$$\text{Bond length} \propto \frac{1}{\text{Bond order}}$$

Benzene ($$\text{C}_6\text{H}_6)$$

Question 1

Which statement best describes the electron density in the π bonds of a conjugated 1,3-diene such as buta-1,3-diene?

Accepted Answer

The electron density is delocalized across all four carbon atoms due to overlapping p orbitals.

Question 2

What is the hybridization of each carbon atom in a conjugated 1,3-diene?

Accepted Answer

sp2

Question 3

Why is the middle C–C σ-bond in a conjugated diene shorter than a typical sp3–sp3 σ-bond?

Accepted Answer

Because the p orbitals on the adjacent carbons overlap, increasing bond order and electron delocalization.

Question 4

Which of the following best explains the stability of the allylic carbocation?

Accepted Answer

The positive charge and π electron density are delocalized over three adjacent sp2-hybridized carbons via resonance.

Question 5

Which resonance structure is the major contributor to the resonance hybrid of an allylic carbocation?

Accepted Answer

The structure where every atom has an octet and the positive charge is on the more electronegative atom.

Question 6

Given the following carbocations, which is most stable?

Accepted Answer

Tertiary carbocation

Question 7

Which of the following is NOT a requirement for resonance to occur?

Accepted Answer

Movement of σ-bonds

Question 8

In the resonance structure of acetate ion, which atom should carry the negative charge in the major contributor?

Accepted Answer

The oxygen atom

Question 9

Which of the following best describes the bond angle in an sp2-hybridized carbon atom?

Accepted Answer

$$120^\circ$$

Question 10

Which scenario would NOT result in resonance?

Accepted Answer

A single bond between two sp3-hybridized carbons

Question 11

Which equation correctly represents the relationship between bond order and bond length in conjugated systems?

Accepted Answer

$$	ext{Bond length} \propto \frac{1}{	ext{Bond order}}$$

Question 12

Which of the following statements about resonance hybrids is correct?

Accepted Answer

The resonance hybrid is an average of all possible resonance structures, with major contributors resembling the hybrid most closely.

Question 13

Which of the following best explains why electron delocalization requires overlapping p orbitals?

Accepted Answer

Overlapping p orbitals allow electrons to move freely across adjacent atoms, creating delocalized π electron density.

Question 14

Which of the following is a real-world example of a molecule with conjugated double bonds?

Accepted Answer

Benzene ($$	ext{C}_6	ext{H}_6)$$

Question 15

Which of the following best describes the effect of resonance on the stability of carbocations?

Accepted Answer

Resonance increases carbocation stability by delocalizing the positive charge over multiple atoms.

Question 16

Which of the following is true about the resonance structures of benzene?

Accepted Answer

Benzene has two resonance structures with alternating double bonds.

Question 17

Which of the following is a characteristic of a resonance major contributor?

Accepted Answer

Every atom has an octet and there are fewer charges.

Question 18

Which of the following best describes the hybridization and bond angle of the carbon atom in ethylene ($$	ext{CH}_2=	ext{CH}_2$$)?

Accepted Answer

sp2 hybridized, $$120^\circ$$ bond angle

Question 19

Which of the following best explains why the allylic carbocation is nearly as stable as a secondary carbocation?

Accepted Answer

The positive charge is stabilized by resonance delocalization across three adjacent sp2-hybridized carbons.

Conjugation, Resonance, and Dienes: Structure and Stability

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