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One Shocked Chemist

Molecular surprises are sometimes right in front of us, if only we’d do the math

Roald Hoffmann

Graphene, Graphane

2011-03MargHoffmannFC.jpgClick to Enlarge ImageThe 2010 Nobel Prize in physics was given to Andre Geim and Konstantin Novoselov, both of the University of Manchester in England, for the isolation and characterization of graphene. The sheetlike structure of carbon in graphite has been long known; the honeycomb sheets of carbon are loosely bound to each other by weak intermolecular forces. But it took the courage of a simple physical procedure, drawing a block of purest graphite across a piece of adhesive tape (technically, “exfoliation of pyrolytic graphite”), for Novoselov, Geim and their coworkers to make reproducibly isolable and manipulable multilayer and monolayer sheets of graphene.

Graphane is a single layer of graphene that is hydrogenated, with one hydrogen added per carbon in the graphene layer. If the hydrogens are added regularly above and below the sheet at alternate carbons, one gets what a chemist would call all-chair cyclohexane rings. One can also get a variant with boat cyclohexane rings, as shown in middle of the third figure (at right), as well as a third one, in the bottom of the third figure, whose structure is related to a common motif in hundreds of inorganic compounds (such as BaIn2 or TiNiSi). (A fourth variant, also built from boat-shaped rings, has been added for this online edition [below, left]).

2011-03MargHoffmannF4C.jpgClick to Enlarge ImageGraphene is real. But has graphane been made? The approach of Daniel C. Elias and his colleagues at the University of Manchester comes closest, but we have no crystal structure, only rough images of the material from transmission electron microscopy. To be sure, there is no shortage of theoretical calculations of graphane.

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