Chemistry carries the highest scoring potential in JEE for anyone who keeps the three branches separate in revision. This set covers physical chemistry numericals, organic reaction mechanisms and named reactions, and inorganic chemistry including periodic trends, chemical bonding and coordination compounds. Organic questions show the mechanism arrow by arrow, so the reasoning transfers to reactions you have not seen before.
In the Williamson ether synthesis, the reactivity of alkyl halides follows the order:
Answer: A
Williamson ether synthesis follows SN2 mechanism, which is favored by primary alkyl halides due to minimal steric hindrance. Reactivity: Primary > Secondary > Tertiary.
Q.2Medium
Which of the following compounds will show aldol condensation?
Answer: C
Aldol condensation requires an α-hydrogen. Acetaldehyde has α-hydrogens and undergoes aldol condensation. Benzaldehyde and formaldehyde lack α-hydrogens.
Q.3Medium
The oxidation of primary alcohol to aldehyde can be selectively done using:
Answer: B
PCC oxidizes primary alcohols to aldehydes without further oxidation to carboxylic acids. KMnO4 and Na2Cr2O7 further oxidize aldehydes to carboxylic acids.
Q.4Medium
Which mechanism is followed in the hydrolysis of alkyl halides under basic conditions?
Answer: B
Basic hydrolysis of alkyl halides follows SN2 mechanism (bimolecular nucleophilic substitution) with OH- as nucleophile, especially for primary halides.
Q.5Medium
In the nitration of benzene, the attacking species is:
Answer: A
Nitration involves formation of NO2+ (nitronium ion) from HNO3 in presence of H2SO4. NO2+ acts as the electrophile in electrophilic aromatic substitution.
Q.6Medium
The dehydration of 2-methylbutan-2-ol gives primarily:
Answer: B
Dehydration follows Zaitsev's rule, producing the most substituted (stable) alkene. 2-methylbut-2-ene is the major product with the double bond at the tertiary position.
Q.7Medium
Which compound will not undergo Cannizzaro reaction?
Answer: C
Cannizzaro reaction occurs with aldehydes lacking α-hydrogens. Acetaldehyde has α-hydrogens, so it undergoes aldol condensation instead of Cannizzaro reaction.
Q.8Medium
The rate of SN1 reaction is independent of:
Answer: B
SN1 is a unimolecular reaction with rate = k[R-X]. It is first-order with respect to alkyl halide only, independent of nucleophile concentration.
Q.9Medium
The acidity order of carboxylic acids is:
Answer: A
Formic acid is most acidic (Ka = 1.8×10-4) due to favorable +I effect of hydrogen. Acidity decreases with increasing alkyl chain length due to +I effect: Formic > Acetic > Propionic.
Q.10Medium
Grignard reagent reacts with CO2 to give:
Answer: C
RMgX + CO2 → RMgX-O2C- → RCOO- MgX+ → RCOOH (after acidification). This is a classic method for carboxylic acid synthesis.
Q.11Medium
The esterification reaction is catalyzed by:
Answer: B
Esterification (Fischer esterification) requires acid catalyst (H2SO4 or HCl) which protonates the carbonyl oxygen, increasing electrophilicity and facilitating nucleophilic attack by alcohol.
Q.12Medium
In the bromination of benzene, the role of FeBr3 is to:
Answer: B
FeBr3 is a Lewis acid that polarizes Br2, generating Br+ (bromonium ion) which acts as the electrophile in electrophilic aromatic substitution of benzene.
Q.13Medium
The compound 2,2-dimethyl-1-propanol when heated with concentrated H2SO4 gives the major product as:
Answer: B
This is a dehydration reaction where the OH group leaves, and a rearrangement occurs via hydride shift to form the more stable tertiary carbocation, leading to 2-methylbut-2-ene (more substituted alkene, Zaitsev's rule).
Q.14Medium
Which isomer of dimethylbenzene (xylene) will show only 2 signals in 1H-NMR?
Answer: C
Para-xylene has high symmetry: all four aromatic protons are equivalent (one signal) and all six methyl protons are equivalent (one signal), giving only 2 total signals in 1H-NMR.
Q.15Medium
In the preparation of phenol from cumene (isopropylbenzene), the intermediate cumene hydroperoxide is cleaved in acidic conditions to give:
Answer: B
The cumene hydroperoxide undergoes an acid-catalyzed rearrangement (Hock rearrangement) where the isopropyl group rearranges to give phenol and acetone as the cleavage products.
Q.16Medium
Which of the following carboxylic acids is most acidic?
Answer: B
CF3-COOH is most acidic because fluorine is highly electronegative and strongly withdraws electron density through inductive effects, stabilizing the conjugate base carboxylate ion.
Q.17Medium
The reaction of benzene with excess Cl2 in the presence of FeCl3 followed by hydrolysis gives:
Answer: B
Chlorobenzene formed initially is more deactivated than benzene, but further chlorination can occur at ortho/para positions under excess Cl2 conditions, yielding a mixture of polychlorobenzenes.
Q.18Medium
Which statement about aldol condensation is correct?
Answer: C
Aldol condensation requires a compound with α-hydrogens that can form an enolate/enol as the nucleophilic component, and a carbonyl compound as the electrophile. Ketones can also be used.
Q.19Medium
The rate of E1 elimination reaction depends on:
Answer: B
E1 elimination is a two-step mechanism where the rate-determining step is the formation of carbocation (unimolecular). The rate depends only on substrate concentration, following first-order kinetics.
Q.20Medium
In the conversion of benzene to benzoic acid through the Kolbe reaction, the carboxylic acid is ultimately derived from:
Answer: B
In the Kolbe carboxylation of phenols, CO2 is directly incorporated into the aromatic ring ortho to the hydroxyl group under high temperature and pressure with alkali, forming salicylic acid derivatives.
