CHEM 233 LESSON 2 EXAM (PDF) | 2026 EXAM QUESTIONS
AND ANSWERS + RATIONALES | STUDY GUIDE | 100%
CORRECT
1. Pick out the conformation for butane which has the gauche conformation.
A) A
B) B
C) C
D) D
Correct Answer: The gauche conformation is the one where the two methyl groups are staggered
with a 60° dihedral angle, placing them close together.
Rationale: In a Newman projection of butane, the gauche conformation is a staggered conformer
where the two methyl groups are 60° apart, resulting in a slightly higher energy than the anti
conformation due to steric strain .
2. Identify the more stable of the two pictured molecules.
A) The molecule on the left
B) The molecule on the right
C) They are of equal stability
D) Cannot be determined from the information given
Correct Answer: The more stable molecule is the one with the larger substituent in the equatorial
position.
Rationale: In cyclohexane conformations, the more stable chair conformation has the larger
substituents equatorial to minimize 1,3-diaxial interactions and steric strain .
3. If an acyclic alkane hydrocarbon contains n carbon atoms, how many hydrogen atoms must it
also contain?
A) 2n
B) 2n + 2
C) n - 2
D) n
Correct Answer: 2n + 2
Rationale: Acyclic alkanes have the general formula CₙH₂ₙ₊₂ because they are saturated
hydrocarbons with no rings or double bonds .
4. How many secondary hydrogens does the following compound contain? (Cycloalkane structure)
A) 2
B) 4
C) 8
D) 12
, Correct Answer: 8
Rationale: Secondary hydrogens are attached to secondary carbons (carbons bonded to two other
carbons). The compound has 8 such hydrogens .
5. How many degrees of unsaturation does the following structure have?
A) 5
B) 3
C) 7
D) 6
E) 4
Correct Answer: 4
Rationale: Degrees of unsaturation can be calculated from the molecular formula or by counting
rings and pi bonds. The structure has 4 degrees of unsaturation .
6. Which of these molecules has the lowest boiling point?
A) CH₄
B) CH₃CH₃
C) CH₃CH₂CH₃
D) CH₃CH₂CH₂CH₃
Correct Answer: CH₄
Rationale: Boiling point increases with molecular weight and surface area due to stronger
London dispersion forces. Methane (CH₄) has the lowest molecular weight and weakest
intermolecular forces, giving it the lowest boiling point .
7. Which of the following molecules have the highest heat of combustion?
A) CH₃CH₂CH₂CH₂CH₃
B) CH₃CH₂CH₃
C) CH₄
D) CH₃CH₂CH₂CH₃
Correct Answer: CH₃CH₂CH₂CH₂CH₃ (n-pentane)
Rationale: Heat of combustion increases with the number of carbons. Pentane has the most
carbons and therefore the highest heat of combustion .
8. Identify the circled functional group found in Penicillin G.
A) Amine
B) Aldehyde
C) Carboxylic acid
D) Carbonyl
E) Hydroxyl
, Correct Answer: Carboxylic acid
Rationale: Penicillin G contains a carboxylic acid functional group (-COOH) as part of its
structure .
9. Which of the following is an aldehyde?
A) Option A
B) Option B
C) Option C
D) Option D
Correct Answer: The compound with the -CHO functional group.
Rationale: Aldehydes are characterized by a carbonyl group bonded to at least one hydrogen
atom, with the general formula R-CHO .
10. The energy barrier for carbon-carbon bond rotation in propane is mainly due to:
A) Angle strain
B) Torsional strain
C) Bond strain
D) Steric strain
Correct Answer: Torsional strain
Rationale: The energy barrier for rotation around the C-C bond in propane is due to torsional
strain, which arises from the eclipsing of C-H bonds as the molecule rotates .
11. Identify the circled functional group found in Kevlar.
A) Ether
B) Amine
C) Ester
D) Amide
E) Carbonyl
Correct Answer: Amide
Rationale: Kevlar contains amide functional groups (-CONH-) connecting the aromatic rings.
Amides are characterized by a carbonyl group directly bonded to a nitrogen atom .
12. Identify the more stable of the two pictured molecules.
A) Molecule 1
B) Molecule 2
C) They are of equal stability
D) Cannot be determined
Correct Answer: They are of equal stability
AND ANSWERS + RATIONALES | STUDY GUIDE | 100%
CORRECT
1. Pick out the conformation for butane which has the gauche conformation.
A) A
B) B
C) C
D) D
Correct Answer: The gauche conformation is the one where the two methyl groups are staggered
with a 60° dihedral angle, placing them close together.
Rationale: In a Newman projection of butane, the gauche conformation is a staggered conformer
where the two methyl groups are 60° apart, resulting in a slightly higher energy than the anti
conformation due to steric strain .
2. Identify the more stable of the two pictured molecules.
A) The molecule on the left
B) The molecule on the right
C) They are of equal stability
D) Cannot be determined from the information given
Correct Answer: The more stable molecule is the one with the larger substituent in the equatorial
position.
Rationale: In cyclohexane conformations, the more stable chair conformation has the larger
substituents equatorial to minimize 1,3-diaxial interactions and steric strain .
3. If an acyclic alkane hydrocarbon contains n carbon atoms, how many hydrogen atoms must it
also contain?
A) 2n
B) 2n + 2
C) n - 2
D) n
Correct Answer: 2n + 2
Rationale: Acyclic alkanes have the general formula CₙH₂ₙ₊₂ because they are saturated
hydrocarbons with no rings or double bonds .
4. How many secondary hydrogens does the following compound contain? (Cycloalkane structure)
A) 2
B) 4
C) 8
D) 12
, Correct Answer: 8
Rationale: Secondary hydrogens are attached to secondary carbons (carbons bonded to two other
carbons). The compound has 8 such hydrogens .
5. How many degrees of unsaturation does the following structure have?
A) 5
B) 3
C) 7
D) 6
E) 4
Correct Answer: 4
Rationale: Degrees of unsaturation can be calculated from the molecular formula or by counting
rings and pi bonds. The structure has 4 degrees of unsaturation .
6. Which of these molecules has the lowest boiling point?
A) CH₄
B) CH₃CH₃
C) CH₃CH₂CH₃
D) CH₃CH₂CH₂CH₃
Correct Answer: CH₄
Rationale: Boiling point increases with molecular weight and surface area due to stronger
London dispersion forces. Methane (CH₄) has the lowest molecular weight and weakest
intermolecular forces, giving it the lowest boiling point .
7. Which of the following molecules have the highest heat of combustion?
A) CH₃CH₂CH₂CH₂CH₃
B) CH₃CH₂CH₃
C) CH₄
D) CH₃CH₂CH₂CH₃
Correct Answer: CH₃CH₂CH₂CH₂CH₃ (n-pentane)
Rationale: Heat of combustion increases with the number of carbons. Pentane has the most
carbons and therefore the highest heat of combustion .
8. Identify the circled functional group found in Penicillin G.
A) Amine
B) Aldehyde
C) Carboxylic acid
D) Carbonyl
E) Hydroxyl
, Correct Answer: Carboxylic acid
Rationale: Penicillin G contains a carboxylic acid functional group (-COOH) as part of its
structure .
9. Which of the following is an aldehyde?
A) Option A
B) Option B
C) Option C
D) Option D
Correct Answer: The compound with the -CHO functional group.
Rationale: Aldehydes are characterized by a carbonyl group bonded to at least one hydrogen
atom, with the general formula R-CHO .
10. The energy barrier for carbon-carbon bond rotation in propane is mainly due to:
A) Angle strain
B) Torsional strain
C) Bond strain
D) Steric strain
Correct Answer: Torsional strain
Rationale: The energy barrier for rotation around the C-C bond in propane is due to torsional
strain, which arises from the eclipsing of C-H bonds as the molecule rotates .
11. Identify the circled functional group found in Kevlar.
A) Ether
B) Amine
C) Ester
D) Amide
E) Carbonyl
Correct Answer: Amide
Rationale: Kevlar contains amide functional groups (-CONH-) connecting the aromatic rings.
Amides are characterized by a carbonyl group directly bonded to a nitrogen atom .
12. Identify the more stable of the two pictured molecules.
A) Molecule 1
B) Molecule 2
C) They are of equal stability
D) Cannot be determined
Correct Answer: They are of equal stability
