Lecture 4 - 282 Aromaticity and Benzene Intro to EAS...

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282 Lecture 4 – September 16, 2011 Aromaticity and Benzene Intro to EAS
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2 Benzene – C 6 H 6 v the six π electrons are delocalized – they roam freely within the doughnut- shaped clouds that lie over and under the ring of carbon atoms v Friedrich Kekule s proposed structure of benzene (1865) was very nearly correct v the C-C bonds in benzene have the same length, shorter than a typical single bond but longer than a typical double bond v compounds with unusually large resonance energies, like benzene, are called aromatic compounds
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3 Aromatic Compounds - criteria - To be classified as aromatic, a compound must meet both of the following criteria: 1. It must have an uninterrupted cyclic cloud of π electrons (called a π could) above and below the plane of the molecule v the molecule must be cyclic v every atom in the ring must have a p orbital v the molecule must be planar 2. The π could must contain an odd number of pairs of π electrons v Huckel s rule ( 4n+2 ) π electrons where n – any whole number v an aromatic compound must have 2 ( n = 0), 6 ( n = 1), 10 ( n = 2), 14 ( n = 3), 18 ( n = 4), and so on π electrons
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Lecture 4 - 282 Aromaticity and Benzene Intro to EAS...

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