Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : -halocarboxylic acid on reaction with dil. gives good yield of -amino carboxylic acid whereas the yield of amines is very low when prepared from alkyl halides.
Reason (R) : Amino acids exist in zwitter ion form in aqueous medium.
In the light of the above statements, choose the correct answer from the options given below :
Assertion (A) : -halocarboxylic acid on reaction with dil. gives good yield of -amino carboxylic acid whereas the yield of amines is very low when prepared from alkyl halides.
Reason (R) : Amino acids exist in zwitter ion form in aqueous medium.
In the light of the above statements, choose the correct answer from the options given below :
- (A)Both (A) and (R) are correct and (R) is the correct explanation of (A).✓ Correct
- (B)Both (A) and (R) are correct but (R) is not the correct explanation of (A).
- (C)(A) is correct but (R) is not correct.
- (D)(A) is not correct but ( ) is correct.
Answer: (A)
Solution
An -halocarboxylic acid treated with dilute ammonia gives a good yield of the -amino acid, whereas ammonolysis of an ordinary alkyl halide gives only a poor yield of the primary amine, because that amine is itself nucleophilic and is alkylated over and over to secondary, tertiary and quaternary products. The -amino acid escapes this fate: in the aqueous medium it exists as the zwitter ion, in which the nitrogen is held as the protonated group and is no longer nucleophilic, so it cannot attack any further halide and the singly substituted product is preserved. Both statements are correct, and the zwitterionic existence of the amino acid is precisely what keeps the yield high, so the reason is the correct explanation of the assertion.
JEE Main · 2023 · 01 Feb 2023 · Shift 2 · Single correct option