Organic chemistry most important questions

🔬 Top 10 Organic Chemistry Questions

1. Which of the following is the most stable carbocation?

A) Methyl carbocation B) Tertiary butyl carbocation C) Primary carbocation D) Secondary carbocation

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Answer: B) Tertiary butyl carbocation
Tertiary carbocations are more stable due to hyperconjugation and inductive effects from 3 surrounding carbon atoms.

2. Which compound undergoes Cannizzaro reaction?

A) Formaldehyde B) Acetaldehyde C) Acetone D) Ethanol

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Answer: A) Formaldehyde
Cannizzaro reaction occurs in aldehydes without α-hydrogen. Formaldehyde fits this condition.

3. What is the IUPAC name of CH₃–CH₂–COOH?

A) Ethanoic acid B) Methanoic acid C) Propanoic acid D) Butanoic acid

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Answer: C) Propanoic acid
It is a 3-carbon carboxylic acid, so the correct name is propanoic acid.

4. Which reagent is used to convert alcohol to alkene?

A) NaBH₄ B) H₂/Pd C) H₂SO₄/Heat D) KMnO₄

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Answer: C) H₂SO₄/Heat
Acidic dehydration of alcohols forms alkenes via elimination (E1/E2 mechanism).

5. Which of the following is aromatic?

A) Cyclobutane B) Benzene C) Cyclohexane D) Butadiene

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Answer: B) Benzene
Benzene follows Huckel’s rule with 6 π electrons, making it aromatic.

6. Tollen’s reagent is used to test for:

A) Ketones B) Alcohols C) Aldehydes D) Carboxylic acids

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Answer: C) Aldehydes
Tollen’s reagent gives a silver mirror test for aldehydes only.

7. The product of aldol condensation is:

A) Alcohol B) β-hydroxy aldehyde/ketone C) Ether D) Acid

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Answer: B) β-hydroxy aldehyde/ketone
Aldol condensation leads to formation of β-hydroxy carbonyl compound.

8. Which compound shows tautomerism?

A) Acetic acid B) Acetone C) Benzene D) Ethanol

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Answer: B) Acetone
Acetone shows keto-enol tautomerism, a reversible structural isomerism.

9. Which of the following is most reactive towards nucleophilic substitution?

A) Vinyl chloride B) Benzyl chloride C) Chlorobenzene D) Chloroethane

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Answer: B) Benzyl chloride
Benzyl carbocation is resonance stabilized, making substitution easier.

10. Which is a secondary amine?

A) CH₃NH₂ B) CH₃–NH–CH₃ C) (CH₃)₃N D) CH₃CH₂NH₂

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Answer: B) CH₃–NH–CH₃
A secondary amine has two alkyl groups attached to nitrogen atom.

11. Which of the following is not an electrophile?

A) AlCl₃ B) NO₂⁺ C) BF₃ D) NH₃

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Answer: D) NH₃
NH₃ has a lone pair of electrons, so it's a nucleophile, not an electrophile.

12. The hybridization of carbon in ethyne is:

A) sp B) sp² C) sp³ D) dsp²

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Answer: A) sp
In ethyne (C₂H₂), each carbon forms two sigma bonds and two pi bonds — indicating sp hybridization.

13. Which of the following compounds shows geometrical isomerism?

A) But-2-ene B) But-1-ene C) Propene D) Ethene

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Answer: A) But-2-ene
Geometrical isomerism (cis-trans) is possible in alkenes with two different groups on each doubly bonded carbon.

14. Which is the correct order of acidity?

A) Phenol > Ethanol > Acetic acid B) Acetic acid > Phenol > Ethanol C) Ethanol > Phenol > Acetic acid D) Phenol > Acetic acid > Ethanol

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Answer: B) Acetic acid > Phenol > Ethanol
Carboxylic acids are most acidic, followed by phenols, then alcohols.

15. Which compound gives a positive iodoform test?

A) Ethanol B) Methanol C) Propanol-1 D) Acetic acid

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Answer: A) Ethanol
Iodoform test is positive for compounds with CH₃–CO– or CH₃–CH(OH)– group.

16. What is the product of the reaction between phenol and bromine water?

A) o-Bromophenol B) p-Bromophenol C) 2,4,6-Tribromophenol D) Bromobenzene

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Answer: C) 2,4,6-Tribromophenol
Phenol reacts with bromine water to give white precipitate of tribromophenol.

17. What type of reaction is the formation of esters from acids and alcohols?

A) Addition B) Elimination C) Substitution D) Condensation

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Answer: D) Condensation
Esterification is a condensation reaction where water is removed.

18. Which reagent converts an aldehyde to a primary alcohol?

A) KMnO₄ B) NaBH₄ C) HNO₃ D) H₂SO₄

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Answer: B) NaBH₄
Sodium borohydride is a reducing agent used to convert aldehydes to alcohols.

19. Which of the following is used in Friedel-Crafts reaction?

A) HCl B) AlCl₃ C) HNO₃ D) FeCl₃

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Answer: B) AlCl₃
AlCl₃ is a Lewis acid catalyst in Friedel-Crafts alkylation/acylation reactions.

20. Which one gives only one monosubstituted product on chlorination?

A) Ethane B) Propane C) 2-Methylpropane D) Neopentane

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Answer: D) Neopentane
Neopentane is symmetrical and gives only one monochlorinated product.