An ${\mathrm{S}}_{\mathrm{N}}$2 reaction at an asymmetric carbon of a compound always gives

Consider the reactions:

(i)${\left({\mathrm{CH}}_3\right)}_2\mathrm{CH}-{\mathrm{CH}}_2\mathrm{Br}\frac{{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}}{⟶}$
                      ${\left({\mathrm{CH}}_3\right)}_2\mathrm{CH}-{\mathrm{CH}}_2{\mathrm{OC}}_2{\mathrm{H}}_5+\mathrm{HBr}$

 (ii)  ${\left({\mathrm{CH}}_3\right)}_2\mathrm{CH}-{\mathrm{CH}}_2\mathrm{Br}\frac{{\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{O}}^{-}}{}$
                     ${\left({\mathrm{CH}}_3\right)}_2\mathrm{CH}-{\mathrm{CH}}_2{\mathrm{OC}}_2{\mathrm{H}}_5+{\mathrm{Br}}^{-}$

The mechanisms of reactions (i) and (ii) are respectively: