CHEM 219 Module 5 Exam: Aromatic Compounds 2026/2027 UPDATE
1. What is the hybridization of all carbon atoms in the benzene ring?
A. sp3
B. sp
C. sp2
D. dsp2
Answer: C
Rationale: In benzene, each carbon is bonded to two other carbons and one hydrogen,
forming a planar hexagonal structure with sp2 hybridization.
2. According to Hückel’s Rule, a compound is aromatic if it is cyclic, planar, fully
conjugated, and contains how many pi electrons?
A. 4n
B. 4n + 2
C. 2n + 2
D. 3n + 1
Answer: B
Rationale: Hückel’s rule states that an aromatic system must have (4n + 2) pi electrons,
where n is a non-negative integer.
3. Which of the following describes the bond lengths in benzene?
A. Alternating long single and short double bonds
B. All bonds are of equal length, between a single and double bond
C. All bonds are equal to standard C=C double bonds
D. Three long bonds and three short bonds
Answer: B
,Rationale: Due to resonance delocalization, all C-C bonds in benzene are identical in length
(1.39 Å), which is intermediate between a single and double bond.
4. What is the common name for hydroxybenzene?
A. Aniline
B. Phenol
C. Toluene
D. Anisole
Answer: B
Rationale: Phenol is the IUPAC-accepted common name for a benzene ring with a hydroxyl
(-OH) group.
5. Which reagent is typically used for the nitration of benzene?
A. NaNO2 and HCl
B. HNO3 and H2SO4
C. NH3 and KMnO4
D. HNO2 and H2O
Answer: B
Rationale: Nitration requires a mixture of concentrated nitric acid and sulfuric acid to
generate the nitronium ion (NO2+) electrophile.
6. In the chlorination of benzene, what is the purpose of adding FeCl3?
A. It acts as a solvent
B. It stabilizes the benzene ring
C. It acts as a base to remove a proton
D. It acts as a Lewis acid catalyst to generate the Cl+ electrophile
Answer: D
Rationale: FeCl3 is a Lewis acid that reacts with Cl2 to create a more powerful
electrophilic species capable of attacking the stable aromatic ring.
, 7. Which of the following substituents is a strong activator and an ortho/para
director?
A. -NO2
B. -Cl
C. -NH2
D. -COOH
Answer: C
Rationale: The amino group (-NH2) has a lone pair that can be donated into the ring by
resonance, making it a strong activator and directing substitution to the ortho and para
positions.
8. What is the electrophile in the Friedel-Crafts alkylation reaction?
A. A carbocation
B. An acylium ion
C. A halogen atom
D. A nitronium ion
Answer: A
Rationale: In Friedel-Crafts alkylation, an alkyl halide reacts with a Lewis acid (like AlCl3)
to form a carbocation, which serves as the electrophile.
9. Which molecule is considered ‘anti-aromatic’?
A. Cyclobutadiene
B. Pyridine
C. Benzene
D. Naphthalene
Answer: A
Rationale: Cyclobutadiene is cyclic, planar, and conjugated but has 4 pi electrons (4n
where n=1), making it highly unstable and anti-aromatic.
1. What is the hybridization of all carbon atoms in the benzene ring?
A. sp3
B. sp
C. sp2
D. dsp2
Answer: C
Rationale: In benzene, each carbon is bonded to two other carbons and one hydrogen,
forming a planar hexagonal structure with sp2 hybridization.
2. According to Hückel’s Rule, a compound is aromatic if it is cyclic, planar, fully
conjugated, and contains how many pi electrons?
A. 4n
B. 4n + 2
C. 2n + 2
D. 3n + 1
Answer: B
Rationale: Hückel’s rule states that an aromatic system must have (4n + 2) pi electrons,
where n is a non-negative integer.
3. Which of the following describes the bond lengths in benzene?
A. Alternating long single and short double bonds
B. All bonds are of equal length, between a single and double bond
C. All bonds are equal to standard C=C double bonds
D. Three long bonds and three short bonds
Answer: B
,Rationale: Due to resonance delocalization, all C-C bonds in benzene are identical in length
(1.39 Å), which is intermediate between a single and double bond.
4. What is the common name for hydroxybenzene?
A. Aniline
B. Phenol
C. Toluene
D. Anisole
Answer: B
Rationale: Phenol is the IUPAC-accepted common name for a benzene ring with a hydroxyl
(-OH) group.
5. Which reagent is typically used for the nitration of benzene?
A. NaNO2 and HCl
B. HNO3 and H2SO4
C. NH3 and KMnO4
D. HNO2 and H2O
Answer: B
Rationale: Nitration requires a mixture of concentrated nitric acid and sulfuric acid to
generate the nitronium ion (NO2+) electrophile.
6. In the chlorination of benzene, what is the purpose of adding FeCl3?
A. It acts as a solvent
B. It stabilizes the benzene ring
C. It acts as a base to remove a proton
D. It acts as a Lewis acid catalyst to generate the Cl+ electrophile
Answer: D
Rationale: FeCl3 is a Lewis acid that reacts with Cl2 to create a more powerful
electrophilic species capable of attacking the stable aromatic ring.
, 7. Which of the following substituents is a strong activator and an ortho/para
director?
A. -NO2
B. -Cl
C. -NH2
D. -COOH
Answer: C
Rationale: The amino group (-NH2) has a lone pair that can be donated into the ring by
resonance, making it a strong activator and directing substitution to the ortho and para
positions.
8. What is the electrophile in the Friedel-Crafts alkylation reaction?
A. A carbocation
B. An acylium ion
C. A halogen atom
D. A nitronium ion
Answer: A
Rationale: In Friedel-Crafts alkylation, an alkyl halide reacts with a Lewis acid (like AlCl3)
to form a carbocation, which serves as the electrophile.
9. Which molecule is considered ‘anti-aromatic’?
A. Cyclobutadiene
B. Pyridine
C. Benzene
D. Naphthalene
Answer: A
Rationale: Cyclobutadiene is cyclic, planar, and conjugated but has 4 pi electrons (4n
where n=1), making it highly unstable and anti-aromatic.
