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Question #44620

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The Question

An organic chemist intends to synthesize the sterically hindered ether, 2-isopropoxy-2-methylpropane (isopropyl tert-butyl ether), and attempts two distinct Williamson ether synthesis pathways at $340\text{ K}$ :

Pathway I: Reaction of 2-bromo-2-methylpropane with sodium isopropoxide in isopropanol. Pathway II: Reaction of 2-bromopropane with sodium 2-methylpropan-2-olate in 2-methylpropan-2-ol.

Let $X$ and $Y$ be the major organic products formed in Pathway I and Pathway II, respectively. Which of the following correctly identifies $X$ , $Y$ , and the most viable alternative method to synthesize the target ether in high yield?

Options

A.
$X =$ 2-methylprop-1-ene; $Y =$ propene; Alternative: Acid-catalyzed addition of isopropanol to 2-methylprop-1-ene.
B.
$X =$ 2-methylprop-1-ene; $Y =$ 2-isopropoxy-2-methylpropane; Alternative: Pathway II is already the optimal method.
C.
$X =$ 2-isopropoxy-2-methylpropane; $Y =$ propene; Alternative: Pathway I is already the optimal method.
D.
$X =$ 2-methylprop-1-ene; $Y =$ propene; Alternative: Reaction of 2-bromopropane with 2-methylpropan-2-ol under $S_N1$ conditions at $298\text{ K}$ .

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Steric Hindrance in SN2|Williamson Ether Synthesis Constraints

Why This Question Is Tricky

Common Mistakes

This question tests the kinetic limitations of the Williamson ether synthesis.

Students are traditionally taught the 'Textbook Rule': to synthesize unsymmetrical ethers, use the less hindered alkyl halide.

A common trap is blindly applying this rule to secondary halides.

While a primary halide with a tertiary alkoxide successfully yields an ether via $S_N2$ , a secondary halide reacting with a bulky tertiary alkoxide (like tert-butoxide) predominantly undergoes $E2$ elimination due to severe steric clashes in the $S_N2$ transition state.

Recognizing that both pathways fail forces the student to identify acid-catalyzed alkene addition as the correct synthetic route for highly branched tertiary ethers.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Haloalkanes and Haloarenes - Class 12
Concept	Steric Hindrance in SN2
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free