NMR STUDIES OF N-NITROSAMINES .3. SATURATED DINITROSAMINES

The predominant conformations of the five isomeric 1,4-dinitroso-2,3,5,6-tetramethylpiperazines were established from measurements of proton chemical shifts and proton-proton coupling constants. Three of the isomers exist as mixtures of forms with cisoid and transoid orientations of the two nitroso groups; the remaining two isomers are almost exclusively transoid. It is suggested that the transoid γ and transoid ε{lunate} isomers prefer to be in twist-boat conformations, while the α isomer has a chair conformation with all four methyl groups axial. The conformation of N,N′-dinitrosopiperazine itself is also discussed. The N,N′-dinitroso derivative of N,N′-dimethylethylenediamine was used as a model compound to establish additivity of chemical shift effects from the two nitroso groups in the absence of conformational differences between isomers. The configurations of the γ and δ isomers of 2,3,5,6-tetramethylpiperazine were established by an NMR study of the 1-methyl-4-nitroso derivative of the γ isomer. © 1969.