The homoaromaticity from the field of organic chemistry can be found in conjugated cyclic systems that are able to skip a part of the ring. They are thus unlike regular aromaticity, which is found only in planar conjugated systems. Just like regular aromatic compounds also homo -aromatic compounds are more stable than would be expected from the pure conjugation.
Concept of homoaromaticity
The concept of homoaromaticity was developed by Saul Winstein and the first on a 3- bicyclo [ 3.1.0] hexyl cation was observed ( Fig. 1).
It was found that the solvolysis reaction proceeded much faster when the tosyl leaving group was in the equatorial and not axial position on the ring, which anchimeric support of the cyclopropane σ - bond to the non-classical ion was facilitated. The positive charge in this ion is delocalized over three carbon atoms which have two π - electrons and so satisfy the Hückel rule. A total of three methyl groups are excluded from the conjugated system, so it is in the ion to a Trishomoaromatic.
Another example of a homoaromatic system is the containing six π - electrons homotropylium ion ( Fig. 2).
The bridged bicyclo [ 3.2.1] octa -3 ,6 -dien- 2- ylkation, which is shown in Figure 3, is bishomoantiaromatisch because it contains four π - electrons, which is anti -aromatic. The cation is represented at a low temperature in a super acid solvent, consisting of fluorosulfonic acid and sulphuryl chloride fluoride. The cation may recombine with a methoxide anion, a 50/50-Mischung of the isomers formed. The antiaromatic behavior of the system could be detected in solvolysis experiments using NMR analysis and the reaction rates.