An analysis of 1H, 13C and 15N NMR substituent chemical shifts in para- and meta-substituted (Z)-phenylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole

The H-1, C-13 and N-15 chemical shifts of the title compounds have been measured in CDCl3 solutions. The data obtained allowed a map of the ground-state electronic distribution in such (Z)-arylhydrazones to be sketched, indicating to what extent the substituent in the aryl component of the arylhydrazono moiety affects the electronic density at the key atoms involved in the mononuclear heterocyclic rearrangements (MHR) characteristic of these substrates: the hydrogen atom bound to N-alpha (which affects the nucleophilic character of N-alpha), N-2 (which affects the electrophilic character of N-2 itself) and C-5 (which affects the nucleofugacity of the N-4/C-5/O-1 system).