Synthesis, spectral characterization, solution and solid-state conformations of N-nitroso-2,7-diaryl-1,4-diazepan-5-ones by NMR and XRD studies

Abstract

Nitroso derivative of 2,7-diaryl-1,4-diazepan-5-ones 9–12 are synthesized and characterized using spectroscopic techniques such as IR, EI-MS and NMR spectra. The stereochemical investigation of nitroso compounds has been carried out with 1D (1H, 13C & DEPT-135) and 2D (COSY & HSQC) NMR spectral data. Rotational isomers (syn and anti rotamers) of 9–12 are identified and categorized by room temperature NMR spectral studies. Furthermore, the conformation of the ring and the orientation of NN=O function have been arrived on the basis of chemical shifts, coupling constants and dihedral angles. In solution state, syn and anti rotamers of the compounds 9–11 exist in equilibrium between flattened boat conformation with quasi-axial orientations of the aryl groups at C-2 and C-7. Nevertheless, compound 12 and its syn and anti rotamers prefer to adopt equilibrium between chair conformations with axial orientation of aryl substituents. In order to validate the solution state conformation, the compound 12 is crystallized and the crystal structure is solved by single crystal XRD study. The compound 12 exists in an alternate chair conformation and aryl groups at C-2 & C-7 occupy axial orientations in solid state also.