Aromatic substitution

Question 1

If ‘X’ is an electron donor what will the relative speed of substitution be?

Answer 1

Fast

Question 2

If ‘X’ is an electron withdrawing group, what will the relative speed of substitution be?

Answer 2

Slow

Question 3

Why is substitution faster with electron donating groups?

Answer 3

More electron density, better nucleophile

Question 4

Why is substitution slower with electron withdrawing groups?

Answer 4

Less electron density, worse nucleophile

Question 5

What positions are activated by resonance?

Answer 5

Ortho and para

Question 6

What positions are deactivated by resonance, and so where does substitution occur?

Answer 6

Deactivates ortho and para, sub. at meta

Question 7

Which effects are stronger, mesomeric or induction? Why?

Answer 7

Mesomeric. Resonance structures are more stable.

Question 8

In terms of NMR spec and chemical shift, why do electron donating groups increase substitution at ortho and para positions?

Answer 8

Resonance structure cause electron density to be shared across ortho and para positions. This creates more shielding, decreasing chemical shift and making these positions more nucleophilic.

Question 9

Draw the mechanism for the activation/deactivation by resonance.

Answer 9

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