Chemistry of N-Nitroso Compounds. 7. Conformational Preferences of Hexahydro-N1,N4-dinitroso-r-2,c-7-diphenyl-1H-1,4-diazepines: Use of Modified 1D HOHAHA and NOE Techniques

Article abstract of DOI:10.1021/jo00128a018

Modified HOHAHA and NOE experiments on three N,N'-dinitrosohexahydrodiazepines, at temperatures ranging from -50 deg C to 120 deg C, indicated that each of the title compounds exists as an equilibrium mixture of two families of conformations, the major family consisting of four rotamers and the minor consisting of, possibly, four rotamers resulting from two parallel dynamic processes viz., the restricted N-N rotation at two N-NO bonds and the pseudorotation of the seven-membered ring.The 3-isopropyl derivative 10, at 50 deg C, exhibited only four resonances for each kind of proton/carbon, indicating that the rate of pseudorotation is fast compared to the NMR time scale.The 1H resonances, broad at room temperature, became decalesced at -50 deg C as result of the slow pseudorotation process.In all the three dinitroso compounds, of the two sets of twist-chair conformers, the major rotamers (ca. 95percent) have the alkyl group (at C3) axially disposed while the minor rotamers have quasiquatorial alkyl groups.On the other hand, the alkyl group at C6 of the 3,6-dimethyl derivative 11 adopts equatorial orientation in all its conformers.