The previously proposed carbanion cleavage-recombination mechanism for the Wittig rearrangement is shown to be incompatible for ethers containing sec-alkyl or r-alkyl groups. In these cases, particularly for bridgehead bicycloalkyl groups, the migration tendency has no relation to the stability of the corresponding alkyllithium compounds. It is possible to rationalize all previous and present experimental findings of this reaction by invoking a cleavagerecombination mechanism involving free-radical pairs. n 1942, Wittig discovered that benzyl alkyl ethers (6) R. L.
SynopsisThe mechanism of the low profile behavior in certain single-phase polyester systems has been examined. It appears that as polymerization occurs, crosslinked beads (
SynopsisThe mechanism by which low profile character is achieved in unsaturated polyester systems has been investigated. Using techniques of microscopy, data are developed that support a model in which micro stress cracking is induced to relieve stress promoted by polymerization shrinkage. Thus the strain is accommodated internally in a molded part, rather than through macroscopic shrinkage of the article.
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