4,6-Dinitro-benzofuroxan and -benzofurazan adducts of 1,8-bis(dimethylamino)naphthalene. A conformational study by low temperature nuclear magnetic resonance

Low temperature 1H nuclear magnetic resonance spectra of the zwitterionic and anionic carbon-bonded adducts resulting from the addition of 4,6-dinitrobenzofuroxan (DNBF) or 4,6-dinitrobenzofurazan (DNBZ) to 1,8-bis(dimethylamino)naphthalene, the proton sponge PS, have been recorded at 500 MHz inDMF-d7. They reveal the presence of two conformers due to restricted rotation around the [Formula: see text] bond between C-4 of PS and the sp3 carbon C-7′ of the negatively charged DNBF− or DNBZ− moiety. The geometry of these conformers was deduced from nuclear Overhauser enhancement difference spectra. The results show that in all systems there is a large preference for the less strained s-trans type of conformation, whose population lies between 80 and 90%. An interesting feature is the dependence of the chemical shift of the peri H5 proton on the conformation. In accordance with previously reported peri effects, a significant deshielding of H5 is observed in the major conformers, where this proton is spatially close to H7′. In contrast, H5 moves upfield in the minor conformers, in which it lies in the vicinity of the DNBF− or DNBZ− moiety.