Chapter 21-1

Chapter 21-1 - CHEM 262 Wei You Chapter 21. Benzene and the...

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11 CHEM 262 Wei You Chapter 21. Benzene and the Concept of Aromaticity (1)
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22 Early Proposed Structure of Benzene C6H6
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33 Structure of Benzene C H C H C H C H C H C H C C C C C C H H H H H H http://en.wikipedia.org/wiki/Friedrich_August_Kekul%C3%A9_von_Stradonitz Problem : did not account for the unusual chemical reactivity of benzene
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140 pm 140 pm 140 pm 140 pm 140 pm 140 pm 146 pm 134 pm All C—C bond distances = 140 pm 44
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55 sp 2 - sp 2 σ σ sp 2 -1 s 109 pm 120° 120° 120° 139 pm C C C C C C H H H H H H The Resonance Model
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Benzene - Stability 66
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Concept of Aromaticity The underlying criteria for aromaticity were recognized in the early 1930s by Erich Hückel, based on molecular orbital (MO) calculations To be aromatic, a compound must be cyclic have one empty p orbital on each atom of the ring be planar or nearly planar so that there is continuous or nearly continuous overlap of all p orbitals of the ring fit the Huckel Rule of having (4 n + 2) pi electrons in the ring 77
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This note was uploaded on 06/12/2010 for the course CHEM 261 taught by Professor Austell during the Spring '08 term at UNC.

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Chapter 21-1 - CHEM 262 Wei You Chapter 21. Benzene and the...

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