Quadricyclane

Quadricyclane is a highly strained tetracyclic hydrocarbon. Despite its strain energy of 78.7 kcal/mol, it is stable at low temperatures.

In 1961, the laboratories of two outstanding organic chemists reported the synthesis of quadricyclane by the sensitized ultraviolet irradiation of norbornadiene¹ in solution. The feat was accomplished by George S. Hammond*, Nicholas J. Turro, and Alfred Fischer at Caltech (Pasadena, CA) and by William G. Dauben* and Robert L. Cargill at the University of California, Berkeley. In both papers, the authors called the compound the now-obsolete “quadricyclene”.

In the 1980s and again in the early 2000s, the photochemical conversion of norbornadiene to quadricyclane was proposed as a way to store solar energy; but back then it was thought that the Sun does not emit enough ultraviolet radiation to make this method practical. In a 2021 account of norbornadiene/quadricyclane photoswitches for molecular solar thermal energy storage applications, however, Jessica Orrego-Hernández, Ambra Dreos, and Kasper Moth-Poulsen* at Chalmers University of Technology (Gothenburg, Sweden) described liquid storage systems that can store solar energy for as long as 18 years. They also proposed solid-state coatings for windows that can store incoming sunlight.

In December 2022, Ning Li and colleagues at the Chinese Academy of Sciences (Dalian), Dalian National Laboratory for Clean Energy, and the University of Chinese Academy of Sciences (Beijing) reported that C₁₂ quadricyclane derivatives made from cellulose-derived 2,5-hexanedione² are ideal components of sustainable aviation fuels.