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8 (cyclooctatetraenide anion), with ten π electrons obeys the 4n + 2 rule for n = 2 and is planar, while the 1,4-dimethyl derivative of the dication, with six π electrons, is also believed to be planar and aromatic. [8] The Cyclononatetraenide anion (C 9 H – 9) is the largest all-cis monocyclic annulene/annulenyl system that is planar and ...
Some such structures may contain aromatic π-sextets, namely groups of six π-electrons localized in a benzene-like moiety and separated by adjacent rings through C–C bonds. An aromatic π-sextet can be represented by a circle, as in the case of the anthracene molecule (below). Clar's rule states that for a benzenoid polycyclic aromatic ...
Aromaticity is found in ions as well: the cyclopropenyl cation (2e system), the cyclopentadienyl anion (6e system), the tropylium ion (6e), and the cyclooctatetraene dianion (10e). Aromatic properties have been attributed to non-benzenoid compounds such as tropone. Aromatic properties are tested to the limit in a class of compounds called ...
In contrast to the rarity of Möbius aromatic ground state molecular systems, there are many examples of pericyclic transition states that exhibit Möbius aromaticity. The classification of a pericyclic transition state as either Möbius or Hückel topology determines whether 4N or 4N + 2 electrons are required to make the transition state aromatic or antiaromatic, and therefore, allowed or ...
The lowest triplet state of an annulene is, according to Baird's rule, aromatic when it has 4n π-electrons and antiaromatic when the π-electron count is 4n + 2, where n is any positive integer. This trend is opposite to that predicted by Hückel's rule for the ground state , which is usually the lowest singlet state (S 0 ).
1,4-Dioxotetralin and its aromatized tautomer 1,4-naphthalenediol coexist in equal abundance in solution. The isomerization of cyclohexadienones gives the aromatic tautomer phenol . [ 14 ] [ 15 ] Isomerization of 1,4-naphthalenediol at 200 °C produces a 2:1 mixture with its keto form, 1,4-dioxotetralin.
Homoaromaticity, in organic chemistry, refers to a special case of aromaticity in which conjugation is interrupted by a single sp 3 hybridized carbon atom. Although this sp 3 center disrupts the continuous overlap of p-orbitals, traditionally thought to be a requirement for aromaticity, considerable thermodynamic stability and many of the spectroscopic, magnetic, and chemical properties ...
With the aid of these rules the UV absorption maximum can be predicted, for example in these two compounds: [8] In the compound on the left, the base value is 214 nm (a heteroannular diene). This diene group has 4 alkyl substituents (labeled 1,2,3,4) and the double bond in one ring is exocyclic to the other (adding 5 nm for an exocyclic double ...