- Radialene
; 1999; 64(7) pp 2287 - 2292; (Article) DOI|10.1021/jo9818] . For some members the unsubstituted parent radialenes are elusive but many substituted derivatives are known.
Radialenes are related to open-chain
dendralenes and also to compounds likebutadiene andbenzene which also consist of a ring of sp2 hydridized carbon atoms.Radialenes are investigated in
organic chemistry for their unusual properties and reactivity but have not ventured outside the laboratory. Reported uses are as experimental building blocks for novel organic conductors and ferromagnets "Planar [6] Radialenes: Structure, Synthesis, and Aromaticity ofBenzotriselenophene and Benzotrithiophene" Asit Patra, Yair H. Wijsboom, Linda J. W. Shimon, and Michael BendikovAngew. Chem. Int. Ed. 2007, 46, 8814 –8818 DOI|10.1002/anie.200703123] . The first radialene called "hexaethylidencyclohexane" was synthesised in 1961 [ de icon "Zur Kenntnis der Hexaalkylbenzole. 3. Mitteilung. Über einen neuen Kohlenwasserstoff C18H24 (Hexaäthylidencyclohexan)"Helvetica Chimica Acta Volume 44, Issue 2, Date: 1961, Pages: 380-386 H. Hopff, A. K. Wick] .Conformation
[3] and [4] radialenes are expected to have a planar
molecular geometry with all carbon atoms in the same plane. This is verified experimentally in "hexamethyl [3] radialene" and "cyclobutanetetraonetetrakis(hydrazone)". "Decamethyl [5] radialene" has a twist envelope geometry with C2 symmetry while achair conformation is calculated for [6] radialene and found experimentally for "hexa-(ethylidene)cyclohexane"Due to their specific pi-electron distributions, hydrocarbons such as
perylene andtriphenylene are not considered radialenes. One studydescribes a [6] radialene composed of thiophene units [Coupling reaction reagentbis(1,5-cyclooctadiene)nickel(0) . Equal amount of tetramer formed ] ::
This compound is reported as planar with D3h symmetry (
X-ray diffraction ) but notaromatic : thecarbon-carbon bond lengths are unusually long (145 pm vs. 140 pm forbenzene ) and the calculated NICS value is close to zero.ynthesis & properties
The parent [3] , [4] , [5] and [6] radialenes polymerize when in contact with oxygen.
[4] Radialene
The unsubstituted [4] radialene has been prepared in an
elimination reaction of "cis,trans,cis-tetra(bromomethyl)cyclobutane" withsodium methoxide inethanol ["The Chemistry of Photodimers of Maleic and Fumaric Acid Derivatives. IV.1 Tetramethylenecyclobutane" Gary W. Griffin and Laurence I. PetersonJ. Am. Chem. Soc. ; 1962; 84(17) pp 3398 - 3400; DOI|10.1021/ja00876a033]Hydrogenation withplatinum on carbon gives "cis,cis,cis-tetramethylcyclobutane" in accordance with the proposed structure. On standing in air atroom temperature the compound accepts oxygen and polymerizes.References
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