Cycloarenes, a new class of aromatic compounds, II. molecular structure and spectroscopic properties of kekulene

The molecular structure of kekulene (1) was determined by X‐ray structure analysis. From the bond lengths of 1 a remarkable localisation of aromatic sextets and double bonds is concluded (cf. formula 1b). – The problem of annulenoid versus benzenoid diatropicity in 1 is discussed on the basis of 1H NMR absorptions. These data, in agreement with recent theoretical calculations, support a predominant ring‐current induction in the benzenoid subunits of 1 and rule out a significant contribution of annulenoid structures like 1a. – Absorption and emission spectra of 1 are discussed as are the zero‐field splitting parameters of the excited triplet state of 1