Styrylpyrylium Salts: and NMR High-Resolution Spectroscopy (1D and 2D)

and NMR high-resolution spectroscopy (1D and 2D) ( , -COSY, HSQC, HMBC) for four styrylpyrylium perchlorates were carried out and signal attributions are reported. Chemical shifts observed on NMR spectra for the styrylpyrylium salts were compared with net atomic charge for carbon obtained by AM1 semiempirical calculations. The position of the styryl group present low effect on chemical shifts for carbon atoms, while the presence of methyl group led to the unshielding of the substituted carbon. 1. Introduction NMR spectroscopy reports for pyrylium salts from few authors are available [1, 2]. This investigation presents some complexity in the attribution of the chemical shifts to atoms. The data on pyrylium salts NMR spectroscopy with substitution effects analysis are useful to understand various properties well known for pyrylium cations [3–6]. Particularly emission properties (fluorescence and phosphorescence) of styrylpyrylium salts are reported in relation with proton, chemical shifts in 1H NMR of the pyrylium ring [7, 8]. However carbon chemical shift data relative to pyrylium ring, proton and carbon chemical shift for styryl group remain unknown, as for us. In this study, we report high-resolution 1D and 2D 1H and 13C NMR analysis results for four styrylpyrylium salts (Figure 1). Figure 1: Structures of studied styrylpyrylium salts. 13C chemical shifts of the pyrylium ring, phenyl, and styryl groups are presented with correlation with Austin Model 1(AM1) theoretical calculations. The substitution effects of methyl, phenyl, and styryl groups and their positions on the pyrylium ring were discussed as regards atomic chemical shifts. 2. Results and Discussion Spectra are recorded with compounds dissolved in d6-DMSO. Proton NMR chemical shifts recording for studied styrylpyrylium salts were reported in Table 1 and those for carbon 13 in Table 2. Table 1: 1H NMR (600 MHz) data: chemical shifts in ppm as unit of measurement; multiplicity and constant coupling J given in Hz for four styrylpyrylium salts 1, 2, 3 and 4. Table 2: 13C-NMR data, 9.40？T (100.6？MHz) or 14.09？T (150.9？MHz) of compounds 1, 2, 3 and 4: Chemical shifts (in ppm as unit of measurement) and net atomic charge (q) of styrylpyrylium salts carbons. On all spectra, we observed general pyrylium salts characteristics and also specific data due to styryl group with its extracyclic double bond. Data are comparable to those of previous work at low resolution obtained by A. R. Katritzky and coll [1]. Here the study at high resolution gives high precision on chemical shifts for proton and carbon and