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H ü ckel Theory

H ü ckel Theory. Hückel’s Molecular Orbital Theory By Sean Hanley. Overview. Explain H ü ckel’s Rule Aromatic Compounds Explain Molecular Orbital (MO) Theory H ü ckel Theory in Quantum Sense So What??. H ü ckel’s Rule.

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H ü ckel Theory

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  1. 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 • n4n + 2 Pi electrons 0 4(0) + 2 = 2 1 4(1) + 2 = 6 2 4(2) + 2 = 10 3 4(3) + 2 = 14 4 4(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 samedenoted 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????

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