Showing papers by "Dante Macciantelli published in 1981"

Conformational studies by dynamic nuclear magnetic resonance spectroscopy. Part 21. Structure, conformation, and stereodynamics of sulphinylhydrazines

Abstract: 1 H and 13C n.m.r. spectroscopy at low temperature allowed the detection of restricted rotation about the N–N bond in sulphinylhydrazines. In the case of the di-isopropyl derivative the existence of two conformers due to a ‘correlated orientation’(gear effect) was also discovered. The trend of the measured ΔG‡ values and the interpretation of the chemical shifts suggested conformational assignments which were supported by an X-ray diffraction investigation of the solid.

Conformational studies by dynamic nuclear magnetic resonance. Part 20. Internal motion in hydrazones and related derivatives

Abstract: Restricted rotation about the N–N bond in unhindered, non-conjugated hydrazones (e.g. Me2N–NCH2) has been detected by 13C n.m.r. below –150°C. The results indicate that the NC plane is coplanar with the dynamically averaged plane of the sp3 nitrogen, in contrast with hindered hydrazones (containing the 2,2,6,6-tetramethylpiperidinyl ring, TMP) where the NC moiety adopts a perpendicular conformation. Effects due to the slowing of ring reversal were not observed in hydrazones containing the TMP ring, but were detected in other hindered derivatives such as TMP–NH2 and TMP–NO. A most interesting feature becomes apparent in two hydrazones with the 2,6-cis-dimethylpiperidinyl (DMP) ring, DMP–NCH2 and DMP–NCHPh. In the same molecule the NC moiety is coplanar with the averaged sp3 nitrogen plane when the methyls are axial, but perpendicular when the methyls are equatorial.