Chapter 13. Conjugated Pi Systems. Introduction. A conjugated system involves at least one atom with a p orbital adjacent to at least one p bond. e.g. Allylic Substitution and the Allyl Radical. vinylic carbons (sp 2 ). allylic carbon (sp 3 ).
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.
Allylic Substitution and the Allyl Radical
vinylic carbons (sp2)
allylic carbon (sp3)
2A.Allylic Chlorination(High Temperature)
Allylic vs vinyl bond energies:
Allylic vs vinyl activation energies:
2B.Allylic Bromination with N-Bromo-succinimide (Low Concentration of Br2)
3. The Stability of the Allyl Radical
3A.Molecular Orbital Description of the Allyl Radical
3B.Resonance Description of the Allyl Radical
The Allyl Cation
Resonance Theory Revisited
5A. Rules for Writing Resonance Structures
not resonance structures
not a proper
5B.Estimating the Relative Stability of Resonance Structures
this carbon has
this carbon has
Alkadienes and Polyunsaturated Hydrocarbons
1,3-Butadiene: Electron Delocalization
7A.Bond Lengths of 1,3-Butadiene
7B.Conformations of 1,3-Butadiene
7C.Molecular Orbitals of 1,3-Butadiene
The Stability of Conjugated
Stability due to conjugation:
9A.The Electromagnetic Spectrum
c x ℓ
A=e x c x ℓ
lmax(methanol) 242.5 nm
(e = 13,100)
9C.Absorption Maxima for Nonconjugatedand Conjugated Dienes
9D. Analytical Uses of UV–Vis Spectroscopy
Electrophilic Attack on ConjugatedDienes: 1,4 Addition
10A.Kinetic Control versus Thermodynamic Control of a Chemical Reaction
The 1,4-product is thermodynamically more stable.
The Diels–Alder Reaction: A 1,4-Cycloaddition Reaction of Dienes
11A.Factors Favoring the Diels–AlderReaction
11B.Stereochemistry of the
The Diels–Alder reaction is stereospecific: The reaction is a syn addition, and the configuration of the dienophile is retained in the product.
The diene, of necessity, reacts in the s-cis rather than in the s-trans conformation.
The Diels–Alder reaction occurs primarily in an endo rather than an exo fashion when the reaction is kinetically controlled.
R is exo
R is endo
END OF CHAPTER 13