAdoo, D.J. Griffin, L.L. Unimolecnlar Reactions of Ionized Alkanes Theoretical Study of the Potential Energy Surface for CH3 and CH4 Losses From Ionized Butane and Isohn-tane. J. Am. Chem. Soc. 1994, 94, 11078-11088. 

Theoretical studies of catalytic alkane-dehydrogenation reactions by [(PCP )IrH2], PCP rf-C6H3(CH2P112)2-l, 3 and [cpIr(PH3)(H)]+, suggest that they proceed through similar steps in both cases namely (i) alkane oxidation, (ii) dihydride reductive elimination, (iii) /3-II transfer from alkyl ligand to metal, (iv) elimination of olefin.402 The calculated barriers to steps (i), (ii), and (iv) are more balanced for the PCP system than for cp(PH3). 

In addition to the electronic difference between PR3 and PH3, bulkier ligands on the phosphine can change the reaction through their steric effect. Using the R = Bu on the anthraphos system, Haenel et al. calculated the available molecular surface (AMS) around the metal center as a measure of the space available to the alkane (13b). They correlated the AMS to the relative reactivities of the catalysts and the results show that two bulky tert-butyl groups on each P certainly limit the access to the metal center, and thus, may reduce the reactivity. Other theoretical studies on the pincer complexes showed that this steric contribution/ limitation plays a less important role than the activation barriers introduced by the catalyst itself (22), where the increase in energy barrier induced by the bulky 4Bu is smaller than the original barriers calculated... 

Nonpolar Systems. Most of the early theoretical studies on radiation action were carried out on water and aqueous solutions. This was a consequence not only of Its Importance In radiation biology but also of the greater amount of experimental data and the simplicity of Its radiation chemical reactions as compared with organic systems. Recently, however, more studies on non-polar systems such as alkanes have appeared (24). It Is a long step to solid polymers but methods are being continually refined. 

Boronat, M., Virrruela, M., and Corma, A.A. (1998) Theoretical study of the mechanism of the hydride transfer reaction between alkanes and alkenes catalyzed by an acidic zeolite. J. Phys. Chem., 102 (48), 9853-9858. 

In recent years, many Fluoro derivatives have been studied as potential high energy constituents of proplnts. Many of these compounds are liquids and some are highly explosive. The Bis(2-Fluoro-2,2-Dinitroethyl) Formal, FEFO has been studied by the military and the AEC (Ref 30). Some theoretical studies of Bis-Difluoramino Alkanes have been reported (Refs 26 26e)... 

HO-initiated oxidation of the alkanes become complex with increase in carbon number. Namely, a large variety of alkyl radicals can be produced by the H-atom abstraction from the primary, secondary and tertiary C—H bonds in the parent alkane [88]. The resulting ROO ( C4) radicals have been shown by Atkinson et al. to yield R0N02 as well as RO + N02 upon reaction with NO [100-102]. A major complication in the alkane oxidation mechanism arises from the variety of competitive reaction channels that RO radicals can undergo, e.g., 02-reaction, unimolecular dissociation and internal isomerization. There have been a number of experimental and theoretical studies of these reactions [31,88]. 

Corma and co-workers152 have performed a detailed theoretical study (B3PW91/6-31G level) of the mechanism of the reactions between carbenium ions and alkanes (ethyl cation with ethane and propane and isopropyl cation with ethane, propane, and isopentane) including complete geometry optimization and characterization of the reactants, products, reaction intermediates, and transition states involved. Reaction enthalpies and activation energies for the various elemental steps and the equilibrium constants and reaction rate constants were also calculated. It was concluded that the interaction of a carbenium ion and an alkane always results in the formation of a carbonium cation, which is the intermediate not only in alkylation but also in other hydrocarbon transformations (hydride transfer, disproportionation, dehydrogenation). 

J. W. Raymonda and W. T. Simpson, J. Chem. Phys., 47, 430 (1967). Experimental and Theoretical Study of Sigma-Bond Electronic Transitions in Alkanes. 

Yoshizawa K, T Kamachi, Y Shiota (2001) A theoretical study of the dynamic behavior of alkane hydroxylation by a compound I model of cytochrome P450. J. Am. Chem. Soc. 123 (40) 9806-9816... 

Yoshizawa, K.. (2002) Theoretical study on kinetic isotope effects in the C-H bond activation of alkanes by iron-oxo complexes, Coordination Chemistry Reviews 226, 251-259. 

The overwhelming majority of the theoretical studies were performed on cluster models of the catalytic site, hi spite of the fact that the role of space confinement and the secondary interactions with the framework atoms is well-known, there are only a few electronic structure calculations on lattice models involving hydrocarbons, using either periodic DFT calculations, or embedding methods. In this brief account of the subject we attempt to overview some of the recent computational results of the literature and present some new data obtained from ab initio DFT pseudopotential plane wave calculations on Cl - C4 alkanes in the chabazite framework. 

Most of the unsaturated CpCo carbonyls are active catalysts in alkyne oligomerization (Section 5.1.4), as CO can be displaced for aUcynes. In addition to cyclization reactions, CpCo(CO) complexes have been studied as C-H bond activators. Bergman determined that, unlike the corresponding rhodium and iridium complexes, CpCo(CO) is unreactive toward C-H activation. Theoretical studies were used to probe the inability of CpCo(CO) to activate alkanes, and it... 

Important advances in the field of C-H bond activation have involved the photochemical reactions of boryl complexes such as Cp W(CO)3(Bcat) (98, cat = 1,2-02-3,5-Me2C6H2). Transient species derived from these complexes efficiently activate the C-H bonds of alkanes and arenes (see Alkane Carbon-Hydrogen Bond Activation), and they can convert hydrocarbon solvents into alkylboronate esters (equation 27). Experimental and theoretical studies have shown that these reactions proceed via a boron-assisted, a-bond metathesis see a-Bond Metathesis) pathway involving back donation of electron density from the tungsten atom to a formally unoccupied p orbital centered on the boryl ligand. ... 

In a combined experimental and theoretical study, Borovkov et alP examined the properties of w-alkane radical cations in solution. Here, we shall just focus on one single aspect of their work, i.e., the conformers of one of the alkanes, w-nonane, C9H2o-In its simplest form of the highest symmetry, its structure can be described as a zigzag chain formed by the 9 carbon atoms. To each of the carbon atoms, 2 hydrogen atoms... 

From the viewpoint of the combustion chemist, mechanistic and theoretical studies of abstraction reactions serve two purposes. First, they can determine the overall rate coefficient for an abstraction over a range of temperatures, especially when there are limited experimental data. Second, the combustion modeller wishes to know the rate of abstraction at any particular site on a hydrocarbon molecule. For reaction (10) this is trivial as there is only one type of site a primary C—H bond. However, for more complex fuels there will be a variety of different sites which to a first-order approximation can be considered as primary, secondary and tertiary C—H bonds. As mentioned in the introduction to this section, Atkinson et al. [10] and Walker [11] have attempted to describe radical/ alkane kinetics with the following simple model based on equation (2.4)... 

Solvent reorientation and isomerization of trans-stilbene in alkane solutions has been studied by ps time scale anisotropic absorption and polarization239 Coupling of solute and solvent decreases as the size of the solvent molecules increases. The applicability of currently favoured models for the activated barrier crossing in the photoisomerization of stilbene is discussed, A method for measuring quantum yields in the photoisomerization of trans-stilbene gives high accuracy without use of a chemical actinometer . Evidence has been found for dynamic solvent effects on the photoisomerization of 4,4 -dimethoxystilbene in which the effects of temperature and hydrostatic pressure were made in n-alkane and n-alkyl alcohol. A ps laser time-resolved study fits frequency dependent solvent shifts but gives results inconsistent with the free volume model. Photophysical and theoretical studies of trans and 9-... 

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