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33S NMR spectroscopy. 4. Substituent effects on the 33S nuclear quadrupole coupling constants and electric field gradient in 3- and 4-substituted benzenesulphonates studied by DFT calculations in vacuo and in aqueous solution
No full text33S nuclear quadrupole coupling constants (χ ) and the principal component of the electric field gradient (qzz ) in 3- and 4-substituted benzenesulphonates are dependent on the electronic properties of substituents. Previously reported experimental results were interpreted with the support of theoretical calculations in vacuo and in aqueous solution. To obtain good reproducibility of the experimental data, the introduction of the solvent effect into the calculations was mandatory. The best results were obtained at the B3LYP/6-311++G(3d,p) level using the Integral Equation Formalism for the Polarisable Continuum Model (IEF-PCM) to reproduce the solvent effect. In vacuo, for neutral substituents, the substituent effect on sulphur qzz can be mainly ascribed to electronic interactions (i.e., inductive and mesomeric effects transmitted through the aromatic ring). For charged substituents () there is also a relevant contribution of coulomb origin, owed to the electric charge on the substituent itself, which polarises the S–O and C–S bonds. In aqueous solution, short-range solute–solvent interactions (i.e., hydrogen bonding) can be neglected, and the solvent effect can be adequately described considering the electrostatic interactions between the moiety and the electric charges on the surface of the cavity embedding the molecule within the solvent. These interactions amplify the electronic contribution transmitted through the aromatic ring and partially annihilate the coulomb contribution of the intrinsic charges of substituents. The results of the Natural Bond Orbital (NBO) analysis support these results and demonstrate that the polarisation of the S–O and S–C bonds and oxygen lone pairs due to solvent interactions produces only a redistribution of the electron density around the sulphur nucleus, thus inducing the variations of qzz
S-33 NMR spectroscopy. 2. Substituent effects on S-33 chemical shifts and nuclear quadrupole coupling constants in 3- and 4-substituted benzenesulfonates. Correlation between chemical shifts and nuclear quadrupole coupling constants
No full textApplication of MNDO approximation to the calculation of nuclear spin-spin coupling constants .1. Substituent effect on H-1-C-13 coupling constants in methane derivatives
No full textS-33 NMR Spectroscopy 3. Substituent effects on S-33 NMR parameters in 2-substituted ethanesulfonates
No full text33S NMR parameters (chemical shifts and linewidths) in 2-substituted sodium ethanesulfonates,
XCH2CH2SO3Na (X = H, CH3, OH, SH, NH2, Cl, Br, NH3+) depend upon the electronic properties of
substituents. To explain experimental results and obtain additional information on the origin of the
observed substituent effect (SE), sulfur isotropic absolute shielding constants have been calculated at DFT
level of theory (B3LYP/6-311++G(2d,p)) by gauge-including atomic orbitals (GIAO) method. Data have
been interpreted with the aid of natural bond orbital (NBO) method and natural chemical shielding (NCS)
analysis. It has been demonstrated that in the class of compounds considered the diamagnetic contribution
to sulfur-shielding constant is constant and the observed upfield shift of 33S resonance induced by electronwithdrawing
substituents (reverse chemical shift effect) can be related to variations of the paramagnetic
contribution. Substituents with different electronic properties cause variations in the polarization of S–C
and S–O bonds of the –C–SO3
− moiety thus determining changes of the electron density at sulfur nucleus
and consequently the expansion or contraction of 3p sulfur orbitals. Also oxygen lone-pairs and sulfur
core 2p electrons can play an active role in determining the paramagnetic contribution to sulfur shielding.
With regard to linewidth variations, they can be ascribed primarily to changes in the nuclear quadrupole
coupling constant values. B3LYP/6-311++G(2d,p) method allows obtaining a good reproducibility of SE
on the electric field gradient (EFG) at sulfur, although its values tend to be underestimated significantly.
Moreover, 17O shielding constants have been calculated
Conformational studies on 2-substituted ethanesulfonates in aqueous solution by H-1 NMR spectroscopy and DFT calculations
No full textThe conformation of some 2-substituted sodium ethanesulfonates exerting biological functions,
XCH2CH2SO3Na(X=SH, Br, Cl, OH, NH2, SH), has been investigated in aqueous solution by H-1 NMR spectroscopy.
Potential energy curves for rotation about the C–C bond have been calculated at DFT level of theory (B3LYP/6-311++G(2d,p)) in vacuum and in water (by IEF-PCM method). As concerning dianionic
coenzyme M (X = S-), 2-bromo- and 2-chloroethanesulfonate, in vacuum the torsional potential curves and the variations of atomic charges and geometric parameters suggest that electrostatic and steric repulsions between the substituent X and —SO3- moiety determine the preference for anti conformer.
In isethionate (X = OH), anionic taurine (X = NH2), and coenzymeM (X = SH), the formation of an intramolecular
hydrogen bond stabilizes also gauche-like conformers and the torsional potential curves exhibit two minima. According to Natural Bond Orbital analysis, hydrogen bond can be ascribed to electron transfer from two oxygen lone-pairs of the —SO3- moiety to the antibonding Y–H orbital of the substituent
X. In all the compounds examined, hyperconjugative interactions tend to stabilize the gauche conformers with respect to the anti one. This means that conformational preferences in vacuum are determined by a counterbalancing of electrostatic, steric, and hyperconjugative interactions. Calculations
in vacuum are not in agreement with the experimental conformational behaviour of the compounds
examined. In order to reproduce the experimental results at least qualitatively, solvent effect must be introduced
Study of the substituent effect on the beta-electron distribution of substituted oligo(p-phenylenevinylenes) by DFT calculations and NBO analysis
No full textTitle: SUBSTITUENT EFFECTS ON S-33 CHEMICAL-SHIFTS AND NUCLEAR-QUADRUPOLE COUPLING-CONSTANTS IN 4-SUBSTITUTED BENZENESULFONATES
No full textON THE STRUCTURE OF INTERMEDIATE ADDUCTS ARISING FROM DITHIONITE REDUCTION OF PYRIDINIUM SALTS : A NOVEL CLASS OF DERIVATIVES OF THE PARENT SULFINIC ACIDS.
No full text13C and 17O NMR spectroscopy show that adducts arising from dithionite reduction of 3- or 3,5-cyano- or carbamoyl-substituted pyridinium salts to the corresponding 1,4-dihydropyridines, are S-anions of esters of the simplest parent sulfinic acid. A pathway for formation of the 1,4- dihydropyridines, involving an intramolecular hydride transfer, is suggested
On the structure of intermediate adducts arising from dithionite reduction of pyridinium salts: a novel class of derivatives of the parent sulfinic acid
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