Stereoelectronic Effects

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Stereoelectronic Effects
Kirby, Stereoelectronic Effects Carey
Sundberg Part A Chapter 1 Fleming, Chapter 1
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Universal Effects Governing Chemical Reactions
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Universal Effects Governing Chemical Reactions
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Universal Effects Governing Chemical Reactions
"During the course of chemical reactions, the
interaction of the highest filled (HOMO) and
lowest unfilled (antibonding) molecular orbital
(LUMO) in reacting species is very important to
the stabilization of the transition structure."
Fukui,Acc. Chem. Res. 1971, 4, 57.
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Universal Effects Governing Chemical Reactions
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Back to the Hydrogen Atom
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Other Covalent Arrangements
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Hybridization vs Electronegativity
Electrons in 2S states "see" a greater effective
nuclear charge than electrons in 2P states. This
becomes apparent when the radial probability
functions for S and P-states are examined The
radial probability functions for the hydrogen
atom S P states are shown below.
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Hybridization vs Electronegativity
Electrons in 2S states "see" a greater effective
nuclear charge than electrons in 2P states.
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Hybridization vs Electronegativity
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DonorAcceptor Properties of C-C C-O Bonds
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Hierarchy of Donor Acceptor States
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Donor Acceptor Properties of "Weak" Bonds
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Hyperconjugation
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Negative Hyperconjugation
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A New Resonance Picture for Acetone?
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A New Resonance Picture for Acetone?
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A New Resonance Picture for Carbonyls?
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A New Resonance Picture for Carbonyls?
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The Anomeric Effect More Negative
Hyperconjugation
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The CCl bond lengths in the molecule shown below
are not the same. Which is longer?
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The CCl bond lengths in the molecule shown below
are not the same. Which is longer?
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Stereoelectronic Effects in Other Systems
Which is more stable?
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Stereoelectronic Effects in Other Types of Systems
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Lone Pair Delocalization The Gauche Effect
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What Is The More Stable Form Of An Ester?
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What Is The More Stable Form Of An Ester?
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Lone Pair Delocalization The Gauche Effect
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Lone Pair Delocalization The Gauche Effect
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Stereoelectronic Effects in Ring Forming
Reactions Baldwin's Rules
Baldwin, J. Chem. Soc., Chem. Comm. 1976, 734,
736. Baldwin, J. Chem. Soc., Chem. Comm. 1977
233. Baldwin, J. Org. Chem. 1977, 42,
3846. Baldwin, Tetrahedron 1982, 38, 2939.
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Baldwin's Rules For Ring Closure
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Tetrahedral Carbon
Trigonal Carbon
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Trigonal Carbon Exocyclic Enolate Alkylation
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Digonal Carbon Cyclizations onto Acetylenes
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Epoxide Ring Formation/Cleavage
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Hard-Soft Acid-Base Theory
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Hard and Soft Acids and Bases (HSAB-Principle)
Hard Acids prefer to interact with hard bases
Soft acids prefer to interact with soft bases.
Softness Polarizability soft nucleophiles have
electron clouds that can be polarized (deformed)
easily.
Hardness Charged species with small ion radii,
high charge density.
Fleming, Chapter 3, p33-46
Pearson, JACS 1963, 85, 3533.
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Hard and Soft Acids and Bases (HSAB-Principle)
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Hard and Soft Acids and Bases (HSAB-Principle)
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Hard and Soft Acids and Bases (HSAB-Principle)