Molecular structure and infrared spectra of the monomeric 3-(methoxy)-1,2-benzisothiazole 1,1-dioxide (methyl pseudosaccharyl ether)

Abstract

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@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 3pd)] was applied to analyze the vibrational spectra and the geometry of the title molecule. In agreement with the experiment, the CAOAC linkage in MBID is predicted by these calculations to exhibit considerably short (1.320 Å ) and long (1.442 Å ) (N@)CAO and (H 3 )CAO bonds, respectively, and a hybridization of the central oxygen atom close to sp 2 (the CAOAC angle is predicted to be ca. 117°). This CAOAC bonding pattern fits the well-known high reactivity of MBID upon thermal rearrangement, which has been shown to result in easy selective [1,3 0 ]-isomerization of the compound.

Spectroscopic and theoretical investigation of the conformational space of a pyrazolo-thiazole precursor of extended dipole diazafulvenium methide intermediates

“…On the other hand, a good agreement between experimental and predicted frequencies was observed for both dimethyl sulphite [23] and sulphate [24] when the B3LYP method was used with the aug-cc-pVQZ augmented split valence quadruple-f basis set, whereas for 3-chloro-1,2-benzisothiazole-1,1-dioxide an accurate reproduction of the frequencies associated with the S@O bond stretching modes could also be achieved at the B3LYP/6-311++G(3df,3pd) level [25]. Indeed it has been noticed that an extensive set of polarization functions is necessary to correctly reproduce frequencies of hypervalent S@O bonds, at least when the B3LYP functional is used [25]. Since the size of the DPTD molecule makes calculations with an extensive set of polarization functions unpractical the following strategy was used in the present study to optimize the calculated values for the S@O stretching modes in the DPTD molecule: firstly, the vibrational frequencies of these modes calculated at the B3LYP/6-311++G(3df,3pd) level for 3-chloro-1,2-benziothiazole-1,1-dioxide [25] were compared to those obtained using the smallest B3LYP/6-311++G(d,p) basis set; then, a proper scaling factor was obtained taking into account the frequency ratios [B3LYP/6-311++G(d,p) to B3LYP/6-311++G(3df,3pd)] for the antisymmetric and symmetric S@O stretching vibrations (1.046 and 1.051, respectively); the mean value (1.048) was used as scaling factor for the B3LYP/6-311++G(d,p) S@O stretching frequencies calculated for DPTD.…”

“…Optimization of the input structures was initially done at the B3LYP/6-31+G(d) level of theory, the minimum energy struc- tures being subsequently re-optimized and the vibrational frequencies calculated at the B3LYP level with the /6-311++G(d,p) split-valence triple-f basis set. The underestimation of the theoretically predicted frequencies for S@O stretching vibrations has been reported for different types of compounds when calculated at the DFT (B3LYP) level with the 6-311++G(d,p) basis set [22][23][24][25]. On the other hand, a good agreement between experimental and predicted frequencies was observed for both dimethyl sulphite [23] and sulphate [24] when the B3LYP method was used with the aug-cc-pVQZ augmented split valence quadruple-f basis set, whereas for 3-chloro-1,2-benzisothiazole-1,1-dioxide an accurate reproduction of the frequencies associated with the S@O bond stretching modes could also be achieved at the B3LYP/6-311++G(3df,3pd) level [25].…”

“…The underestimation of the theoretically predicted frequencies for S@O stretching vibrations has been reported for different types of compounds when calculated at the DFT (B3LYP) level with the 6-311++G(d,p) basis set [22][23][24][25]. On the other hand, a good agreement between experimental and predicted frequencies was observed for both dimethyl sulphite [23] and sulphate [24] when the B3LYP method was used with the aug-cc-pVQZ augmented split valence quadruple-f basis set, whereas for 3-chloro-1,2-benzisothiazole-1,1-dioxide an accurate reproduction of the frequencies associated with the S@O bond stretching modes could also be achieved at the B3LYP/6-311++G(3df,3pd) level [25]. Indeed it has been noticed that an extensive set of polarization functions is necessary to correctly reproduce frequencies of hypervalent S@O bonds, at least when the B3LYP functional is used [25].…”

Investigations into the Mechanism of Solvolysis of 3-aryloxybenzisothiazoles

“…1,45−47 This requirement results essentially from the presence in the molecules of hypervalent S atoms, as indicated by the strong improvement of the calculated vibrational data for the >SO 2 stretching and bending modes (compared to other vibrations) upon inclusion in the basis set of diffusion and polarization functions. 47,48 The use of the DFT/B3LYP or O3LYP method with the 6-311++G(3df,3dp) basis set was found to be appropriate to attain reliable results at moderate computational effort. 1,45−49 In the present study, geometries were optimized using the Direct Inversion in the Iterative Subspace (DIIS) method.…”

Matrix-isolation FTIR, theoretical structural analysis and reactivity of amino-saccharins: N-(1,1-dioxo-1,2-benzisothiazol-3-yl)-N-methyl amine and -N,N-dimethyl amine

“…In recent studies on this family of compounds, we investigated the structure and spectroscopic properties of simple alkyloxy-and allyloxy-derivatives [specifically, 3-(methoxy)-1,2-benzisothiazole 1,1-dioxide and 3-(allyloxy)-1,2-benzisothiazole 1,1-dioxide] and the mechanisms involved in their thermal rearrangement to the corresponding N-alkyl or N-allyl isomers [9][10][11][12][13][14]. In those studies, the interpretation of the experimental data strongly relied on quantum chemical theoretical calculations, which had to be first duly calibrated in order to consider the specificities of the molecular systems under analysis.…”