Fastness chlorination test

To test these alternative hypotheses, a tremendous amount of work has been done, by Brown and by others. For example, camphene hydrochloride is known to undergo ethanolysis 6000 times as fast as rer/-butyl chloride, and this had been attributed to anchimeric assistance with formation of a bridged ion. Brown pointed out that the wrong standard for comparison had been chosen. He showed that a number of substituted (3°) cyclopentyl chlorides (examine the structure of camphene hydrochloride closely) also react much faster than rerr-butyl chloride. He attributed these fast reactions—including that of camphene hydrochloride—to relief of steric strain. On ionization, chloride ion is lost and the methyl group on the ap hybridized carbon moves into the plane of the ring four non-bonded interactions thus disappear, two for chlorine and two for methyl. For certain systems at least, it became clear that one need not invoke a nonclassical ion to account for the facts. 

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