The preparation and H-NMR analysis of a set of 1,3-dinitroso-4,6-dialkyl benzenes are described. The nitroso group orientation with respect to the aromatic ring is sterically anchored to yield a single conformation in these structures in which the two meta nitroso groups point toward each other. The resulting CH at C2 between the nitroso functions is 'syn' to both functions and shows a large shielding of its H-NMR signals, which appear with δ-vales of 4.6-5.1 ppm. In contrast, the chemical shift of the CH signal at C5 in the rings occurs at 7.8-8.0 ppm, more in-line with expectations for these electron deficient arenes. H-NMR spectral comparisons are made to the electronically similar 1,3-dinitrobenzene analogues. The doubly syn CH's at C2 in the dinitroso structures are more shielded by 3.6-3.7 ppm than the same CH signals at C2 in the dinitrobenzenes. The observed large shielding at C2 is explained by the large NMR-induced magnetic anisotropy of the nitroso function, which is dramatically displayed in these structures. Compared to the syn shielding effect observed for monofunctional 2-alkyl nitrosobenzenes, the NO shielding in the 1,3-dinitroso benzenes is found to be more than additive (i.e. more than doubled). Explanation of the more than additive magnetic anisotropy effect in these bis(dinitroso)benzene will be offered.

Bis(nitroso)benzenes with oriented nitroso groups: Observation of large -N=O magnetic anisotropy by H-NMR

ACS Fall 2021

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