The structure and first ¹H NMR spectral assignment of piperazine-C₆₀ adducts

The 1H NMR spectrum of the piperazine-C60 monoadduct has been assigned for the first time almost 10 years after it was synthesised. The preparation and characterisation of the first (C2-substituted piperazine)-C60 monoadduct are also described, revealing the C2-substituent as occupying an exo position on the addend

Localisation and reversal of paratropic ring currents in molecules with formal anti-aromatic electron counts

The aromatic character of the six smallest members of the of alpha,omega-bicyclopentadiene-polyacene series (1(n)) has been assessed using magnetic and energetic criteria. Current density maps (CTOCD-DZ/6-31G**//B3LYP/6-31G**) show that. along the series, the ring current changes from paratropic in pentalene (1(0)) and s-indacene (1(1)), through quenched in 1(2) and 1(3), to diatropic in 1(4) and 1(5). These changes are rationalised in terms of orbital contributions to current. Valence bond calculations (VB/6-31G//B3LYP/6-31G**) in which the pi system is composed of strictly atomic p-orbitals, show that the electronic structures in these homologous series can be described in terms of the two closed-shell Kekule resonance structures for the smallest molecules, but that in the larger molecules allyl-polyacene-allyl biradical structures prevail, owing to the larger resonance energies. This trend in electronic structure parallels the switch from paratropic to diatropic character

The spin-coupled picture of clamped benzenes

Spin-coupled investigations into the clamped benzenes tris(bicyclo[2.1.1]hexano)benzene and tris(benzocyclobutadieno)benzene probe the effects of clamping groups by distinguishing between a central aromatic benzene moiety and localized π bonding in central 1,3, 5-cyclohexatriene-like rings, in terms of resonance between spin functions, orbital snapshot diagrams, and orbital overlap integrals