Question 1

Which of the following statements best explains why all C–C bonds in benzene are of equal length?

Accepted Answer

The p-electrons in benzene are delocalized across all six carbons, resulting in bond lengths that are intermediate between single and double bonds.

Question 2

Which of the following compounds is aromatic according to Hückel’s rule?

Accepted Answer

Benzene ($C_6H_6$)

Question 3

The heat of hydrogenation ($\Delta H^\circ_{hydro}$) for benzene is much less negative than expected for a hypothetical cyclohexatriene. What does this indicate about benzene?

Accepted Answer

Benzene is more stable due to aromatic stabilization energy.

Question 4

Which of the following is the correct criterion for a molecule to be aromatic?

Accepted Answer

Cyclic, planar, fully conjugated, and contains $(4n+2)$ $\pi$-electrons.

Question 5

Which of the following best describes the molecular orbital (MO) picture of benzene?

Accepted Answer

All six $\pi$ electrons occupy bonding MOs, and no electrons occupy antibonding MOs.

Question 6

Which of the following is the correct IUPAC name for the compound commonly known as toluene?

Accepted Answer

Methylbenzene

Question 7

A compound is cyclic, planar, fully conjugated, and contains 8 $\pi$-electrons. According to Hückel’s rule, this compound is:

Accepted Answer

Antiaromatic

Question 8

Which of the following is a heterocyclic aromatic compound?

Accepted Answer

Furan

Question 9

Which of the following statements about the reactivity of benzene is correct?

Accepted Answer

Benzene undergoes substitution reactions with bromine ($Br_2$) in the presence of $FeBr_3$.

Question 10

Which of the following IR absorption bands is characteristic of the Csp2–H stretch in aromatic compounds?

Accepted Answer

$3150-3000$ cm$^{-1}$

Question 11

Which of the following best explains why cyclooctatetraene is not aromatic?

Accepted Answer

It is not planar and fails to delocalize $\pi$ electrons.

Question 12

Which of the following is the correct name for a benzene ring with a methyl group at position 1 and a nitro group at position 3?

Accepted Answer

m-nitrotoluene

Question 13

Which of the following ions is aromatic and why?

Accepted Answer

Cyclopropenyl cation, because it is cyclic, planar, fully conjugated, and has 2 $\pi$-electrons.

Question 14

Which of the following best describes the difference between phenyl and benzyl groups?

Accepted Answer

Phenyl is $C_6H_5-$, while benzyl is $C_6H_5CH_2-$.

Question 15

Which of the following is NOT a criterion for aromaticity according to Hückel’s rule?

Accepted Answer

The molecule must contain only carbon atoms.

Question 16

Which of the following best explains why cyclobutadiene is antiaromatic?

Accepted Answer

It is cyclic, planar, fully conjugated, and has 4 $\pi$-electrons.

Question 17

Which of the following is the correct $^1$H NMR chemical shift range for aryl hydrogens in benzene?

Accepted Answer

$6.5-8.0$ ppm

Question 18

Which of the following is a real-life application of aromaticity in medicine?

Accepted Answer

Aromatic heterocycles such as pyridine and indole are found in many pharmaceuticals and natural products.

Benzene and Aromatic Compounds: Structure, Stability, and Aromaticity

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