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Explain the mechanism of S_(N^1) reaction by highlighting the stereochemistry behind it. |
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Answer» Solution :(i) `S_(N^1)` stands for unimolecular nucleophilic substitution reaction of first order reaction. (ii) The rate of the following `S_(N^1)` reaction depends UPON the concentration of alkyl halide (RX) and it is independent of the concentration sof the nucleophile `(OH^(-))` used. (iii) `R - Cl+ OH^(-) to R- OH + Cl^(-)` (iv) This `S_(N^1)` reactionfollows first order kinetics and it occurs in two steps: (v) `S_(N^1)` reaction mechanism takes place in tertiary BUTYL BROMIDE with aqueous KOH as follows: `CH_3-underset(CH_3)underset(|)overset(CH_3)overset(|)C-Br underset(Br)overset(OH(aq))tounderset("Tert. butyl alcohol")(CH_3- underset(CH_3)underset(|)overset(CH_3)overset(|)C-OH)` (vi) The 2 steps of the reaction are: Step 1: Formation of carbocation: The polar C-Br bond breaks first forming a carbocation and bromide ION. This step is slow and hence it is the rate determining step.  The carbocation has two equivalent lobes of the vaccant 2P orbital, So it can react equally fast form either face. Step 2: The nucleophile immediately reacts with the carbocation. This step is fast and hence does not affect the rate of the reaction.  The nucleophile OH can attack carbocation from both the sides. |
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