Question 1

Which of the following statements about benzene is/are true?
I) It is less reactive than acyclic trienes.
II) All of the carbon-carbon bond lengths are the same.
III) The most stable conformer is a puckered chair.

Accepted Answer

I and II

Question 2

Which of the following statements about molecular orbitals is correct?
I) The number of molecular orbitals in a system is greater than the number of atomic orbitals combined.
II) Non-bonding orbitals are the same energy as a lone p orbital.
III) The higher energy orbitals generally have fewer nodal surfaces.

Accepted Answer

II only

Question 3

Which of the following best describes the aromaticity of cyclopropenyl cation ($$C_3H_3^+$$)?

Accepted Answer

It is aromatic because it has 2 $$\pi$$ electrons and a fully filled bonding molecular orbital.

Question 4

Which of the following is the correct order of reactivity for electrophilic aromatic substitution (EAS) for the following compounds?
I) Benzene
II) Toluene ($$C_6H_5CH_3)
$$III) Nitrobenzene ($$C_6H_5NO_2)$$

Accepted Answer

II \u003e I \u003e III

Question 5

A student attempts to nitrate benzene, then brominate, then chlorinate. Which of the following best describes the expected major product sequence?

Accepted Answer

The nitro group directs the next substitution to the meta position, so bromine will add meta to NO$$_2$$, and chlorine will add ortho/para to Br.

Question 6

Which of the following best represents the electrophile in the sulfonation of benzene?

Accepted Answer

$$SO_3$$^+$$

Question 7

Which of the following compounds is the LEAST basic?
A) Aniline ($$C_6H_5NH_2)
B) $$Pyridine
C) Nitroaniline
D) Anisole ($$C_6H_5OCH_3)$$

Accepted Answer

Nitroaniline

Question 8

Which of the following best explains why all carbon-carbon bond lengths in benzene are equal?

Accepted Answer

Benzene has resonance structures that delocalize the $$\pi$$ electrons over all six carbons.

Question 9

Which of the following is a requirement for a compound to be aromatic?

Accepted Answer

It must be cyclic, planar, fully conjugated, and have $$4n+2$$ $$\pi$$ electrons.

Question 10

A chemist wants to synthesize p-bromonitrobenzene from benzene. Which sequence gives the best yield?

Accepted Answer

Nitration, then bromination

Question 11

Which of the following best describes the intermediate formed during the nitration of chlorobenzene?

Accepted Answer

A resonance-stabilized arenium ion with the nitro group at the ortho or para position relative to chlorine.

Question 12

Which of the following best explains why the cyclopentadienyl anion ($$C_5H_5^-) is $$aromatic?

Accepted Answer

It is planar, cyclic, fully conjugated, and has 6 $$\pi$$ electrons.

Question 13

Which of the following is the most stable radical?
A) Benzyl radical
B) Methyl radical
C) Ethyl radical
D) Vinyl radical

Accepted Answer

Benzyl radical

Question 14

Which of the following best describes the Frost circle diagram for the cyclopropenyl cation ($$C_3H_3^+$$)?

Accepted Answer

It has one filled bonding molecular orbital and two empty anti-bonding orbitals, indicating stability.

Question 15

Which of the following best represents a conjugated $$\pi-$$system?

Accepted Answer

A system with alternating single and double bonds allowing $$\pi$$ electron delocalization.

Question 16

In the electrophilic aromatic substitution of toluene, which position is most favored for substitution and why?

Accepted Answer

Ortho and para positions, because the methyl group is an electron-donating group that stabilizes the intermediate carbocation.

Question 17

Which of the following best explains why nitroaniline is less basic than aniline?

Accepted Answer

The nitro group is electron-withdrawing and decreases the electron density on the nitrogen atom.

Question 18

Which of the following is true about the molecular orbital diagram of the allyl cation ($$C_3H_5^+$$)?

Accepted Answer

It has two $$\pi$$ electrons occupying the lowest energy bonding orbital.

Question 19

A patient is exposed to benzene in an industrial accident. Which property of benzene is most relevant to its toxicity?

Accepted Answer

Its aromatic stability allows it to persist in biological systems and disrupt cellular processes.

Organic Chemistry Exam II Study Guidance: Aromaticity, Molecular Orbitals, Nomenclature, Synthesis, and Mechanisms

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