Новосибирский институт органической химии им. Н.Н. Ворожцова СО РАН

Лаборатория изучения механизмов органических реакций

Rzepa's semibullvalene

Henry Rzepa has found intriguing noncharged nonclassical structure: 1,5-dimethyl-2,6-diazatricyclo[3.3.0.02,8]octa- 3,6-diene-4,8-dicarbonitrile. Is this structure bishomoaromatic? There is NICS data.

Energy (without ZPE) and NMR chemical shifts by DFT/PBE/L22 (cc-pCVTZ) (PRIRODA program) for DFT/PBE/L1 (cc-pVDZ) geometry.

On figure(s) below click on the level title to download xyz file
with calculated (DFT/PBE/L22) chemical shifts (5-th column)		 ==>
Click on energy level to view 3D structure (run jmol java-applet) ==>

0.00 0.00 0.04 0.04 0.24 0.24 0.56 0.56 0.94 0.94 1.34 1.34 1.69 1.69 1.91 1.91 2.17 2.17 2.30 2.30 2.42 2.42 2.67 2.67 3.20 3.20 4.28 4.28 Not N5-C4 but N6-C4



NICS of the nonclassic structure (-16.3 ppm) is more negative than classic one (about -10 ppm) or than the structure with two cycloprorane rings (-9.9 ppm). (In the classic structures negative NICS is due to sigma aromaticity of cycloprorane.)

Thus, NICS data support bishomoaromaticity of the nonclassic structure.