Carbanions and enolates

28 questions on Carbanions and enolates from the General Organic Chemistry III: Reaction Intermediates chapter: 6 NEET level, 11 JEE Main, 11 JEE Advanced. Each one opens with its answer and solution.

• The methyl carbanion CH3^- has the carbon atom in which hybridisation and shape? NEET level
• Considering only the inductive effect of alkyl groups (usual solution-phase argument), which of the following carbanions is the most stable? NEET level
• Which of the following hydrocarbons is the strongest Bronsted acid? NEET level
• Which of the following carbanions is stabilised by resonance? NEET level
• The alpha hydrogens of propanone (CH3COCH3) are much more acidic than those of propane mainly because NEET level
• Which of the following compounds gives a yellow precipitate of iodoform on warming with I2 and NaOH? NEET level
• Which is the correct order of decreasing acidity of the C-H bonds in the following compounds? CH3NO2, CH3COCH3, CH3COOC2H5, CH3CH3 JEE Main level
• Which of the following carbanions is the most stable? JEE Main level
• 2-Methylcyclohexan-1-one is treated with LDA (lithium diisopropylamide) in THF at -78 degC (kinetic control). Which proton is removed fastest? JEE Main level
• Which of the following carbonyl compounds have no alpha hydrogen and therefore cannot form an enolate? JEE Main level
• Butan-2-one is stirred for a long time with excess NaOD in D2O so that every alpha hydrogen exchanges. How many hydrogen atoms of one molecule are replaced by d... JEE Main level
• Methylmagnesium bromide, CH3MgBr, behaves as a source of CH3^-. With which of the following does it release methane? JEE Main level
• Arrange the carbanions in decreasing order of stability (usual NCERT-level argument based on hybridisation and alkyl substitution): HC#C^-, CH2=CH^-, CH3CH2^-, ... JEE Main level
• Propanone is treated with one equivalent of LDA in THF at -78 degC and then with iodomethane. What is the major product? JEE Main level
• Which is the correct order of decreasing acidity of the most acidic C-H hydrogens in pentane-2,4-dione (I), ethyl 3-oxobutanoate (II), diethyl propanedioate (II... JEE Main level
• Assertion (A): Cyclopenta-1,3-diene (pK_a approx 16) is far more acidic than cyclohepta-1,3,5-triene (pK_a approx 36). Reason (R): The cyclopentadienyl anion is... JEE Main level
• Hexane-2,5-dione, CH3COCH2CH2COCH3, is warmed with dilute aqueous NaOH. The major final product, formed by an intramolecular aldol condensation, is JEE Main level
• How many different enolate ions can 3-methylpentan-2-one, CH3-CO-CH(CH3)-CH2CH3, form by removal of one alpha proton, if the E and Z isomers of an enolate are c... JEE Advanced level
• Propanone is stirred with but-3-en-2-one (CH2=CH-CO-CH3) in the presence of aqueous NaOH and the mixture is heated. A Michael addition is followed by an intramo... JEE Advanced level
• Ethyl 3-oxobutanoate is treated successively with (i) NaOEt, then CH3CH2Br; (ii) NaOEt, then CH3I; (iii) hot aqueous NaOH, then dilute acid and warming. The fin... JEE Advanced level
• Diethyl propanedioate is treated with (i) NaOEt, then CH3CH2Br; (ii) NaOEt, then CH3I; (iii) aqueous acid with heating. The final organic product is JEE Advanced level
• Diethyl hexanedioate (diethyl adipate) is treated with NaOEt in ethanol (Dieckmann condensation), and the cyclic product is then heated with aqueous acid. The f... JEE Advanced level
• Propanone (1 mol) is treated with benzaldehyde (2 mol) in aqueous ethanolic NaOH at room temperature, and both aldol additions go on to dehydration. The product... JEE Advanced level
• 4-Nitrobutan-2-one, CH3-CO-CH2-CH2-NO2, is treated with one equivalent of a weak base. Which hydrogen is removed most easily? JEE Advanced level
• Which of the following statements about the enolate ion CH2=C(CH3)-O^- derived from propanone are correct? JEE Advanced level
• Which of the following esters, when treated with one equivalent of NaOEt in ethanol followed by acidification, give a self-condensation (Claisen) product in goo... JEE Advanced level
• Each of the following is stirred for a long time with excess NaOD in D2O so that every alpha C-H exchanges (no other C-H bonds exchange). Which incorporate exac... JEE Advanced level
• Which of the following optically active ketones lose their optical activity when stirred with dilute aqueous NaOH for some time? JEE Advanced level