Reactivity of biologically important reduced pyridines VI. Lack of through-resonance stabilization in the ferricyanide-mediated oxidation of substituted 1-Phenyl-1,4-Dihydronicotinamides

✍ Scribed by Marcus E. Brewster; James J. kaminski; Zoltan Gabanyi; Klara Czako; Agnes Simay; Nicholas Bodor

• Publisher: Elsevier Science
• Year: 1990
• Tongue: French
• Weight: 436 KB
• Volume: 46
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(01)85415-6

✦ Synopsis

Bronsted-type analysis for the log of the reaction rates for fe~cyan~de-~diated oxidation for a series of l-(4-substituted phenyl)-1,4_dihydronicotinamide and the pKa's for the corresponding component anilines produced a linear (rs0.993) relationship over the range of p-N(CH,), to p-CF,. This observation is consistent with the importance of the initial electron loss in determining the reaction rate. One compound studied i.e.. l-(4-nitmphenyl)-1,4dihydronicotfnamide, was conspiatous in that it did not lie on the calculated regression line even though Hammetf analysis revealed no deviation from linearity for this species. This Situation was SUggeSted to be due lo stertc and other restriction to planarity of the l-phenyl substituents. These tadors would preclude direct interaction of the 4phenyl moiety with the heterocyclic pyrfdine nitrogen. These conclusions were based on expe~mental and theoretical (AM1 and MNDO) semi-empirical molecular otital studies.