Abstract
The exchange and isomerization of pent-1-ene, cis-pentene, cis-hept-2-ene, trans-hept-3-ene, 2-methylbut-2-ene and 2,3-dimethylbut-2-ene have been investigated on iron films in the presence of a large excess of perdeuteropropene. Further evidence has been given for the occurrence of a direct intramolecular hydrogen shift in double bond migration, and, in cis-trans isomerization, for a direct process without the formation or the breaking of any CH bond. The classical Horiuti-Polanyi mechanism seems to be restricted to cis-trans isomerization and involves only two consecutive steps. The pronounced maxima for d 8, d 5 and d 4 deutero-isomers in the distributions of but-1-ene, pent-1-ene and 3-methylbut-1-ene obtained from the corresponding alk-2-enes show that the isomerization mechanisms involve a dissociative adsorption at a vinylic carbon atom, accompanied by a complete exchange of all the adjacent primary allylic hydrogen atoms. It is suggested that interconversions between σ-π-binuclear surface complexes are responsible for this process.
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