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Pass CHEM 233 Lesson 2 –
Stereochemistry, Nomenclature &
Ring Strain Mastery 2026
1. What is the molecular formula of an acyclic alkane with 6 carbon atoms?
A) C₆H₁₂
B) C₆H₁₄
C) C₆H₁₀
D) C₆H₆
*Answer: B) C₆H₁₄
Rationale: Acyclic alkanes follow CₙH₂ₙ₊₂; for n=6, H=14.
2. Which type of strain is most significant in cyclopropane?
A) Torsional strain
B) Steric strain
C) Angle strain
D) Ring strain
*Answer: C) Angle strain
Rationale: Cyclopropane has bond angles ~60° far from the ideal 109.5°,
causing high angle strain.
3. How many degrees of unsaturation does a compound with formula C₅H₈ have?
A) 0
B) 1
C) 2
D) 3
*Answer: C) 2
Rationale: (2×5+2−8)/2 = 2.
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4. Which conformation of cyclohexane is the most stable?
A) Boat
B) Twist-boat
C) Chair
D) Half-chair
*Answer: C) Chair
Rationale: The chair conformation has all bonds staggered, minimizing
torsional and angle strain.
5. What is the IUPAC name for CH₃CH₂CH(CH₃)CH₃?
A) Pentane
B) 2-Methylbutane
C) 2-Methylpentane
D) 3-Methylbutane
*Answer: B) 2-Methylbutane
Rationale: Longest chain is 4 carbons (butane) with a methyl at C2.
6. Which functional group contains a carbonyl bonded to a hydrogen?
A) Ketone
B) Aldehyde
C) Carboxylic acid
D) Ester
*Answer: B) Aldehyde
Rationale: Aldehydes have R−CHO, with H attached to the carbonyl carbon.
7. How many secondary hydrogens are in 2,3-dimethylpentane?
A) 2
B) 4
C) 6
D) 8
*Answer: B) 4
Rationale: Secondary carbons are at C3 (and C2 in this symmetric molecule),
each with 2 H; total 4.
8. Which of the following has the highest boiling point?
A) n-pentane
B) isopentane
C) neopentane
D) All equal
*Answer: A) n-pentane
Rationale: Linear alkanes have greater surface area and stronger London
dispersion forces.
9. The anti conformation of butane has a dihedral angle of:
A) 0°
B) 60°
C) 120°
D) 180°
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*Answer: D) 180°
Rationale: Anti means the two methyl groups are opposite each other.
10. Which of these is a meso compound?
A) 2,3-dichlorobutane (R,R)
B) 2,3-dichlorobutane (S,S)
C) 2,3-dichlorobutane (R,S)
D) 1,2-dichloroethane
*Answer: C) 2,3-dichlorobutane (R,S)
Rationale: The (R,S) isomer has an internal plane of symmetry.
11. What is the empirical formula of cyclohexane?
A) CH₂
B) C₆H₁₂
C) CH
D) C₆H₆
*Answer: A) CH₂
Rationale: C₆H₁₂ reduces to CH₂.
12. Which substituent causes the most 1,3-diaxial strain in cyclohexane?
A) Methyl
B) Ethyl
C) Isopropyl
D) tert-Butyl
*Answer: D) tert-Butyl
Rationale: tert-Butyl is the bulkiest, so axial placement is highly unfavorable.
13. How many rings are in a compound with formula C₆H₁₀ and one double bond?
A) 0
B) 1
C) 2
D) 3
*Answer: B) 1
Rationale: DBE=2; one for the double bond, one for the ring.
14. Which of these is not a conformational isomer?
A) Eclipsed
B) Staggered
C) Anti
D) Cis-trans
*Answer: D) Cis-trans
Rationale: Cis-trans are configurational (geometric) isomers, not conformers.
15. What is the correct IUPAC name for the structure with a cyclopentane ring and a
bromine at C1 and ethyl at C1?
A) 1-Bromo-1-ethylcyclopentane
B) 1-Ethyl-1-bromocyclopentane
C) 1-Bromo-1-ethylcyclopentane
D) Ethyl bromocyclopentane
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*Answer: A) 1-Bromo-1-ethylcyclopentane
Rationale: Alphabetical order: bromo before ethyl.
16. Which functional group is present in Kevlar?
A) Ester
B) Amide
C) Carboxylic acid
D) Amine
*Answer: B) Amide
Rationale: Kevlar is a polyamide formed from aromatic monomers.
17. The gauche conformation is less stable than anti due to:
A) Angle strain
B) Torsional strain
C) Steric strain
D) Ring strain
*Answer: C) Steric strain
Rationale: Gauche butane has the two methyl groups close together, causing
steric repulsion.
18. How many axial hydrogens are in a chair cyclohexane?
A) 3
B) 6
C) 9
D) 12
*Answer: B) 6
Rationale: There are 6 axial positions (up/down alternating).
19. Which compound has no plane of symmetry?
A) Meso-tartaric acid
B) (R)-2-chlorobutane
C) (R,S)-2,3-dichlorobutane
D) Cis-1,2-dichloroethene
*Answer: B) (R)-2-chlorobutane
Rationale: A single chiral center gives a chiral molecule with no plane of
symmetry.
20. What is the heat of combustion trend for alkanes?
A) Increases with branching
B) Decreases with chain length
C) Increases per CH₂ unit
D) Constant for all isomers
*Answer: C) Increases per CH₂ unit
Rationale: Each additional CH₂ adds roughly the same heat of combustion.
21. Which of these is a tertiary carbon?
A) CH₄
B) CH₃CH₃
C) (CH₃)₃CH
Pass CHEM 233 Lesson 2 –
Stereochemistry, Nomenclature &
Ring Strain Mastery 2026
1. What is the molecular formula of an acyclic alkane with 6 carbon atoms?
A) C₆H₁₂
B) C₆H₁₄
C) C₆H₁₀
D) C₆H₆
*Answer: B) C₆H₁₄
Rationale: Acyclic alkanes follow CₙH₂ₙ₊₂; for n=6, H=14.
2. Which type of strain is most significant in cyclopropane?
A) Torsional strain
B) Steric strain
C) Angle strain
D) Ring strain
*Answer: C) Angle strain
Rationale: Cyclopropane has bond angles ~60° far from the ideal 109.5°,
causing high angle strain.
3. How many degrees of unsaturation does a compound with formula C₅H₈ have?
A) 0
B) 1
C) 2
D) 3
*Answer: C) 2
Rationale: (2×5+2−8)/2 = 2.
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4. Which conformation of cyclohexane is the most stable?
A) Boat
B) Twist-boat
C) Chair
D) Half-chair
*Answer: C) Chair
Rationale: The chair conformation has all bonds staggered, minimizing
torsional and angle strain.
5. What is the IUPAC name for CH₃CH₂CH(CH₃)CH₃?
A) Pentane
B) 2-Methylbutane
C) 2-Methylpentane
D) 3-Methylbutane
*Answer: B) 2-Methylbutane
Rationale: Longest chain is 4 carbons (butane) with a methyl at C2.
6. Which functional group contains a carbonyl bonded to a hydrogen?
A) Ketone
B) Aldehyde
C) Carboxylic acid
D) Ester
*Answer: B) Aldehyde
Rationale: Aldehydes have R−CHO, with H attached to the carbonyl carbon.
7. How many secondary hydrogens are in 2,3-dimethylpentane?
A) 2
B) 4
C) 6
D) 8
*Answer: B) 4
Rationale: Secondary carbons are at C3 (and C2 in this symmetric molecule),
each with 2 H; total 4.
8. Which of the following has the highest boiling point?
A) n-pentane
B) isopentane
C) neopentane
D) All equal
*Answer: A) n-pentane
Rationale: Linear alkanes have greater surface area and stronger London
dispersion forces.
9. The anti conformation of butane has a dihedral angle of:
A) 0°
B) 60°
C) 120°
D) 180°
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*Answer: D) 180°
Rationale: Anti means the two methyl groups are opposite each other.
10. Which of these is a meso compound?
A) 2,3-dichlorobutane (R,R)
B) 2,3-dichlorobutane (S,S)
C) 2,3-dichlorobutane (R,S)
D) 1,2-dichloroethane
*Answer: C) 2,3-dichlorobutane (R,S)
Rationale: The (R,S) isomer has an internal plane of symmetry.
11. What is the empirical formula of cyclohexane?
A) CH₂
B) C₆H₁₂
C) CH
D) C₆H₆
*Answer: A) CH₂
Rationale: C₆H₁₂ reduces to CH₂.
12. Which substituent causes the most 1,3-diaxial strain in cyclohexane?
A) Methyl
B) Ethyl
C) Isopropyl
D) tert-Butyl
*Answer: D) tert-Butyl
Rationale: tert-Butyl is the bulkiest, so axial placement is highly unfavorable.
13. How many rings are in a compound with formula C₆H₁₀ and one double bond?
A) 0
B) 1
C) 2
D) 3
*Answer: B) 1
Rationale: DBE=2; one for the double bond, one for the ring.
14. Which of these is not a conformational isomer?
A) Eclipsed
B) Staggered
C) Anti
D) Cis-trans
*Answer: D) Cis-trans
Rationale: Cis-trans are configurational (geometric) isomers, not conformers.
15. What is the correct IUPAC name for the structure with a cyclopentane ring and a
bromine at C1 and ethyl at C1?
A) 1-Bromo-1-ethylcyclopentane
B) 1-Ethyl-1-bromocyclopentane
C) 1-Bromo-1-ethylcyclopentane
D) Ethyl bromocyclopentane
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*Answer: A) 1-Bromo-1-ethylcyclopentane
Rationale: Alphabetical order: bromo before ethyl.
16. Which functional group is present in Kevlar?
A) Ester
B) Amide
C) Carboxylic acid
D) Amine
*Answer: B) Amide
Rationale: Kevlar is a polyamide formed from aromatic monomers.
17. The gauche conformation is less stable than anti due to:
A) Angle strain
B) Torsional strain
C) Steric strain
D) Ring strain
*Answer: C) Steric strain
Rationale: Gauche butane has the two methyl groups close together, causing
steric repulsion.
18. How many axial hydrogens are in a chair cyclohexane?
A) 3
B) 6
C) 9
D) 12
*Answer: B) 6
Rationale: There are 6 axial positions (up/down alternating).
19. Which compound has no plane of symmetry?
A) Meso-tartaric acid
B) (R)-2-chlorobutane
C) (R,S)-2,3-dichlorobutane
D) Cis-1,2-dichloroethene
*Answer: B) (R)-2-chlorobutane
Rationale: A single chiral center gives a chiral molecule with no plane of
symmetry.
20. What is the heat of combustion trend for alkanes?
A) Increases with branching
B) Decreases with chain length
C) Increases per CH₂ unit
D) Constant for all isomers
*Answer: C) Increases per CH₂ unit
Rationale: Each additional CH₂ adds roughly the same heat of combustion.
21. Which of these is a tertiary carbon?
A) CH₄
B) CH₃CH₃
C) (CH₃)₃CH
