Alcohols and Ethers - Result Question 28
####31. In the following reaction sequence, the correct structure (s) of $X$ is (are)
(2018 Adv.)
(a)
(c) $Me$
(b)
(d) $Me$
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Answer:
Correct Answer: 31. (b)
Solution:
- Key idea All the reactions involved in the problem are Nucleophilic substitution of second order i.e., $S _N 2$ which have the speciality of inversion of configuration at the carbon atom involved.
Of the reactions given
Reaction 1 in its generalised format is seen as
$$ R OH \xrightarrow[\text { In diethyl ether }\left(Et _2 O\right)]{PBr _3} R Br $$
Reaction 2 is simple halogen exchange reaction called Finkelstein reaction. Its generalised format is
$$ R X+NaI \xrightarrow{\text { In acetone }\left(Me _2 CO\right)} R I+Na X $$
where $X=Cl$ or $Br$
Reaction 3 in its generalised format seen as
$$ R I+NaN _3 \stackrel{HCONMe _2}{\longrightarrow} R N _3+NaI $$
Now if the given product is
and which is too enantiomerically pure i.e. $100 %$ either dextrorotatory or leavorotatory form, then the ’ $X$ ’ must be
Note The configuration at carbon * atom in ’ $X$ ’ becomes inverted due to $S _N 2$ mechanism which is visible in the product as well.
Thus, the probable reactions will be
