Bicycloaromaticity

Bicycloaromaticity in chemistry is an extension of the concept of homoaromaticity with two aromatic ring currents situated in a non-planar molecule and sharing the same electrons.[1] The concept originates with Melvin Goldstein who first reported about it in 1967.[2][3][4] It is of some importance in academic research. Using MO theory the bicyclo[3.2.2]nonatrienyl cation was predicted to be destabilised and the corresponding anion predicted to be stabilised by bicycloaromaticity.

Bicycloaromaticity has been studied by others in relation to the bicyclo[3.2.2]nonatrienyl cation [5][6] and in relation to specific carbanions.[7] In 2017 experimental evidence was reported for bicycloaromaticity (dual aromaticity) to exist in a bicyclic porphyrinoid.[1][8] This system has been described as aromatic with two ring systems of 26 (n=6) and 34 (n=8) electrons. By oxidation, another system was described as a triplet-state biradical, again considered aromatic by application of Baird's rule.

References
  1. Bicyclic Baird-type aromaticity Won-Young Cha,Taeyeon Kim, Arindam Ghosh,Zhan Zhang,Xian-Sheng Ke, Rashid Ali,Vincent M. Lynch,Jieun Jung, Woojae Kim,Sangsu Lee,Shunichi Fukuzumi,Jung Su Park, Jonathan L. Sessler, Tavarekere K. Chandrashekar & Dongho Kim Nature Chemistry (2017) doi:10.1038/nchem.2834
  2. Bicycloaromaticity. 4m + 2, 4n rule Melvin J. Goldstein Journal of the American Chemical Society 1967 89 (24), 6357-6359 doi:10.1021/ja01000a069
  3. Rearrangements of bicyclo[3.2.2]nonatrienes Melvin J. Goldstein and B. G. Odell Journal of the American Chemical Society 1967 89 (24), 6356-6357 doi:10.1021/ja01000a068
  4. Degenerate Carbocation Rearrangements P.Ahlberg. G.Jonäll , C.Engdahl Advances in Physical Organic Chemistry Volume 19, Pages iii-v, 1-456 (1983) Edited by V. Gold and D. Bethell doi:10.1016/S0065-3160(08)60224-5
  5. Bicycloaromaticity. Stability and rearrangement of the bicyclo[3.2.2]nonatrienyl cation John B. Grutzner and Saul Winstein Journal of the American Chemical Society 1970 92 (10), 3186-3187 doi: 10.1021/ja00713a045
  6. Bicycloaromaticity. Stability and rearrangements of the bicyclo[3.2.2]nonatrienyl anion and cation John B. Grutzner and S. Winstein Journal of the American Chemical Society 1972 94 (7), 2200-2208 doi:10.1021/ja00762a008
  7. Homoaromaticity and bicycloaromaticity in carbanions John B. Grutzner and William L. Jorgensen Journal of the American Chemical Society 1981 103 (6), 1372-1375 doi:10.1021/ja00396a013
  8. Unusual bicyclic molecule extends frontier of aromaticity Katrina Krämer Chemistry World 2017 link
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