Chapter 7 - Chapter 7:Delocalized Electrons Localized...

Info iconThis preview shows pages 1–4. 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
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Chapter 7:Delocalized Electrons Localized electrons belong to a single atom or are confined to a bond between two atoms. 2 3 CH = CH- CH Delocalized electrons neither belong to a single atom nor are confined to a bond between two atoms, but are shared by three or more atoms. 7.1 BENZENE Benzene’s structure puzzles scientists. It had a molecular formula of C 6 H 6 . It was very stable. It didn’t undergo the addition reactions of alkenes. A single substitution created one (monosubstituted) product. Another substitution created three (disubstituted) products. C 6 H 6 C 6 H 5 X C 6 H 4 X 2 + C 6 H 4 X 2 + C 6 H 4 X 2 For every two hydrogens that are missing from the general molecular formula, CnH2n+2, a hydrocarbon has either a bond or a ring. π Benzene has a degree of unsaturation of four (Section 3.1). Benzene can either be an acyclic compound with 4 bonds, a tricyclic compound with one bond, or a tetrcyclic compound. π π In 1865, Friedrich Kekulé proposed that benzene was not a single compound. Benzene was a mixture of two compounds in rapid equilibrium. Localized Electrons Replace H with X Replace H with X CH 3 CH CH CH 3 CH Delocalized Electrons Rapid Equilibrium 7.2 BONDING IN BENZENE Each of benzene’s carbons is sp 2 hybridized. An sp 2 carbon has bond angle of 120°. Thus, benzene is a planar molecule. The p orbitals are close enough for side-to-side overlap. As a result, overlapping p orbitals form a continuous doughnut-shaped cloud of electrons above and below the plane of benzene ring. The six electrons are delocalized – they roam freely within the doughnut-shaped clouds that lie over π and under the ring of carbons. 7.3 RESONANCE CONTRIBUTORS AND RESONANCE HYBRID The approximate structure with localized electrons is called a resonance contributor , resonance structure, or contributing resonance structure. The actual structure with delocalized electrons is called resonance hybrid . The following are resonance contributors of benzene: OR NOTE: Electron delocalization is shown by double headed arrows! Equilibrium is shown by two arrows pointing in opposite directions! The following is the resonance hybrid of benzene: 7.4 HOW TO DRAW RESONANCE CONTRIBUTORS Delocalized electrons result from a p orbital overlapping the p orbitals of more than one adjacent atom. RULES FOR DRAWING RESONANCE CONTRIBUTORS 1. Only move electrons! Never move atoms! 2. Only electrons and lone-pair electrons move! π 3. The total number of electrons in the molecule does not change. Each of the resonance contributors must have the same net charge!...
View Full Document

This note was uploaded on 04/10/2008 for the course CH 3412 taught by Professor Pohlmann during the Spring '08 term at Saint Mary's University Texas.

Page1 / 11

Chapter 7 - Chapter 7:Delocalized Electrons Localized...

This preview shows document pages 1 - 4. Sign up to view the full document.

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