advanced organic chemistry(高等有机合成)

Advanced Organic Chemistry (Chapter 1)
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1.2 Bond Energies, Lengths, and Dipoles
a) Bond lengths are strongly depend on hybridization but little influenced by other factors.
a) Branched chain hydrocarbons (alkanes and alkenes) are more stable than straight-chain isomers. b) The trans isomer in alkenes are more stable than cis isomers.
Chapter 1
Chemical Approach to Chemical Bonding
LUMO of allyl cation Bonding interaction Bonding interaction
HOMO of butadiene
Introduction
Organic Chemistry Main Areas:
CH2
Heterolytic Bond Dissociation (Ionization):
a) Very High in Gas Phase
b) Low in Solution
Advanced Organic Chemistry (Chapter 1)
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Relative Stability of Hydrocarbons: Based on Heat of Formation Data
1. The actual molecule is combination of ALL Lewis structures.
2. Maximum number of valance electrons around each atom (e.g. 2 for H atom and 8 for first row elements)
C-C bonds: decreased s character (17%)
increased p character (83%)
C-H bonds: increased s character (33%)
decreased p character (67%)
Advanced Organic Chemistry (Chapter 1) a. banaei
H C H H
H C C H
H C H
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3. ab-Unsaturated Compounds
H H C H major H H significant C O H C C H H minor H C O H C C H H C O
Structural Features of ab-Unsaturated Compounds: a) C=O band is weaker than in saturated compounds (typically at 1690 cm-1 vs. 1730 cm-1 for saturated compounds) b) b-carbon atom is less shielded (lower electron density) than for simple alkenes (13C-NMR)
2. Advanced Organic Chemistry: "Reactions, Mechanisms and Structure” Jerry March 3rd Edition, John Wiley & Sons, 1985.
Table of Contents: Chapter 1: Chemical Approach to Chemical Bonding Chapter 9: Aromaticity Chapter 2: Stereochemical Principles
Propellanes
[1,1,1] prpellane [2,2,2] prpellane
[4,4,4] prpellane
Angle Strain cause to increased in chemical reactivity involving CLEAVAGE of the central bond.
c) Increased reactivity of C=C vs. simple alkenes toward nuclephies.
Advanced Organic Chemistry (Chapter 1) a. banaei
Confliction
H H3CO NO2 major H3CO NO2 H
c) Placement of negative charge on the most electronegative atom or reverse
Advanced Organic Chemistry (Chapter 1) a. banaei
The Use of Resonance Concept:
a) Structure: Description of bonding in organic molecules and the methods for determining, analyzing, and predicting molecular structure.
b) Dynamics: Study of physical properties and chemical transformations of molecules.
Central Feature of VBT: Exchange (resonance) of electrons between two nuclei.
The Actual molecule is the hybrid of the “Canonical Forms”
For example:
H
Cl
104 85 85
Bond
CH3-H H2C=CH-CH2-H PhCH2-H
Advanced Organic Chemistry (Chapter 1)
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Stable Allyl and Benzyl Radicals:
H2C H C CH2 H2C H C CH2
CH2
CH2
CH2
Advanced Organic Chemistry (Chapter 1) a. banaei
Angle Strain in three and four-membered rings
H2 C H2 C
60 o
C
CH2
C
C
Bent bonds (banana type) in cyclo propane
3. Stable structures that approximate the actual molecule have following features:
a) maximum number of covalent bonds: b) minimum separation of unlike charges
Chapter 3: Conformational, Steric, and Stereo Electronic
Effects Chapter 4: Study and Description of Organic Reaction Mechanisms Chapter 5: Nucleophilic Substitution Chapter 6: Polar Addition and Elimination Reactions Chapter 7: Carbanions and Other Nucleophilic Carbon Species
H Cl
H Cl
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Advanced Organic Chemistry (Chapter 1)
Complex Molecules Lead to Complex Wave Functions
Linus Pauling’s Key Idea: 1) Hybridization Theory 2) Resonance Theory
1. Relative Acidity of Isobutene and Acetone:
H2C CH2 H3C H3C pKa ~ 45 H2C CH2 H3C pKa ~ 25 H2C O H3C H2C O
2. Stability of Allyl Cation:
H H C C H
Advanced Organic Chemistry (Chapter 1)
2s
2p
2sp3( Hybrid Orbital)
Hybrid orbitals are highly directed than s and p orbitals and hence:
More effective Overlap
Stronger bonds
2s 2px, 2py, 2pz 4 (2sp3) Tetrahedral Geometry
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Advanced Organic Chemistry (Chapter 1)
Ethylene: 3 (2sp2)
H H H
Trigonal
H
H
H
H
H
The p bond in ethylene
Acetylene:
2 (2sp)
p-bond
Li
The p bonds in acetylene