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E1cB mechanism

37 questions on E1cB mechanism from the Organic Reaction Mechanisms IV: Elimination chapter: 7 NEET level, 14 JEE Main, 16 JEE Advanced. Each one opens with its answer and solution.

Practice this topic All Organic Reaction Mechanisms IV: Elimination topics

The characteristic intermediate in the E1cB mechanism is a NEET level
In an E1cB elimination, the sequence of events is NEET level
Warming 3-hydroxybutanal with dilute aqueous NaOH gives, by E1cB loss of water, NEET level
4-Methoxybutan-2-one, CH3COCH2CH2OCH3, is treated with NaOD in D2O. At low conversion the recovered starting material is found to have exchanged hydrogen for de... JEE Main level
Which of the following compounds is most likely to undergo base-induced elimination by the E1cB mechanism with NaOEt in ethanol? JEE Main level
In the base-catalysed dehydration of an aldol, hydroxide ion (a very poor leaving group) is lost. The reason this is possible is that JEE Main level
4-Hydroxypentan-2-one, CH3COCH2CH(OH)CH3, is warmed with dilute NaOH. The main product by E1cB is JEE Main level
C6H5SO2CH2CH2OCH3 is treated with a strong base such as NaOEt in ethanol. The organic product is JEE Main level
For Z-CH2CH2-OCH3 eliminating CH3OH with NaOEt by E1cB, the substituent Z which gives the fastest elimination (the most acidic hydrogen alpha to Z) is JEE Main level
Which statements about the base-induced conversion of 4-methoxybutan-2-one, CH3COCH2CH2OCH3, into but-3-en-2-one by the E1cB mechanism are correct? JEE Main level
In which of the following do(es) the elimination step occur by the E1cB mechanism? JEE Main level
5-Hydroxy-5-methylhexan-3-one, CH3CH2-CO-CH2-C(OH)(CH3)2, is warmed with dilute aqueous NaOH. The product is JEE Advanced level
In the NaOH-catalysed condensation of acetophenone with benzaldehyde, the aldol C6H5COCH2CH(OH)C6H5 loses water to give chalcone. The species from which hydroxi... JEE Advanced level
One mole of acetone is condensed with two moles of benzaldehyde in the presence of dilute NaOH to give dibenzalacetone, C6H5CH=CH-CO-CH=CH-C6H5. Counting only t... JEE Advanced level
4-Hydroxy-4-methylpentan-2-one is warmed with dilute NaOH and gives mesityl oxide, (CH3)2C=CH-CO-CH3, not the isomeric CH2=C(CH3)-CH2-CO-CH3. The correct explan... JEE Advanced level
A substrate Z-CH2-CH2-OR (Z is a strong electron-withdrawing group) is treated with EtO- in EtOD. Observations: (i) the rate is first order in substrate and fir... JEE Advanced level
Which of the following can undergo dehydration with dilute NaOH by the E1cB mechanism? JEE Advanced level
Which of the following statements is/are correct about the E1cB mechanism? JEE Advanced level
Which statements are correct for the conversion of hexane-2,5-dione into 3-methylcyclopent-2-en-1-one with dilute NaOH? JEE Advanced level
The first step of the E1cB mechanism is NEET level
3-Hydroxybutanal is heated with dilute aqueous alkali. The product is NEET level
The carbanion intermediate formed when an aldol loses water in basic medium is NEET level
E1cB elimination is most likely when the substrate has NEET level
Phenyl 2-phenoxyethyl sulfone, PhSO2CH2CH2OPh, reacts with NaOEt in ethanol. Which description is correct? JEE Main level
A substrate that undergoes base-induced elimination is recovered partway through the reaction from NaOD/D2O. The recovered unreacted material has deuterium at t... JEE Main level
Which statements about the E1cB mechanism are correct? JEE Main level
In diacetone alcohol, CH3-CO-CH2-C(CH3)2-OH (4-hydroxy-4-methylpentan-2-one), treatment with NaOH causes dehydration by E1cB. Count only the hydrogen atoms whos... JEE Main level
Assertion (A): A beta-hydroxy ketone loses water readily with dilute alkali even though OH^- is a poor leaving group. Reason (R): The enolate formed first is a ... JEE Main level
Which of the following beta-hydroxy aldehydes will NOT dehydrate by the E1cB path with aqueous NaOH? JEE Main level
Ethanal (2 mol) is treated with dilute NaOH and warmed. The organic product is then hydrogenated over Ni (excess H2). The final product is JEE Advanced level
For the elimination of PhSO2CH2CH2X in NaOD/D2O the rate of beta-H/D exchange is 40 times the rate of alkene formation. The most reasonable conclusion is JEE Advanced level
Which of the following reactions proceed by an E1cB mechanism? JEE Advanced level
Benzaldehyde and acetophenone react with aqueous NaOH to give chalcone. In the dehydration step of the intermediate PhCO-CH2-CH(OH)-Ph, the species that loses O... JEE Advanced level
Which observations would support an E1cB(reversible) mechanism over a concerted E2 mechanism for a base-induced elimination? JEE Advanced level
4-Hydroxy-4-methylpentan-2-one is dehydrated with dilute NaOH. Which statements are correct? JEE Advanced level
Propanal (2 mol) is treated with dilute NaOH and heated. The product obtained after dehydration is JEE Advanced level
For the base-induced loss of water from HOCH2CH2Y, the ease of E1cB elimination follows the acidity of the alpha C-H of CH3Y (typical pKa values: ketone about 1... JEE Advanced level