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It is an unstable, non-planar compound which is non-aromatic. [1] [2] The dianion, however, satisfies Hückel's rule, is thermally stable, and is planar. [3] See also
An antiaromatic compound may demonstrate its antiaromaticity both kinetically and thermodynamically. As will be discussed later, antiaromatic compounds experience exceptionally high chemical reactivity (being highly reactive is not “indicative” of an antiaromatic compound, it merely suggests that the compound could be antiaromatic).
Aromatization is a chemical reaction in which an aromatic system is formed from a single nonaromatic precursor. Typically aromatization is achieved by dehydrogenation of existing cyclic compounds, illustrated by the conversion of cyclohexane into benzene. Aromatization includes the formation of heterocyclic systems. [1]
Annulenes may be aromatic (benzene, [6]annulene and [18]annulene), non-aromatic ([8] and [10]annulene), or anti-aromatic (cyclobutadiene, [4]annulene). Cyclobutadiene is the only annulene with considerable antiaromaticity, since planarity is unavoidable.
Two different resonance forms of benzene (top) combine to produce an average structure (bottom). In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected by the stabilization of conjugation alone.
Aliphatic compounds can be saturated, joined by single bonds , or unsaturated, with double bonds or triple bonds . If other elements ( heteroatoms ) are bound to the carbon chain , the most common being oxygen , nitrogen , sulfur , and chlorine , it is no longer a hydrocarbon, and therefore no longer an aliphatic compound.
Aromaticity can be induced in compounds having a [10]annulene-type core if planarity is forcibly imposed by other substituents. Two methods to do so are known. One method is to formally replace two hydrogen atoms by a methylene bridge ( −CH 2 − ); this gives the planar bicyclic 1,6-methano[10]annulene ( 5 ).
Pentalene is a polycyclic hydrocarbon composed of two fused cyclopentadiene rings. [2] It has chemical formula C 8 H 6.It is antiaromatic, because it has 4n π electrons where n is any integer.