Quinoidal Azaacenes: 99 % Diradical Character

Quinoidal azaacenes with almost pure diradical character (y=0.95 to y=0.99) were synthesized. All compounds exhibit paramagnetic behavior investigated by EPR and NMR spectroscopy, and SQUID measurements, revealing thermally populated triplet states with an extremely low‐energy gap ΔE_ST′ of 0.58 to 1.0 kcal mol^?1. The species are persistent in solution (half‐life≈14–21 h) and in the solid state they are stable for weeks.     

Quinoidal Azaacenes: 99 % Diradical Character

Quinoidal azaacenes with almost pure diradical character (y=0.95 to y=0.99) were synthesized. All compounds exhibit paramagnetic behavior investigated by EPR and NMR spectroscopy, and SQUID measurements, revealing thermally populated triplet states with an extremely low-energy gap ΔE_ST′ of 0.58 to 1.0 kcal mol⁻¹. The species are persistent in solution (half-life≈14–21 h) and in the solid state they are stable for weeks.     

Inside Cover: A Phosphine‐Mediated Conversion of Azides into Diazo Compounds (Angew. Chem. Int. Ed. 13/2009)

In 1919 H. Staudinger and J. Meyer reported the reductive fragmentation of an azide to an amine. In their Communication on page 2359 ff., E. L. Myers and R. T. Raines report the complementary reaction—cleavage of the other N? N bond in an azide to yield a diazo compound. Both transformations rely on a reagent that contains P^III. The painting, The Alchymist, in Search of the Philosopher's Stone, Discovers Phosphorus, by J. Wright (1771), depicts the discovery of phosphorus by H. Brandt in 1669 (cover art by H. A. Steinberg).