Theoretical studies of [n]paracyclophanes and their valence isomers

Revisiting the von Neumann–Wigner noncrossing rule and validity of a dynamic correlation diagram method

The noncrossing rule for potential energy surfaces can be applied only, as originally postulated by von Neumann and Wigner, to slowly occurring changes; it has, however, over many years, been widely used to rationalize fast chemical reactions. Taking the conversion of Dewar benzene to benzene as an example, we demonstrate a reaction that has a timescale for which crossings are allowed. Since it is now established that elementary chemical reactions proceed over ca. 10–100[Formula: see text]fs, as revealed experimentally by Zewail, the noncrossing rule cannot any longer be said to be valid for most chemical reactions. We further demonstrate that the mechanism of the chemiluminescent conversion of Dewar benzene to benzene is explained by an electronic state diagram derived using a dynamic correlation diagram method which allows crossings, whereas the reaction is not explained by a conventional approach, applying the noncrossing rule using a static correlation diagram method.

A theoretical study of new representatives of closed- and open-circle benzofuran and benzocyclopentadienone oligomers

Strain energies for oxa[n]circulene species relative to the unstrained tetraoxa[8]circulene.

Non-empirical calculations of NMR indirect carbon-carbon coupling constants. Part 10--carbocages

A comprehensive theoretical study of nine classical caged polycycloalkanes (tetrahedrane, prismane, homoprismane, quadricyclane, cubane, pentaprismane, hexaprismane, adamantane and diamantane) was carried out with special focus on the structural behavior of their J(C,C) values calculated at the SOPPA level. The structural behavior of J(C,C) in small carbocages is dominated by steric strain whereas in medium-sized polycycloalkanes the J(C,C) values show no marked peculiarities and follow several well-defined structural trends typical of other alicyclic compounds.