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) $Me$

Show Answer

Answer:

Correct Answer: 31. (b)

Solution:

  1. 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



NCERT Chapter Video Solution

Dual Pane