Bridge Flipping Data from Dynamic ¹H‐NMR Spectra of 2,6‐Dimethyl‐[9](3,5)‐Pyridophane and its Pyrylium and N‐Methylpyridinium Analogs

Dynamic ¹H‐NMR spectra between room temperature and −90 °C for the title compounds indicate that the flipping of the nonamethylene bridge is slowed down on cooling (ΔG_c‡ = 9.8 kcal/mol for the 2/8 methylene groups in the pyridinophane with coalescence temperature T_c = −58 °C) but the pseudorotation persists even at −90 °C. The bridge flipping is somewhat easier in the N‐methylpyridinium (ΔG_c‡ = 9.7 kcal/mol, T_c = −63 °C) and in the pyrylophanium perchlorates (ΔG_c‡ = 8.9 kcal/mol, T_c = −78 °C).