Die Bildungsenthalpie 1,6‐überbrückter [10] Annulene

The enthalpies of formation of 1.6‐methano‐[10] annulene (IV) (ΔHf298 (IV, g) = 75.2 ± 0.6 kcal mol−1), 1.6‐imino‐[10] annulene (V) (ΔHf298(V, g) = 87.8 ± 0.7 kcal mol−1) and of 1.6‐oxido‐[10] annulene (VI) (ΔHf298(VI, g) = 47.8 ± 1.2 kcal mol−1) have been determined by combustion calorimetry. The difficulties connected with an attempt to derive meaningfull «resonance energies» are discussed.