Questions about Branched Alkanes in Organic Chemistry
20 multiple-choice questions about Branched Alkanes in Organic Chemistry, each with five alternatives (A–E). At the end, you'll find a complete answer key with detailed explanations.
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Branched Alkanes — Multiple Choice Questions
1. What are branched alkanes?
A) Alkanes with cyclic structures
B) Alkanes with double bonds
C) Alkanes with one or more carbon branches off the main chain
D) Alkanes with a triple bond
E) Alkanes with oxygen atoms
2. Which of the following is a branched alkane?
A) Methane
B) Ethane
C) 2-Methylpropane
D) Propane
E) Butane
3. What is the IUPAC name for the compound commonly known as isobutane?
A) Methane
B) 2-Methylpropane
C) Butane
D) Pentane
E) 3-Methylbutane
4. How does a branched alkane differ structurally from a straight-chain alkane?
A) It contains carbon-carbon double bonds
B) It has at least one carbon not part of the longest chain
C) It has more oxygen atoms
D) It forms a ring
E) It is aromatic
5. What is the molecular formula of 2-methylpropane?
A) C₂H₆
B) C₃H₈
C) C₄H₁₀
D) C₅H₁₂
E) C₆H₁₄
6. What is the prefix used for a one-carbon branch in IUPAC nomenclature?
A) Ethyl
B) Methyl
C) Propyl
D) Butyl
E) Pentyl
7. What is the correct IUPAC name for the molecule shown below?
A four-carbon chain with a methyl group on carbon 2.
A) Butane
B) 2-Methylbutane
C) 2-Methylpropane
D) Isopentane
E) Pentane
8. Which is the correct parent chain in a branched alkane?
A) The chain with the most branches
B) The shortest continuous chain
C) The longest continuous carbon chain
D) Any carbon chain
E) The one with the most hydrogen atoms
9. What is the correct IUPAC name for:
CH₃–CH(CH₃)–CH₂–CH₃?
A) 2-Methylbutane
B) Pentane
C) Isopentane
D) 3-Methylbutane
E) 2,2-Dimethylpropane
10. How many carbon atoms are in 3-methylpentane?
A) 4
B) 5
C) 6
D) 7
E) 8
11. Which rule is followed when numbering the parent chain in branched alkanes?
A) Number from the right always
B) Start from the carbon closest to the end
C) Number from the end nearest a branch
D) Start from the center carbon
E) Alphabetical order of substituents
12. What is the correct IUPAC name for a six-carbon chain with a methyl group on carbon 3?
A) Hexane
B) 3-Methylhexane
C) 2-Methylhexane
D) 4-Methylhexane
E) Methylpentane
13. Which branched alkane is an isomer of hexane?
A) Pentane
B) Butane
C) 3-Methylpentane
D) Propane
E) 2-Methylpropane
14. Which compound has the highest boiling point?
A) Hexane
B) 3-Methylpentane
C) 2,2-Dimethylbutane
D) 2-Methylpentane
E) 2-Methylbutane
15. What is the total number of carbon atoms in 2,3-dimethylbutane?
A) 4
B) 5
C) 6
D) 7
E) 8
16. What is the correct IUPAC name for:
CH₃–C(CH₃)₂–CH₃?
A) Pentane
B) 2-Methylbutane
C) 2,2-Dimethylpropane
D) 2,3-Dimethylbutane
E) Isopentane
17. What is an isomer?
A) A compound with different atoms but the same structure
B) A compound with the same formula but different structures
C) A compound with more oxygen atoms
D) A compound with a ring structure
E) A compound that contains water
18. What is the effect of branching on the boiling point of alkanes?
A) Boiling point increases
B) Boiling point decreases
C) No effect
D) Boiling point doubles
E) Boiling point becomes zero
19. Which of the following has the lowest boiling point?
A) n-Pentane
B) 2-Methylbutane
C) Isopentane
D) 2,2-Dimethylpropane
E) 3-Methylpentane
20. How are branched alkanes separated from straight-chain alkanes in laboratories?
A) Chromatography
B) Combustion
C) Neutralization
D) Filtration
E) Precipitation
- Questions about Hydrocarbons (Organic Chemistry)
- Questions about Straight-Chain Alkanes (Organic Chemistry)
✅ Answer Key with Extended Explanations
1. C – Branched alkanes have side chains or substituents off the main carbon chain.
2. C – 2-Methylpropane is a classic example of a branched alkane.
3. B – Isobutane is the common name for 2-methylpropane.
4. B – In branched alkanes, not all carbons are in a single continuous chain.
5. C – 2-Methylpropane has 4 carbon atoms and 10 hydrogen atoms (C₄H₁₀).
6. B – A one-carbon side chain is named "methyl."
7. B – A four-carbon chain with a methyl group on carbon 2 is 2-methylbutane.
8. C – Always choose the longest continuous chain for the parent name.
9. A – This structure represents 2-methylbutane.
10. C – 3-Methylpentane has 6 carbon atoms: 5 in the main chain, 1 in the branch.
11. C – Number the chain so that substituents get the lowest possible numbers.
12. B – A six-carbon chain with a methyl on carbon 3 is 3-methylhexane.
13. C – 3-Methylpentane is an isomer of hexane (C₆H₁₄).
14. A – Less branching = higher boiling point; straight-chain hexane has the highest.
15. C – 2,3-Dimethylbutane has 4 main chain carbons and 2 in the branches = 6.
16. C – This is 2,2-dimethylpropane (a central carbon with 3 methyls around).
17. B – Isomers have the same molecular formula but different structures.
18. B – Branching reduces surface area, lowering boiling point.
19. D – 2,2-Dimethylpropane is highly branched, thus has the lowest boiling point.
20. A – Chromatography separates molecules based on differences like polarity and shape.
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