EAS mechanism

MS 913 - Benzene EAS Reactions, EDG/EWG, and ortho/meta/para Directors Submitted by Matt on August 6, 2011.

Textbook and Chapter: Carey and Giuliano 8th Ed. (2010), Chapter 12

Keywords: EAS mechanism, EDG and EWG, Friedel-Crafts

Description: Covers electrophilic aromatic substitution (EAS) reactions in detail.

It includes many, many resonance exercises that show why:

  • Electron donating groups (EDG) are ortho-para directors
  • Electron withdrawing groups (EWG) are meta-directors
  • Pyrrole undergoes EAS at C-2 and not C-3
  • Pyridine undergoes EAS at C-3 and not C-2 or C-4
  • Naphthalene undergoes EAS at C-1 and not C-2

Total Problems: 11

Problem # 722

Show how to prepare vinyl benzene from benzene.

Problem # 596

Indicate the eletrophile formed by each set of reagents/conditions below.

Problem # 595
 

Phenol can be prepared from benzene and hydrogen peroxide in the presence of a really strong acid. Propose a mechanism for this reaction.

Problem # 594
 

A chemist tried to prepare compound A from benzene via Friedel-Crafts alkylation and instead produced compound B.

Why did this happen? How could the chemist prepare compound A?

Problem # 593

a) Rationalize the relative stabilities of the cation species below.

 

b) Pyridine undergoes eletrophilic substitution at C-3. Let's compare the resonance forms of EAS carbocation intermediates to see why this is the case. Consider part a) in your explanation.

Problem # 592

Naphthalene undergoes eletrophilic substitution at C-1.

Why is this the case, even though substitution at C-2 gives more resonance forms?

Problem # 591

Pyrrole undergoes eletrophilic aromatic substitution at C-2. Let's compare the resonance forms of EAS carbocation intermediates to see why this is the case. What do you think? Why C-2 and not C-3?

Problem # 590

-NO2 is an EWG and a meta director. Let's draw an EAS reaction's cyclohexadienyl cation intermediates to demonstrate why this is true. I've started you off.

What's good about meta? What's bad about ortho/para?

Problem # 589

 -OR is an EDG and an ortho-para director. Let's draw an EAS reaction's cyclohexadienyl cation intermediates to demonstrate why this is true. I've started you off.

What's good about ortho/para? What's bad about meta?