Allyl ethers ene elimination reactions

There have been no quantitative kinetic studies of allyl alkyl ether eliminations however, a rather extensive study of relative reaction rates has been made . In all cases, the reactions of interest were the 6-center ene eliminations, viz. 

The results are shown in Table 23. Relative rate data were obtained by simultaneous pyrolysis of pairs of ethers. Since the total rate spread of all ethers from the slowest (ethyl allyl) to the fastest (diphenylmethyl-1-methyl allyl) was only a factor of 40, it is apparent that substituent effects are relatively very small (see ester and vinyl ether eliminations). Polarization in the transition states must, therefore, be minimal. Cookson and Wallis ° noted the following rate trends  

In view of the above, a transition state with very little charge separation (A), or one with a reversed polarity (compared to that of the normal eliminations, e.g., esters) (B) was favored. A deuterium isotope effect in a-deuterodiphenylmethyl ether gave kg/kg 1.1. This very low value suggests either little Ca-H bond rupture in the transition state, or that the hydrogen atom is transferred with some 

Unless stated otherwise, the yield of aldehyde or ketone was estimated gravimetrically by precipitation of the 2,4-dinitrophenylhydrazone, and the yield of olefin was estimated by collection in a gas burette. 

The minor products undoubtedly indicate the occurrence of some free radical sensitized decomposition. 

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