复旦大学：《物理化学》精品课程教学资源（PPT课件讲稿）第5章 多原子分子结构 Polyatomic Molecular Structure

Physical Chemistry 20218/21 Chemistry Departme nt of Fudan Universit

Physical ChemistryI Chapter V Polyatomic Molecular Structure 2021/8/21 Chemistry Department of Fudan University 1 Physical Chemistry

85-1 Saturated Polyatomic Molecules 85-1-1. Delocalized Molecular Orbital Molecular Orbital Theory 20218/21 Chemistry Departme nt of Fudan University

Physical ChemistryI Chapter V Polyatomic Molecular Structure 2021/8/21 Chemistry Department of Fudan University 2 §5-1. Saturated Polyatomic Molecules §5-1-1. Delocalized Molecular Orbital Molecular Orbital Theory

Hy=Ey B-O approximate Heve=ery single electronic approximate HIre o LCAO-MO Hi-ES=0 Secular equation 20218/21 Chemistry Departme nt of Fudan University

Physical ChemistryI Chapter V Polyatomic Molecular Structure 2021/8/21 Chemistry Department of Fudan University 3 H = E  B-O approximate e e e H e = E  single electronic approximate i i i H i  = E  LCAO-MO Hij − ESij = 0 Secular equation

Taking CHa as an example 20218/21 Chemistry Departme nt of Fudan University

Physical ChemistryI Chapter V Polyatomic Molecular Structure 2021/8/21 Chemistry Department of Fudan University 4 Taking CH4 as an example H H H H

Taking the four H 1s orbitals as bases E8C33C26S460a 002 Reduce to the irreducible components T=A OT2 20218/21 Chemistry Departme nt of Fudan University

Physical ChemistryI Chapter V Polyatomic Molecular Structure 2021/8/21 Chemistry Department of Fudan University 5 E 8C3 3C2 6S4 6σd 4 1 0 0 2  = A1 T2 Reduce to the irreducible components  Td Taking the four H 1s orbitals as bases

Al +H,+H3+H ) 2 PI=PH (3H1-H2-H3-H) √12 吃=B2=1 (3H2-H1-H3-H) 12 n=1H13=-(3H3-H2-FH1-H1 12 ;=P,H4 3H-H-H-H 12 20218/21 Chemistry Departme nt of Fudan University

Physical ChemistryI Chapter V Polyatomic Molecular Structure 2021/8/21 Chemistry Department of Fudan University 6 ( ) 1 1 2 3 4 1 3 12 1 2 2 T = P ˆ T H = H − H − H − H ( ) 2 2 1 3 4 2 3 12 1 2 2 T = P ˆ T H = H − H − H − H ( ) 3 3 2 1 4 3 3 12 1 2 2 T = P ˆ T H = H − H − H − H ( ) 4 4 2 3 1 4 3 12 1 2 2 T = P ˆ T H = H − H − H − H ( ) 1 1 2 3 4 2 1 1 1  A = P ˆ A H = H + H + H + H

orthonormal n、1)=+的=(H1+H2-H3-H4) (2)=+的=1(H1-H2+H;-H,) 0(3)=+0=(H1-H2-H2+H) 2 20218/21 Chemistry Departme nt of Fudan University

Physical ChemistryI Chapter V Polyatomic Molecular Structure 2021/8/21 Chemistry Department of Fudan University 7 orthonormal ( ) 1 2 3 4 1 2 2 1 1 2 2 2 T ( ) = T +T = H + H − H − H ( ) 1 2 3 4 1 3 2 1 2 2 2 2 T ( ) = T +T = H − H + H − H ( ) 1 2 3 4 1 4 2 1 (3) 2 2 2 T = T +T = H − H − H + H

four symmetry matched molecular orbitals are: VA =CAS+Cpa TPx +Cr2(1) V, =CrP,+C r (2) V =CP+CT Or (3 20218/21 Chemistry Departme nt of Fudan University

Physical ChemistryI Chapter V Polyatomic Molecular Structure 2021/8/21 Chemistry Department of Fudan University 8 A1 A A A1  = C s + C'  ' (1) T T2 p CT px C x  = +  ' (2) T T2 p CT py C y  = +  ' (3) T T2 p CT pz C z  = +  four symmetry matched molecular orbitals are:

8 5-1-2 Localized Molecular Orbital Valence Bond Theory 20218/21 Chemistry Departme nt of Fudan University

Physical ChemistryI Chapter V Polyatomic Molecular Structure 2021/8/21 Chemistry Department of Fudan University 9 §5-1-2. Localized Molecular Orbital Valence Bond Theory 1 2 3 x x z y

C: sp3 hybridization B1=s+P+p,+p 2 Hybrid 2=s-P+p,-p Orbitals 内=(s+-p,-p) 212 =l-Px-pvtp2 20218/21 Chemistry Departme nt of Fudan University

Physical ChemistryI Chapter V Polyatomic Molecular Structure 2021/8/21 Chemistry Department of Fudan University 10 ( ) x y z = s + p + p + p 2 1 1 ( ) x y z = s − p + p − p 2 1 2 ( ) x y z = s + p − p − p 2 1 3 ( ) x y z = s − p − p + p 2 1 4 C: sp3 hybridization Hybrid Orbitals