Ethane, dissociation

We shall discuss in detail only one example, and for the sake of simplicity we shall take the (actually undissociated) sym. diphenylethane. Let us first consider what happens when the ethane dissociates. In the first step, the C —C bond breaks and there are formed two phenyl-methyl radicals, which however can resonate between only the structures A and B of Fig. 3. 

Each of the various processes of adsorption may have desorptions of the reverse forms, for example, dissociative adsorption may have as its reverse, associative desorption. However, the process of chemisorption may not be reversible [ 1.2.2(c)]. Desorption may lead to species other than that adsorbed, for example, ethane dissociatively adsorbed on clean nickel gives little or no ethane upon desorption, 1-butene dissociatively adsorbed to methylallyl and H on zinc oxide gives mainly 2-butenes upon desorption, and some W03 may evaporate from tungsten covered with adsorbed oxygen. 

Englezos begins study of kinetics of methane, ethane dissociation... 

Heavier aldehydes behave similarly, eg ethanal dissociates to methane, carbon oxide, and two different sets of free radicals. The reaction mode depends on the... 

Figure 4. Proportional depletion by reaction with energy-dependent k2 E) and according to the Lindemann-Hinshelwood model (constant kz). The curve has been calculated at 999 K for ethane dissociation at the transition pressure.

Although the vibrational frequencies can be varied arbitrarily, there is un upper limit to the A5. The loosest of all transition states (highest AS ) is one in which the TS has all of the properties of the dissociated products. If a molecule such as ethane dissociates to two methyl radicals, a total of six vibrations are converted to five... 

We shall consider in this review mainly the information to be obtained from ka on unimolecular dynamics. We shall in this context first review the ethane dissociation-methyl radical recombination system, to show what can be done for such a well-studied model reaction and what could eventually be done for other reactions as well. We shall then give a short summary for the most recent results on various classes of unimolecular reactions. We are afraid that this enumeration is not complete, and we apologize for any important omissions. Mechanistic and physical organic aspects, which have previously been extensively reviewed, will not be discussed. 

Table 4 Experimental and theoretical results on methyl radical recombination and ethane dissociation...

PI2.4 At high temperatures, ethane dissociates via the reaction (ethane cracker)... 

From the results of classical trajectory calculations intrinsic non-RRKM behavior has been predicted for ethane dissociation, ethyl radical dissociation,and methyl isocyanide isomerization. These predictions are supported by classical trajectory calculations for model H-C-C -> H + C=C dissociation. To generalize, classical trajectory calculations have predicted intrinsic non-RRKM behavior for molecules with isolated high frequency modes [e.g, CH3NC, clusters like Li (H20)j, and van der Waals molecules], molecules like acetylene with linear geometries for which bending and stretching motions are nearly separable, and molecules with tight activated complexes. 

W. L. Hase, The criterion of minimum state density in unimolecular rate theory. An application to ethane dissociation, J. 

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