The vibrational and temperature dependence of the indirect nuclear spin–spin coupling constants of the oxonium (H 3O +) and hydroxyl (OH −) ions (original) (raw)
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The vibrational and temperature dependence of the magnetic properties of the oxonium ion (H3O+)
Chemical Physics, 1994
First-and second-order polarization propagator calculations of magnetizability, rotational g-factor, spin-rotation constant, and hydrogen and oxygen shielding property surfaces are reported for the gas phase oxonium ion. Using these surfaces and the nonrigid inverter ro-vibrational eigenfunctions, effective magnetic molecular constants are obtained for the lowest ro-inversional states of H3i70+ and Ds170+. The predicted constants exhibit sizable and non-monotonic dependence on the vibrational and rotational quantum numbers. We find nearly temperature independence of both the 'H and "0 shieldings, mainly due to cancellation effects between contributions from the inversional and the symmetric stretching modes. We compute a downfield shift in 'H as well as "0 shieldings of HsO+ relative to pure water in agreement with earlier observations. The influence of hydrogen bonding on these shifts, as well as on the deuterlum-induced isotope shifts on the "0 shielding, is discussed. 0301-0104/94/$07.00 8 1994 Elsevier Science B.V. All rights reserved SSDfO301-0104 (94)00080-T K
Journal of Computational Chemistry, 2018
Relativistic and nonrelativistic calculations have been performed on hydrogen peroxide, dihydrogen disulfide, dihydrogen diselenide, and dihydrogen ditelluride, H 2 X 2 (X = O, S, Se, Te), to investigate the consequences of relativistic effects on their structures as well as their nuclear magnetic resonance (NMR) spin-spin coupling constants and spin-spin coupling constant polarizabilites. The study has been performed using both one-component nonrelativistic and four-component relativistic calculations at the density functional theory (DFT) level with the B3LYP exchange-correlation functional. The calculation of nuclear spin-spin coupling constant polarizabilities has been performed by evaluating the components of the third order tensor, nuclear spin-spin coupling polarizability, using quadratic response theory. From this, the pseudoscalar associated with this tensor has also been calculated. The results show that relativistic corrections become very important for H 2 Se 2 and H 2 Te 2 and hint that a new chiral discrimination technique via NMR spectroscopy might be possible for molecules containing elements like Se or Te.
Physical Chemistry Chemical Physics, 2009
We recently showed, by analyzing contributions from localized molecular orbitals, that the anomalous deuterium isotope effect in the one-bond indirect nuclear spin-spin coupling constant of methane, also called the unexpected differential sensitivity, can be explained by the transfer of s-orbital character from the stretched bond to the other unchanged bonds [ChemPhysChem, 2008[ChemPhysChem, , 9, 1259. We now extend this analysis of isotope effects to the molecules BH 4 À , NH 4 + , SiH 4 , H 2 O and NH 3 in order to test our conclusions on a wider rage of XH 4 compounds and to investigate whether the lone-pair orbitals are really responsible for the absence of a similar effect in water and ammonia as proposed earlier [J.
Nuclear charge-distribution effects on the NMR spectroscopy parameters
The Journal of Chemical Physics, 2012
We present here a systematic study about the influence of the size and type of nuclear chargedistribution models (Gaussian and point-like) on the NMR spectroscopic parameters, the nuclear magnetic shielding σ and the indirect nuclear spin J-coupling. We found that relativistic effects largely enhance the nuclear charge-distribution effects (NChDE) on those parameters being them quite sensitive to the nuclear model adopted for calculations. Results for two rare gas atoms (Kr, Rn) and few molecular systems like HX, (X = Br, I, At), CH 4 , SnH 4 , SnIH 3 , SnI 2 H 2 , and PbIH 3 are presented. J-couplings are more sensitive than shieldings in both, relativistic and non-relativistic (NR) regimes. The highest effect (close to 11% of variation in relativistic calculations with that two different nuclear models) is observed for J(Pb-I) in PbIH 3. A similar effect is found for J(Pb-H) in the same molecule, close to 9%. The NChDE for σ (Sn) in SnI 4−n H n with n = 1, 2 is as large as few ppm (between 3 and 8.56 ppm). For J(Sn-H) in this set of molecules, it goes from 37 Hz for SnH 4 to 54 Hz for SnI 2 H 2. Furthermore, we found that the vicinal NChDE is very small though not zero. For 1 J(Sn-H) in SnIH 3 , the NChDE of iodine is close to 2 Hz (0.1%). We also studied the NChDE on the ground state electronic energies of atoms and molecules. We found that these effects are only important within the relativistic regime but not within the NR one. They are in good agreement with previous works.
Isotope effects on spin-spin coupling
Journal of the American Chemical Society, 1986
The change in the spin-spin coupling in high-resolution NMR spectra brought about by isotopic substitution is examined. A review of available experimental values shows some general trends which can be explained by changes in the dynamical averaging upon isotopic substitution. The theoretical basis for the signs of observed primary isotope effects on one-bond coupling is proposed. With use of a simple physical model for one-and two-bond coupling, and dynamic calculations on H -C a -H as an example, the relative magnitudes and signs of the primary and secondary isotope effects on these couplings are interpreted. With an MO calculation of 'J(PH) in PH, and H2P(0)OH as a function of PH bond length, the opposite signs and the magnitudes of the primary isotope effects on 'J(PH) in these molecules are reproduced. The negative contribution of the lone pair to the derivative (dJ(PH)/dAr), in PH,, which does not occur in H2P(0)OH, is found to be responsible for the positive sign of the primary isotope effect on PH coupling in PH, (and by extension, also for the other P'I'H couplings and the SeH coupling in H2Se).
Recent Advances in Theoretical and Physical Aspects of NMR Chemical Shifts
Kimika, 2015
In the first part of this review, theoretical aspects of nuclear magnetic shielding include (a) general theory, for example, newly developed approaches in relativistic theory of nuclear shielding, the relation between the spin-rotation tensor and shielding in relativistic theory, ab initio methods for treating open shell systems and a complete theory of chemical shifts in paramagnetic systems, the link between the definitions of the elusive concepts aromaticity and anti-aromaticity and the magnetic properties: the magnetizability tensor and the nuclear magnetic shielding tensor via delocalized electron currents and electron current maps, (b) ab initio and DFT calculations, both relativistic and non-relativistic, for various nuclei in various molecular systems using various levels of theoretical treatment. Physical aspects include (a) anisotropy of the shielding tensor, usually from solid state measurements, and calculations to support these, (b) shielding surfaces and rovibrational averaging, paying special attention to the sensitive relationship between shielding and bond angles or torsion angles that makes shielding such a powerful tool for structural/conformational determination in macromolecules, (c) chemical shifts that arise from isotopic substitution of NMR nucleus or neighboring nuclei, (d) intermolecular effects on nuclear shielding, and (e) absolute shielding scales.
The Journal of Chemical Physics, 1999
The effect of rotation and vibration on the nuclear magnetic resonance ͑NMR͒ shielding constants was computed for HF, F 2 , N 2 , CO, and HBr. The shielding constants for H, C, N, O, and F nuclei were calculated using sum-over-states density functional perturbation theory ͑SOS-DFPT͒. Diatomic ro-vibrational states were calculated from a discrete variable representation using Morse potentials and potential curves calculated with density functional theory. Our ro-vibrational corrections to shielding constants for HF, CO, F 2 , and N 2 molecules are in good agreement with experimental data and CCSD͑T͒ calculations. These results together with satisfactory first and second derivatives of the shielding constants with respect to interatomic distances confirm that the shielding surfaces produced by the SOS-DFPT method are of good accuracy, providing reassurance of the use of these methods for more complex systems. The unusual temperature dependence of the hydrogen chemical shift in HBr and a first attempt to include both relativistic spin-orbit and ro-vibration effects are discussed.
Chemical Physics, 1997
The effect of hydrogen binding and vibrational .notions on the oxygen and hydrogen nuclear magnetic shielding constants in the OH-and mono-hydrated OH-ic.1 (H,O,) is investigated by ab initio calculations. A large down-field shift in "0 shieldings and a small down-field shift in the 'H shieldings is found for H,O, relative to OH-. The dependence of the nuclear magnetic shielding constants in H .lO, on the strongly anharmonic symmetric and antisymmetric 0-H. .. 0 stretching motions and on the internal rotation motion of the outer hydrogens is studied with the non-rigid bender model Hamiltonian [V. Spirko, W. P. Kraemer and A. cejchan, J. Mol. Spectrosc. 136 (1989) 3401 at the level of the random phase approximation (RPA). The dependence of the shielding constants in OH-on the bond length is investigated at the level of the RPA and the second order polarization propagator approximation (SOPPA). Pertinent (analytic) nuclear magnetic shielding functions are obtained by fitting to the ab initio shielding points and these functions are used to calculate the vibrational averages using the corresponding vibrational eigenfunctions. The predicted effective shielding constants of H,O, exhibit a sizable and non-monotonic dependence on the stretching vibrational quantum numbers, whereas the dependence on the internal rotation is practically negligible. The effective shielding constants of OH-show an even larger dependence on the vibrational quantum number. The effect of the end-over-end rotational motion, however, is small.
2008
We present a new relativistic formulation for the calculation of nuclear magnetic resonance ͑NMR͒ shielding tensors. The formulation makes use of gauge-including atomic orbitals and is based on density functional theory. The relativistic effects are included by making use of the zeroth-order regular approximation. This formulation has been implemented and the 199 Hg NMR shifts of HgMe 2 , HgMeCN, Hg͑CN͒ 2 , HgMeCl, HgMeBr, HgMeI, HgCl 2 , HgBr 2 , and HgI 2 have been calculated using both experimental and optimized geometries. For experimental geometries, good qualitative agreement with experiment is obtained. Quantitatively, the calculated results deviate from experiment on average by 163 ppm, which is approximately 3% of the range of 199 Hg NMR. The experimental effects of an electron donating solvent on the mercury shifts have been reproduced with calculations on HgCl 2 ͑NH 3 ͒ 2 , HgBr 2 ͑NH 3 ͒ 2 , and HgI 2 ͑NH 3 ͒ 2 . In addition, it is shown that the mercury NMR shieldings are sensitive to geometry with changes for HgCl 2 of approximately 50 ppm for each 0.01 Å change in bond length, and 100 ppm for each 10°change in bond angle.
The Journal of Chemical Physics, 1997
The enhancement of nuclear magnetic resonance ͑NMR͒ relaxation rates produced by paramagnetic solutes is physically rather different for electron spin Sϭ1/2 paramagnetic species than for Sу1 species due to the presence of zero-field splitting interactions in the electron spin Hamiltonians of the latter. When the zfs energy is larger than the electronic Zeeman energy, the electron spin precessional motion is spatially quantized with respect to the molecule-fixed principal axis system ͑PAS͒ of the zfs tensor rather than along the external laboratory magnetic field. An analytical theory of the orthorhombic zfs limit has been derived in which the motion of the electron spin variables is described in the zfs-PAS and that of the nuclear spin variables in the laboratory coordinate frame. The resulting theoretical expressions are simple in form and suggest a physically transparent interpretation of the experiment. The NMR relaxation enhancement R 1p results from additive contributions, R 1x , R 1y , and R 1z , arising from the molecular-frame Cartesian components of the time-dependent electron spin magnetic moment operator r (t). Each Cartesian component R 1r depends on the dipolar power density at the nuclear Larmor frequency that is produced by the corresponding Cartesian component of r (t). The theory displays the dependence of the relaxation enhancement on the variables of molecular structure in a very simple and physically transparent form: R 1r ϰr Ϫ6 ͓1ϩ P 2 (cos r)͔, where r is the interspin distance and cos r is the direction cosine of the interspin vector with the rth principal axis of the zfs tensor. New experimental data are presented for the model Sϭ1 complex ͓trans-Ni͑II͒͑acac͒ 2 ͑H 2 O͒ 2 ͔ (acacϭacetylacetonato) in dioxane solvent. The magnetic field dependence of the proton T 1 of the axial water ligands has been measured over the range 0.15-1.5 T, the lower end of which corresponds to the zfs limit. The experimental data have been analyzed using the new analytical theory for the zfs-limit regime in conjunction with spin dynamics simulations in the intermediate regime. Dipolar density power plots are presented as graphical devices which clearly exhibit the physical information in the experiment, and which permit a rapid differentiation of the sensitive and insensitive parameters of theory. The data analysis depends strongly on the zfs parameter ͉E͉ and on the electron spin relaxation time S,z along the zfs-PAS z-axis, but only very weakly on the other parameters of theory. A fit of the data to theory provided the values ͉E͉ϭ1.8Ϯ0.1 cm Ϫ1 and S,z ϭ8.0Ϯ0.3 ps.