RESONANCE EFFECT

The resonance structures

• Differ only in the arrangement of electrons

• Differ in number of paired and unpaired electrons

• Differ largely in their energy content

• Do not lie in the same plane

Which compound has a conjugated system?

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Answer explanation

Conjugation occurs when pairs of π systems are separated by one σ bond and aligned properly; the pair of π systems may be two π bonds or a π bond and an atomic orbital

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

Which compound has a conjugated system?

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Answer explanation

conjugation occurs when pairs of π systems are separated by one σ bond and aligned properly; the pair of π systems may be two π bonds or a π bond and an atomic orbital (usually a p orbital) of the correct symmetry

Tags

NGSS.HS-PS1-1

Which is a defective resonance contributor of the following cation?

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Answer explanation

The cation is a protonated ethanamide. Resonance contributors should be different only in the locations of electrons (as in (a)-(c)), but the distribution of hydrogens is different in (d)

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

Which of (a)-(d) is the most important resonance contributor for the following?

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Answer explanation

The negative charge of this enolate is more effectively accommodated by the carbonyl oxygen of the keto group than by that of the ester group.

Tags

NGSS.HS-PS1-2

Which is the most important resonance contributor for the following?

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Answer explanation

The negative charge is better accommodated by the O (more electronegative) than by C, and (c) (with more bonds) is more stable than (d).

Tags

NGSS.HS-PS1-2

Which compound does not have a conjugated system?

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Answer explanation

the two π bonds are separated by two σ bonds with an intervening tetrahedral carbon.

Tags

NGSS.HS-PS1-1

Which compound does not have a conjugated system?

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Answer explanation

The negative carbon in (a) and the oxygens in (b) and (c) bearing lone pairs in p orbitals can conjugate with the double bonds. A tetrahedral carbon separates the CN triple bond and the OH lone pair in (d).

Which of the following is a defective resonance contributor of p-acetylphenol?

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Answer explanation

A resonance contributor should be a legitimate Lewis structure; structure (b) contains a negative carbon with an impossible set of bonds.

Tags

NGSS.HS-PS1-2

Which of the following is a defective resonance contributor of the acetamidinium ion?

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Answer explanation

Resonance contributors should differ only in the location of electrons, but the distribution of hydrogens is different in structure (c).

Tags

NGSS.HS-PS1-2