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Explain the mechanism of S_(N)1 reaction by highlighting the stereo chemistry behind it |
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Answer» Solution :The rate of the following `S_(N)1` reaction depends upon concentration of alkyl halide (RX) and is independent of the concentration of the nucleophile `(OH^(-))`. Hence Rate of the reaction=k [alkyl halide] `S_(N)1` reaction mechanism by taking a reaction between tertiary butyl bromide with aqueous KOH. `underset("Tert-Butyl bromide")(CH_(3)-underset(CH_(3))underset(|)overset(CH_(3))overset(|)(C)-Br) underset(Br)overset(OH^((aq))) to underset("Tert Butyl ALCOHOL")(CH_(3)-underset(CH_(3))underset(|)overset(CH_(3))overset(|)(C)-OH)` This reaction takes place in two STEPS as shown below Step-1 FORMATION of carbocation * The polar C-Br bond breaks forming a carbocation and bromide ion. this step is slow and hence it is the rate determining step.  * The carbocation has 2 equivalent lobes of the vacant 2p orbital, so it can react equally rapidly from either face. Step-2: * The nucleophile immediately reacts with the carbocation. this step is fast and hence does not affect the rate of the REACTIONS.  * As shown above, the nucleophilic reagent `OH^(-)` can ATTACK carbocation from both the sides. |
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