organic chemistry n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Organic Chemistry PowerPoint Presentation
Download Presentation
Organic Chemistry

Loading in 2 Seconds...

play fullscreen
1 / 41

Organic Chemistry - PowerPoint PPT Presentation


  • 179 Views
  • Uploaded on

Organic Chemistry. Chapter 7 - Resonance. Electron Delocalization and Resonance. Localized electrons = restricted to a particular region Delocalized electrons do not belong to a single atom or exclusively to a bond between 2 atoms. Kekule Structure. Benzene C 6 H 6

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Organic Chemistry' - arleen


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
organic chemistry

Organic Chemistry

Chapter 7 - Resonance

electron delocalization and resonance
Electron Delocalization and Resonance
  • Localized electrons = restricted to a particular region
  • Delocalized electrons do not belong to a single atom or exclusively to a bond between 2 atoms
kekule structure
Kekule Structure
  • Benzene C6H6
    • Rapid Equilibrium between 2 structures
    • Proposed by Fredrich Kekule(1865 German chemist)

Rapid Equilibrium

benzene structure
Benzene Structure
  • Kekule Structures of Benzene were accepted in the 1930’s when X-ray studies showed ALL SIX C-H bonds equal and ALL SIX C-C bonds equal!
bonding in benzene
Bonding in Benzene
  • Each C is sp2 hybridized
  • Each C has an unhybridized p orbital perpendicular to the plane of the ring
  • The 6 p orbitals overlap to form a  cloud
resonance hybrid
Resonance Hybrid
  • A compound with delocalized e- is said to have resonance
    • resonance contributor
    • resonance structure
    • contributing resonance structure
resonance hybrid1
Resonance Hybrid
  • Benzene
    • contributing resonance structures
resonance hybrids
Resonance Hybrids

Drawing resonance hybrids

  • 1) Only e- move(not atoms)
  • 2) Only  and non-bonding e- move
  • 3) Total # e- stays same(as does unpaired e-)
resonance hybrids1
Resonance Hybrids

e- can be moved only by…

 e- move toward + or toward  bond

resonance hybrids2
Resonance Hybrids

e- can be moved only by…

Nonbonding pair e- toward a  bond

resonance hybrids3
Resonance Hybrids

e- can be moved only by…

Nonbonding single e- toward a  bond

resonance hybrids4
Resonance Hybrids
  • Drawing resonance hybrids
practice drawing resonance
Practice Drawing Resonance

Practice

Practice

Practice

slide16
What makes a Resonance Structure Have Decreased Stability?
    • 1) an atom with an incomplete octet
    • 2) a negative charge that is not on the most electronegative atom
    • 3) a positive charge not on the most electropositive atom
    • 4) charge separation
examples to examine
Examples To Examine

Equal Stability

B is less stable than A

resonance energy
Resonance Energy
  • 1) The greater the predicted stability of a resonance contributor, the more it contributes to the resonance hybrid.
  • 2) The greater the number of relatively stable resonance contributors, the greater the resonance energy.
  • 3) The more nearly equivalent the resonance contributors, the greater the resonance energy.
resonance energy1
Resonance Energy

The more nearly equivalent the resonance contributors,

the greater the resonance energy

allylic cations
Allylic Cations
  • Allylic cations have delocalized e-
  • They are more stable due to resonance contributors:
benzylic cations
Benzylic Cations
  • Benzylic cations have delocalized e-
  • They are more stable due to resonance contributors:
consequences
Consequences
  • Because of the allyl and benzyl cations and radicals are more stable, some products can be formed easier.

Mechanisms Mechanisms Mechanisms

Look at how conjugation affects reactions

effects on pk a
Effects on pKa
  • Carboxylic acids are stronger acids than alcohols due to resonance effects
phenol
Phenol
  • Why is this alcohol as acidic as it is?
    • -OH is on an sp2 hybridized C
    • In phenol, some resonance contributors have a + charge on O
    • 3 of phenol’s structures have separated charges
molecular orbital theory
Molecular Orbital Theory
  • Molecular Orbital Theory can also help explain increased stability
  • READ THROUGH THIS SECTION OF THE BOOK
thermodynamic vs kinetic control
Thermodynamic vs. Kinetic Control
  • If the kinetic product and thermodynamic product differ, the major product will depend on reaction conditions.
  • If carried out at mild (low-temp) conditions, the reaction will be irreversible and the kinetic product will be favored.
  • If carried out at sufficiently vigorous (hi-temp) conditions, the reaction will be reversible and the thermodynamic product will be favored.
thermodynamic vs kinetic control1
Thermodynamic vs. Kinetic Control
  • Kinetic product and thermodynamic product:

Formed fastest

Most stable

thermodynamic vs kinetic control2
Thermodynamic vs. Kinetic Control
  • Reaction conditions control products!

Kineticproduct – low temp

Thermodynamic product – high temp

diels alder reaction

Kurt Alder

Cologne University Cologne

Otto Diels

Kiel University Kiel

Diels-Alder Reaction
  • This reaction makes new carbon carbon bonds
  • Uses a conjugated diene and a dienophile
diels alder reaction1

Kurt Alder

Cologne University Cologne

Otto Diels

Kiel University Kiel

Diels-Alder Reaction
  • Electron withdrawing groups (O or N) increases the reactivity of the dienophile and increase the reactivity

acts as an electrophile

diels alder reaction2

Kurt Alder

Cologne University Cologne

Otto Diels

Kiel University Kiel

Diels-Alder Reaction
  • 1,4 addition to a conjugated diene
diels alder stereochemistry

Kurt Alder

Cologne University Cologne

Otto Diels

Kiel University Kiel

Diels-Alder Stereochemistry
  • If a chiral center is created, equal amounts of R, S produced (racemic)
diels alder stereochemistry1

Kurt Alder

Cologne University Cologne

Otto Diels

Kiel University Kiel

Diels-Alder Stereochemistry
  • Stereospecific: cis dienophile remains cis
    • trans dienophile remains trans
diels alder examples

Kurt Alder

Cologne University Cologne

Otto Diels

Kiel University Kiel

Diels-Alder Examples
  • Dienophiles can also be C triple bond C
bicycloalkanes
Bicycloalkanes
  • Nomenclature
    • parent is the alkane of the same number of carbons as are in two rings
    • number from a bridgehead, along longest bridge back to the bridgehead, then along the next longest bridge, etc.
    • show the lengths of bridges in brackets, from longest to shortest

1

2

6

7

3

5

4