lecture 21.1

lecture 21.1 - 21-21-1Organic Organic H BrownWilliam H...

Info iconThis preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 21-21-1Organic Organic ChemistryChemistryWilliam H. BrownWilliam H. BrownChristopher S. FooteChristopher S. FooteBrent L. IversonBrent L. Iverson21-21-2Benzene andBenzene andand the Concept ofand the Concept ofAromaticityAromaticityChapter 21Chapter 2121-21-3Benzene - Kekulé Benzene - Kekulé ◆The first structure for benzene was proposed by August Kekulé in 1872◆This structure, however, did not account for the unusual chemical reactivity of benzeneCHCHCHCHCHCHCCCCCCHHHHHH21-21-4Benzene - Resonance ModelBenzene - Resonance Model◆The concepts of hybridization of atomic orbitals and the theory of resonance, developed in the 1930s, provided the first adequate description of benzene’s structure•the carbon skeleton is a regular hexagon•all C-C-C and H-C-C bond angles 120°sp2-sp2σσσπ2-1 σ109 pm120120120139 pmCCCCCCHHHHHH21-21-5Benzene - The Resonance ModelBenzene - The Resonance Model◆The pi system of benzene•(a) the carbon framework with the six 2porbitals•(b) overlap of the parallel 2porbitals forms one torus above the plane of the ring and another below it•this orbital represents the lowest-lying pi-bonding molecular orbital21-21-6Benzene - Resonance Benzene - Resonance ◆We often represent benzene as a hybrid of two equivalent Kekulé structures•each makes an equal contribution to the hybrid and thus the C-C bonds are neither double nor single, but something in betweenBenzene as a hybrid of two equivalentcontributing structures21-...
View Full Document

This note was uploaded on 03/30/2008 for the course CHEM 262 taught by Professor Forbes during the Spring '08 term at UNC.

Page1 / 19

lecture 21.1 - 21-21-1Organic Organic H BrownWilliam H...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online