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In the final step of the mechanism, elimination occurs over substitution, why is this?

Reaction scheme

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  • $\begingroup$ For tertiary carbocations elimination products are generally produced, nothing special here. On the other hand rearrangement that happens earlier is a bit interesting. $\endgroup$ – Mithoron Dec 15 '17 at 16:28
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The simple answer is that water is a very weak nucleophile and substitution does happen reversibly, but usually dissociates immediately. After which, the final reaction shown happens.

There is likely a (very) minor product that follows along the substitution pathway with an alcohol final product.

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  • $\begingroup$ So if water added to the carbocation, the c-o is cleaved mostly as oppose to deprotonating and forming the alcohol? $\endgroup$ – Cubefield Dec 15 '17 at 16:05
  • $\begingroup$ That is essentially correct $\endgroup$ – Rampallian Dec 15 '17 at 16:09
  • $\begingroup$ Moreover, for the bottom two examples here: prnt.sc/hny81u why is the substitution product formed over elimination? $\endgroup$ – Cubefield Dec 15 '17 at 16:10

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