The Question is from neet-chemistry alcohols-phenols-ethers , and it was created by the author THIRUPATHI REDDY

Question

Which of the following reagents would be LEAST effective in converting 1-methylcyclohexanol to 1-methylcyclohexene?

THIRUPATHI REDDY · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
 **Primary Concept**: Dehydration of alcohols
 **Related Topics**: Acid-catalyzed reactions, elimination reactions, leaving group ability
 **Prerequisites**: Understanding of reaction mechanisms (specifically E1 and E2), knowledge of common reagents used in organic chemistry.
## SOLUTION PATHWAY
**Given Information**:
The reaction involves converting a secondary alcohol (1-methylcyclohexanol) into an alkene (1-methylcyclohexene). This is a dehydration reaction.
**Method & Steps**:
1. Identify the reagents and their mechanisms:
	Concentrated $H_2SO_4$ and concentrated HCl both act as strong acids, promoting E1 and E2 elimination mechanisms.  $POCl_3$ in pyridine facilitates a dehydration reaction via an E2 mechanism. TsCl in pyridine followed by NaOEt is a two-step process. TsCl converts the alcohol into a tosylate, a good leaving group, followed by an E2 elimination with the strong base NaOEt.
2.  Evaluate the effectiveness of each reagent:
	$H_2SO_4$ is a very effective dehydrating agent for alcohols. 
	HCl is a strong acid, but less effective than $H_2SO_4$ for dehydration due to its weaker dehydrating ability.
	$POCl_3$ in pyridine is an excellent reagent for dehydrating secondary alcohols.
	TsCl/pyridine followed by NaOEt is a very effective method for dehydration, particularly for sterically hindered alcohols.
3. Determine the least effective reagent:
	Based on the above analysis, concentrated HCl is the least effective among the given options for dehydrating 1-methylcyclohexanol to 1-methylcyclohexene.
	Result: HCl
	Verification: The other reagents are known to efficiently perform this dehydration. HCl's lower dehydration efficiency compared to sulfuric acid, and the more effective E2 mechanisms of the other options, confirms the selection.
## OPTION ANALYSIS
A :x: Concentrated $H_2SO_4$ is a strong dehydrating agent, very effective in this conversion.
B ✓: Concentrated HCl is a weaker acid and less effective dehydrating agent compared to $H_2SO_4$, $POCl_3$, or the TsCl/NaOEt method.
C :x: $POCl_3$ in pyridine is a very effective reagent for this type of dehydration.
D :x: TsCl in pyridine followed by NaOEt is a highly effective two-step process for dehydration, forming a good leaving group before elimination.
## LEARNING AIDS
 **Common Mistakes**:
  1.Assuming all strong acids are equally effective in dehydration: Acid strength and dehydrating ability are not always directly proportional.  $H_2SO_4$ is a better dehydrating agent than HCl.
  2.Overlooking the mechanism: Understanding the mechanism helps determine the effectiveness of each reagent.  E2 reactions are generally faster and more efficient than E1 reactions.
 **Quick Tips**:
  1.Remember the order of effectiveness for dehydrating agents: $POCl_3 > H_2SO_4 > HCl$.
  2.Consider the leaving group ability: Better leaving groups lead to faster and more efficient elimination reactions.

THIRUPATHI REDDY · Answer

Concentrated $H_2SO_4$

THIRUPATHI REDDY · Answer

The correct Option is "Concentrated HCl"

THIRUPATHI REDDY · Answer

$POCl_3$ in pyridine

THIRUPATHI REDDY · Answer

TsCl in pyridine followed by NaOEt

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