Dual Substituent Parameter Modeling of Theoretical, NMR and IR Spectral Data of 5-Substituted Indole-2,3-diones

Correlations of AM1 and PM3 theoretical data, (13)C-NMR substituent chemical shifts ((13)C-SCS) and IR carbonyl group wave numbers [ν(C(3)═O)] were studied using dual substituent parameter (DSP) models for 5-substituted indole-2,3-diones. For the C(7) atom a reverse substituent effect attributed to extended π-polarization was observed. On the other hand, the DSP approaches for the C(3) atom showed normal substituent effects with some contribution of reverse effect supported strongly by (13)C-SCS correlations. In the ν(C(3)═O) and p(C(3)═O) DSP correlations the field effect contribution predominates over the resonance effect, which justifies the using of earlier suggested vibrational coupling (V-C) model for 5- and 6-substituted indole-2,3-diones.