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Section 13 - Conjugated Systems and UV Spectroscopy

Conjugated Systems and UV Spectroscopy - Section 13 of Organic Chemistry Notes is 19 pages in length (page 13-1 through page 13-19) and covers ALL you'll need to know on the following lecture/book topics:

SECTION 13 – Conjugated Systems and UV-Spectroscopy

13-1 -- Three Classes of Dienes
  · Conjugated Dienes
  · Cumulenes (“Allenes”)
  · Other, Isolated Double Bonds (d.b.’s)
13-1 -- Relative Stabilities of Dienes
  · Heats of Formation (ΔH°f) – Values and Comparisons
13-2 -- Double Bonds of Conjugated Dienes
  · Prefer to be Coplanar
  · “Cisoid” or S-Cis Conformation
  · “Transoid” or S-Trans Conformation
  · Resonance Description
13-4 -- Reactions of Dienes – Summary (3 Main Reactions)
13-4 -- Additions of Electrophiles
  · Markovnikov Addition
  · 1,2-Addition Product vs. 1,4-Addition Product
  · Mechanism of the Reaction
  · Equilibration via an SN1 Mechanism
  · Kinetic Control vs. Thermodynamic Control
13-6 -- Addition of Halogens (X2)
  · Also Gives 1,2-Addition Product and 1,4-Addition Product
  · Mechanism of the Reaction
  · With Br2, Mechanism May Go via a Bromonium Ion Intermediate
13-6 -- The Diels-Alder Reaction (Huge Topic!)
  · General Form of the Reaction
  · The Diene (4e- Component) and the Dienophile (2e- Component)
  · Diene Conformation Must be S-Cis
  · Diels-Alder Reaction is Concerted – All Bonding Changes Occur Simultaneously
  · Formation of 1 New π-Bond and 2 New σ-Bonds
  · Diels-Alder Reaction is Stereospecific
  · Formation of Products that are Enantiomers and/or Meso Compounds
  · Electronic Requirements of the Diels-Alder Reaction
  · The “Endo Effect”
  · Endo Substituents vs. Exo Substituents
13-13 -- Ultraviolet-Visible (UV-Vis) Spectroscopy
  · Excitation of Electrons (e-‘s)
  · Promoting e- from Bonding Molecular Orbital (MO) or Non-Bonding MO
  · Bonding Molecular Orbitals (MO’s) and Antibonding MO’s
  · Non-Bonding MO’s
  · The “Excited State”
  · Lowest-Energy Transitions (the HOMO-LUMO gap, and ΔE)
  · Conjugated π-Systems
  · The Electromagnetic Spectrum and Complimentary Colors
  · A Typical UV-Vis Spectrum
  · Beer’s Law (A = Є . c . b)
  · The Extinction Coefficient (Є) = “Molar Absorptivity”
  · λmax Increases with Increasing Conjugation
  · Delocalization of π-MO’s
  · Systems with Non-Bonding e-‘s and π-Electrons
  · π --> π* Transitions vs. n --> π* Transitions
  · 3 General Rules for λmax
  · What are Chromophores?

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