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Organic Reaction Mechanisms IV: Elimination
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E1cB mechanism
JEE Main level
Single correct option
Difficulty 2 of 3
o4139
Which of the following beta-hydroxy aldehydes will NOT dehydrate by the E1cB path with aqueous
NaOH
?
A
CH
X
3
−
CH
(
OH
)
−
C
(
CH
X
3
)
X
2
−
CHO
(3-hydroxy-2,2-dimethylbutanal)
B
CH
X
3
−
CH
(
OH
)
−
CH
X
2
−
CHO
(3-hydroxybutanal)
C
CH
X
3
−
CH
(
OH
)
−
CH
(
CH
X
3
)
−
CHO
(3-hydroxy-2-methylbutanal)
D
(
CH
X
3
)
X
2
C
(
OH
)
−
CH
X
2
−
CHO
(3-hydroxy-3-methylbutanal)
Answer: A
E1cB requires an alpha-hydrogen to form the enolate. In 3-hydroxy-2,2-dimethylbutanal the alpha carbon is quaternary and has no H, so it cannot dehydrate by this route. The other three each have at least one alpha-H.
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