Robert Curl Jr.

Lecture & Discussion: The Chemistry of Elemental Carbon


Abstract

Because of its remarkable ability to make strong single, double, and triple bonds with itself, the chemistry of elemental carbon is remarkably rich. The forms of carbon containing single bonds only are the tetrahedral networks of diamond and lonsdaleite. Diamond, in particular, has valuable practical uses especially in cutting softer materials and as an efficient transporter of heat.

A completely different elemental structure is the hexagonal network of alternating single and double bonds (in aromatic resonance) of graphene. Scientific and economic interest in structures based upon this motif, as often modified by the introduction of five and seven membered rings, became intense with the discovery in 1985 that if elemental carbon vapor condenses under the right conditions molecular carbon spheroidal shells (fullerenes) form. The development in 1990 of a simple method for making macroscopic quantities of these molecules resulted in enormous interest in the fullerenes and in general in heightened interest in the structures and uses of all forms of elemental carbon. The discovery in 1992 that a single layer of graphene could roll into a tube and join edges (a single-walled carbon nanotube) and that this material could be produced in quantity resulted in new opportunities for studying and using this material. The theory of these tubes showed that these tubes could come in a variety of chiralities and diameters and showed that 2/3 of these varieties should conduct electricity like a semiconductor and the other 1/3 like a metal. These electronic properties and the enormous predicted tensile strength of the tubes suggested a number of important applications for these tubes. The latest major development in elemental carbon chemistry is the isolation of graphene. Although a reasonable theoretical treatment of a single graphene sheet was published in 1947 and it has been well known even longer that graphite consists of stacked layers of graphene, it was not until 2004 that a graphene sheet was isolated and its properties studied experimentally.

In spite of all these developments, we are still profoundly ignorant of the structure of charcoal - known to
homo erectus
a million years ago and used at least thirty thousand years ago by
homo sapiens
to produce the first works of art: the oldest known of which are the cave drawings at Chauvet. And our structural ignorance extends to at least two other well-known forms of elemental carbon.


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