Aromaticity - Lecture notes 11 PDF

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Summary

basic of aromicity. Critria for a compound to be aromatic. Anti and non aromatic compounds....

Description

Aromaticity. The Huckel (4n + 2) 1t Rule To be aromatic a compound must conform to all the following criteria : 1. The molecule should be cyclic and planar 2. There should be a p-orbital on every atom of an aromatic ring, i.e., cyclic molecule is fully conjugated. 3. The cyclic arrangement of p-orbitals in an aromatic compound must contain (4n + 2) 7telectrons, where n is an integer (0, 1, 2, 3 .4,5,etc). In other words, aromatic compounds have 2, 6, 10, 14, 18, ... pi (∏) electrons. OH

Benzene

Phenol

CH3

Toluene

Biphenyl

Aromaticity: The special characteristics of aromatic compounds are called aromaticity. 1. Special unsaturation 2. Undergoes electrophilic substitution rather than addition.

Anti-Aromatic: Cyclic and planar compounds that have conjugated pi bond but contain 4n pi-electrons, where n is an integer (0, 1, 2, 3 .4,5,etc) are called anti-aromatic compounds.

1,3-Cyclobutadiene (Anti-aromatic)

Non-Aromatic: Cyclic compounds that have conjugated pi bond but not planar and do not follow Huckel rule’s are called Non-aromatic compounds.

1,2,5,7-Cyclooctatetraene (Non-aromatic) This compound is not cyclic and does not follow Huckel’s rule....