Perturbation of the fuchsone chromophore by 3,5-methyl substitution. Sterically crowded exocyclic double bond

Abstract

Several 3,5-methyl substituted fuchsones have been synthesized and characterized by means of UV and NMR spectroscopy as well as dipole moment measurements. Two basic types of behaviour of the longest wavelength band have been found for these derivatives in comparison to 2,6-substituted analogues i.e. hypochromic effect and bathochromic shift. These effects can be attributed to a steric crowding of the C(4)-C(7) double bonds. The role of the steric interactions in the ground state and in the excited state is discussed.

The Synthesis of Novel p‐Quinone Methides: O‐Dealkylation of5‐(p‐Alkyloxyaryl)‐10,11‐dihydrodibenzo[a,d]cyclohepten‐5‐ols and Related Compounds

“…The theoretical and stereochemical aspects, the UV and IR spectra of simple p-QMs derived from trityl systems had been studied in detail, but their synthetic uses or chemical reactions have surprisingly not been that well documented. [29][30][31][32][33][34][35] Furthermore, the simplest p-QM, 4-methylene-cyclohexa-2,5-dienone, has eluded isolation until only fairly recently, when it was trapped by complex formation with metals. [36,37] Tricyclic analogues based on fluorene and xanthene, have also not as yet been successfully synthesized by any of these acid-mediated methods, although fluorenyl derivatives were prepared using Wittig reaction methodology, as well as by oxidative methods, requiring either anhydrous or rather drastic reaction conditions.…”