Section 13 - Conjugated Systems and UV Spectroscopy
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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:
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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