H-1 AND C-13 NMR-STUDY OF 1-SUBSTITUTED ISATINS AND THEIR CORRESPONDING 3-(DICYANOMETHYLIDENE)INDOL-2-ONES

The assignments of the H-1 and C-13 NMR signals of 1-substituted isatins and their corresponding 3-(dicyanomethylidene)indol-2-ones were derived by analysis of the C-13-H-1 spin coupling patterns and by inspection of the two-dimensional C, H shift correlation spectra. Erroneous literature assignments have been corrected. A significant difference between the 5-DELTA-deuterium isotope effects on the C-13 chemical shifts of the CN groups cis and trans to the heterocyclic amide fragment (D)HNC = O was observed in partially deuteriated 3-(dicyanomethylidene)indol-2-one. This geometric dependence was used to assign the two CN groups that are otherwise difficult to assign.