Pollyynes and the formation of fullerenes

Summary

The synthesis and microwave study of linear cyanopolyynes, HC₅N and HC₇N, in the mid-1970s was followed by the unanticipated detection of these, and longer chains (HC₉N and HC₁₁N), in space. To gain insight into the way in which such species and carbon clusters in general might form, an experiment was devised in 1985 to simulate conditions in carbon stars, involving the laser vaporization of graphite in a supersonic nozzle and detection of the resulting carbon species by mass spectrometry. This initiative resulted in the serendipitious discovery of an entirely new allotrope of carbon, C₆₀, named buckminsterfullerene after the inventor of the geodesic dome.

Introduction

Acetylenes continue to provide a seemingly inexhaustible reservoir of novel materials, with extended conjugated systems embodied in polyynes, polyenes (polyacetylenes), enynes, cumulenes and various combinations thereof featuring prominently. Researches into conducting polymers are a case in point (Masuda & Higashimura 1984; Wegner 1981), as is the quest for natural products (Bohlmann et al. 1973; Jones & Thaller 1978) and their derivatives, some of which display high levels of pharmacological activity. A set of unique circumstances, which augur well for synthesis is partly responsible for this situation; notably the relatively high acidity of the alkynyl hydrogen (facilitating substitution and oxidative coupling) and the ease with which the triple bond can be induced to polymerize or participate in cycloadditions. The ubiquitous C₂ unit also acts as a focus for combustion studies and, for example, for investigations into the nature of soot. The results of such work often turn out to be wholly unexpected and this is particularly true in the way fullerenes were discovered.