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A Direct Energetic Measure of Aromaticity Based on a Cleavage of the Rings in Cyclic Compounds

A Direct Energetic Measure of Aromaticity Based on a Cleavage of the Rings in Cyclic Compounds. Speaker: Ke An Advisor: Jun Zhu. 1. 2013/11/08. Main Content. Introduction. Motivation. Results and Discussion. Conclusion. 2. Introduction. 1. Criteria of Aromaticity. Structural Criteria

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A Direct Energetic Measure of Aromaticity Based on a Cleavage of the Rings in Cyclic Compounds

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  1. A Direct Energetic Measure of Aromaticity Based on a Cleavage of the Rings in Cyclic Compounds Speaker: Ke An Advisor: Jun Zhu 1 2013/11/08

  2. Main Content Introduction Motivation Results and Discussion Conclusion 2

  3. Introduction 1. Criteria of Aromaticity • Structural Criteria • Magnetic Criteria • Planarity • Equal bond length tendency • Krygowski et al, Chem. Rev. 2001, 101,1385. • Diamagnetic susceptibility exaltation (Λ) • Pascal, P. Ann. Chim. Phys. 1910, 19, 5 • Pink, Trans. Faraday Soc. 1948, 4, 407 • Schleyer,Pure Appl. Chem. 1996, 68, 209 • H+ NMR Chemical Shift • Paquette et al, J. Am. Chem. Soc. 1990, 112, 8776 • Sekiguchi et al, J. Am. Chem. Soc.1991, 113, 7081 • NICS (Nucleas-Independent Chemical Shifts) • Schleyer et al, J. Am. Chem. Soc. 1996, 118, 6317 3

  4. Introduction 1. Criteria of Aromaticity • Reactive Criteria • Energetic Criteria • Electrophilic aromatic substitution • HOMA= 1-257.7/n∑(dopt-di)2 • Krygowski et al, Tetra. Lett. 1972, 13, 3839. • RE (resonance energy) • Schaad et al, Chem. Rev. 2001, 101, 1465. • ASE (aromatic stabilization energy) • Cryanski et al, Tetrahedron2003, 59, 1657. • ISE (isomerization stabilization energy)Schleyer et al, Org. Lett. 2002, 4, 2873. • Wannere et al, Org. Lett. 2003, 5, 2983. • J. Zhu et al, Org. Lett. 2013, 15, 2442. 4

  5. Introduction 2. Isomerization Stabilization Energy Schleyer et al, Org. Lett. 2002, 4, 2873. Wannere et al, Org. Lett. 2003, 5, 2983. 5

  6. Introduction 3. Baird’s Rule Rules for ground state aromaticity are reversed in the lowest  triplet state. 4n rings: “aromatic character” 4n+2 systems: “antiaromaticity”. Baird, N.C. J. Am. Chem. Soc. 1972, 94, 4941 6

  7. Motivation To develop an energetic method to evaluate the triplet aromaticity. nonaromatic aromatic 7

  8. Results and Discussion 8

  9. Results and Discussion Structures and energies of anti- and syn-butadiene conformations in their S0 and T1 states. 9

  10. Results and Discussion 10

  11. Results and Discussion 11

  12. Results and Discussion Plot of ISE vs NICS(T1;1)zz for a series of planar monocyclic species with 4n and 4n+2  electrons in the T1 state. 12

  13. Conclusion • The ISE method can be extended to confirm the aromaticity of the T1 state of 4n-cyclic species. • Most annulenes with 4n+2  -electrons in the T1 state have a strong tendency to reduce their antiaromaticity by nonplanar deformations. 13

  14. Thanks For Your Attention ! 14

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