Enthalpy of isomerization of quadricyclane to norbornadiene

Solar energy is abundant all over the world, but to be useful, the energy received must either be transformed to electricity, heat or latent chemical energy. The latter two options have the advantages that the energy can be stored. In molecular solar-thermal energy storage (MOST), solar energy is stored in chemical bonds; this is achieved using compounds undergoing photoinduced isomerisation to metastable isomers. Using a catalyst, the isomer can be recycled to its original form and the stored energy released as heat. This chapter describes the principles of the MOST concept and goes into details about the most studied MOST systems. The last part of the chapter deals with the integration of MOST systems into operational devices.

Molecular Solar-Thermal Energy Storage: Molecular Design and Functional Devices

2-Arylhexachloronorbornadiene undergoes photoisomerization to the corresponding quadricyclane, which returns back to the norbornadiene upon heating without catalyst Effect of aryl substituents on the thermal reversion suggests that both spin delocalization and polar effect equally contribute to the stabilization of the transition state

Effect of Aryl Substituents on 2-Aryl-1,4,5,6,7,7-hexachloronorbornadiene–Quadricyclane Reversible Isomerization

The isomerization pathways of model high energy structures are of interest because of their relation to high energy density fuels. Electron resonance has been found to greatly affect the relative activation barriers for several isomerization pathways, and the major goal of this research was to accurately describe its role in determining the relative barriers for strain energy release pathways. This research was centered around the potential energy surfaces (PESs) for σ bond breaking and π bond rotation in these highly strained structures. Of particular interest was how resonance and or electronegativity would affect the allowed or disallowed nature of the activation barriers in these systems. The two model systems of benzvalene and dihydrobenzvalene have been explored previously. These tricyclic structures were shown to be able to undergo a pericyclic ring opening mechanism. That particular process can either occur in either a conrotatory manner or a disrotatory manner. The disrotatory process was found to be Woodward-Hoffman symmetry allowed in benzvalene, but the conrotatory process was found to be Woodward-Hoffman symmetry allowed in dihydrobenzvalene. The only difference between these two structures was the presence or absence of a π bond. Much of the current work was focused on deliberately manipulating the allowed and disallowed nature of these type of pericyclic reactions in an attempt to see if the line that is drawn between the allowed and disallowed processes of a particular molecular system could be “blurred”. It was also interesting to see that in certain extreme

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Dana S. Bechtold

Papers

Kinetics of the isomerization of quadricyclane to norbornadiene promoted by tin(II) chloride and palladium(II) chloride