Synthesis of Four Pseudo‐Resonance Structures of 3‐substituted Isoindolin‐1‐ones and Study of Their NMR Spectra

Four substituted isoindolin‐1‐one derivatives were synthesized from the corresponding fluorine‐containing aromatic amines. In CDCl₃ solution, all compounds exhibited two sets of NMR signals with ratios from 1:0.7 to 1:0.8. In contrast, only one major set of NMR signals was observed in CD₃OD, the minor signals showing ratio ∼1:0.07–0.20. Variable‐temperature (VT) ¹H NMR experiments revealed that the two sets of signals did not coalesce into a single set from 298–348 K. By converting one pseudo‐resonance structure into its corresponding methyl ether, it displayed only one set of NMR spectrum instead of two in CDCl 3 . One absorption near 1674–1697 cm −1 was recorded for amide carbonyl for all compounds' IR spectra in CDCl 3 solution. No any aldehyde signals was observed in IR or 1 H NMR spectra. All results showed that the pure compound did not process the ring‐opening and ring‐closing via aldehyde to afford two hemiacetals with about 1:0.7 to 0.8 in CDCl 3 solution.