Substituent effects for some substituted 3-benzyl-2-phenyl-1,3-thiazolidin-4-ones using ¹H and ¹³C NMR

Substituents placed on the phenyl rings of 3-benzyl-2-phenyl-1,3-thiazolidin-4-one affect the electron density surrounding both the methine proton, H_m, at C(2), H_a and H_b at C(5), and H_c and H_d at the benzyl carbon. The electron density changes are also exhibited at the C(2), C(4), C(5) and the benzyl carbons. These electron density changes are reflected, respectively, in the differing chemical shifts for the ¹H and ¹³C NMR spectra for these atoms relative to the unsubstituted compound. Correlations for the effects of various substituents in both the 2-phenyl and 3-benzyl rings with the ¹H and ¹³C chemical shifts, for the aforementioned sites, are discussed using Hammett σ constants. The large chemical shift difference observed for the geminal N-benzylic protons, H_c and H_d is discussed.