The Question is from neet-chemistry alcohols-phenols-ethers , and it was created by the author Mr. S M HUSSAIN

Question

Consider the reaction of a chiral secondary alcohol with thionyl chloride ($SOCl_2$). Which of the following statements regarding the stereochemistry of the product is MOST accurate?

Mr. S M HUSSAIN · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
	**Primary Concept**: Nucleophilic Substitution
	**Related Topics**: Stereochemistry, Reaction Mechanisms, Organic Chemistry
	**Prerequisites**: Understanding of $S_N1$ and $S_N2$ reactions, chirality, and stereochemical configurations.
## SOLUTION PATHWAY
**Given Information**:
	Reaction of a chiral secondary alcohol with $SOCl_2$.
**Method & Steps**:
	1. **Formation of Chlorosulfite Intermediate:**
		Reasoning: The alcohol reacts with $SOCl_2$ to form an alkyl chlorosulfite intermediate.
		Formula/Rule: $R-OH + SOCl_2 ightarrow R-O-SO-Cl + HCl$
	2. **Internal Nucleophilic Substitution ($S_Ni$):**
		Working: The chloride ion, released during the formation of the chlorosulfite intermediate, acts as an internal nucleophile, attacking the chiral carbon from the same side as the leaving group (chlorosulfite).
		Key Point: This internal nucleophilic substitution ($S_Ni$) mechanism is facilitated by the formation of a tight ion pair.
	3. **Retention of Configuration:**
		Result: The reaction predominantly proceeds with retention of configuration due to the $S_Ni$ mechanism.
		Verification: Although some inversion can occur through a competing $S_N2$ pathway (especially in the absence of a base like pyridine), retention is the major product.
## OPTION ANALYSIS
[A] :x: The reaction proceeds with inversion of configuration. This is incorrect. Inversion would be expected in a typical $S_N2$ reaction, but the reaction with $SOCl_2$ proceeds mainly through an $S_Ni$ pathway.
[B] ✓: The reaction proceeds predominantly with retention of configuration. This is the correct answer. The $S_Ni$ mechanism leads to retention of configuration.
[C] :x: The reaction proceeds with complete racemization. This is incorrect. Racemization implies equal amounts of both enantiomers. While a small amount of inversion might occur, the reaction predominantly results in retention.
[D] :x: The stereochemistry of the product is unpredictable. This is incorrect. The stereochemistry is predictable, with retention being the major outcome.
## LEARNING AIDS
	**Common Mistakes**:
		1. Assuming $S_N2$ mechanism: Incorrectly assuming that the reaction proceeds via a typical $S_N2$ pathway, leading to the prediction of inversion of configuration. How to avoid: Remember that $SOCl_2$ reactions with alcohols often favor $S_Ni$.
		2. Ignoring the role of pyridine: Pyridine, when present, acts as a base, further promoting the $S_Ni$ mechanism and increasing retention. How to avoid: Consider the effect of any added base.
	**Quick Tips**:
		1. $SOCl_2$ and retention: Associate $SOCl_2$ with predominantly retention of configuration in reactions with alcohols.
		2. $S_Ni$ mechanism visualization: Visualize the internal nucleophilic attack occurring on the same side as the leaving group in the $S_Ni$ mechanism.

Mr. S M HUSSAIN · Answer

The reaction proceeds with inversion of configuration.

Mr. S M HUSSAIN · Answer

The correct Option is "The reaction proceeds predominantly with retention of configuration."

Mr. S M HUSSAIN · Answer

The reaction proceeds with complete racemization.

Mr. S M HUSSAIN · Answer

The stereochemistry of the product is unpredictable.

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