Matrix-isolation FT-IR spectra and theoretical study of dimethyl sulfate

Abstract

The preferred conformations of dimethyl sulfate and their vibrational spectra were studied by matrix-isolation FT-IR spectroscopy and theoretical methods (DFT and MP2, with basis sets of different sizes, including the quadruple-zeta, aug-cc-pVQZ basis). Conformer GG (of C2 symmetry and exhibiting OSOC dihedral angles of 74.3 degrees ) was found to be the most stable conformer in both the gaseous phase and isolated in argon. Upon annealing of the matrix, the less stable observed conformer (GT; with C1 symmetry) quickly converts to the GG conformer, with the resulting species being embedded in a matrix-cage which corresponds to the most stable matrix-site for GG form. The highest energy TT conformer, which was assumed to be the most stable conformer in previous studies, is predicted by the calculations to have a relative energy of ca. 10 kJ mol-1 and was not observed in the spectra of the matrix-isolated compound.

Hydrogen Bonding in the Sulfuric Acid–Methanol–Water System: A Matrix Isolation and Computational Study

“…These were noted to increase at long deposition time as compared to the ν(OH) complexation related bands and even relative to the pure methanol bands. These bands fit well the positions of bands of matrix isolated dimethyl sulfate, as reported by Borba et al, 35 Table 3 (calculated wavenumbers given in Table S11 in the Supporting Information). Several of them are also close to the position of some bisulfate bands, 2,3 but the ν(OH) band of the latter was not observed in our experiments.…”

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

“…Indeed, most of the standard computational methods and basis sets have been shown to be unable to properly treat this moiety, leading to considerable discrepancies between the experimental and theoretically predicted values for the S@O bond lengths and for the vibrational frequencies associated with this bond [22][23][24][25]. The underestimation of the theoretically predicted frequencies for the S@O stretching vibrations was noticed previously for different types of compounds containing the S@O bond, from simple molecules, as dimethyl sulfate [26], dimethyl sulfite [27] or the SSO À anion [28], to more complex species, like 5-methyl-1H,3H-pyrrolo [1,2c] [1,3]thiazole-6,7-dicarboxylate 2,2-dioxide [29]. Although a good agreement of the experimental and predicted frequencies was achieved for both dimethyl sulfate and sulfite when the B3LYP method was used together with the split valence quadruple-f basis set (aug-cc-pVQZ) [26,27], calculations on pseudosaccharins at this level of theory are currently unpractical due to its excessive computational cost.…”

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

“…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].…”