Furthermore, the -carbonyl methine group of homoannulene ester 15, facing away from the potential homoaromatic system, displays an expected chemical shift of  = 3.81 ppm (Fig. , top). In stark contrast, the -carbonyl methine 1 H NMR resonance of homoannulene carboxylic acid 16, placed directly above the homoaromatic system, is significantly shifted up-field to  = 0.89 ppm, although being placed directly adjacent an electron-withdrawing ketone (Fig. , bottom). Even taking the anisotropic effect of the double bonds into account , this unusually high up-field shift of  = 2.92 ppm unambiguously indicates the presence of a diamagnetic ring current , which shields the methine hydrogen of 16 . Both key spectral properties (downfield shift of hydrogen atoms 5 and 6 and shift of bridgehead methine hydrogen) are missing in elassovalene (3) , whose analogous methine hydrogen appears at  = 1.77 ppm (and Csp2-H appear at 6.30 and 6.64 ppm, respectively). Homoannulene ester 15 as well as homoannulene carboxylic acid 16 possess an interrupted cyclic  system. The observation of a strong ring current therefore indicates the existence of through-space interaction of the  system leading to a delocalization of -electrons 2 . Therefore, the fused barbaralone framework prepared in this study seems to structurally enable an efficient homoconjugation by an elongated bridge that facilitates the through-space interaction of carbon atoms C(4)⋅⋅⋅C (9) through steric congestion. Combined, these findings serve as important indication that homoannulene ester 15 and homoannulene carboxylic acid 16 are neutral homoaromatic compounds. One of the paramount characteristics for homoaromatic compounds is bond length equalization of the single and double bonds involved . With the X-ray structures of 14, 15 and 16 available for detailed analysis, we observed significant shortening of the single bonds and elongation of the double bonds (Fig. ). As limits, bond lengths of isolated C-C-single (1.54 Å) and C=C-double bonds (1.34 Å) as well as the "ideal" bond length equalization of benzene (1.39 Å) are considered for comparison . These values are compared to the longest C-Csingle bond and the shortest C=C-double bond, respectively, of the respective neutral homoaromatic molecules 14a, 15 and 16 (see the Supplementary Figure for detailed analysis of all bond lengths).