Collect. Czech. Chem. Commun. 1981, 46, 2540-2556

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

Bohumír Kouteka, Lubomír Musila, Jiří Veleka, Antonín Lyčkab, Dobroslav Šnoblb, Miroslava Synáčkováa and Milan Součeka

a Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague 6
b Research Institute of Organic Syntheses, 532 18 Pardubice-Rybitví


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.