Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryREPEATER 20242 Marks
Question
Write salient features of $S N^1$ mechanism.
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Answer
Salient features of $S N^1$ mechanism : (1) Two step mechanism. (2) Heterolyis of $C-X$ bond in the slow and reversible first step to form planar carbocation intermediate. (3) Attack of the nucleophile on the carbocation intermediate in the fast second step to form the product. (4) When $S N^1$ reaction is carried out at chiral carbon in an optically active substrate, the product formed is nearly racemic. This indicates that $S N^1$ reaction proceeds mainly with racemization. This means both the enantiomers of product are formed in almost equal amount. Racemization in $S N^1$ reaction is the result of formation of planar carbocation intermediate. Nucleophile can attack planar carbocation from either side which results in formation of both the enantiomers of the product.
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