Cycloarenes, a New Class of Aromatic Compounds, II. Molecular Structure and Spectroscopic Properties of Kekulene

Abstract

Abstract 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 1 H 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 .