《有机化学》课程PPT教学课件（Official PPT of Organic Chemistry 6th LG Wade by Prentice Hall，L. G. Wade, Jr.）Chapter 07 Structure and Synthesis of Alkenes

Organic Chemistry,6th Edition L.G.Wade,Jr. Chapter 7 Structure and Synthesis of Alkenes

Chapter 7 Structure and Synthesis of Alkenes Organic Chemistry, 6th Edition L. G. Wade, Jr

Introduction Hydrocarbon with carbon-carbon double bonds ·Sometimes called olefins,“oil- forming gas” Chapter 7 2

Chapter 7 2 Introduction • Hydrocarbon with carbon-carbon double bonds • Sometimes called olefins, “oil￾forming gas

Functional Group Pi bond is the functional group. More reactive than sigma bond. Bond dissociation energies: >C=C BDE 611 kJ/mol >C-C BDE -347 kJ/mol >Pi bond 264 kJ/mol => Chapter 7 3

Chapter 7 3 Functional Group • Pi bond is the functional group. • More reactive than sigma bond. • Bond dissociation energies: ➢C=C BDE 611 kJ/mol ➢C-C BDE -347 kJ/mol ➢Pi bond 264 kJ/mol =>

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. > Chapter 7 4

Chapter 7 4 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. =>

Bond Lengths and Angles 1.33 54 H 116.6° 121.7 ethylene ethane Hybrid orbitals have more s character. Pi overlap brings carbon atoms closer. Bond angle with pi orbital increases. >Angle C=C-His121.7° >Angle H-C-His116.6° => Chapter 7 5

Chapter 7 5 Bond Lengths and Angles • Hybrid orbitals have more s character. • Pi overlap brings carbon atoms closer. • Bond angle with pi orbital increases. ➢Angle C=C-H is 121.7 ➢Angle H-C-H is 116. 6 =>

Pi Bond Sideways overlap of parallel p orbitals. No rotation is possible without breaking the pi bond (264 kJ/mole). Cis isomer cannot become trans without a chemical reaction occurring. CH3 A. CH3 H.C H:C H cis no overlap with the ends perpendicular trans Copyright 2005 Pearson Prentice Hall,Inc. Chapter 7 6

Chapter 7 6 Pi Bond • Sideways overlap of parallel p orbitals. • No rotation is possible without breaking the pi bond (264 kJ/mole). • Cis isomer cannot become trans without a chemical reaction occurring. =>

Elements of Unsaturation A saturated hydrocarbon:CH2n+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. > Chapter 7 7

Chapter 7 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. =>

Propose a Structure: for CsHs 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.= Chapter 7 8

Chapter 7 8 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

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. HH H C-C-N C- 三> HHHH Chapter 7 9

Chapter 7 9 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 =>

Structure for CH-N? Since nitrogen counts as half a carbon, the number of H's if saturated is 2(6.5)+2=15. Number of missing H's is 15-7 =8. ·Elements of unsaturation is8÷2=4. => Chapter 7 10

Chapter 7 10 Structure for C6H7N? • Since nitrogen counts as half a carbon, the number of H’s if saturated is 2(6.5) + 2 = 15. • Number of missing H’s is 15 – 7 = 8. • Elements of unsaturation is 8 ÷ 2 = 4. =>