文档介绍：Chapter 7 Structure and Synthesis of Alkenes
Jo Blackburn
Richland College, Dallas, TX
Dallas munity College District
ã 2003, Prentice Hall
Organic Chemistry, 5th Edition L. G. Wade, Jr.
1
Chapter 7*
Functional Group
Pi bond is the functional group.
More reactive than sigma bond.
Bond dissociation energies:
C=C BDE 146 kcal/mol
C-C BDE -83 kcal/mol
Pi bond 63 kcal/mol =>
2
Chapter 7*
Orbital Description
Sigma bonds around C are sp2 hybridized.
Angles are approximately 120 degrees.
No nonbonding electrons.
Molecule is planar around the double bond.
Pi bond is formed by the sideways overlap of parallel p orbitals perpendicular to the plane of the molecule. =>
3
Chapter 7*
Bond Lengths and Angles
Hybrid orbitals have more s character.
Pi overlap brings carbon atoms closer.
Bond angle with pi orbitals increases.
Angle C=C-H is
Angle H-C-H is 116. 6=>
4
Chapter 7*
Pi Bond
Sideways overlap of parallel p orbitals.
No rotation is possible without breaking the pi bond (63 kcal/mole).
Cis isomer cannot e trans without a chemical reaction occurring.
=>
5
Chapter 7*
Elements of Unsaturation
A saturated hydrocarbon: CnH2n+2
Each pi bond (and each ring) decreases the number of H’s by two.
Each of these is an element of unsaturation.
To calculate: find number of H’s if it were saturated, subtract the actual number of H’s, then divide by 2. =>
6
Chapter 7*
Propose a Structure:
First calculate the number of elements of unsaturation.
Remember:
A double bond is one element of unsaturation.
A ring is one element of unsaturation.
A triple bond is two elements of unsaturation. =>
for C5H8
7
Chapter 7*
Heteroatoms
Halogens take the place of hydrogens, so add their number to the number of H’s.
Oxygen doesn’t change the C:H ratio, so ignore oxygen in the formula.
Nitrogen is trivalent, so it acts like half a carbon.
C
H
H
C
H
H
N
C
H
H
H
=>
8
Chapter 7*
Structure for C6H7N?
Since nitrogen counts as half a carbon, the number of