Czs-2-Butene

Recall that Mechanism I for the decomposition of NO2 and the mechanism for the isomerization reaction of czs-2-butene both predict a simple first-order rate law ... 

The three isomerizations, czs-2-butene frans-2-butene, 1-butene 2-butene, and butenes isobutylene, require increasingly severe reaction conditions. When the position of the double bond is shifted, cis—trans isomerization also occurs, and mixtures of butenes result when the carbon skeleton... 

With such strong base catalysts, carbanions can be formed even from simple olefins. Evidence for carbanionic intermediates is found in butene isomerization. Starting from 1-butene, the rate of czs-2-butene formation is twenty times higher than the rate of frans-2-butene formation (42) ... 

Formation of the cyclic osmate, which occurs with syn stereochemistry, retains the cis-trans stereochemistry of the double bond because osmate formation is a single-step reaction. Oxidation of the osmate does not affect the stereochemistry of the carbon-oxygen bond, and the diol produced from czs-2-butene is a stereoisomer of the diol produced from trans-2-butene. We ll study this type of isomerism in Chapter 9. 

Write balanced equations for the hydrogenation of 1-butene and czs-2-butene. 

If we were to measure the so-called heats of hydrogenation (AH hydrog) for two double-bond isomers and find their difference, we could determine the relative stabilities of cis and trans isomers without having to measure an equilibrium position. czs-2-Butene, for instance, has Aff"hyjjrog = 120 kJ/mol ( 28.6 kcal/mol), while aus-2-butene has A/f°hydrog = -116 kJ/mol (-27.6 kcal/mol)—a difference of 4 kj/mol. 

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