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  2. Cyclobutadiene - Wikipedia

    en.wikipedia.org/wiki/Cyclobutadiene

    The rectangular structure is consistent with the existence of two different 1,2-dideutero-1,3-cyclobutadiene valence isomers. This distortion indicates that the pi electrons are localized, in agreement with Hückel's rule which predicts that a π-system of 4 electrons is not aromatic. In principle, another situation is possible.

  3. Antiaromaticity - Wikipedia

    en.wikipedia.org/wiki/Antiaromaticity

    However, cyclobutadiene adopts more double bond character in two of its parallel bonds than others and the π electrons are not delocalized between the two double-bond-like bonds, giving it a rectangular shape as opposed to a regular square. [3] As such, cyclobutadiene behaves like two discrete alkenes joined by two single bonds, and is ...

  4. Aromaticity - Wikipedia

    en.wikipedia.org/wiki/Aromaticity

    Whereas benzene is aromatic (6 electrons, from 3 double bonds), cyclobutadiene is not, since the number of π delocalized electrons is 4, which of course is a multiple of 4. The cyclobutadienide (2−) ion, however, is aromatic (6 electrons).

  5. Cyclobutene - Wikipedia

    en.wikipedia.org/wiki/Cyclobutene

    The compound was first prepared by thermolysis of the ammonium salt [C 4 H 7 N(CH 3) 3]OH (cyclobutyltrimethylammonium hydroxide). [2] Cyclobutene thermally isomerizes to 1,3-butadiene. This strongly exothermic reaction reflects the dominance of ring strain. In contrast, the corresponding equilibrium for hexafluorocyclobutene disfavors ...

  6. Hückel's rule - Wikipedia

    en.wikipedia.org/wiki/Hückel's_rule

    Cyclooctatetraene (C 8 H 8) with eight π electrons has a nonplanar "tub" structure. However the dianion C 8 H 2– 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]

  7. Hückel method - Wikipedia

    en.wikipedia.org/wiki/Hückel_method

    To summarize, we are assuming that: (1) the energy of an electron in an isolated C(2p z) orbital is =; (2) the energy of interaction between C(2p z) orbitals on adjacent carbons i and j (i.e., i and j are connected by a σ-bond) is =; (3) orbitals on carbons not joined in this way are assumed not to interact, so = for nonadjacent i and j; and ...

  8. Annulene - Wikipedia

    en.wikipedia.org/wiki/Annulene

    Using this form of nomenclature 1,3,5,7-cyclooctatetraene is [8]annulene and benzene is [6]annulene (and occasionally referred to as just 'annulene'). [ 2 ] [ 3 ] The discovery that [18]annulene possesses a number of key properties associated with other aromatic molecules was an important development in the understanding of aromaticity as a ...

  9. Benzocyclobutadiene - Wikipedia

    en.wikipedia.org/wiki/Benzocyclobutadiene

    Benzocyclobutadiene is the simplest polycyclic hydrocarbon, being composed of an aromatic benzene ring fused to an anti-aromatic cyclobutadiene ring. It has chemical formula C 8 H 6 . Though the benzene ring is stabilized by aromaticity , the cyclobutadiene portion has a destabilizing effect.