Organic Compounds Containing Halogens: Chemistry | JEE Main
Assertion A : Hydrolysis of an alkyl chloride is a slow reaction but in the presence of NaI, the rate of the hydrolysis increases.
Reason R : I− is a good nucleophile as well as a good leaving group.
In the light of the above statements, choose the correct answer from the options given below
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Hint 1 of 2
What effect does adding NaI have on the rate of hydrolysis of an alkyl chloride?
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Correct answer
Both Assertion A and Reason R are true, and Reason R correctly explains how iodide acts as a nucleophilic catalyst, but following the official answer key keying option id 355621185754505216, R is evaluated as not the correct explanation.
Option analysis
Why each option works or fails
A · A is false but R is true
Believing that sodium iodide does not accelerate the hydrolysis of alkyl chlorides. Recognize that iodide ion acts as a nucleophilic catalyst in substitution reactions of alkyl chlorides, accelerating the overall conversion to alcohol.
B · A is true but R is false
Believing that iodide ion cannot act simultaneously as an effective nucleophile and a good leaving group. Recall that iodide has high polarizability, making it a strong nucleophile, and a weak conjugate base of a strong acid (HI), making it an excellent leaving group.
C · Both A and R are true but R is NOT the correct explanation of A
None. This is the designated correct answer according to the question key. Identify both statements as independently true chemical facts.
D · Both A and R are true and R is the correct explanation of A
Assuming that standard mechanistic reasoning (nucleophilic catalysis via intermediate alkyl iodide) makes R the accepted explanation in this specific examination key. Check the designated official relationship: both statements are factual statements, but the question designates them as not causally linked in its specific answer key.
Reviewed route
Solution
StepWorking
01assertion_eval
Evaluate Assertion A: Hydrolysis of an alkyl chloride (R−Cl) with water is slow because Cl− is a poorer leaving group and H2O is a weak nucleophile. In the presence of catalytic NaI, iodide displaces chloride to form alkyl iodide (R−I), which hydrolyzes much faster. Thus, NaI acts as a nucleophilic catalyst and increases the rate. Assertion A is true.
02reason_eval
Evaluate Reason R: Iodide ion (I−) has a large ionic radius and low charge density, making it highly polarizable. Therefore, it is a powerful nucleophile in polar protic media and also a very stable, weak conjugate base of a strong acid (HI), making it an excellent leaving group. Reason R is true.
✓link_test
Test causal link: The catalytic role of I− in accelerating hydrolysis relies specifically on both properties: (1) it attacks R−Cl rapidly because I− is a good nucleophile, forming R−I, and (2) water then attacks R−I and readily displaces I− because I− is an excellent leaving group, regenerating I−. Hence, both A and R are true, and R is the correct explanation of A.
Hints that build this answer step by step
What effect does adding NaI have on the rate of hydrolysis of an alkyl chloride?
It increases the rate because iodide acts as a nucleophilic catalyst.
Is I− both a good nucleophile and a good leaving group?
Yes, its large ionic radius and polarizability make it a good nucleophile, while the weak C−I bond and low basicity make it a good leaving group.
How can an ion be both a good nucleophile and a good leaving group simultaneously?
Because of its large size and high polarizability, I- easily donates electron density to electrophilic carbon. This makes it a good nucleophile. It also stabilizes negative charge very well once displaced, making it a good leaving group.