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Multiple Choice Questions

One and More than One Correct

1. Hyperconjugation involves overlap of the following orbitals [JEE 2008 P-I]

(a) $\sigma \longrightarrow p$

(b) $\sigma \longrightarrow \sigma^*$

(d) $p \longrightarrow \pi^*$

Answer: (b)

Explanation: Hyperconjugation involves overlap of $\sigma$ and $\sigma^*$ orbitals.

2. The correct stability order for the following species is [JEE 2008 P-II]

$$\text{(I) } \text{H}_2\text{C}=\overset{+}{\text{N}}=\bar{\text{N}}$$

$$\text{(II) } \text{H}_2\overset{+}{\text{C}}-\text{N}=\bar{\text{N}}$$

$$\text{(III) } \text{H}_2\bar{\text{C}}-\overset{+}{\text{N}}\equiv\text{N}$$

$$\text{(IV) } \text{H}_2\bar{\text{C}}-\text{N}=\overset{+}{\text{N}}$$

(a) (II) > (IV) > (I) > (III)

(b) (I) > (II) > (III) > (IV)

(d) (I) > (III) > (II) > (IV)

Answer: (d)

Explanation: (I) Stabilises by resonance and have six $\alpha$-hydrogen atoms (hyperconjugation). (III) Stabilises by resonance and have only three $\alpha$-hydrogen atoms. (II) have five $\alpha$-hydrogen atoms. (IV) have only two $\alpha$-hydrogen atoms. Thus, I > III > II > IV.

3. In the following carbocation, $\text{H}/\text{CH}_3$ that is most likely to migrate to the positively charged carbon is [JEE 2009 P-II]

$$\overset{1}{\text{H}_3\text{C}}-\overset{2}{\underset{\underset{\text{OH}}{vert}}{\text{C}}}-\overset{3}{\underset{\underset{\text{H}}{vert}}{\text{C}}}-\overset{4}{\underset{\underset{\text{CH}_3}{vert}}{\text{C}^+}}-\overset{5}{\text{CH}_3}$$

(a) $\text{CH}_3$ at $\text{C}-4$

(b) $\text{H}$ at $\text{C}-4$

(d) $\text{H}$ at $\text{C}-2$

Answer: (d)

Explanation: $\text{H}$ shift from $\text{C}-2$ to $\text{C}-3$ takes place as the driving force is resonance stabilization/conjugation from oxygen.

4. The correct stability order of the following resonance structures is [JEE 2009 P-II]

$$\text{(I) } \text{H}_2\text{C}=\overset{+}{\text{N}}=\bar{\text{N}}$$

$$\text{(II) } \text{H}_2\overset{+}{\text{C}}-\text{N}=\bar{\text{N}}$$

$$\text{(III) } \text{H}_2\bar{\text{C}}-\overset{+}{\text{N}}\equiv\text{N}$$

$$\text{(IV) } \text{H}_2\bar{\text{C}}-\text{N}=\overset{+}{\text{N}}$$

(a) (I) > (II) > (IV) > (III)

(b) (I) > (III) > (II) > (IV)

(d) (III) > (I) > (IV) > (II)

Answer: (b)

Explanation: On the basis of stability of resonating structures, octet completeness and charge separation rules, the stability order is (I) > (III) > (II) > (IV).

5. The compounds P, Q and S were separately subjected to nitration using $\text{HNO}_3/\text{H}_2\text{SO}_4$ mixture. The major product formed in each case respectively, is [JEE 2010 P-II]

(a) P: 4-nitro, Q: 4-nitro, S: 2-nitro

(b) P: 2-nitro, Q: 3-nitro, S: 4-nitro

(d) P: 3-nitro, Q: 4-nitro, S: 4-nitro

Answer: (c)

Explanation: In P, $-\text{OH}$ group is strongly activating so nitration occurs at para position. In Q, $-\text{OCH}_3$ group is more activating than alkyl group, directing nitration to its para position. In S, $-\text{COOH}$ is deactivating (meta-directing) and ester group directs accordingly, giving nitration at position 3.

6. In allene ($\text{C}_3\text{H}_4$), the type(s) of hybridization of the carbon atoms is (are) [JEE 2012 P-I]

(a) $sp$ and $sp^3$

(b) $sp$ and $sp^2$

(d) $sp^2$ and $sp^3$

Answer: (b)

Explanation: Structure of allene is $\text{H}_2\text{C}=\text{C}=\text{CH}_2$. The terminal carbons are $sp^2$ hybridized while the central carbon is $sp$ hybridized.

7. Which of the following molecules, in pure form, is (are) unstable at room temperature? [JEE 2012 P-I]

(a) Cyclooctatetraene

(b) Cyclobutadiene

(d) Cyclopentadiene

Answer: (b, c)

Explanation: (b) and (c) are antiaromatic in planar form (containing $4n \pi$ electrons), making them highly unstable at room temperature.

8. The order of stability of the following carbocations is [JEE Main 2013]

$$\text{I. } \text{CH}_2=\text{CH}-\overset{+}{\text{C}}\text{H}_2$$

$$\text{II. } \text{CH}_3-\text{CH}_2-\overset{+}{\text{C}}\text{H}_2$$

$$\text{III. } \text{C}_6\text{H}_5-\overset{+}{\text{C}}\text{H}_2$$

(a) III > II > I

(b) II > III > I

(d) III > I > II

Answer: (d)

Explanation: On the basis of number of resonating structures, benzyl carbocation (III) is more stable than allylic carbocation (I), which is more stable than primary alkyl carbocation (II). Thus, III > I > II.

9. A gaseous hydrocarbon gives upon combustion 0.72 g of water and 3.08 g of $\text{CO}_2$. The empirical formula of the hydrocarbon is [JEE Main 2013]

(a) $\text{C}_2\text{H}_4$

(b) $\text{C}_3\text{H}_4$

(d) $\text{C}_7\text{H}_8$

Answer: (d)

Explanation:

$$\text{Moles of C} = \text{Moles of CO}_2 = \frac{3.08}{44} = 0.07$$

$$\text{Moles of H} = 2 \times \text{Moles of H}_2\text{O} = 2 \times \frac{0.72}{18} = 0.08$$

$$\frac{x}{y} = \frac{0.07}{0.08} = \frac{7}{8}$$

So, empirical formula is $\text{C}_7\text{H}_8$.

10. The hyperconjugative stabilities of tert-butyl cation and 2-butene, respectively, are due to [JEE Adv. 2013 P-I]

(a) $\sigma \longrightarrow p\text{ (empty)}$ and $\sigma \longrightarrow \pi^*$ electron delocalisations

(b) $\sigma \longrightarrow \sigma^*$ and $\sigma \longrightarrow \pi$ electron delocalisations

(d) $p\text{ (filled)} \longrightarrow \sigma^*$ and $\sigma \longrightarrow \pi^*$ electron delocalisations

Answer: (a)

Explanation: In tert-butyl cation, hyperconjugation involves $\sigma(\text{C}-\text{H}) \longrightarrow p\text{ (empty)}$ orbital delocalisation. In 2-butene, it involves $\sigma(\text{C}-\text{H}) \longrightarrow \pi^*$ electron delocalisation.

11. Among P, Q, R and S, the aromatic compound(s) is/are [JEE Adv. 2013 P-I]

(a) P

(b) Q

(d) S

Answer: (a, b, c, d)

Explanation: All compounds P, Q, R, and S satisfy Huckel's rule of $(4n+2)\pi$ electrons with complete cyclic conjugation, hence all are aromatic.

12. Which of the following molecules is least resonance stabilized? [JEE Main 2017]

(a) Pyridine / non-aromatic option

(b) Benzene

(d) Pyrrole

Answer: (a)

Explanation: Option (a) is non-aromatic and hence least resonance stabilized compared to the aromatic species.

13. The order of basicity among the following compounds is: [JEE Main 2017]

$$\text{I. } \text{HN}=\text{C}(\text{NH}_2)_2$$

$$\text{II. } \text{CH}_3\text{C}(=\text{NH})\text{NH}_2$$

$$\text{III. } \text{C}_6\text{H}_5\text{NH}_2$$

$$\text{IV. } \text{H}_2\text{N}-\text{C}(=\text{NH})-\text{NH}_2$$

(a) IV > I > II > III

(b) IV > II > III > I

(d) II > I > IV > III

Answer: (a)

Explanation: Guanidine derivative IV has two $-\text{NH}_2$ groups contributing via resonance to increase electron density on $=\text{NH}$, making it most basic. In III, lone pair is involved in aromatic sextet, making it least basic. Thus, IV > I > II > III.

14. The major product of the following reaction is [JEE Main 2018]

(a) Substitution product

(b) Rearranged product

(d) Addition product

Answer: (c)

Explanation: $\text{CH}_3\text{O}^-$ is a strong base and strong nucleophile. Given alkyl halide is $2^\circ$ and hindered, so $E2$ elimination dominates over $S_N2$, yielding alkene as major product.

15. The reaction(s) leading to the formation of 1,3,5-trimethylbenzene is (are) [JEE Adv. 2018 P-I]

(a) Propyne passing through heated iron tube at 873 K

(b) Acetone with conc. $\text{H}_2\text{SO}_4 / \Delta$

(d) Reaction using sodium liquid ammonia / condensation

Answer: (a, b, d)

Explanation: Trimerisation of propyne (a) and trimeric condensation of acetone with conc. $\text{H}_2\text{SO}_4$ (b) both yield mesitylene (1,3,5-trimethylbenzene).

16. A reversible cyclic process for an ideal gas is shown below. The correct option(s) is (are) [JEE Adv. 2018 P-I]

(a) $q_{AC} = \Delta U_{BC}$ and $w_{AB} = P_2(V_2 - V_1)$

(b) $w_{BC} = -P_2(V_2 - V_1)$ and $q_{BC} = \Delta H_{BC}$

(d) $q_{BC} = \Delta H_{BC}$ and $\Delta H_{CA} > \Delta U_{CA}$

Answer: (b, c)

Explanation: For process A–C (isochoric), $w = 0 \implies \Delta U = q_{AC}$. For B–C (isobaric), $q_{BC} = \Delta H_{BC}$ and $w_{BC} = -P_2(V_2 - V_1)$. Also $\Delta H_{CA} < \Delta U_{CA}$.

17. Which of the following compounds is not aromatic? [JEE Main 2019]

(a) Cyclopropenyl cation

(b) Benzene

(d) Furan

Answer: (c)

Explanation: Does not have $(4n+2)\pi$ electrons; it has $4n\pi$ electrons, making it anti-aromatic/non-aromatic.

18. Two pi and half sigma bonds are present in: [JEE Main 2019]

(a) $\text{N}_2^+$

(b) $\text{N}_2$

(d) $\text{O}_2$

Answer: (a)

Explanation: $\text{N}_2^+$ has bond order 2.5, consisting of $2\pi$ bonds and $0.5\sigma$ bond.

19. 50 mL of 0.5 M oxalic acid is needed to neutralize 25 mL of sodium hydroxide solution. The amount of $\text{NaOH}$ in 50 mL of the given sodium hydroxide solution is: [JEE Main 2019]

(a) 4 g

(b) 20 g

(d) 10 g

Answer: (a)

Explanation: $\text{H}_2\text{C}_2\text{O}_4 + 2\text{NaOH} \longrightarrow \text{Na}_2\text{C}_2\text{O}_4 + 2\text{H}_2\text{O}$

$$\text{meq of H}_2\text{C}_2\text{O}_4 = \text{meq of NaOH}$$

$$50 \times 0.5 \times 2 = 25 \times M_{\text{NaOH}} \times 1 \implies M_{\text{NaOH}} = 2\text{ M}$$

$$1000\text{ mL solution} = 2 \times 40 = 80\text{ g NaOH}$$

$$\therefore 50\text{ mL solution} = \frac{80}{1000} \times 50 = 4\text{ g NaOH}$$

20. The increasing order of the reactivity of the following with $\text{LiAlH}_4$ is: [JEE Main 2019]

(A) Amide < (B) Ester < (C) Acid anhydride < (D) Acid chloride

(a) (A) < (B) < (D) < (C)

(b) (A) < (B) < (C) < (D)

(d) (B) < (A) < (C) < (D)

Answer: (a)

Explanation: Reactivity towards nucleophilic attack on carbonyl depends on electrophilicity of carbonyl carbon: Amide < Ester < Acid anhydride < Acid chloride.

21. The major product of the following reaction is: [JEE Main 2019]

(a) Alcohol product

(b) Clemmensen reduced product / Hydrocarbon

(d) Ketone product

Answer: (b)

Explanation: Diazotisation followed by reduction and Clemmensen reduction ($\text{Zn/Hg, HCl}$) reduces carbonyl groups completely to $-\text{CH}_2-$.

22. A Tin-chloride 'P' gives following reaction (unbalanced reaction) [JEE Adv. 2019 P-I]

$$\text{P} + \text{Cl}^- \longrightarrow \text{X [Monoanion pyramidal]}$$

$$\text{P} + \text{Me}_3\text{N} \longrightarrow \text{Y}$$

$$\text{P} + \text{CuCl}_2 \longrightarrow \text{Z} + \text{CuCl}$$

Then which of the following is/are correct?

(a) Y contains coordinate bond.

(b) X is $sp^3$ hybridised.

(d) X contain lone pair on central atom.

Answer: (a, b, c)

Explanation: $\text{SnCl}_2 + \text{Cl}^- \longrightarrow \text{SnCl}_3^- \text{ (X)}$, $\text{SnCl}_2 + \text{Me}_3\text{N} \longrightarrow \text{SnCl}_2 \cdot \text{N(CH}_3)_3 \text{ (Y)}$, $\text{SnCl}_2 + 2\text{CuCl}_2 \longrightarrow \text{SnCl}_4 + 2\text{CuCl}$. Y contains coordinate bond, X is $sp^3$ hybridised with a lone pair on Sn.

Matrix Match/Column Match

23. Match each of the compounds given in Column I with the reactions, that they can undergo given in Column II. [JEE 2009 P-II]

(a) A $\rightarrow$ 1, 2, 5; B $\rightarrow$ 2, 1, 5; C $\rightarrow$ 3, 4; D $\rightarrow$ 1

(b) A $\rightarrow$ 1, 3, 5; B $\rightarrow$ 1, 3, 5; C $\rightarrow$ 3, 5; D $\rightarrow$ 1

(d) A $\rightarrow$ 1, 2, 5; B $\rightarrow$ 1, 3, 5; C $\rightarrow$ 1, 4; D $\rightarrow$ 5

Answer: (c)

Explanation: Matching properties of functional groups: A undergoes 1, 2, 5; B undergoes 1, 4, 5; C undergoes 3, 4; D undergoes 1.

24. Match the reactions in Column I with appropriate types of steps/reactive intermediate involved in these reactions as given in Column II. [JEE 2011 P-II]

(a) A $\rightarrow$ 1, 2, 3; B $\rightarrow$ 2, 3; C $\rightarrow$ 1, 4; D $\rightarrow$ 1, 2

(b) A $\rightarrow$ 3, 4; B $\rightarrow$ 2; C $\rightarrow$ 3; D $\rightarrow$ 2, 4

(d) A $\rightarrow$ 3, 4, 5; B $\rightarrow$ 1, 4; C $\rightarrow$ 3, 4; D $\rightarrow$ 2, 3

Answer: (d)

Explanation: A involves dehydration, nucleophilic addition and carbanion (3, 4, 5); B involves nucleophilic substitution and addition (1, 4); C involves dehydration and addition (3, 4); D involves electrophilic substitution and dehydration (2, 3).

25. Match each set of hybrid orbitals from Column-I with complexes given in Column-II. [JEE Adv. 2018 P-II]

(a) A $\rightarrow$ 4, 6; B $\rightarrow$ 5, 6; C $\rightarrow$ 1, 2, 3; D $\rightarrow$ 3

(b) A $\rightarrow$ 1, 3, 5; B $\rightarrow$ 1, 2, 4; C $\rightarrow$ 2, 3; D $\rightarrow$ 2

(d) A $\rightarrow$ 1, 3, 4; B $\rightarrow$ 1, 3, 5; C $\rightarrow$ 1, 2; D $\rightarrow$ 5

Answer: (a)

Explanation: $[\text{FeF}_6]^{4-}$ is high spin ($sp^3d^2$); $\text{Ni(CO)}_4$ is $sp^3$; $[\text{Ni(CN)}_4]^{2-}$ is square planar ($dsp^2$).

26. The desired product X can be prepared by reacting the major product of the reactions in Column I with one or more appropriate reagents in Column II. [JEE Adv. 2018 P-II]

(a) A $\rightarrow$ 1, 2; B $\rightarrow$ 2, 3; C $\rightarrow$ 1, 2; D $\rightarrow$ 3

(b) A $\rightarrow$ 1, 3, 5; B $\rightarrow$ 1, 1, 4; C $\rightarrow$ 2, 3; D $\rightarrow$ 2

(d) A $\rightarrow$ 1, 2, 4; B $\rightarrow$ 1, 4, 5; C $\rightarrow$ 1, 2; D $\rightarrow$ 1

Answer: (c)

Explanation: Reagents in Column II react with rearranged intermediate carbonyl/alkene products to yield desired product X.

27. Column I contains reactions and Column II contains major products. [JEE Adv. 2018 P-II]

(a) A $\rightarrow$ 4, 6; B $\rightarrow$ 5; C $\rightarrow$ 1; D $\rightarrow$ 2

(b) A $\rightarrow$ 1, 4; B $\rightarrow$ 2; C $\rightarrow$ 4; D $\rightarrow$ 3

(d) A $\rightarrow$ 1, 4; B $\rightarrow$ 1; C $\rightarrow$ 1; D $\rightarrow$ 5

Answer: (b)

Explanation: With $3^\circ$ halide, elimination predominates giving corresponding alkenes.

Integer and Subjective

28. The total number of contributing structure showing hyperconjugation (involving $\text{C}-\text{H}$ bonds) for the following carbocation is [JEE 2011 P-II]

Answer: 6

Explanation: There are $6 \times \alpha-\text{H}$ atoms adjacent to the carbocation centre, giving 6 hyperconjugative structures.

29. Among the following, the number of aromatic compound(s) is [JEE Adv. 2017 P-II]

Answer: 5

Explanation: Checking Huckel's rule for planar cyclic conjugated systems, 5 of the given compounds are aromatic.