2-Methyl propyl bromide reacts with $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O}^{-}$ and gives 'A' whereas on reaction with $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$ it gives 'B'. The mechanism followed in these reactions and the products 'A' and 'B' respectively are :
$\mathrm{S}_{N} 1, A=$ tert-butyl ethyl ether; $\mathrm{S}_{N} 2, B=$ iso-butyl ethyl ether
$\mathrm{S}_{\mathrm{N}} 1, \mathrm{~A}=$ tert-butyl ethyl ether; $\mathrm{S}_{\mathrm{N}} 1, \mathrm{~B}=$ 2-butyl ethyl ether
$\mathrm{S}_{\mathrm{N}} 2, \mathrm{~A}=$ iso-butyl ethyl ether; $\mathrm{S}_{\mathrm{N}} 1, \mathrm{~B}=$ tert-butyl ethyl ether
$\mathrm{S}_{\mathrm{N}} 2, \mathrm{~A}=$ 2-butyl ethyl ether; $\mathrm{S}_{\mathrm{N}} 2, \mathrm{~B}=$ iso-butyl ethyl ether
