A Mechanistic Preview of Addition Reactions

The following flow chart connects three of the reactions we have discussed that involve carbocation intermediates. Each arrow may represent more than one elementary step in a mechanism. 

Arrows 1 and 2 summarize the conversion of alcohols to alkyl halides, 3 and 4 the dehydrohalo-genation of an alkyl halide to an alkene by the El mechanism, and 1 and 4 the formation of an alkene by dehydration of an alcohol. 

The reaction indicated by arrow 5 constitutes a major focus of the next chapter. There we will explore reactions that give overall addition to the double bond by way of carbocation intermediates. One such process converts alkenes to alkyl halides (5 + 2), another converts alkenes to alcohols (5 + 6). 

52 Based on the S l mechanism for the reaction of tertiary alcohols with HCl as summarized in arrows 1 and 2, which arrow(s) represent(s) more than one elementary step  

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