Semiempirical theory of magnetic resonance parameters. I. Theory of chemical shielding constants, using gauge-invariant atomic orbitals, parameterization, and carbon-13 chemical shifts

Garber, Albert R.; Ellis, Paul D.; Seidman, Kurt; Schade, Kathryn

doi:10.1016/0022-2364(79)90026-x

Cited by 14 publications

(6 citation statements)

References 32 publications

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“…Let us discuss the origin of the appearance of peaks II and III. The three peaks I, II, and III can be assigned by means of the -gauche effect concept.11, 14 The methylene carbon appears at high field by 4-6 ppm if any carbon atom three bonds away is in a gauche, rather than a trans, conformation. This has been justified by both experiment and theory and been successfully used to predict the chemical shift of each stereosequence of polymers.15 From this point of view, it is shown that peaks I, II, and III can be assigned to the methylene carbons arising from the trans zigzag structure region and folded structure region, respectively.…”

Section: Discussionmentioning

confidence: 99%

Conformation of cyclic paraffins and polyethylene in the solid state as studied by carbon-13 CP/MAS NMR

Ando¹,

Yamanobe²,

Sorita³

et al. 1984

Macromolecules

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13C high-resolution NMR spectra of cyclic paraffins (C24H48, C28H6e, C32Hg4, C36H72, C^Hgo, C48H96, C64H128, and CggH^), «-paraffins (n-CigH^, «-€22646, and n-C32He6), and a crystalline polyethylene were measured in the solid state. It was shown that the 13C NMR resonance lines of the folded structure region and the trans zigzag structure region in the cyclic paraffins C40H80, C48Hgg, C64H128, and C8oH160 are chemically shifted from one another and that the chemical shifts of «-paraffins with an all-trans zigzag form in the solid state parallel those of the trans zigzag structure region in cyclic paraffins. Their difference is 4-12 ppm. These results demonstrate that cyclic paraffins assume a crystalline conformation with the shape of two parallel straight chains bridged at both ends, producing a freezing of molecular motion. Similarly, it is shown that the 13C NMR signals of the crystalline component and the other component (folded structure or noncrystalline structure) in a dilute-solution-grown crystalline polyethylene are chemically shifted from one another. In this case the latter peak appears as a high-field shoulder on the signal due to the crystalline form. Their difference is about 2.3 ppm. These results are compared with those in cyclic paraffins, and the fold structure is discussed.

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Section: Discussionmentioning

confidence: 99%

Conformation of cyclic paraffins and polyethylene in the solid state as studied by carbon-13 CP/MAS NMR

Ando¹,

Yamanobe²,

Sorita³

et al. 1984

Macromolecules

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“…The established procedures usually require evaluation of different primitive integrals for different operators, whereas the corresponding reduction formulas may be cumbersome to derive even for an sp basis. 44 Because our program supports d orbitals, the number of required reduction formulas and elementary integrals would have been significantly larger than in earlier semiempirical implementations, 44 making this route unmanageable. We therefore decided to pursue a more general approach to the two-center integrals, even at a potentially increased computational cost.…”

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confidence: 99%

“…18 results in a non-Hermitian expression. 44,51 Taking the antisymmetric part, we arrive at the final semiempirical expression for H a : Ž . in eq.…”

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confidence: 99%

“…An expression equivalent to eq. 22 was used in earlier INDO 44 and MNDO 51 models. Several INDO studies employed either the London term alone, 40,46 or supplemented it with the orbital momentum term.…”

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confidence: 99%

“…22 was shown to be crucial for a qualitatively correct description of shielding in linear molecules. 44 For analysis of the chemical shifts it is desirable to separate the chemical shift tensor into diamagnetic and paramagnetic contributions. The natural choice 7 is to designate all terms due to the unperturbed density as diamagnetic, and the terms containing the first-order density as paramagnetic.…”

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confidence: 99%

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NMR chemical shifts in MNDO approximation: Parameters and results for H, C, N, and O

Patchkovskii

Thiel

1999

J. Comput. Chem.

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A simplex optimized INDO calculation of ¹³C chemical shifts in hydrocarbons

Chesnut¹,

Whitehurst²

1980

J Comput Chem

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The variable-size simplex optimization method is used to reparametrize the I + A and / 3 parameters of an INDO approximation to the perturbed Hartree-Fock calculation of 13C chemical shifts in hydrocarbons. The absolute shifts for 39 nuclei in a set of molecules containing up to four carbons are reproduced within a standard error of 9.9 ppm for an unconstrained optimization and to a standard error of 10.0 ppm for an optimization constrained to yield gross atomic charges in agreement with double-zeta ab initio calculations. INTRODUCTIONSecond-order properties such as nuclear spinspin couplings and chemical shifts are sensitive probes of the electronic structure of molecules in that variations in these quantities often indicate subtle electronic changes. To relate such observed changes to the proper physical phenomenon it is, of course, necessary to have a theory capable of reproducing these second-order effects as well as the equally important lower-order properties of

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Semiempirical theory of magnetic resonance parameters. I. Theory of chemical shielding constants, using gauge-invariant atomic orbitals, parameterization, and carbon-13 chemical shifts

Cited by 14 publications

References 32 publications

Conformation of cyclic paraffins and polyethylene in the solid state as studied by carbon-13 CP/MAS NMR

Conformation of cyclic paraffins and polyethylene in the solid state as studied by carbon-13 CP/MAS NMR

NMR chemical shifts in MNDO approximation: Parameters and results for H, C, N, and O

A simplex optimized INDO calculation of ¹³C chemical shifts in hydrocarbons

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Semiempirical theory of magnetic resonance parameters. I. Theory of chemical shielding constants, using gauge-invariant atomic orbitals, parameterization, and carbon-13 chemical shifts

Cited by 14 publications

References 32 publications

Conformation of cyclic paraffins and polyethylene in the solid state as studied by carbon-13 CP/MAS NMR

Conformation of cyclic paraffins and polyethylene in the solid state as studied by carbon-13 CP/MAS NMR

NMR chemical shifts in MNDO approximation: Parameters and results for H, C, N, and O

A simplex optimized INDO calculation of 13C chemical shifts in hydrocarbons

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Product

Resources

About

A simplex optimized INDO calculation of ¹³C chemical shifts in hydrocarbons