Clar Structure in Inorganic BN Analogues of Polybenzenoid Hydrocarbons: Exist or Not? Speaker: Jingjing Wu Advisor: Jun Zhu 2014/4/11 1

Main contents Introduction Computational method Results and discussion Conclusion Questions 2

Introduction Clar structure was proposed by Eric Clar in the 1950s according to the experimental observations. Since then, Clar structure have attracted increasing interest from both experimentalists and theoreticians. Clar, E.; Kelly, W. Journal of the American Chemical Society 1954, 76, Clar, E.; McCallum, A. Tetrahedron 1960, 10, Figure 1. All wavelengths(Å) were measured in benzene expect 2 and the significance of benzenoid rings for the stability of aromatic hydrocarbons in color change.

Figure 2. Clar structural representations of heptabenzene isomers, symmetries and relative Gibbs free energies (kcal/mol) compare with 6. Zhu, J.; Dahlstrand, C.; Smith, J. R.; Villaume, S.; Ottosson, H. Symmetry 2010, 2, Introduction 4

Computational methods Package: Gaussian 03 DFT method: B3LYP Basis set: 6-311G** 5

Results and discussion Figure 3. ELFπ bifurcation values [BV (ELFπ)] of B-N bonds, the BV (ELFπ) ranges of each ring (in ring) [ΔBV (ELFπ)], the relative Gibbs free energies (kcal mol­­ -1 ), symmetries at B3LYP/6-311G** level. π-Bonds with BV(ELFπ)’s about in either of the three intervals BV(ELFπ)’s < 0.64, 0.64 ≤ BV(ELFπ) < 0.91, 0.91≤ BV(ELFπ), are denoted as single, π, and double bonds, respectively. 6

Table 1. Six-center Index and NICS(ppm) (NICS (1) and NICS (0) indicate 1 Å above the plane and in the plane of ring, respectively) Indices Calculated for the Different Rings Indices Molecule SymmetryRingSCINICS(1)/NICS(0) C 2v / / / /-0.3 Cs Cs / / / / / / /-0.9 7

Cs Cs / / / / / / /-0.8 Cs Cs / / / / / / /-1.2 Results and discussion 8

Cs Cs / / / / / / /-1.0 C 2v / / / /-0.3 D 6h /-8.9 C 2v

Results and discussion 10

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Figure 4. Optimized (B3LYP/6-311G(d, p)) structures for BN-acenes (31-106), their increasing number of rings and π-sextets, relative Gibbs free energies (kcal mol -1 ) of isomers and symmetries. 12

Figure 5. Optimized (B3LYP/6-311G(d, p)) structures for PBHs (31’-106’), their increasing number of rings and π-sextets, relative Gibbs free energies (kcal mol -1 ) of isomers and symmetries. 13

Results and discussion Figure 6. Plot of the ring number (n = ) of [n]acenes number against the energy differences of the most and least stable isomers. 14

15 Conclusion 1. Different aromatic indices indicated BN analogues has less aromaticity and even nonaromaticity. 2. More π-sextets containing, more stable the structure is. 3.Clar structures in inorganic BN analogues does exist according to the correlation (r 2 = 0.975) between the ring number (n = ) of BN analogues of [n]acenes number and energy differences of the most and least stable isomers.

Questions How to explain this situation? 16 Figure 7. Optimized (B3LYP/6-311G(d, p)) structures for BN analogues, their increasing number of rings and π-sextets, relative Gibbs free energies (kcal mol -1 ) of isomers.