Ethane mechanism

The reaction between hydrogen and chlorine is probably also of this type and many organic free radical reactions (e.g. the decomposition of ethanal) proceed via chain mechanisms. 

The origin of a torsional barrier can be studied best in simple cases like ethane. Here, rotation about the central carbon-carbon bond results in three staggered and three eclipsed stationary points on the potential energy surface, at least when symmetry considerations are not taken into account. Quantum mechanically, the barrier of rotation is explained by anti-bonding interactions between the hydrogens attached to different carbon atoms. These interactions are small when the conformation of ethane is staggered, and reach a maximum value when the molecule approaches an eclipsed geometry. 

In a polluted or urban atmosphere, O formation by the CH oxidation mechanism is overshadowed by the oxidation of other VOCs. Seed OH can be produced from reactions 4 and 5, but the photodisassociation of carbonyls and nitrous acid [7782-77-6] HNO2, (formed from the reaction of OH + NO and other reactions) are also important sources of OH ia polluted environments. An imperfect, but useful, measure of the rate of O formation by VOC oxidation is the rate of the initial OH-VOC reaction, shown ia Table 4 relative to the OH-CH rate for some commonly occurring VOCs. Also given are the median VOC concentrations. Shown for comparison are the relative reaction rates for two VOC species that are emitted by vegetation isoprene and a-piuene. In general, internally bonded olefins are the most reactive, followed ia decreasiag order by terminally bonded olefins, multi alkyl aromatics, monoalkyl aromatics, C and higher paraffins, C2—C paraffins, benzene, acetylene, and ethane. 

Lower alkanes such as methane and ethane have been polycondensed ia superacid solutions at 50°C, yielding higher Hquid alkanes (73). The proposed mechanism for the oligocondensation of methane requires the involvement of protonated alkanes (pentacoordinated carbonium ions) and oxidative removal of hydrogen by the superacid system. 

For most processes, the optimum operating point is determined by a constraint. The constraint might be a product specification (a product stream can contain no more than 2 percent ethane) violation of this constraint causes off-specification product. The constraint might be an equipment hmit (vessel pressure rating is 300 psig) violation of this constraint causes the equipment protection mechanism (pressure relief device) to activate. As the penalties are serious, violation of such constraints must be very infrequent. 

An example of the application of molecular mechanics in the investigation of chemical reactions is a study of the correlation between steric strain in a molecule and the ease of rupture of carbon-carbon bonds. For a series of hexasubstituted ethanes, it was found that there is a good correlation between the strain calculated by the molecular mechanics method and the rate of thermolysis. Some of the data are shown in Table 3.3. 

Table 3.3. Correlation between Intramolecular Strain from Molecular Mechanics (MM) Calculations and Activation Energies for Dissociation of C—C Bonds in Substituted Ethanes"...

The following mechanism has been postulated for the decomposition of ethane into ethylene and hydrogen. The overall rate expression is first order in ethane. 

The decomposition of ethane has been extensively studied and several mechanisms have been postulated. The main products of the reaction are ethylene, C2F14, and hydrogen, Hj. However, there are small amounts of methane, CH4, butane, and other products. 

Condensation of thiophenoxide anions with various fluonnated polychloro- or polybromoethanes gives fluoroalkyl phenyl sulfides [57, 52, 55], These formal substitutions involve fluonnated olefins as intermediates [52, 55], In the case of perhalogenated ethanes, the mechanism shows a similarity with that of dihalo-genodifluoroinethane [52] (equations 46 and 47)... 

The key study for our development of molecular mechanics was that by Scbachtschneider and Snyder (1969), who showed that transferable force constants can be obtained provided that a few off-diagonal terms are not neglected. These authors found that olf-diagonal terms are usually largest when neighbouring atoms are involved. A final point for consideration is that the C atom in OCS is obviously chemically different from a C atom in ethane and from a C atom in ethyne. It is necessary to take account of the chemical environment of a given atom. 

In mechanical refrigeration, a multicomponent refrigerant consisting of nitrogen, methane, ethane, and propane is used through a cascade cycle. When these liquids evaporate, the heat required is obtained from... 

It was shown quite early that this approximation gave at most a very small barrier for ethane, a result thought at that time to be in agreement with experiment. When the existence of a barrier of about 3 kcal became known, Eyring et al. reinvestigated the quantum-mechanical theory and considered various higher-order approximations in order to see if any of them could reasonably provide the needed barrier, but they were not successful. 

The proposed polymerization mechanism is shown in Scheme 9.12. Thermal decomposition of the hexasubstituted ethane derivative yields hindered tertiary radicals that can initiate polymerization or combine with propagating species (primary radical termination) to form an oligomeric macroinitiator. The addition of the diphenylalkyl radicals to monomer is slow (e.g. k[ for 34 is reported as KT M"1 s l at 80 °C84) and the polymerization is characterized by an inhibition period during which the initiator is consumed and an oligomeric macroinitiator is formed. The bond to the Cl I formed by addition to monomer is comparatively thermally stable. 

Nelson54 studied the products of radiolysis of aqueous solution by variable-field CIDNP pulse radiolysis. On the basis of the chemical shifts the following products were identified methyl methanesulfinate, methanol, l,2-bis(methylsulfinylethane) [CH3S(0)CH2CH2S(0)CH3], dimethyl sulfone, dimethyl sulfide, methane and ethane. The high field polarization was used to study the mechanism of formation of polarized products. 

This mechanism is further proved by the observation that addition of 0.05 m Br to aqueous DMSO results in reduced intensity of the ethane signal. Bromide ion at this concentration does not effectively compete with DMSO for OH (kom-DMso = 7 x 109 m 1s 1, [DMSO] = 0.23m, k0H + Br = 1-1 x 1010m-1s-1) and the effect of Br can be due to its reaction with the cation of DMSO30 34 found also in pure DMSO, (CH3)2SO + is reduced by Br- and consequently cannot react with the spur electrons. 

From such crude data as are to be found in the literature we can calculate approximate values of the equilibrium constants, and hence of the free energies of dissociation for the various hexaarylethanes. From our quantum-mechanical treatment, on the other hand, we obtain only the heats of dissociation, for which, except in the single case of hexaphenylethane, we have no experimental data. Thus, in order that we may compare our results with those of experiment, we must make the plausible assumption that the entropies of dissociation vary only slightly from ethane to ethane. Then at a given temperature the heats of dissociation run parallel to the free energies and can be used instead of the latter in predicting the relative degrees of dissociation of the different molecules. 

The following mechanism has been reported for ethane iodination ... 

Transient computations of methane, ethane, and propane gas-jet diffusion flames in Ig and Oy have been performed using the numerical code developed by Katta [30,46], with a detailed reaction mechanism [47,48] (33 species and 112 elementary steps) for these fuels and a simple radiation heat-loss model [49], for the high fuel-flow condition. The results for methane and ethane can be obtained from earlier studies [44,45]. For propane. Figure 8.1.5 shows the calculated flame structure in Ig and Og. The variables on the right half include, velocity vectors (v), isotherms (T), total heat-release rate ( j), and the local equivalence ratio (( locai) while on the left half the total molar flux vectors of atomic hydrogen (M ), oxygen mole fraction oxygen consumption rate... 

H NMR data has been reported for the ethylzinc complex, Zn(TPP—NMe)Et, formed from the reaction of free-base N-methyl porphyrin H(TPP—NMe) with ZnEti. The ethyl proton chemical shifts are observed upheld, evidence that the ethyl group is coordinated to zinc near the center of the porphyrin. The complex is stable under N2 in the dark, but decomposed by a radical mechanism in visible light.The complex reacted with hindered phenols (HOAr) when irradiated with visible light to give ethane and the aryloxo complexes Zn(TPP—NMe)OAr. The reaction of Zn(TPP—NMe)Et, a secondary amine (HNEt2) and CO2 gave zinc carbamate complexes, for example Zn(TPP—NMclOiCNEti."" ... 

Other reactions which apparently involve transfer to nucleophiles include those of [MeCo(salen)] with MeMgl to give ethane as well as methane and H2 64), and of [MeCo(DMG)2X]complexes with CN and PhNMe , apparently to give MeCN and PhNMe2 161). The mechanisms of these processes have not been studied. Nevertheless it is known that the reaction of methyl- and ethylcobalamin with cyanide (products not known) requires oxygen, and shows an induction period [see Chapter 13 of ref. 136)). 

A steady-state analysis of this mechanism shows that the reaction is Vi order in ethane at low degrees of conversion. 

Because ethyl radicals have been observed in the preceding experiment, which also suggest that these radicals are stable at 50 K, the initial formation of ethyl radicals would undoubtedly lead to the observation of the radicals. A possible mechanism may be proposed by analogy to molecular organometallic chemistry. Negishi et al. have shown that the reaction of zir-conocene dichloride with AlEts hberates ethane and forms a coordinated ethylene according to [129] ... 

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