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The IR C = 0 stretching vibrational wave numbers, 'H, I C and N NMR chemical shifts are reported for 5and 6substituted indole-2,3-diones and correlated with Hammett substituent constants and semiempirical AMI data. As an alternative to the previous assignment of the C = 0 stretching vibrational wave numbers the two v ( C = 0 ) absorption bands can also be interpreted as the symmetric and asymmetric stretching vibrational modes in the mechanically coupled cyclic α-dicarbonyl system. The use of 2D NMR techniques enabled to make correct assignments of the C N M R chemical shifts, which are substantially different from those reported earlier. Introduct ion lndole-2,3-dione (isatin), its derivatives and the products of their further reactions represent an important class of biologically active organic compounds. Many isatin derivatives exhibit antibacterial and antifungal activities, (1,2). Moreover, anti-HIV (3) and cytostatic activity (4) as well as inhibition of the cell proliferation (5) has been found. Finally, several new isatin based spiroazetidinones have been proved as efficient anticonvulsants (6). O'Sullivan and Sadler (7 10) proposed for the infrared spectra of 5and 6substituted isatins a model in which the higher wave numbers absorption band in the region of 1775 -1760 cm ( i n CHC13) belongs to the stretching vibration of the C 2 = 0 carbonyl group (i.e. the adjacent one to the benzene ring). The substituent effects on the wave numbers of these bands have been also investigated. The C NMR chemical shifts were reported for a few 5substituted isatins (11), however the substituent effect on the NMR data of the 5and 6substituted isatin derivatives have not been studied systematically and the assignment of chemical shifts was found to be incorrect. The aim of this work was therefore a detailed study of substituent effects in the series of 5and 6substituted isatins (1-12) (Scheme 1) using IR and NMR spectroscopy as well as semiempirical AM 1 theoretical data. 387 Unauthenticated Download Date | 6/7/19 12:09 AM Vol. 7, No. 4, 2001 Substituent effects and vibrtional coupling in indole-2,3diones: An ir,nmr and theoretical study Results and Discusion The characteristic infrared spectral data of a series of 5and 6substituted indole-2,3-diones (isatins) (1-12) measured in dilute solutions in trichloromethane and partly also in tetrachlormethane are listed in Table I. X , .X : = 1 Η, Η: 2 CH, . Η; 3 OCH-,, Η; 4 F, Η; 5 Cl, Η; 6 Br, Η; 7 NO, , Η; 8 COCH-„ Η; 9 H,CH, ; 10Η, OCH, 11 Η. CI 12 Η, Br

Substituent Effects and Vibrational Coupling in Indole-2,3-diones: An IR , NMR and Theoretical Study