Effect of σ,π conjugation on199Hg chemical shifts

Conclusions The¹⁹⁹Hg NMR spectra of compounds of the type HgCC=C and HgCC=0 have been studied and it has been shown that C-Hg/ conjugation produces a sharp increase in the shielding of the mercury nucleus.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1038–1042, May, 1982.     

Carbon-13 nuclear magnetic resonance chemical shifts and 13C-199Hg coupling constants for symmetrical dialkylmercurials

The carbon-13 chemical shifts and coupling constants (J[¹³C? ¹⁹⁹Hg]) have been determined for a series of eleven symmetrically substituted organomercurials. Empirical substituent parameters can be calculated which correlate observed and predicted chemical shifts for dialkylmercurials.     

Nuclear magnetic resonance shielding constants and chemical shifts in linear 199Hg compounds: a comparison of three relativistic computational methods

We investigate the importance of relativistic effects on NMR shielding constants and chemical shifts of linear HgL(2) (L = Cl, Br, I, CH(3)) compounds using three different relativistic methods: the fully relativistic four-component approach and the two-component approximations, linear response elimination of small component (LR-ESC) and zeroth-order regular approximation (ZORA). LR-ESC reproduces successfully the four-component results for the C shielding constant in Hg(CH(3))(2) within 6 ppm, but fails to reproduce the Hg shielding constants and chemical shifts. The latter is mainly due to an underestimation of the change in spin-orbit contribution. Even though ZORA underestimates the absolute Hg NMR shielding constants by ～2100 ppm, the differences between Hg chemical shift values obtained using ZORA and the four-component approach without spin-density contribution to the exchange-correlation (XC) kernel are less than 60 ppm for all compounds using three different functionals, BP86, B3LYP, and PBE0. However, larger deviations (up to 366 ppm) occur for Hg chemical shifts in HgBr(2) and HgI(2) when ZORA results are compared with four-component calculations with non-collinear spin-density contribution to the XC kernel. For the ZORA calculations it is necessary to use large basis sets (QZ4P) and the TZ2P basis set may give errors of ～500 ppm for the Hg chemical shifts, despite deceivingly good agreement with experimental data. A Gaussian nucleus model for the Coulomb potential reduces the Hg shielding constants by ～100-500 ppm and the Hg chemical shifts by 1-143 ppm compared to the point nucleus model depending on the atomic number Z of the coordinating atom and the level of theory. The effect on the shielding constants of the lighter nuclei (C, Cl, Br, I) is, however, negligible.     

The effect of selfassociation of mercurated carbonyl compounds of mercury-199 chemical shifts

Temperature and concentration dependences of mercury-199 chemical shifts in benzene solutions of bis(methylethylketone)mercury Hg(CH₂COC₂H₅) (I) and α-bis(methylacetoacetone)mercury Hg(CH₂COCH₂COOCH₃)₂ (II) are determined by the ¹H-{¹⁹⁹Hg}method. The NMR data obtained and the IR spectra are indicative of selfassociation of I and II in solution with the formation of weak intermolecular coordination bonds Hg ← :OC. The enthalpies of complex formation calculated on the assumption of one mercury atom bonding with only one carbonyl function are equal to ?3.2 ± 0.1 kcal/mol and ?2.2 ± 0.1 kcal/mol for I and II, respectively.     

Surface nuclear spin relaxation of 199Hg

We report the results of a detailed study of surface relaxation of 199Hg nuclear spins in paraffin coated cells. From measurements of the magnetic field and temperature dependence of the spin relaxation rates we determine the correlation time for magnetic fluctuations and the surface adsorption energy. The data indicate that surface relaxation is caused by dipolar coupling to paramagnetic sites on the surface. We also observe changes in the spin relaxation rate caused by ultraviolet radiation resonant with the 254 nm transition in Hg.     

Fully relativistic coupled cluster and DFT study of electric field gradients at Hg in 199Hg compounds

We investigate the magnitude and interplay of relativistic and electron correlation effects on the electric field gradient (EFG) at the position of Hg in linear and bent HgL(2) (L = CH(3), Cl, Br, I) and trigonal planar [HgCl(3)](-) compounds using four-component relativistic Dirac-Coulomb (DC) and non-relativistic (NR) calculations at the Hartree-Fock (HF), DFT, MP2 and coupled cluster (CC) levels. The relativistic and electron correlation contributions to EFG have opposite signs and are not additive, demonstrating the importance of taking into account relativistic and electron correlation contributions on an equal footing. DC-MP2 overestimates the electron correlation correction by 0.48-0.56 a.u. for Hg-halides and by 0.8 a.u. for Hg(CH(3))(2), respectively, while DC-CCSD underestimates the correlation correction by 0.57-0.66 a.u. compared to the reference DC-CCSD-T data. EFGs obtained at the DC-DFT level vary considerably with the functional; DC-CAMB3LYP and DC-BH&H reproduce DC-CCSD-T results within 0.08-0.24 a.u. (1%-3%) for Hg(CH(3))(2) and Hg-halides, respectively. An updated value of the nuclear quadrupole moment of the I = 5/2 excited state of (199)Hg, Q((199)Hg) = 0.675(12) b is derived from the literature. This value compares well with that derived from our calculated EFG at the DC-CCSD-T level and the experimental data for Hg(CH(3))(2); Q((199)Hg) = 0.650 b.     

Linear dependence of 1J13C, 199Hg) and 2J(1H,C,199Hg) for dibenzylmercury in various solvents

The ¹J(¹³C, ¹⁹⁹Hg) spin–spin coupling constants have been studied for dibenzylmercury in various solvents. A linear correlation was found between ¹J(¹³C, ¹⁹⁹Hg) and the ²J(¹H, C, ¹⁹⁹Hg) constants obtained earlier for the same solutions.     

稠环芳烃系列化合物化学位移的计算 IV.^1H化学位移加合性规律的量子力学基础

Based on a starting point of the McWeeny Huckel-London perturbation theory approximation, a formula similar to the fourmula of additivity rule for the calculations of the chemical shifts of condensed aromatic hydrocarbons has been derived. The quantum mechanical basis of additivity rule is thus indicated by this formula. It is shown that by using the concept of aromatic shift and sigma ratio, this method for calculation of proton chemical shifts has the virtues of definite physical meaning and simple calculation. It can also be extended to the calculation of the proton chemical shifts of substituents fr the molecules of this series.     

Sensitized photo-oxidation of thiophenolates a singlet oxygen reaction

Tetraphenylporohyrin-sensitized photo-oxidation of thiophenolates leads to the corresponding benzenesulfonates. The reaction proceeds via attack of singlet oxygen on the thiophenolate anion. A reaction mechanism is proposed.     

199Hg and13C NMR spectra of bromine-substituted benzyl derivatives of mercury

Conclusions ¹⁹⁹Hg chemical shifts indicate that in dibenzyl derivatives of mercury and in benzylmercury bromides, there is, conjugation of the C-Hg bond with the orbitals of the aromatic ring, and also intramolecular coordination of the Hg atom with the Br atoms located in the o-position relative to the CH₂HgBr group, leading to the formation of a five-membered chelate ring. Such coordination interaction does not have an appreciable effect on the¹³C chemical shifts or the J_C-Hg constants.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 793–799, April, 1985.     

The solvation of the mercury(II) ion-a 199Hg NMR study

The solvation of the mercury(II) ion in solvents with different solvation properties, water, dimethylsulfoxide, N,N-dimethylthioformamide, and liquid ammonia, has been studied by means of (199)Hg NMR. The (199)Hg chemical shift shows a pronounced dependence on the coordination number of the mercury(II) ion in the solvates resulting in a difference of over 1200 ppm between basically tetrahedral and octahedral complexes. The chemical shifts can furthermore be associated with electron-pair donor properties of the solvents. The spin-lattice relaxation times of the (199)Hg nucleus in the solvates have been measured at different applied magnetic fields, concentrations, temperatures, and isotope substitutions. Possible mechanisms for the (199)Hg relaxation were proposed and the chemical shielding anisotropy in the solvates has been estimated. The (199)Hg relaxation rates and the anisotropy are correlated with the structure of the solvate complexes in solution obtained from recent LAXS and EXAFS studies.     

31P chemical shifts in N-aryliminotriphenylphosphoranes

³¹P chemical shifts in N-aryliminotriphenylphosphoranes and the corresponding N-methylated phosphonium salts are presented. They can be correlated with those theories of the bonding in phosphorus-nitrogen ylides which involve partial double bonding as a result of p^π–d^π overlap.     

15N chemical shifts in aziridines

For a number of 1-substituted aziridines and also some 1,2-disubstituted aziridines it has been shown that electron-donating substituents on the nitrogen atom produce a downfield shift of the ¹⁵N resonance. The ¹⁵N chemical shifts of aziridines correlate with the ¹⁵N shifts in N,N-dimethylamines and primary amines as well as with the ¹⁷O shifts in oxiranes. A correlation is also observed between the ¹⁵N chemical shifts and the electronegativity of the substituents on the nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, 1336–1339, October, 1988.     

NMR chemical shifts. Substituted acetylenes

The MPW1PW91/6-311+G(2d,p) and MP2/6-311+G(2d,p) GIAO nuclear shieldings for a series of monosubstituted acetylenes have been calculated using the MP2/6-311G(2d,p) geometries. Axially symmetric substituents such as fluorine may lead to large changes in the isotropic shielding but have little effect on the tensor component (zz) about the C[triple bond]C bond axis. On the other hand, substituents such as vinyl and aldehyde groups lead to essentially no difference in the isotropic shielding but are calculated to give a large zz paramagnetic shift to the terminal carbon of the acetylene group, without having much effect on the inner carbon. The tensor components of the chemical shifts for trimethylsilylacetylene, methoxyacetylene, and propiolaldehyde have been measured and are in reasonable agreement with the calculations. The downfield shift at the terminal carbon of propiolaldehyde along with a small upfield shift at the adjacent carbon has been found to result from the coupling of the in-plane pi MO of the acetylene with the pi* orbital that has a node near the central carbon. The tensor components for acetonitrile also have been measured, and the shielding of cyano and acetylenic carbons are compared.