Which of the following compounds exhibits keto-enol tautomerism?
Answer: B
Acetone (CH3-CO-CH3) has α-hydrogen atoms and can exist in equilibrium between keto and enol forms.
Q.82Medium
In the reaction of phenylmagnesium bromide (Grignard reagent) with CO2 followed by hydrolysis, the main product is:
Answer: B
Grignard reagent attacks CO2 to form a salt, which upon hydrolysis gives benzoic acid.
Q.83Hard
The order of reactivity in electrophilic aromatic substitution for halogens is:
Answer: A
Fluorine is most reactive due to the best balance of electronic effects and hyperconjugation, while iodine is least reactive.
Q.84Easy
Which of the following is not a nucleophile?
Answer: C
NO2+ (nitronium ion) is an electrophile with positive charge, not a nucleophile. All others have lone pairs or negative charge.
Q.85Easy
The Williamson ether synthesis involves reaction of an alkoxide with:
Answer: B
Williamson ether synthesis uses SN2 reaction between alkoxide (R-O-) and alkyl halide (R'-X) to form R-O-R'.
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Q.86Medium
In the Clemmensen reduction of a ketone, the reducing agent used is:
Answer: A
Clemmensen reduction uses zinc amalgam with concentrated HCl to convert C=O to CH2, unlike Wolff-Kishner which uses hydrazine.
Q.87Medium
The major product when 2-methylbut-3-en-1-ol undergoes PCC oxidation is:
Answer: A
PCC (Pyridinium chlorochromate) selectively oxidizes primary alcohols to aldehydes without further oxidation, and doesn't affect C=C.
Q.88Easy
Which of the following shows the most stable carbocation?
Answer: C
Tertiary carbocation (CH3)3C+ is most stable due to maximum hyperconjugation and inductive stabilization from three alkyl groups.
Q.89Hard
In the acetoacetic ester synthesis, the initial condensation is between acetoacetic ester and alkyl halide in the presence of:
Answer: A
Sodium ethoxide creates the enolate of acetoacetic ester, which then undergoes SN2 with alkyl halide for alkylation.
Q.90Medium
The compound that will show maximum hydrogen bonding is:
Answer: B
Amides have both N-H (hydrogen bond donor) and C=O (hydrogen bond acceptor), allowing formation of strong intermolecular hydrogen bonds.
Q.91Medium
Which of the following alkenes will undergo hydroboration-oxidation to give a secondary alcohol as the major product?
Answer: A
Hydroboration-oxidation follows anti-Markovnikov's rule and gives Markovnikov's hydration product after oxidation. 1-methylcyclohexene gives secondary alcohol, while pent-1-ene gives primary and 2-methylbut-2-ene gives tertiary alcohol.
Q.92Easy
In the ozonolysis of but-2-ene, the products formed are:
Answer: A
But-2-ene (CH₃-CH=CH-CH₃) on ozonolysis gives two identical fragments, each being acetaldehyde (CH₃CHO). The double bond cleaves symmetrically.
Q.93Easy
Which mechanism is involved in the reaction of tert-butyl bromide with aqueous NaOH?
Answer: A
tert-Butyl bromide is a tertiary alkyl halide. Tertiary substrates preferentially undergo SN1 mechanism due to stable tertiary carbocation formation. SN2 is hindered by steric effects.
Q.94Medium
The reaction of phenol with excess bromine in water produces:
Answer: A
Phenol is highly activated towards electrophilic aromatic substitution due to the electron-donating -OH group. Bromine can add at all three ortho and para positions with excess bromine, giving 2,4,6-tribromophenol.
Q.95Easy
Which of the following compounds will give a positive Tollens test?
Answer: B
Tollens test is positive for aldehydes. Propanal (CH₃CH₂CHO) is an aldehyde and gets oxidized to carboxylic acid, reducing Ag⁺ to Ag (silver mirror). Acetone is a ketone, ether and alcohol do not give positive test.
Q.96Medium
In the dehydration of 2-methylbutan-2-ol, the major product is:
Answer: B
Dehydration of 2-methylbutan-2-ol follows Zaitsev's rule, producing the most stable (most substituted) alkene. 2-methylbut-2-ene is a trisubstituted alkene and is the major product.
Q.97Medium
The addition of HBr to propene in the presence of peroxides follows:
Answer: B
Peroxides initiate free radical mechanism (Kharasch effect). In free radical addition, HBr adds anti-Markovnikov to propene, giving 1-bromopropane as the major product. The Br radical adds first to the terminal carbon.
Q.98Easy
Which of the following is the correct IUPAC name for the compound CH₃-CHBr-CH₂-CH₃?
Answer: A
The parent chain is butane (4 carbons). Numbering from the end nearest to substituent gives Br at position 2. IUPAC name is 2-bromobutane. Option D is a common name.
Q.99Medium
In the nitration of benzene with HNO₃/H₂SO₄, the rate-determining step involves attack by:
Answer: A
The HNO₃/H₂SO₄ mixture generates NO₂⁺ (nitronium ion), which is the electrophile attacking the benzene ring in the rate-determining step. This is a classic electrophilic aromatic substitution.
Q.100Hard
Which intermediate is formed when acetyl chloride reacts with benzene in the presence of AlCl₃?
Answer: A
In Friedel-Crafts acylation, AlCl₃ facilitates the formation of the acetyl cation (CH₃CO⁺) from acetyl chloride. This electrophilic acylium ion then attacks the benzene ring.
