An improved carbon-13 nuclear shielding scale

Raynes, W.T.; McVay, Rebecca; Wright, Stephanie

doi:10.1039/f29898500759

Cited by 49 publications

(27 citation statements)

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“…However, we shall start with a more recent experimental value 38 of 116.88 ͑Ϯ0.9͒ ppm obtained for the low density ͑0.9 atm͒ isotopomer H 13 C 13 CH at 300 K based on the shielding scale of Ref. 37. The error of ͑Ϯ0.9͒ ppm arises almost wholly from the error in the absolute 13 C-shielding of carbon monoxide.…”

Section: Calculations At Equilibrium Geometrymentioning

confidence: 98%

Nuclear magnetic shielding in the acetylene isotopomers calculated from correlated shielding surfaces

Wigglesworth

Raynes

Kirpekar

et al. 2000

The Journal of Chemical Physics

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Articles you may be interested inCurrent density maps, magnetizability, and nuclear magnetic shielding tensors of bis-heteropentalenes. I. Dihydro-pyrrolo-pyrrole isomers Natural chemical shielding analysis of nuclear magnetic resonance shielding tensors from gauge-including atomic orbital calculations Ab initio, symmetry-coordinate and internal valence coordinate carbon and hydrogen nuclear shielding surfaces for the acetylene molecule are presented. Calculations were performed at the correlated level of theory using gauge-including atomic orbitals and a large basis set. The shielding was calculated at equilibrium and at 34 distinct geometries corresponding to 53 distinct sites for each nucleus. The results were fitted to fourth order in Taylor series expansions and are presented to second order in the coordinates. The carbon-13 shielding is sensitive to all geometrical parameters and displays some unexpected features; most significantly, the shielding at a carbon nucleus ͑C 1 , say͒ is six times more sensitive to change of the C 1 C 2 H 2 angle than it is to change of the H 1 C 1 C 2 angle. In addition, for small changes, ͑C 1 ͒ is more sensitive to the C 2 H 2 bond length than it is to the C 1 H 1 bond length. These, and other, examples of ''unexpected differential sensitivity'' are discussed. The proton shielding surface is much more as expected with ͑H 1 ͒ being most sensitive to the C 1 H 1 bond length, less so to the CC bond length and hardly at all to the C 2 H 2 bond length. The surfaces have been averaged over a very accurate force field to give values of ͑C͒, ͑H͒, and ͑D͒ for the ten isotopomers containing all possible combinations of 12 C, 13 C, 1 H, and 2 H nuclei at 0 K and at a number of selected temperatures in the range accessible to experiment. For the carbon shielding the dominant nuclear motion contribution comes from the bending at ''the other'' carbon atom with the combined stretching contributions being only 20% of those from bending. For the proton shielding it is the stretching of the CH bond containing the proton of interest which provides the major nuclear motion contribution. For ͑C͒ in H 13 C 13 CH at 300 K our best result is 117.59 ppm which is very close to the experimental value of 116.9 ͑Ϯ0.9͒ ppm. For ͑H͒ in H 13 C 13 CH at 300 K we obtain 29.511 ppm which is also in very close agreement with the experimental value of 29.277 ͑Ϯ0.001͒ ppm. Calculated values are also very close to recent, highly accurate carbon and proton isotope shifts in the ten isotopomers; carbon isotope shifts differ by no more than 10% from the measured values and proton isotope shifts are generally in even better agreement than this. The observed anomaly whereby the 13 C isotope shift in H 13 C 12 CD is greater than that in D 13 C 12 CH both with respect to H 13 C 12 CH is explained in terms of the bending contribution at ''the other'' carbon. The observed nonadditivity of deuterium isotope effects on the carbon shielding can be traced to a cross term involving second order bending.

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Section: Calculations At Equilibrium Geometrymentioning

confidence: 98%

Nuclear magnetic shielding in the acetylene isotopomers calculated from correlated shielding surfaces

Wigglesworth

Raynes

Kirpekar

et al. 2000

The Journal of Chemical Physics

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“…Secondary references for proton and ''(2 shielding in this work are the nuclei of methane for which o(H) = 30.61 1 (f 0.024) ppm at 25°C45 and G('~C) = 194.8 (k0.9) ppm at 27°C. 46 Although we have measured our shielding differences with respect to toluene-d, , for the purposes of comparison we given them in Table 7 relative to the secondary reference methane for several of the compounds studied in the present work. Our values for both 'H and 'jC shielding, which are for 348 K, are more precise than earlier values but are generally in agreement with them.…”

Section: K -'mentioning

confidence: 99%

Intermolecular and intramolecular effects on the ¹H and ¹³C shielding in some gaseous hydrocarbons at various temperatures—experimental results

Bennett

Raynes

1991

Magnetic Reson in Chemistry

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The proton and "C shielding constants in CH, , C,H,, C,H, and some other gaseous hydrocarbons have been studied as functions of density at temperatures in the range 180-370 K. The linear coefficients describing the density dependence of the shielding, after correcting for bulk susceptibility, increase substantially as the temperature is reduced, indicating stronger intermolecular interactions. (Some of the required magnetic susceptibilities were determined in this work by an NMR method). The "C measurements for CH, are close to those of an earlier study; the results for the other gases are new. The linear coefficient is substantially greater for the carbon shielding of the methyl group in propane than for the methylene group at any temperature, but there is virtually no distinction between tbe linear coefficients for the proton shielding in this gas. Values for du,/dT, the temperature dependence of the shielding extrapolated to zero density, are also presented for both proton and "C shielding in the bydrocarboos. They are positive and negative in different instances. It is shown from this and earlier gas-phase studies that standard literature values of the methane "C shielding relative to the ''C shielding in tbe other bydrocarboos are in error.

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“…An estimate of the 13 C shielding of tetramethylsilane ͑TMS͒, 188 ppm, can be obtained from spin rotational measurements of carbon monoxide. 23 Both the proportionality constant and the shielding value of TMS are left as fitting parameters obtained from a linear regression analysis. The best estimate of the shielding from the chemical shifts is j = m ␦ j + ref .…”

Section: A Magnetic Shielding and Chemical Shift Tensorsmentioning

confidence: 99%

Intermolecular shielding contributions studied by modeling the C13 chemical-shift tensors of organic single crystals with plane waves

Johnston

Iuliucci

Facelli

et al. 2009

The Journal of Chemical Physics

120

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In order to predict accurately the chemical shift of NMR-active nuclei in solid phase systems, magnetic shielding calculations must be capable of considering the complete lattice structure. Here we assess the accuracy of the density functional theory gauge-including projector augmented wave method, which uses pseudopotentials to approximate the nodal structure of the core electrons, to determine the magnetic properties of crystals by predicting the full chemical-shift tensors of all 13 C nuclides in 14 organic single crystals from which experimental tensors have previously been reported. Plane-wave methods use periodic boundary conditions to incorporate the lattice structure, providing a substantial improvement for modeling the chemical shifts in hydrogen-bonded systems. Principal tensor components can now be predicted to an accuracy that approaches the typical experimental uncertainty. Moreover, methods that include the full solid-phase structure enable geometry optimizations to be performed on the input structures prior to calculation of the shielding. Improvement after optimization is noted here even when neutron diffraction data are used for determining the initial structures. After geometry optimization, the isotropic shift can be predicted to within 1 ppm.

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An improved carbon-13 nuclear shielding scale

Cited by 49 publications

References 1 publication

Nuclear magnetic shielding in the acetylene isotopomers calculated from correlated shielding surfaces

Nuclear magnetic shielding in the acetylene isotopomers calculated from correlated shielding surfaces

Intermolecular and intramolecular effects on the ¹H and ¹³C shielding in some gaseous hydrocarbons at various temperatures—experimental results

Intermolecular shielding contributions studied by modeling the C13 chemical-shift tensors of organic single crystals with plane waves

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An improved carbon-13 nuclear shielding scale

Cited by 49 publications

References 1 publication

Nuclear magnetic shielding in the acetylene isotopomers calculated from correlated shielding surfaces

Nuclear magnetic shielding in the acetylene isotopomers calculated from correlated shielding surfaces

Intermolecular and intramolecular effects on the 1H and 13C shielding in some gaseous hydrocarbons at various temperatures—experimental results

Intermolecular shielding contributions studied by modeling the C13 chemical-shift tensors of organic single crystals with plane waves

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Intermolecular and intramolecular effects on the ¹H and ¹³C shielding in some gaseous hydrocarbons at various temperatures—experimental results