1. Hückel’s Molecular Orbital Theory By Sean Hanley
Hückel Theory
Hückel’s Molecular Orbital Theory
By Sean Hanley

2. Overview Explain Hückel’s Rule Aromatic Compounds
Explain Molecular Orbital (MO) Theory
Hückel Theory in Quantum Sense
So What??

3. Hückel’s Rule
Any conjugated monocyclic polyene that is planar and has (4n+2)π and/or nonbonding electrons, with n = 0,1,2, etc., will exhibit the special stability associated with aromaticity. (1930)

4. Hückel’s Rule n 4n + 2 Pi electrons
(0) + 2 = (1) + 2 = (2) + 2 = (3) + 2 = (4) + 2 = 18

5. Which are Aromatic??? 3 2 1 5 2 3 4 8 6 7

6. Some Common Aromatic Compounds

7. Comparison of Molecules
Benzene is Stabilized by 36 kcal/mol called the Empirical Resonance Energy

8. Molecular Orbital Theory Simplified
Hybrid Orbitals
The Bonding of Chemistry
Atomic Orbitals

9. Shape of P and D orbitals

10. Atomic Orbitals to Molecular Orbitals

11. Molecular Orbital Theory
Dioxygen O2

12. Molecular Orbital Theory
2 Bonds

13. Molecular Orbital Theory
Dicarbon + ion

14. Molecular Orbital Theory
1.5 Bonds

15. Overlap of Orbitals
2pz orbitals overlap causing stabilization a semi bonding
Ethene Example
sp^2 hybridized
1 Double Bond
Ψpi= c12pzA + c22pzB

16. Ethene Example Determinant associated with Wave function H11=H22
Sij set to zero unless i=j
Sii=1
Diagonal elements are assumed to be the same for all carbon atoms denoted α (Alpha)
Nearest neighbor carbon atoms assumed the same denoted β (Beta)

17. Benzene Structure

18. Benzene Pi System

19. Benzene Hückel Theory

20. Benzene Pz Wave Functions

21. MO Diagram of Benzene

22. Benzene MO

23. Aromatic Stabilization

24. Aromatic Stabilization

25. Recent Research in Aromaticity
In 2000 chemists in Germany formulated a rule to determine when a fullerene would be aromatic. In particular, they found that if there were 2(n+1)^2 π electrons
Buckminsterfullerene (Buckyball), with 60 π electrons, is non-aromatic, since 60/2=30

26. Questions????