Title: Stereoelectronic Effects
1Stereoelectronic Effects
Kirby, Stereoelectronic Effects Carey
Sundberg Part A Chapter 1 Fleming, Chapter 1
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2Universal Effects Governing Chemical Reactions
3Universal Effects Governing Chemical Reactions
4Universal 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.
5Universal Effects Governing Chemical Reactions
6Back to the Hydrogen Atom
7Other Covalent Arrangements
8Hybridization 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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11Hybridization vs Electronegativity
Electrons in 2S states "see" a greater effective
nuclear charge than electrons in 2P states.
12Hybridization vs Electronegativity
13DonorAcceptor Properties of C-C C-O Bonds
14Hierarchy of Donor Acceptor States
15Donor Acceptor Properties of "Weak" Bonds
16Hyperconjugation
17Negative Hyperconjugation
18A New Resonance Picture for Acetone?
19A New Resonance Picture for Acetone?
20A New Resonance Picture for Carbonyls?
21A New Resonance Picture for Carbonyls?
22The Anomeric Effect More Negative
Hyperconjugation
23The CCl bond lengths in the molecule shown below
are not the same. Which is longer?
24The CCl bond lengths in the molecule shown below
are not the same. Which is longer?
25Stereoelectronic Effects in Other Systems
Which is more stable?
26Stereoelectronic Effects in Other Types of Systems
27Lone Pair Delocalization The Gauche Effect
28What Is The More Stable Form Of An Ester?
29What Is The More Stable Form Of An Ester?
30Lone Pair Delocalization The Gauche Effect
31Lone Pair Delocalization The Gauche Effect
32Stereoelectronic 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.
33Baldwin's Rules For Ring Closure
34Tetrahedral Carbon
Trigonal Carbon
35Trigonal Carbon Exocyclic Enolate Alkylation
36Digonal Carbon Cyclizations onto Acetylenes
37Epoxide Ring Formation/Cleavage
38Hard-Soft Acid-Base Theory
39Hard 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.
40Hard and Soft Acids and Bases (HSAB-Principle)
41Hard and Soft Acids and Bases (HSAB-Principle)
42Hard and Soft Acids and Bases (HSAB-Principle)