Graphene is a wonderful and promising material that has been the subject of intense study over the last few years. I try to keep abreast of new trends in chemistry, although graphene has only been on the outskirts of my vision. I’m an organic chemist, and I have been for over 12 years, ever since I earned my Ph.D. in that subject. Graphene is a molecule that contains only carbon, which by definition would usually put it under my area of responsibility. Organic chemists are interested in carbon-containing compounds. If the molecule doesn’t have carbon in it’s makeup, it falls to inorganic chemists to study and investigate it. A molecule made of nothing but carbon, then, would seem to be the ultimate organic molecule.
However, graphene lacks any chemical “handholds”. When I look at a molecular structure, my training and experience leads me to pick out tiny areas of the molecule which (despite their size) possess most of the reactivity. These small parts are called functional groups, and they are the sites at which reactions are going to take place. The rest of the molecule simply goes along for the ride. These groups are usually heteroatoms such as oxygen, nitrogen, and sulfur, although phosphorus and the halogens (bromine, chlorine, iodine) also play a role. The point is, despite carbon being the central interest of organic chemistry, carbon really doesn’t have interesting reactivity when it comes to substitution chemistry, especially if it’s already fully coordinated.
Graphene is sheet-like molecule containing of carbon atoms all linked to each other in a repeating hexagon. When I look at the molecule, I start to panic a little, because it doesn’t have any functional groups beyond the double bonds – and those are very hard to substitute in a compound such as this. So, graphene hasn’t really been of interest to me, despite all of its interesting properties. That changed recently when I read of an advance made by chemists at Rice University. They published their results in the journal Nature Communications, which publishes short prestigious papers in chemistry. The researchers describe a two-step technique which transforms graphene into the fully hydrogenated version, named graphane. A mask is used, which allows a pattern to be placed onto the surface. The result is a vast ocean of untouched graphene with small pockets of graphane, which has carbon-hydrogen bonds. These bonds are much more reactive than the carbon-carbon bonds that were previously presen. Exposing the graphane to diazonium salts (nitrogen containing reactants) leads to a functionalized graphene substrate that can be carried onwards in a multistep organic synthesis.
This discovery will open up graphene as a starting material for the extremely versatile and powerful tools of organic chemistry. Given that unsubstituted graphene was sufficiently interesting to earn a Nobel prize, substituted graphene will no doubt lead to some exciting results. As an organic chemist, I’m very happy that my field will finally be able to contribute towards these developments.
The source of this molecule can be found at:
Sun, Z., et al. “Towards hybrid superlattices in graphene”. Nature Communications 2011, 2, 559.