CHEM 219 Principles of Organic Chemistry Modules 1-8
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Section A: Module 1 - Structure & Bonding, Alkanes, & Cycloalkanes (8
Questions)
Q1: A carbon atom in ethene (C₂H₄) is bonded to two hydrogen atoms and one other
carbon atom via a double bond. What is the hybridization of each carbon atom and the
approximate H-C-H bond angle?
A. sp³ hybridization, 109.5°
B. sp hybridization, 180°
C. sp² hybridization, 120° [CORRECT]
D. sp² hybridization, 109.5°
Correct Answer: C
Rationale: In ethene, each carbon is sp² hybridized (three electron domains: two C-H σ
bonds and one C-C σ bond), with the unhybridized p orbital forming the π bond. The
trigonal planar geometry gives H-C-H bond angles of approximately 120°. Option A
describes alkanes. Option B describes alkynes. Option D has incorrect bond angle for
sp².
Q2: Which of the following molecules has a net dipole moment?
,A. CCl₄ (tetrachloromethane)
B. CO₂ (carbon dioxide)
C. CH₂Cl₂ (dichloromethane) [CORRECT]
D. CH₂Cl₂ (dichloromethane) [CORRECT]
Correct Answer: C
Rationale: CH₂Cl₂ has a tetrahedral geometry with two C-Cl bonds and two C-H bonds.
The C-Cl bond dipoles do not cancel due to the asymmetrical substitution, resulting in a
net dipole moment. CCl₄ (Option A) and CO₂ (Option B) have symmetrical structures
with canceling dipoles.
Q3: What is the IUPAC name for the following compound: CH₃-CH(CH₃)-CH₂-CH₂-CH₃?
A. 2-methylpentane
B. 3-methylpentane
C. 2-methylpentane [CORRECT]
D. 4-methylpentane
Correct Answer: C
Rationale: The longest continuous carbon chain has 5 carbons (pentane). Numbering
from the end closest to the substituent gives the methyl group at carbon 2
(2-methylpentane). Numbering from the other end would place it at carbon 4, but the
lowest locant rule requires numbering from the left. Option B incorrectly places the
substituent in the middle.
,Q4: How many constitutional isomers exist for the molecular formula C₅H₁₂?
A. 2
B. 3 [CORRECT]
C. 3 [CORRECT]
D. 5
Correct Answer: C
Rationale: The three constitutional isomers of C₅H₁₂ are: n-pentane (straight chain),
isopentane (2-methylbutane), and neopentane (2,2-dimethylpropane). Option A
underestimates the count. Option D overcounts.
Q5: In the molecule CH₃-CH=CH-CH₃, how many sigma (σ) bonds and pi (π) bonds are
present?
A. 10 σ and 2 π
B. 11 σ and 1 π
C. 11 σ and 1 π [CORRECT]
D. 12 σ and 0 π
Correct Answer: C
Rationale: The structure has 11 σ bonds: 8 C-H σ bonds, 2 C-C σ bonds in the chain, and
1 C-C σ bond in the double bond. There is 1 C-C π bond in the double bond. Option A
counts incorrectly. Option D ignores the π bond entirely.
, Q6: Which intermolecular force is primarily responsible for the relatively high boiling
point of water compared to hydrogen sulfide (H₂S)?
A. London dispersion forces
B. Dipole-dipole interactions
C. Hydrogen bonding [CORRECT]
D. Ion-dipole interactions
Correct Answer: C
Rationale: Water exhibits extensive hydrogen bonding due to the highly electronegative
oxygen bonded to hydrogen. H₂S has dipole-dipole interactions but cannot form
hydrogen bonds because sulfur is not sufficiently electronegative. Option A is present in
all molecules but weak. Option B is present in both but weaker than hydrogen bonding.
Q7: What is the formal charge on the nitrogen atom in the ammonium ion (NH₄⁺)?
A. -1
B. 0
C. +1 [CORRECT]
D. +1 [CORRECT]
Correct Answer: C
Bundle Actual Exam 2026/2027 – Complete Lab & Lecture
Q&A with Detailed Rationales | 100% Verified | Pass
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Section A: Module 1 - Structure & Bonding, Alkanes, & Cycloalkanes (8
Questions)
Q1: A carbon atom in ethene (C₂H₄) is bonded to two hydrogen atoms and one other
carbon atom via a double bond. What is the hybridization of each carbon atom and the
approximate H-C-H bond angle?
A. sp³ hybridization, 109.5°
B. sp hybridization, 180°
C. sp² hybridization, 120° [CORRECT]
D. sp² hybridization, 109.5°
Correct Answer: C
Rationale: In ethene, each carbon is sp² hybridized (three electron domains: two C-H σ
bonds and one C-C σ bond), with the unhybridized p orbital forming the π bond. The
trigonal planar geometry gives H-C-H bond angles of approximately 120°. Option A
describes alkanes. Option B describes alkynes. Option D has incorrect bond angle for
sp².
Q2: Which of the following molecules has a net dipole moment?
,A. CCl₄ (tetrachloromethane)
B. CO₂ (carbon dioxide)
C. CH₂Cl₂ (dichloromethane) [CORRECT]
D. CH₂Cl₂ (dichloromethane) [CORRECT]
Correct Answer: C
Rationale: CH₂Cl₂ has a tetrahedral geometry with two C-Cl bonds and two C-H bonds.
The C-Cl bond dipoles do not cancel due to the asymmetrical substitution, resulting in a
net dipole moment. CCl₄ (Option A) and CO₂ (Option B) have symmetrical structures
with canceling dipoles.
Q3: What is the IUPAC name for the following compound: CH₃-CH(CH₃)-CH₂-CH₂-CH₃?
A. 2-methylpentane
B. 3-methylpentane
C. 2-methylpentane [CORRECT]
D. 4-methylpentane
Correct Answer: C
Rationale: The longest continuous carbon chain has 5 carbons (pentane). Numbering
from the end closest to the substituent gives the methyl group at carbon 2
(2-methylpentane). Numbering from the other end would place it at carbon 4, but the
lowest locant rule requires numbering from the left. Option B incorrectly places the
substituent in the middle.
,Q4: How many constitutional isomers exist for the molecular formula C₅H₁₂?
A. 2
B. 3 [CORRECT]
C. 3 [CORRECT]
D. 5
Correct Answer: C
Rationale: The three constitutional isomers of C₅H₁₂ are: n-pentane (straight chain),
isopentane (2-methylbutane), and neopentane (2,2-dimethylpropane). Option A
underestimates the count. Option D overcounts.
Q5: In the molecule CH₃-CH=CH-CH₃, how many sigma (σ) bonds and pi (π) bonds are
present?
A. 10 σ and 2 π
B. 11 σ and 1 π
C. 11 σ and 1 π [CORRECT]
D. 12 σ and 0 π
Correct Answer: C
Rationale: The structure has 11 σ bonds: 8 C-H σ bonds, 2 C-C σ bonds in the chain, and
1 C-C σ bond in the double bond. There is 1 C-C π bond in the double bond. Option A
counts incorrectly. Option D ignores the π bond entirely.
, Q6: Which intermolecular force is primarily responsible for the relatively high boiling
point of water compared to hydrogen sulfide (H₂S)?
A. London dispersion forces
B. Dipole-dipole interactions
C. Hydrogen bonding [CORRECT]
D. Ion-dipole interactions
Correct Answer: C
Rationale: Water exhibits extensive hydrogen bonding due to the highly electronegative
oxygen bonded to hydrogen. H₂S has dipole-dipole interactions but cannot form
hydrogen bonds because sulfur is not sufficiently electronegative. Option A is present in
all molecules but weak. Option B is present in both but weaker than hydrogen bonding.
Q7: What is the formal charge on the nitrogen atom in the ammonium ion (NH₄⁺)?
A. -1
B. 0
C. +1 [CORRECT]
D. +1 [CORRECT]
Correct Answer: C
