Study guides › C/P › Organic Chemistry
Aromatic Compounds & Amines
Aromatic rings resist addition and prefer substitution, and amines are the organic bases of biology. You will apply Hückel's rule, predict electrophilic substitution products from directing effects, make and rank amines, and recognize heterocycles and nucleophilic aromatic substitution.
Study this chapter in PrepMed (free)
What this chapter covers
- Aromaticity & Hückel's Rule. Aromatic stability explains why benzene substitutes instead of adding, and it is the first thing to check in any ring question.
- Electrophilic Aromatic Substitution. EAS is the signature reaction of benzene. Know the electrophile in each variant and the limits of Friedel–Crafts.
- Directing Effects of Substituents. Predicting where the second group goes, and how fast, is one of the most tested skills in aromatic chemistry.
- Amines: Basicity & Preparation. Amines are the main organic bases on the MCAT. Rank their basicity and know the routes that make them.
- Heterocycles & Nucleophilic Aromatic Substitution. Heterocycles fill biochemistry, and SNAr shows how a ring can act as an electrophile when it has the right groups.
Key points to know
- Aromatic = cyclic + planar + fully conjugated + 4n + 2 π electrons
- Antiaromatic = same but 4n π electrons (very unstable)
- EAS: arene attacks E⁺, arenium ion forms (slow), H⁺ is lost, ring is aromatic again
- NO₂⁺ from HNO₃/H₂SO₄; halogens need FeX₃ or AlX₃
- Donors activate and direct ortho/para; withdrawers deactivate and direct meta
- Halogens deactivate but direct ortho/para
- Classify amines by carbons on N; tert-butylamine is primary
- Basicity: alkylamine > ammonia > pyridine > aniline > amide (amide essentially not basic)
Try a practice question
Hückel's rule says a planar, cyclic, fully conjugated ring is aromatic when it has
- 4n π electrons
- 4n + 2 π electrons
- 4n + 2 σ electrons
- an even number of ring carbons
Show the answer
B. Aromatic rings have 2, 6, 10, ... π electrons. A 4n count in a planar conjugated ring is antiaromatic. Sigma electrons and the carbon count are irrelevant to the rule.
Common questions
What does this chapter cover?
Aromatic Compounds & Amines covers Aromaticity & Hückel's Rule, Electrophilic Aromatic Substitution, Directing Effects of Substituents, Amines: Basicity & Preparation, Heterocycles & Nucleophilic Aromatic Substitution.
What should I know first?
Aromatic = cyclic + planar + fully conjugated + 4n + 2 π electrons Antiaromatic = same but 4n π electrons (very unstable) EAS: arene attacks E⁺, arenium ion forms (slow), H⁺ is lost, ring is aromatic again
24 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.