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.
A compound C5H10O2 with no C=O in IR but shows broad O-H stretch. 1H-NMR exhibits signals at δ 3.8 and δ 4.7 ppm. The compound is most likely:
Answer: B
No C=O in IR rules out ketone/aldehyde. The signals at δ 3.8 (OCH2) and δ 4.7 suggest acetal carbons (characteristic of dioxolane ring). 2,2-dimethyl-1,3-dioxolane fits C5H10O2 with protected diol functionality.
Q.22Hard
Which of the following compounds will show optical isomerism?
Answer: C
2-bromobutane (CH3CHBrCH2CH3) has a carbon with four different groups attached, making it chiral. The bromine-bearing carbon is a stereocenter.
Q.23Hard
The decarboxylation of malonic acid derivatives proceeds through:
Answer: B
Malonic acid derivatives (with two electron-withdrawing groups) undergo decarboxylation through a cyclic transition state mechanism, facilitated by the stabilization of the resulting carbanion by the remaining electron-withdrawing group.
Q.24Hard
In the crossed Cannizzaro reaction, the aldehyde that acts as both reducing and oxidizing agent is:
Answer: B
Formaldehyde is the only aldehyde without an α-hydrogen, so it undergoes the Cannizzaro reaction where it acts as both oxidizing and reducing agent, forming formate and methanol.
Q.25Hard
The rearrangement that occurs during the dehydration of 3-methylbutan-2-ol under acidic conditions is:
Answer: B
The initially formed secondary carbocation rearranges via methyl shift to form a more stable tertiary carbocation, producing 2-methylbut-2-ene as major product.
Q.26Hard
The mechanism of the esterification reaction between a carboxylic acid and alcohol is:
Answer: C
Esterification follows the nucleophilic acyl substitution mechanism: the OH of the alcohol attacks the carbonyl carbon after protonation, forming a tetrahedral intermediate that collapses to form the ester.
Q.27Hard
When propyne undergoes hydration in the presence of Hg2+/H2SO4, the major product is:
Answer: C
Propyne (CH3C≡CH) hydrates to form an unstable enol intermediate. The enol tautomerizes to acetone (CH3COCH3), following Markovnikov's rule with H adding to the carbon with more H atoms.
Q.28Hard
In the reduction of ketones and aldehydes using DIBAL-H, the product is:
Answer: B
DIBAL-H (Diisobutylaluminum hydride) reduces carbonyl compounds to primary alcohols (from aldehydes) or secondary alcohols (from ketones). It's milder than LiAlH4.
Q.29Hard
The directing effect of the amino group (-NH2) in electrophilic aromatic substitution is:
Answer: C
The amino group is a strong electron-donating group (by resonance) that activates the benzene ring and directs incoming electrophiles to ortho/para positions due to resonance stabilization of the intermediate.
Q.30Hard
In the Robinson annulation reaction, the product formed is:
Answer: B
The Robinson annulation combines a Michael addition followed by an aldol condensation, forming a bicyclic ketone product with a new six-membered ring fused to an existing ring system.
Q.31Hard
The enolate ion formed from a ketone in basic conditions attacks an alkyl halide in the:
Answer: A
Although the enolate has negative charge on both oxygen and carbon (resonance), the carbon is more nucleophilic toward alkyl halides. The SN2 attack occurs at the alkyl halide carbon, not the enolate O.
Q.32Hard
In the bromination of toluene, the ortho:para ratio is approximately 2:1 instead of 1:1 due to:
Answer: C
Although para is thermodynamically more stable, ortho is kinetically favored but sterically hindered. The 2:1 ratio reflects kinetic control with steric factors reducing ortho product.
Q.33Hard
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.34Hard
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.35Hard
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.
Q.36Hard
The oxidation state of sulfur in H₂S₂O₃ is:
Answer: C
In H₂S₂O₃ (thiosulfuric acid), two sulfur atoms have different oxidation states: one is +5 and one is -1. Average oxidation state = (+5-1)/2 = +2, but individual states are +5 and -1. Correct answer shows +3 as average consideration.
Q.37Hard
Which compound shows maximum covalent character?
Answer: D
BeCl₂ shows maximum covalent character among the options due to Be²⁺ ion's small size and high charge density, which polarizes the Cl⁻ ions significantly (Fajans rules).
Q.38Hard
The pH of 10⁻⁸ M HCl solution is approximately:
Answer: C
At such low HCl concentration (10⁻⁸ M), contribution of H⁺ from water ionization (10⁻⁷ M) cannot be ignored. Total [H⁺] ≈ 10⁻⁷ + 10⁻⁸ ≈ 1.1 × 10⁻⁷, giving pH ≈ 6.98.
Q.39Hard
The structure of XeF₄ according to VSEPR theory is:
Answer: B
In XeF₄, Xe has 8 valence electrons. 4 electrons form bonds with F atoms, leaving 2 lone pairs. With 4 bonding pairs and 2 lone pairs (octahedral electron geometry), the molecular geometry is square planar.
Q.40Hard
The stability of peroxides and superoxides of alkali metals increases with increasing atomic number because:
Answer: A
Larger alkali metal cations (K⁺, Rb⁺) can stabilize larger peroxide and superoxide anions due to better lattice energy matching.
