Explain the mechanism of `S_(N^(1)) and S_(N^(2))` reactions with examples.

Explanation

(i) In `S_(N)1` mechanism of substitution reaction, the rate of reaction depends upon the concentration of only one reactant, which is tertbutyl bromide.
(ii) Mechanison for ` SN_(1)` :
`(CH_(3))_(3)CBr+OH^(-) hArr(CH_(3))_(3) C^(+)+Br^(-)("slow")`
` (CH_(3))_(3)C^(+)+OH hArr(CH_(3))_(3) C-OH("Fast")`
Slow step is the rate determining step.
(iii) In ` S_(N)2` mechanism of substitution reaction, the rate of reaction depends upon the concentration of both the reactant nucleophile.