Carbon‐13 n.m.r. and CNDO/S study of 1,3‐indandione and heterocyclic analogues

Abstract

Abstract-I3C n.m.r. spectra are reported for 1,3-indandione, phthalic anhydride, thiophthalic anhydride, and phthalimide in chloroform-d solution. The 13C chemical shifts have also been calculated by means of Pople's perturbation theory using CNDO/S wave functions; the agreement between theoretical and experimental values is improved when an empirical charge-dependent term is added to the calculated diamagnetic and paramagneitc contributions.As PART of a study on heterodicarbonyl compounds by spectroscopic and theoretical methods,lS2 we have measured the 13C n.m.r. spectra and performed quantummechanical calculations, based on the independentelectron MO theory of P~p l e ,~ for phthalic anhydride (l), thiophthalic anhydride (2), phthalimide (3) and their carbocyclic analogue 1,3-indandione (4). n EXPERIMENTAL Phthalic anhydride, phthalimide and 1,3-indandione were commercially available materials. Thiophthalic anhydride was synthesized as described in the literatui-e.4The I3C n.m.r. spectra were measured on a Varian XL-100 12-WG spectrometer operating in the pulsed Fourier transform mode at 25.15 MHz with D heteronuclear lock; proton noise decoupling was performed through the Gyrocode system at 100 MHz. Measurements were made in 10 mm sample tubes containing 0.5 M solutions of the compounds (with the exception of phthalimide, sparingly soluble, of which a saturated solution was examined), in CDCI, with TMS (c. 1 vol. "/u) as internal reference. As an example, the 13C FT n.m.r. spectrum of 1,3-indandione (4) is shown in Fig. 1. Spectral analysisThe carbonyl signal was readily identified from its low field position. The signal of the quaternary carbon C-2 was distinguished from the resonance of C-4 with the help of the splitting pattern observed in the C-H coupled spectrum. Assignment of the highest field aromatic resonance to C-3 is in agreement with the data available for an N-derivative of phthalimide5 and for the *Author to whom correspondence should be addressed. Table 1.The most striking aspect of the carbon resonances in this series of compounds concerns the spread of the carbony1 chemical shifts. This follows the trend 0 < NH < S < CH, and is as large as 34 ppm.The current qualitative interpretation of the downfield shift of carbonyl signals from TMS invokes the polarity of the carbonyl bond,^ while the scatter of the chemical shift values is accounted for in terms of factors affecting the bond polarity.8 On this basis, assuming other effects being equal, the carbonyl shifts of compounds 1-4 should be expected to increase with decreasing electron acceptor power of the X atom, since withdrawal of electron charge from the carbonyl oxygen towards the X atom is expected to decrease the carbonyl r-bond polarity. This argument implies the trend shown by the measured shifts. In addition, the differences in electronegativity as calculated by D e~a r ,~ O(4-8 eV), N(4.2), S(2-5) and C(2.5), are fairly well reflected in the chemical shifts.Although a direct correlation between the carbonyl resonance and the n -> r* ...

Silver complexes with succinimide as models for the interaction of silver(I) with the uracil residue

“…A series of five-membered heterocyclic dicarbonyl compounds (V) were examined by Galasso and O // w o V co-workers. 31 An inverse correlation was found between for the carbonyl carbon atom and the electrophilic character of X: increasing the electronegativity of X reduces the polar character of the C=0 bond (i.e. the relative weight of formulas like IVb and IVc), thereby increasing electron density at the carbon, which is shifted to high field.…”