Cross-Aromaticity in annulated benzene and analogs

1. Cross-Aromaticity in annulated benzene and analogs Advisor: Jun Zhu Reporter: Yulei.Hao Date: 2014.3.14

2. Content Background Computational Methods Results and Discussion Futher Work

3. Background Mills–Nixon effect：Geometric changes of the benzene ring due to annulation by small, strained rings. in terms of the stability of the Kekulé resonance structures, it favor the resonance structure with the double bonds exo to the strained annulated ring. α β α=360。-2β Mills, W.H.; Nixon, I.G. J.Chem.Soc. 1930, 2510

4. Background Coupling of diazo-compounds and Bromination Fuller, F. J.; Valente, J. E. J.Chem.Cryst. 1996, 26, 815. Mills, W.H.; Nixon, I.G. J.Chem.Soc. 1930, 2510

5. Background “The field of the cycloproparene chemistry can be aptly regarded as something of a Cinderella area since the simple beginnings have led to a wealth of fascinating and fruitful chemistry far beyond expectation in 1960s.” ----Brian Halton Chem. Rev. 2003, 103, 1327-1369 The synthesis some of cycloproparens: TM.1 [1] Vogel, E.; Grimme, W.; Korte, S. Tetrahedron Lett. 1965, 6, 3625.

6. TM.2 TM.3 TM.4 [2] [3] [4]

7. Computational Methods G03 program OPT： B3LYP/6-311++G* NICS: B3LYP/6-311++G*

8. Results and Discussion Figure 1. Monomers of annulated rings in calculation. Figure 2. Combination of non-π aromatic monomers. Table 2. Comparing NICS values(ppm) of 1, 2, 3 and 4 with their monomers. a Numbers in the brackets are NICS(1)zz opposite the dihedral.

9. Results and Discussion Figure 3. Selected bond distances(Å) for 5-15. Figure 4. Selected bond distances(Å) for 16-22.

10. Results and Discussion We can conclude that the bond length in benzene and naphthalene of these compounds change slightly after fused by small strained rings, impling the retained π aromaticity. Table 3. ΔR(Å) for compounds 5-22. Rdefined as the endo distance minus the exo distance. The bond between the two rings is used as the exo bond, and the maximum of the difference is used for the asymmetric compounds.

11. The aromaticity of both are not destroyed. Table 4. NICS(0) and NICS(1)zz of computed compounds

12. Results and Discussion We can conclude that the π-aromaticity in benzene and naphthalene weaken the σ-aromaticity in cyclopropene, and strengthen the σ-antiaromaticity in cyclobutene. Table 3. Smooth line of NICS(0) vs exo bond distance of compounds 5-22.

13. Results and Discussion Figure 5. The Gibbs Free Energy(in kcal.mol-1) of some compounds to their isomers. We can conclude that those compounds with higher symmetry are more stable.

14. Futher Work ……

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