- Molecular structure and infrared spectra of the monomeric 3-(methoxy)-1,2-benzisothiazole 1,1-dioxide (methyl pseudosaccharyl ether)
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The computational description of saccharin (1,2-benzisothiazol-3(2H)-one-1,1-dioxide) and its derivatives is difficult due to the presence of hypervalent S{double bond, long}O bonds in their structures. Therefore, in this investigation, the HF, DFT/B3LYP and MP2 methods were used to predict the geometry and the infrared spectrum of the saccharyl derivative 3-(methoxy)-1,2-benzisothiazole 1,1-dioxide (MBID). Their relative predictive capabilities were then evaluated by comparing the obtained results with experimentally available data, namely the newly obtained IR spectra of MBID isolated in low-temperature inert matrices. For each method, different basis sets [6-31++G(d,p), 6-31++G(3df,3pd), 6-311++G(d,p), 6-311++G(2df,2pd), 6-311++G(3df,3pd), aug-cc-pVDZ and aug-cc-pVTZ] were considered. The best overall agreement has been achieved at the B3LYP/6-311++G(3df,3pd) and B3LYP/6-31++G(3df,3pd) levels of theory, showing the adequacy of the B3LYP functional to describe the investigated properties in this type of compounds and stressing the relevance of including high-order polarization functions in the basis set. The chosen level of theory [B3LYP/6-311++G(3df,3pd)] was applied to analyze the vibrational spectra and the geometry of the title molecule. In agreement with the experiment, the C{single bond}O{single bond}C linkage in MBID is predicted by these calculations to exhibit considerably short (1.320 ?) and long (1.442 ?) (N{double bond, long})C{single bond}O and (H3)C{single bond}O bonds, respectively, and a hybridization of the central oxygen atom close to sp2 (the C{single bond}O{single bond}C angle is predicted to be ca. 117°). This C{single bond}O{single bond}C bonding pattern fits the well-known high reactivity of MBID upon thermal rearrangement, which has been shown to result in easy selective [1,3′]-isomerization of the compound.
- Kaczor, Agnieszka,Almeida, Rui,Gómez-Zavaglia, Andrea,Cristiano, Maria de Lurdes S.,Fausto, Rui
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- Collection of ion-trap mass spectre of sulfonylurea pyrolysis products
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The pyrograms of 14 sulfonylureas, i.e. herbicides characterized by high biological activity and low application dose are discussed and the mass spectra of over 30 relevant pyrolysis products as obtained with a heated filament pyrolyzer interfaced to a capillary gas chromatograph/ion-trap detector mass spectrometer are presented. Such a data compilation is useful for diagnostic purposes for both intact sulfonylureas and their metabolites after degradation in soil, because metabolites and pyrolysis products are often identical and most of their mass spectra are lacking in commercially available mass spectral libraries. The performance of the ion-trap detector based on the quality of the mass spectra is briefly discussed.
- Galletti,Dinelli,Chiavari
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p. 333 - 338
(2007/10/02)
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