Chapter 3 The Nature of Organic Reactions: Alkenes

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Chapter 3 The Nature of Organic Reactions Alkenes
b-carotene
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Alkene - Hydrocarbon With Carbon-Carbon Double
Bond
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3.1 Naming alkenes

• 1. Parent hydrocarbon
• the longest C chain that contains the CC bond
• Using the suffix ene
• 2. Number beginning at
• Nearer the end of CC
• Nearer the first branch point
• 3. Substituents
• Number list them alphabetically
• Diene, triene..

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Cycloalkenesubstituents
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PROBLEM 3.1
PROBLEM 3.2
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3.2 Electronic Structure

• Sp2, Angle120, no rotation
• Rotation of ? Bond Is Prohibitive (unlike a C-C
  single bond).

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3.3 Cis-Trans Isomers of Alkenes
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3.3 Cis-Trans Isomers of Alkenes
Stability steric (spatial) strain
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3.3 Cis-Trans Isomers of Alkenes
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3.4 E,Z Designation
Sequence rules
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1. Higher atomic number gets higher priority
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2. Look at the 2nd atoms -CH3lt-C2H5 -C-C lt
-C-Cl -O-Hlt-O-CH3
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3. Multiple bonds atoms the same number of
single bonded atoms
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Practice problem
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3.5 Kinds of Organic Reactions

• Addition reactions two molecules combine
• AB ? C

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Elimination reactions
Substitution reactions
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Rearrangement reactions
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3.6 How Reactions Occur Mechanisms
Mechanism a detailed account of the motions of
the valence electrons Mechanism is a model for a
chemical reaction represents our best guess as to
what is occurring.
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Heterogenic Homogenic Polar Radical Reactions
FIGURE 3.4 Some one-step reaction mechanisms.
The motion and number of electrons are depicted
with single-and double-headed arrows that start
with the electron(s) and end at an atom or bond.
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3.7 Mechanisms of polar Rxns

• Polar reactions Polar reactions are more common
• Electron-rich
• Electron poor

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• Nucleophiles
• electron-rich reagent
• Electron donor
• Electrophiles
• Electron poor reagent
• Electron acceptor

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3.8 The Mechanism of an Organic Reaction

• Example of polar reaction
• Electron density CC gt C-C

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FIGURE 3.6 MECHANISM The mechanism of the
electrophilic addition of HCl to ethylene. The
reaction takes place in two steps and involves an
intermediate carbocation.
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3.9 Describing a Reaction

• Energy diagrams
• transition state
• Intermediate If a reaction occurs in more than
  one step, it must involve species that are
  neither the reactant nor the final product

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3.9 Describing a Reaction Reaction Energy
Diagrams and Transition States
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3.10 Describing a Reaction Energetics and
Catalysis
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PRACTICE PROBLEM 3.7
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