For homoannulene ester 15, a homoaromatic cycloheptatrienyl fragment seems to be present as indicated by the bond length equalization (shortest double bond is 1.364 Å (Fig. , red arrows) and the longest single bond is 1.420 Å long (Fig. , blue arrows)). The formal vinyl substituents in the barbaralone substructure show alternating (single and double) bond lengths (ca. 1.45 and ca. 1.34 Å, respectively), indicating a 6 homoaromatic compound with two vinyl substituents. Also, for homoannulene carboxylic acid 16, equalized bond lengths are observed (1.428 and 1.360 Å for longest C-C-single and shortest C=C-double bond in the cycloheptatriene moiety). In contrast, non-oxidized triasterane 14a displays the expected bond length alternation for a 1,3-diene and lacks any indication for homoconjugation. We compared our observations to Quast's barbaralane 4 (Fig. ), which to our knowledge shows the most neutral homoaromatic properties reported so far (1.459 and 1.347 Å for longest C-C-single and shortest C=C-double bond). Homoannulene ester 15 and carboxylic acid 16 show significantly higher bond length equalization than barbaralane 4. Indeed, the bond length equalization observed for 15 and 16 is rather comparable to Vogel's methano [10]annulene 17 (1.372-1.419 Å ), which is considered aromatic and longest single bond (blue arrows) of the (homo)aromatic part of methano [10]annulene (17) , barbaralane 4 by Quast , triasterane 14a, homoannulene ester 15 and homoannulene carboxylic acid 16.