.2.2.2.2.21,2,3,4,5,6)Cyclophane or superphane is a 6-fold bridged

cyclophane In organic chemistry, a cyclophane is a hydrocarbon consisting of an aromatic unit (typically a benzene ring) and a chain that forms a bridge between two non-adjacent positions of the aromatic ring. More complex derivatives with multiple aromatic ...

with all arene positions in the benzene dimer taken up by ethylene spacers. The compound has been of some scientific interest as a model for testing

aromaticity In chemistry, aromaticity is a chemical property of cyclic (ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to sat ...

and was first synthesised by

Virgil Boekelheide Virgil Boekelheide (28 July 1919 – 24 September 2003) was an American organic chemist and a professor in the department of chemistry at the University of Oregon. He is known for his work on aromatic compounds, particularly cyclophanes, and a ...

in 1979. Superphane is the base compound for a large group of derivatives with structural variations. The analogs with 2 to 5 bridges are also known compounds. The benzene rings have been replaced by other aromatic units, such as those based on

ferrocene Ferrocene is an organometallic compound with the formula . The molecule is a complex consisting of two cyclopentadienyl rings bound to a central iron atom. It is an orange solid with a camphor-like odor, that sublimes above room temperature, ...

or stabilized

cyclobutadiene Cyclobutadiene is an organic compound with the formula . It is very reactive owing to its tendency to dimerize. Although the parent compound has not been isolated, some substituted derivatives are robust and a single molecule of cyclobutadiene is ...

. Numerous derivatives are known with variations in the type and length of the bridging units.

Synthesis

The first synthesis of superphane itself by Boekelheide involved forming pairs of bridging units. At each stage, two ''o''-chloromethyl toluene structures are

pyrolyzed The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...

to form ''o''-

xylylene In organic chemistry, a xylylene (sometimes quinone-dimethide) is any of the constitutional isomers having the formula C6H4(CH2)2. These compounds are related to the corresponding quinones and quinone methides by replacement of the oxygen atom ...

s, either directly or via

benzocyclobutene Benzocyclobutene (BCB) is a benzene ring fused to a cyclobutane ring. It has chemical formula . BCB is frequently used to create photosensitive polymers. BCB-based polymer dielectrics may be spun on or applied to various substrates for use in ...

intermediates. Upon further pyrolysis, these each undergo electrocyclic ring-opening to form ''o''-

s. These structures were not isolated—they immediately react via +4

cycloaddition In organic chemistry, a cycloaddition is a chemical reaction in which "two or more unsaturated molecules (or parts of the same molecule) combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity". ...

reactions to form two adjacent bridges between the aromatic rings. The process started from 2,4,5-trimethylbenzyl chloride 1, which was pyrolyzed at 700 °C to give benzocyclobutene 2 and further pyrolyzed to the

cyclooctane Cyclooctane is a cycloalkane with the molecular formula (CH2)8. It is a simple colourless hydrocarbon, but it is often a reference compound for saturated eight-membered ring compounds in general. Cyclooctane has a camphoraceous odor. Conformatio ...

dimer 3.

Rieche formylation Rieche formylation is a type of formylation reaction. The substrates are electron rich aromatic compounds, such as mesitylene or phenols, with dichloromethyl methyl ether acting as the formyl source. The catalyst is titanium tetrachloride Tita ...

afforded 4 (after separation from other regioisomers),

aldehyde reduction In organic chemistry, carbonyl reduction is the organic reduction of any carbonyl group by a reducing agent. Typical carbonyl compounds are ketones, aldehydes, carboxylic acids, esters, and acid halides. Carboxylic acids, esters, and acid halides ...

using

sodium borohydride Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula Na BH4. This white solid, usually encountered as an aqueous basic solution, is a reducing agent that finds applic ...

gave diol 5, and then

chlorination Chlorination may refer to: * Chlorination reaction, a halogenation reaction using chlorine * Water chlorination Water chlorination is the process of adding chlorine or chlorine compounds such as sodium hypochlorite to water. This method is us ...

using

thionyl chloride Thionyl chloride is an inorganic compound with the chemical formula . It is a moderately volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately per year bein ...

) gave dichloride 6. Another pyrolysis gave tetrabridged cyclophane 7, another

formylation reaction A formylation reaction in organic chemistry refers to organic reactions in which an organic compound is functionalized with a formyl group (-CH=O). The reaction is a route to aldehydes (''C''-CH=O), formamides (''N''-CH=O), and formate esters (' ...

gave dialdehyde 8, another reduction/chlorination sequence gave dichloride 9, and a final pyrolysis gave superphane 10 as hard white crystals with

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends ...

325–327 °C. Superphane synthesis Boekelheide

Other synthetic routes were published by Hopf (1983) and another by Boekelheide (1984).

Structure and properties

X-ray analysis shows D_6h

molecular symmetry Molecular symmetry in chemistry describes the symmetry present in molecules and the classification of these molecules according to their symmetry. Molecular symmetry is a fundamental concept in chemistry, as it can be used to predict or explain ...

with the aromatic planes separated by 262 pm. The sp²-sp³ carbon carbon bonds are out of planarity with the benzene rings by 20°. The

strain energy In physics, the elastic potential energy gained by a wire during elongation with a tensile (stretching) force is called strain energy. For linearly elastic materials, strain energy is: : U = \frac 1 2 V \sigma \epsilon = \frac 1 2 V E \epsilon ...

is estimated at 20 kcal/mole.

Proton NMR Proton nuclear magnetic resonance (proton NMR, hydrogen-1 NMR, or 1H NMR) is the application of nuclear magnetic resonance in NMR spectroscopy with respect to hydrogen-1 nuclei within the molecules of a substance, in order to determine the str ...

shows just one peak at 2,98 ppm and

carbon NMR Carbon-13 (C13) nuclear magnetic resonance (most commonly known as carbon-13 NMR spectroscopy or 13C NMR spectroscopy or sometimes simply referred to as carbon NMR) is the application of nuclear magnetic resonance (NMR) spectroscopy to carbon. It i ...

two at 32 ppm and 144 ppm.

References

{{Reflist Hydrocarbons Benzene derivatives Cyclophanes