Organic Chemistry,7th Edition L.G.Wade,Jr. Chapter 2 Structure and Properties of Organic Molecules Copyright 2010 Pearson Education,Inc
Chapter 2 Copyright © 2010 Pearson Education, Inc. Organic Chemistry, 7th Edition L. G. Wade, Jr. Structure and Properties of Organic Molecules
Wave Properties of Electrons nodal plane nucleus represented by nucleus wave function (instantaneous picture) nodal plane Standing wave vibrates in fixed location. Wave function,y,is a mathematical description of size,shape,and orientation. Amplitude may be positive or negative. Node:Amplitude is zero. Chapter 2 2
Chapter 2 2 Wave Properties of Electrons • Standing wave vibrates in fixed location. • Wave function, , is a mathematical description of size, shape, and 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 3
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 molecular orbital (MO)is lower in energy than the original atomic orbitals. The antibonding MO is higher in energy than the atomic orbitals. Chapter 2 4
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 molecular orbital (MO) is lower in energy than the original atomic orbitals. • The antibonding MO is higher in energy than the atomic orbitals
o Bonding MO Constructive interaction:The two Is orbitals are in phase and have the same sign. add bonding molecular orbital represented by: o bonding MO Pearson Prentice Hall.inc Formation of a o-bonding MO:When the 1s orbitals of two hydrogen atoms overlap in phase with each other,they interact constructively to form a bonding MO. Chapter 2 5
Chapter 2 5 s Bonding MO Formation of a s-bonding MO: When the 1s orbitals of two hydrogen atoms overlap in phase with each other, they interact constructively to form a bonding MO
o*Antibonding MO Destructive interaction:The two Is orbitals are out of phase. antibonding molecular orbital represented by: node r本antibonding MO Copyright2010 Pearson Prentice Hall,Inc. Formation of a o*antibonding MO:When two 1s orbitals overlap out of phase,they interact destructively to form an antibonding MO. Chapter 2 6
Chapter 2 6 s* Antibonding MO Formation of a s* antibonding MO: When two 1s orbitals overlap out of phase, they interact destructively to form an antibonding MO
H2:s-s Overlap node antibonding energy 1s atomic orbital atomic orbital bonding molecular orbital Copyright2010 Pearson Prentice Hall,Inc. Chapter 2 7
Chapter 2 7 H2 : s—s Overlap
Cl2:p-p Overlap (lower energy) P Px o bonding MO Copyright 2010 Pearson Prentice Hall,Inc. When two p orbitals overlap along the line between the nuclei,a bonding orbital and an antibonding orbital result. Most of the electron density is centered along the line between the nuclei. This linear overlap is another type of sigma bonding MO. Chapter 2 8
Chapter 2 8 Cl2 : p—p Overlap • When two p orbitals overlap along the line between the nuclei, a bonding orbital and an antibonding orbital result. • Most of the electron density is centered along the line between the nuclei. • This linear overlap is another type of sigma bonding MO
Solved Problem 1 Draw the o*antibonding orbital that results from the destructive overlap of the two px orbitals just shown. Solution This orbital results from the destructive overlap of lobes of the two p orbitals with opposite phases.If the signs are reversed on one of the orbitals,adding the two orbitals gives an antibonding orbital with a node separating the two nuclei: node (higher energy) Px o*antibonding MO Copyright 2010 Pearson Prentice Hall,Inc. Chapter 2 9
Solved Problem 1 Chapter 2 9 Draw the s* antibonding orbital that results from the destructive overlap of the two px orbitals just shown. This orbital results from the destructive overlap of lobes of the two p orbitals with opposite phases. If the signs are reversed on one of the orbitals, adding the two orbitals gives an antibonding orbital with a node separating the two nuclei: Solution
s and p Orbital Overlap (lower energy) o bonding MO node (higher energy) Px (-)5 σ*antibonding MO Copyright2010 Pearson Prentice Hall.Inc. Overlap of an s orbital with a p orbital also gives a bonding MO and an antibonding MO. Chapter 2 10
Chapter 2 10 s and p Orbital Overlap • Overlap of an s orbital with a p orbital also gives a bonding MO and an antibonding MO