《国外有机化学》 英文版 Chapter 2 Structure and properties of Organic Molecules

Organic Chemistry, 5th Edition L.G. Wade. Jr Chapter 2 Structure and Properties of Organic Molecules Jo blackburn Richland college, dallas TX Dallas County Community College District c 2003. Prentice hall

Chapter 2 Structure and Properties of Organic Molecules Organic Chemistry, 5th Edition L. G. Wade, Jr. Jo Blackburn Richland College, Dallas, TX Dallas County Community College District © 2003, Prentice Hall

Wave Properties of electrons Standing wave vibrates in fixed location Wave function, v, mathematical description of size, shape orientation Amplitude may be positive or negative Node: amplitude is zero > the 2 p, orbital Chapter 2

Chapter 2 2 Wave Properties of Electrons • Standing wave vibrates in fixed location. • Wave function, , mathematical description of size, shape, orientation • Amplitude may be positive or negative • Node: amplitude is zero + _ + - =>

Wave Interactions Linear combination of atomic orbitals >between different atoms is bond formation >on the same atom is hybridization Conservation of orbitals Waves that are in phase add together Amplitude increases Waves that are out of phase cancel out > Chapter 2

Chapter 2 3 Wave Interactions • Linear combination of atomic orbitals ➢between different atoms is bond formation ➢on the same atom is hybridization. • Conservation of orbitals • Waves that are in phase add together. Amplitude increases. • Waves that are out of phase cancel out. =>

Sigma Bonding Electron density lies between the nuclei a bond may be formed by s-s, p-p, s-p or hybridized orbital overlaps The bonding mo is lower in energy than the original atomic orbitals The antibonding Mo is higher in energy than the atomic orbitals > Chapter 2

Chapter 2 4 Sigma Bonding • Electron density lies between the nuclei. • A bond may be formed by s-s, p-p, s-p, or hybridized orbital overlaps. • The bonding MO is lower in energy than the original atomic orbitals. • The antibonding MO is higher in energy than the atomic orbitals. =>

2: overlap node antibonding g energy Is tomic orbital atomic orbital bonding molecular orbi Chapter 2

Chapter 2 5 H2 : s-s overlap =>

CI2: p-p overlap Constructive overlap along the same axis forms a sigma bond +(+ o bonding mo Chapter 2

Chapter 2 6 Cl2 : p-p overlap => Constructive overlap along the same axis forms a sigma bond

HCI: S-p overlap Question Draw the predicted shape for the bonding molecular orbital and the antibonding molecular orbital of the hcl molecule Answer: See bottom of page 42 in your text Chapter 2

Chapter 2 7 HCl: s-p overlap Question: Draw the predicted shape for the bonding molecular orbital and the antibonding molecular orbital of the HCl molecule. Answer: See bottom of page 42 in your text. =>

Pi Bonding Pi bonds form after sigma bonds Sideways overlap of parallel p orbitals node destructive(antibonding) interaction T antibonding mo ener constructive(bonding) interaction T bonding mo Chapter 2

Chapter 2 8 Pi Bonding • Pi bonds form after sigma bonds. • Sideways overlap of parallel p orbitals. =>

Multiple Bonds a double bond(2 pairs of shared electrons) consists of a sigma bond and a pi bond a triple bond (3 pairs of shared electrons consists of a sigma bond and two pi bonds half of Tr bond H H C o bond C H(sp sp(H H p. half of r bond Chapter 2

Chapter 2 9 Multiple Bonds • A double bond (2 pairs of shared electrons) consists of a sigma bond and a pi bond. • A triple bond (3 pairs of shared electrons) consists of a sigma bond and two pi bonds. =>

Molecular Shapes Bond angles cannot be explained with simple s and p orbitals. Use VsEPr theory. Hybridized orbitals are lower in energy because electron pairs are farther apart Hybridization is lCao within one atom just prior to bonding Chapter 2 10

Chapter 2 10 Molecular Shapes • Bond angles cannot be explained with simple s and p orbitals. Use VSEPR theory. • Hybridized orbitals are lower in energy because electron pairs are farther apart. • Hybridization is LCAO within one atom, just prior to bonding. =>