Life on earth is based on compounds that have carbon frames and backbones. Today, chemists have added to the world of biomolecules and biopolymers approximately 107 different synthetic molecules and polymers, the structures of which also depend on the formation of strong, stable carbon–carbon bonds. Although the stability of carbon–carbon bonds has been recognized for more than a century, the two natural modifications graphite and diamond were, until recently, the only allotropic forms of carbon on earth that were available in macroscopic quantities and were structurally well characterized. With the synthesis of macroscopic quantities of buckminsterfullerene (C60) and the higher fullerenes (C70, C76, C78, etc.) and the exploration of the fascinating properties of these all-carbon spheres, this situation has completely changed. In the coming decades, the design, preparation, and study of novel molecular and polymeric allotropic forms of carbon will be a central topic in chemistry. Research in this area will dramatically advance the fundamental knowledge on carbon-based matter and, as already illustrated by the ongoing work on C60, generate unprecedented technological perspectives. This review surveys synthetic organic-chemical approaches toward the preparation and study of all-carbon molecules and polymers that differ from the familiar networks of graphite and diamond as well as from the fullerenes. We will also discuss the ongoing research on fullerenes with a particular focus on the synthetic approaches to these all-carbon spheres and their transition metal complexes.

Synthetic approaches toward molecular and polymeric carbon allotropes

Das Leben auf der Erde beruht auf Verbindungen mit einem Kohlenstoffgerust. Bis zum heutigen Tage haben Chemiker die Welt der Biomolekule und Biopolymere um etwa 107 verschiedene synthetische Molekule und Polymere erweitert, deren Struktur ebenfalls von der Bildung stabiler CC-Bindungen abhangt. Obwohl die Stabilitat von CC-Bindungen seit uber hundert Jahren wohlbekannt ist, waren Graphit und Diamant bis vor kurzem die einzigen auf der Erde in makroskopischen Mengen verfugbaren und strukturell charakterisierten Kohlenstoffallotrope. Mit der Darstellung makroskopischer Mengen an Buckminsterfulleren C60 und an hoheren Fullerenen wie C70, C76, und C78 sowie der Erforschung der faszinierenden Eigenschaften dieser Kohlenstoffkugeln hat sich diese Situation inzwischen drastisch geandert. Im Laufe der kommenden Jahrzehnte wird der Entwurf, die Darstellung und das Studium neuer molekularer und polymerer allotroper Formen des Kohlenstoffs eine zentrale Stellung in der Chemie einnehmen. Dies wird zu einer wesentlichen Vertiefung unserer grundlegenden Kenntnisse uber die aus Kohlenstoff aufgebaute Materie fuhren und — wie die aktuelle C60-Forschung zeigt — vollig neue Perspektiven fur technologische Entwicklungen bieten. Dieser Artikel gibt eine ubersicht uber organisch-chemische Synthesestrategien fur ausschlieslich aus Kohlenstoff aufgebaute Molekule und Polymere, welche strukturell von den bekannten Graphit- und Diamant-Netzwerken und auch von den Fullerenen abweichen. Wir diskutieren auch die aktuelle Fullerenforschung, wobei wir besonderes Gewicht auf die Synthesestrategien legen wollen, welche zu den Fullerenen sowie deren ubergangsmetallkomplexen fuhren.

Strategien zum Aufbau molekularer und polymerer Kohlenstoffallotrope

Cyclobutarenes and Related Compounds

The oxygen quenching rate constants of aliphatic ketones (acetone, 2-pentanone, 2-hexanone, 4-heptanone) and diketones (biacetyl and camphorquinone) have been determined for the singlet- and triplet-excited state by time-resolved fluorescence and triplet transient absorption spectroscopy, and the quantum yields for singlet oxygen formation were measured. It was observed that the quenching rate constants for the singlet state of aliphatic ketones are considerably smaller than for their triplet states. The efficiencies for singlet oxygen production of the aliphatic ketones were 0.2−0.3, while those of most diketones fall in the 0.4−0.6 range. The changes in the efficiencies for singlet oxygen production and of the oxygen-quenching rate constants for singlet- and triplet-excited n,π* states, ketones and azoalkanes are discussed in terms of variations in excited state energies and charge-transfer interactions with oxygen.

Oxygen Quenching of Excited Aliphatic Ketones and Diketones

Efficient acetalisation of aldehydes catalyzed by titanium tetrachloride in a basic medium

First measurements of absolute rate constants for oxacarbene intermediates produced in the photochemistry of benzocyclobutenedione

Decafluorobenzophenone triplets, which have a triplet energy very close to that of benzophenone, are much more reactive than benzophenone in quenching reactions that involve hydrogen transfer and/or charge transfer. An excellent correlation has been observed between the rate constants for charge transfer quenching and the oxidation potential of the substrate. In the case of 2-propanol, where the reactivity can be fully accounted for by hydrogen transfer, decafluorobenzophenone is 35 times more reactive than benzophenone. Pentafluorobenzophenone shows intermediate behaviour. Keywords: laser photolysis, benzophenones, triplet states, charge transfer, photoreduction.

D. R. Boate

Papers

First measurements of absolute rate constants for oxacarbene intermediates produced in the photochemistry of benzocyclobutenedione

A laser flash photolysis study of the behaviour of polyfluorophenyl ketones in solution

First Measurements of Absolute Rate Constants for Oxacarbene Intermediates Produced in the Photochemistry of Benzocyclobutenedione.