Investigation of Four Sets of NMR Spectra for One Racemic Compound of Pseudoresonance Structures.

A racemic compound, ()-3-[(1,3*)-3-hydroxy-1,3-dihydroisobenzofuran-1-yl]-2-(naphthalen-1-yl)-isoindolin-1-one (), was synthesized and found to exhibit four distinct sets of H and C NMR signals in CDCl solution. The four sets of H NMR signals displayed relative integration ratios of approximately 1:1:0.8:0.8. Subsequent PCC oxidation of yielded racemic ()-2-(naphthalen-1-yl)-3-[()-3-oxo-1,3-dihydroisobenzofuran-1-yl]-isoindolin-1-one (), which showed simplified NMR behavior with only two sets of H and C NMR signals (1:1 ratio) in CDCl. Interestingly, compound exhibited two sets of H NMR signals in DMSO- that gradually coalesced into a single set upon variable-temperature NMR analysis (298-353 K). To further investigate the structural dynamics, racemate was converted to its corresponding acetate derivative () in CHCl. Notably, the acetate displayed only two sets of NMR signals (near 1:0.9 ratio) in CDCl, contrasting with the original four sets (1:1:0.8:0.8) observed for compound . This critical observation eliminated the possibility that hemiacetal isomeric structures were responsible for the NMR multiplicity in CDCl. These findings suggest that the two sets of H NMR signals with 0.8:0.8 integration ratios originated from two atropisomers with near 1:1 ratios.