functional group chemistry

Question 1

What happens when an aromatic ring already has a group attached?

Answer 1

The aromatic ring acts as a nucleophile, and its reactivity depends on the electron density distribution caused by the substituent.

Question 2

What are the positions on a substituted aromatic ring?

Answer 2

The positions are:

Ortho: Adjacent to the substituent.
Meta: One carbon away from the substituent.
Para: Directly opposite the substituent.

Question 3

What is an electron-donating group (EDG)?

Answer 3

EDGs add electron density to the aromatic ring, particularly at the ortho and para positions, increasing reactivity at those sites.

Question 4

What is an electron-withdrawing group (EWG)?

Answer 4

EWGs remove electron density from the aromatic ring, making the meta position more reactive and the ortho and para positions less reactive.

Question 5

How do you determine if a group is electron-donating or electron-withdrawing?

Answer 5

This is determined by the balance of two factors:

Inductive Effect: Polarization of bonds due to electronegativity differences.
Resonance Effect: Movement/delocalization of electrons in the molecule.

Question 6

What is the significance of the carbocation formed during electrophilic aromatic substitution?

Answer 6

EDG stabilizes the carbocation formed at ortho and para positions, making these positions more favorable.
EWG destabilizes the carbocation at ortho and para positions, favoring the meta position.

Question 7

How do halogens behave as substituents on aromatic rings?

Answer 7

Halogens are electron-withdrawing due to their electronegativity, making the ring less reactive. However, they direct substitution to the ortho and para positions due to resonance effects.

Question 8

What is the general effect of substituents on aromatic ring reactivity?

Answer 8

Electron-Donating Groups (EDG): Make the ring more reactive and favor ortho/para substitution.
Electron-Withdrawing Groups (EWG): Make the ring less reactive and favor meta substitution.

Question 9

What mechanism explains these reactivity patterns?

Answer 9

Electrophilic Aromatic Substitution (EAS) involves the formation of a carbocation intermediate. The stability of this intermediate determines the site of substitution.

Question 10

Can you summarize the role of electron-donating and electron-withdrawing groups?

Answer 10

EDGs: Stabilize carbocations, increase ring reactivity, and favor ortho/para substitution.
EWGs: Destabilize carbocations, decrease ring reactivity, and favor meta substitution.