2-methylpropene to tert-butyl alcohol Reaction Mechanism
It is an acid-catalyzed hydration of the double bond. First, the double bond is protonated to yield the tert-butyl cation which is most stabilized by hyperconjugation (protonation at C2 would form a less stable primary cation). The cation is captured by nucleophilic attack of water, which after deprotonation yields tert-butanol and the regenerated proton.

$$\ce{(H3C)2C=CH2 + H3O+ &lt;=&gt; (H3C)3C+ + H2O} \tag 1$$

$$\ce{(H3C)3C+ + H2O &lt;=&gt; (H3C)3C-OH2^{+}} \tag 2$$

$$\ce{(H3C)3C-OH2^{+} + H2O -&gt;~ (H3C)3C-OH + H3O+} \tag 3$$