Higher acyclic internal olefins

In the electrochemical system WCle/e /AI/CH2CI2 the trend in metathesis reactivity is pent-2-ene hex-2-ene non-4-ene (Gilet 1983). With Re207/CsN03/ AI2O3 as catalyst the general order of reactivity of linear olefins (C5-C9) is alk-2-ene alk-3-ene alk-4-ene alk-l-ene (Kawai 1988). 

Most of the available data on stereoselectivity of metathesis of acyclic olefins relate to cis- and trans-2-olefins, but it is convenient here also to consider some results for propene, but-l-ene, and pent-l-ene, also cis,cis- and trans,fra i-deca-2,8-diene. 

The occurrence of rapid secondary metathesis reactions makes it absolutely essential to extrapolate results back to zero time if they are to be properly interpreted. The changes in trans/cis ratio of reactants and products with time also carry useful kinetic information, although the mechanism then becomes so complex that any attempt at interpretation requires a number of assumptions. 

Some examples of extrapolation procedures are shown in Figs. 6.1-6.4. As the abscissa, one may use time, percentage conversion of reactant, or trans/cis ratio for a cis reactant (the inverse for a trans reactant). The third method, illustrated in Fig. 6.2, is expected, on the basis of a simplified theory, to give a linear extrapolation, as found experimentally. This is the best method, provided that the rate of isomerization of the reactant is not much faster than the rate of productive metathesis, which, however, is the case with branched olefins (Fig. 6.3). 

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