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Questions and Answers
Which of the following best describes the resonance effect?
Which of the following best describes the resonance effect?
- The steric hindrance caused by bulky groups in a molecule.
- The inductive effect produced by electronegative atoms.
- The polarity produced in a molecule by the interaction of two π-bonds or between a π-bond and a lone pair of electrons on an adjacent atom. (correct)
- The effect of sigma bonds on the stability of a molecule.
In a positive resonance effect (+R effect), the transfer of electrons occurs towards the atom or substituent group attached to the conjugated system.
In a positive resonance effect (+R effect), the transfer of electrons occurs towards the atom or substituent group attached to the conjugated system.
False (B)
What are the two types of resonance effects?
What are the two types of resonance effects?
Positive Resonance Effect (+R effect) and Negative Resonance Effect (-R effect)
In aniline, the positive resonance effect (+R effect) increases electron density at certain positions in the ______ ring.
In aniline, the positive resonance effect (+R effect) increases electron density at certain positions in the ______ ring.
Match the following groups with their corresponding resonance effect:
Match the following groups with their corresponding resonance effect:
Which of the following substituents would exhibit a -R effect?
Which of the following substituents would exhibit a -R effect?
Resonance structures always contribute equally to the overall structure of a molecule.
Resonance structures always contribute equally to the overall structure of a molecule.
Explain why the resonance structure of a molecule with a carbon atom having an incomplete octet is considered a less important contributor.
Explain why the resonance structure of a molecule with a carbon atom having an incomplete octet is considered a less important contributor.
In comparing resonance structures, which factor generally contributes to greater stability?
In comparing resonance structures, which factor generally contributes to greater stability?
In nitrobenzene, the transfer of electrons during resonance is ______ the nitro group, demonstrating a -R effect.
In nitrobenzene, the transfer of electrons during resonance is ______ the nitro group, demonstrating a -R effect.
Flashcards
Resonance Effect
Resonance Effect
Polarity produced by interaction of two π-bonds or a π-bond and lone pair on adjacent atom.
Positive Resonance Effect (+R effect)
Positive Resonance Effect (+R effect)
The transfer of electrons is away from an atom or substituent group attached to the conjugated system.
Negative Resonance Effect (-R effect)
Negative Resonance Effect (-R effect)
The transfer of electrons is towards the atom or substituent group attached to the conjugated system.
+R effect groups
+R effect groups
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-R effect groups
-R effect groups
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Study Notes
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Resonance structures of CH3COO show the movement of electrons with curved arrows.
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First, write the structure and put unshared pairs of valence electrons on appropriate atoms.
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Then draw the arrows one at a time moving the electrons to get the other structures.
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Resonance structures of CH2=CH-CHO indicate relative stability of the contributing structures.
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Stability: I > II > III
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I: Most sable, more number of covalent bonds, each carbon and oxygen atom has an octet and no separation of opposite charge.
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II: Negative charge on more electronegative atom and positive charge on more electropositive atom. III: Does not contribute as oxygen has positive charge and carbon has negative charge, hence least stable.
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Two structures are less important contributors as they involve charge separation.
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Additionally, structure I contains a carbon atom with an incomplete octet.
Resonance Effect
- Resonance is the polarity in a molecule by interaction of two π-bonds or between a π-bond and lone pair of electrons on an adjacent atom.
- The effect is transmitted through the chain and designated as the R or M effect.
Positive Resonance Effect (+R effect)
- The transfer of electrons is away from an atom or substituent group attached to the conjugated system.
- The electron displacement creates high electron densities in certain molecule positions.
- Aniline demonstrates this effect.
Negative Resonance Effect (-R effect)
- The transfer of electrons goes toward the atom or substituent group attached to the conjugated system.
- A depiction of this effect is within nitrobenzene.
- Atoms or substituent groups represent +R or -R electron displacement effects.
- +R effect: - halogen, -OH, -OR, -OCOR, -NH2, -NHR, -NR2, -NHCOR,
- -R effect: - COOH, -CHO, >C=O, -CN, -NO2
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