BackAromatic Compounds, Electrophilic Aromatic Substitution, and Aromaticity
Study Guide - Smart Notes
Tailored notes based on your materials, expanded with key definitions, examples, and context.
Aromatic Compounds and Nomenclature
Naming Aromatic Compounds
Aromatic compounds are cyclic, planar molecules with a conjugated system of pi electrons that follow Hückel's rule. Correct nomenclature is essential for clear communication in organic chemistry.
Key Point 1: The IUPAC system names aromatic compounds based on the position and type of substituents on the benzene ring.
Key Point 2: Numbering should provide the lowest possible numbers to the substituents.
Example: The compound with nitro groups at positions 2 and 6 on a benzene ring is named 2,6-dinitroanisole.
Electrophilic Aromatic Substitution (EAS)
Mechanism and Types of Aromatic Reactions
Electrophilic aromatic substitution is a fundamental reaction in organic chemistry, where an electrophile replaces a hydrogen atom on an aromatic ring.
Key Point 1: EAS involves the attack of an aromatic ring on an electrophile, forming a carbocation intermediate (arenium ion).
Key Point 2: Common EAS reactions include nitration, sulfonation, halogenation, and Friedel-Crafts alkylation/acylation.
Example: The reaction of benzene with a Lewis acid and an acyl chloride is a Friedel-Crafts acylation, a type of EAS.
General equation for EAS:
Aromaticity and Aromatic Compounds
Criteria for Aromaticity
Aromaticity is a property of cyclic, planar molecules with a fully conjugated pi electron system that follows Hückel's rule ( pi electrons, where n is an integer).
Key Point 1: The molecule must be cyclic and planar.
Key Point 2: The molecule must have a conjugated system of pi electrons.
Key Point 3: The molecule must contain pi electrons (Hückel's rule).
Example: Benzene (6 pi electrons) and pyridine (6 pi electrons) are aromatic, while cyclobutadiene (4 pi electrons) is antiaromatic.
Compound | Aromatic? | Reason |
|---|---|---|
I | No | Not fully conjugated |
II | No | Not planar or not conjugated |
III | No | Does not follow Hückel's rule |
IV | Yes | Planar, conjugated, 6 pi electrons |
V | No | Not aromatic |
Additional info: Aromatic compounds are especially stable due to delocalization of electrons. Non-aromatic and antiaromatic compounds do not possess this extra stability.
----------------------------------------
