Hydrogen, molecular elimination, from

Isotopic substitutions have been used to verify that molecular hydrogen is eliminated from the same carbon to form the intermediate ethyl-idene. This is similar to the threshold primary process (1) for methane. It is important to note that the 0-0 band of ethane has been assigned at 8.68 eV. Thus, it appears that reaction (9) may be due to a formally dipole forbidden transition. At a photolysis energy of 10 eV, cleavage of one CH bond and elimination of CH2 become important ... 

The geometry of the cis-alkylcyclohexanol is favorable for trans elimination since the hydroxyl and the neighboring trans hydrogen are coplanar, but this is not true for the l,i-trans isomer hence the molecular conformation has to flip over, to set the hydroxyl group in the axial position for the trans elimination to occur. This would require a few kilocalories of energy and for frans-lert-butylcyclohexanol it would be more difficult to achieve than for IroMs-methylcyclohexanol. It is, therefore, possible that the trans elimination from a boat conformation, or possibly even an epimerization from the trans to the cis isomer which then undergoes a trans elimination reaction. Such an epimerization was found to occur under conditions of dehydration of certain alcohols over alumina, as will be seen under 1,4-cyclohexanediol. The more facile elimination of the cis-i-tert-butylcyclohexanol system as compared with the trans system in solution was also reported in the literature 63). 

Recently, Huybrechts and coworkers56 carried out a numerical integration for a hypothetical molecular and radical model for the HC1 elimination from ethyl chloride in the gas phase. The simulation data indicated that a radical chain process does not contribute to the decomposition rate. Only ethylene and hydrogen chloride are formed in the molecular decomposition. 

Intermolecular isotope effects of 1.1—1.4 have been observed for loss of molecular hydrogen (1, 2 elimination) from (CH2OH)+ ions from methanol compared with the corresponding decompositions of the fully or partially deuterated ions [76, 536]. 

The same relationship has been found for molecular hydrogen eliminations from (C2H4)f, (C2HS)+ and (C6H7)+ [443], It has been argued that these results confirm that the reactions are concerted, in the sense that bonding to both of the hydrogen atoms to be eliminated is weakened in the transition state [443, but see 744]. 

Okabe and McNesby were the first to show that the molecular elimination of hydrogen by reaction (2) was an important primary step in the photolysis at 1470 A. The hydrogen from the photolysis of CH3CD3 contained mainly and D2 this is consistent only with an elimination of molecular hydrogen with both... 

Hydrogen elimination. At 1470 A hydrogen is produced almost entirely by molecular elimination, the most important process being the elimination of H2 from the central carbon by reaction (2) and the least important the elimination of H2 from adjacent carbons by reaction (4), This was shown by the fact that the photolysis of CH3CD2CH3 yields hydrogen which contains D2 HD H2 in the... 

The photolysis of n-butane follows a pattern similar to that of propane, with many corresponding reactions. As found for previous hydrocarbons the photolysis includes both molecular and free-radical processes. The molecular elimination of Hj and Dj from C4H10-C4D10 mixtures was first shown by Sauer and Dorfman, who concluded that at 1470 A more than 90 % of the hydrogen came from molecular processes. On the basis of a study of the decomposition of excited -butane molecules generated by electron impact , they attributed hydrogen, methane, ethylene, and other hydrocarbon products to molecular processes, and concluded that free-radical reactions were minimal. 

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