Essay Posted May 10, 2008 Report Share Posted May 10, 2008 Structurally, graphene is chicken wire, composed only of Carbon atoms.These linked hexagons (cyclical molecules) are double bonded (like the single hexagon, benzene) giving them their "aromatic" (volatile) character. ...for those who wondered what Polycyclic Aromatic Hydrocarbons (PAH's) are; although in this case it's just polycyclic aromatic carbon, until it gets oxidized a bit.So.... Thinking about graphene (and graphite) ...and the formation of diamond.... An image recently popped into my head about how the electronic structure must change from those sheets of pi orbitals into s orbitals, crosslinking the sheets of Carbon nuclei as they rearrange from hexagonal into the cubic -tetrahedral, whatever crystal structure that is diamond. :rolleyes: Does that sound right? Critiques, modifications, & alternatives welcome....I know graphene has many new and wonderful potential applications, but I'm just happy elucidating graphene's structure allowed me this visualization.;) Quote Link to comment Share on other sites More sharing options...
UncleAl Posted May 10, 2008 Report Share Posted May 10, 2008 If they wanted graphene for electronic circuits they could synthesize it to spec rather than piddle with sticky tape, graphite, and "studies" (grantology). Carbon-Based Curiosities Blog Archive Sunday Night Polymers- GrapheneTwo-Dimensional Graphene Nanoribbons Chemistry makes stuff, engineering makes things. Crappy stuff makes crappy things. Synthesize any graphene you like to spec, easily 10^15 units at a whack. Pendant arms allow for intermediate solubility. Lay out your 20 nm architecture device with gold connections, dip into the solution. Sequentially cleave the arms to reveal thiols. The circuits build themselves in parallel, a billion gates at a whack each for hundreds of quad-core CPUs on a 30 cm diameter production wafer. Why is everbody running about with their thumbs up their butts? Hire a chemist, solve the problem, then fire the chemist and reward your managers. Bloody stop whining and do it. Quote Link to comment Share on other sites More sharing options...
Essay Posted May 11, 2008 Author Report Share Posted May 11, 2008 Thanks for the graphene blog link. I just enjoyed an hour or so surfing around there. Well worth bookmarking....Carbon-Based Curiosities...and that Hoffman book Wiley::Solids and Surfaces: A Chemist's View of Bonding in Extended Structuressounds worthwhile too. That my speculative visualization does not sit shredded on the floor, after a visit by UncleAl, is high praise indeed I think. :shrug: Quote Link to comment Share on other sites More sharing options...
UncleAl Posted May 11, 2008 Report Share Posted May 11, 2008 As for graphite to diamond, sp2 to sp3 hybridization, the crystal lattice distortion necessary is ~23% distance compression then alternately pucker graphene planes up and down, both normal to to the bedding planes. One way gets you cubic diamond, the other way gets you hexagonal diamond (lonsdaleite). The shockwave from high explosive onto graphite will compress it to diamond in up to 80% yield. If you want larger than sub-micron diamond crystals (abrasive) something more clever is indicated. Quote Link to comment Share on other sites More sharing options...
Essay Posted May 11, 2008 Author Report Share Posted May 11, 2008 As for graphite to diamond, sp2 to sp3 hybridization, the crystal lattice distortion necessary is ~23% distance compression then alternately pucker graphene planes up and down, both normal to to the bedding planes. One way gets you cubic diamond, the other way gets you hexagonal diamond (lonsdaleite). The shockwave from high explosive onto graphite will compress it to diamond in up to 80% yield. If you want larger than sub-micron diamond crystals (abrasive) something more clever is indicated.I don't recall the details of the electronic hybridization (but 'knew' the double bonded, pi cloudy Carbons, changed into tetrahedral single bonded Carbons); but "alternately pucker graphene planes up and down, both normal to to the bedding planes," is a very well worded way of saying what I was trying to picture. Thanks, ...and for the neat graphic too.:( What the heck is: :eek:"the other way gets you hexagonal diamond (lonsdaleite)"?...or I can look that up later.... :autumnleaves:~ Quote Link to comment Share on other sites More sharing options...
UncleAl Posted May 12, 2008 Report Share Posted May 12, 2008 Lonsdaleite - Wikipedia, the free encyclopediaLonsdaleite Mineral DataThe Hexagonal Diamond (Lonsdaleite) StructureLonsdaleite "Aromatic" refers to the diamagnetic electron cloud of pi electrons above and below each ring, and their number: 4n+2 (n=1, 6/planar ring). Benzene is stabilized ~40 kcal/mole versus "cyclohexatriene." Antiaromatic systems have 4n electrons in cyclic conjugation. They are greatly destabilized. Dibenzylideneacetone, (Ph-CH=CH-)2C=O, is bright yellow. Tetraphenylcyclopentadieneone, the bottom arms hooked together to close a five-membered ring by removal of 2 hydrogens and bonding, is incredibly deep purple. The dipole contributor to carbonyl structure, (+)C-O(-), givees the ring anti-aromatic destabilization. All the pi-orbitals are lifted in energy and the optical absorbance decreases in energy from the near-UV to green. Similarly, cyclooctatetraene has 4n electrons (n=2). It avoids antiaromaticity by bending into a chair or boat to break pi-conjugation. However, add two electrons (e.g., react with potassium metal) and get 4n+2 electrons (n=2, aromatic!). Cyclooctatetraene dianion is planar, aromatic, and very stable. Two of them sandwich uranium(IV) - green - like two cyclopentadienide anions (aromatic again!) sandwich iron(II) to form ferrocene - red. Fun stuff. Quote Link to comment Share on other sites More sharing options...
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