Daily Olympiad: Chemistry - Hydrocarbons [20260512] – 8 Practice Problems & Printable PDF

1. Which of the following compounds exhibits position isomerism?

A. Hexane B. 2-Butene C. 1-Butanol and 2-Butanol D. Ethanol and Methanol

Solution

Correct: C

Position isomerism occurs when functional groups differ in position on the carbon chain. 1-Butanol and 2-Butanol are position isomers due to different hydroxyl positions.

2. Which of the following is a correct statement about aromaticity?

A. Aromatic compounds are less stable than their aliphatic counterparts B. Benzene follows Hückel's rule with 4n+2 π electrons C. Aromaticity is limited to monocyclic systems D. All aromatic compounds contain benzene rings

Solution

Correct: B

Benzene has 6 π electrons (n=1 in Hückel's rule), making it aromatic. Aromaticity can exist in both monocyclic and polycyclic systems.

3. The major product of acid-catalysed hydration of 1-butene is

A. 1-Butanol B. 2-Butanol C. 2-Methyl-2-propanol D. 1-Propanol

Solution

Correct: B

Markovnikov's rule dictates that water adds such that the more stable carbocation forms. The hydration of 1-butene forms a secondary carbocation, leading to 2-butanol.

4. The IUPAC name for CH₂=C(CH₃)–CH₂–C≡CH is

A. 1-Methylbuta-1,3-diene B. 3-Methylpent-4-yn-2-ene C. 2-Methylpent-3-en-5-yne D. 2-Methylpenta-1,3-dien-5-yne

Solution

Correct: C

Numbering from the correct end gives the lowest locant. The triple bond takes precedence over the double bond, making the correct name 2-methylpent-3-en-5-yne.

5. Which of the following reacts fastest under SN1 conditions?

A. Tertiary cycloalkyl halide B. Allylic halide C. Primary alkyl halide D. Secondary alkyl halide

Solution

Correct: A

Tertiary carbocations are most stable due to hyperconjugation and inductive effects, making tertiary cycloalkyl halides the fastest in SN1 reactions.

6. Which of the following is not a peroxide effect reaction?

A. Hydrogenation of alkynes B. Addition of HBr to alkenes C. Free radical halogenation of alkanes D. Polymerization of ethylene

Solution

Correct: A

The peroxide effect (anti-Markovnikov addition) only occurs in HBr addition to alkenes. Other options do not involve peroxide-induced radical mechanisms.

7. The compound that gives a white precipitate with AgNO₃ is

A. 1-Chloropropane B. Chlorobenzene C. Vinyl chloride D. 1-Chloropropene

Solution

Correct: D

Precipitates with AgNO₃ form only for terminal alkynes or ionic halides. 1-Chloropropene contains a vinylic chloride that reacts with AgNO₃.

8. The most stable conformation of butane is

A. Synperiplanar B. Synclinal C. Antiperiplanar D. Transoidal

Solution

Correct: C

Antiperiplanar conformation (staggered trans) minimizes steric strain, making it the lowest energy conformation for butane.