13C shielding tensors in p-alkoxybenzenes

Höhener, A.

doi:10.1016/0009-2614(78)80399-6

Cited by 14 publications

(14 citation statements)

References 12 publications

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“…As far as we know, however, the principal values reported for similar compounds with ester groups are not so different from those for the C1 carbon of PCL. − Therefore, the principal values obtained in this paper, σ 11 = 265 ppm, σ 22 = 146 ppm, and σ 33 = 117 ppm, will be used for the CSA simulation of the C1 carbon described below. In contrast, the principal values of the methylene carbon directly attached to the oxygen atom seem to depend on the type of compound. − In the present analysis, σ 11 = 106 ppm, σ 22 = 91 ppm, and σ 33 = 27 ppm 37 for the OCH 2 carbon of poly(tetramethylene oxide), which are determined at −90 °C, are assumed as the principal values for the C6 carbon in the rigid state. As for the principal values of the C3−C5 carbons, σ 11 = 52 ppm, σ 22 = 37 ppm, and σ 33 = 13 ppm, which are derived from the values determined for polyethylenes crystals, ,, are used as reference values in the rigid state.…”

Section: Resultsmentioning

confidence: 89%

One- and Two-Dimensional Solid-State¹³C NMR Analyses of the Solid Structure and Molecular Motion of Poly(ε-caprolactone) Isothermally Crystallized from the Melt

Kaji

Horii

1997

Macromolecules

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The crystalline-noncrystalline structure and molecular motion of poly( -caprolactone) (PCL) isothermally crystallized from the melt have been investigated by one-and two-dimensional solid-state 13 C NMR spectroscopy. The 13 C spin-lattice relaxation time (T1C) analysis reveals that the PCL sample contains three components with different T1C values, which are assignable to the crystalline, mobile crystalline, and noncrystalline components. By the 13 C spin-spin relaxation time (T2C) analysis, it is found that the noncrystalline component can be further resolved into the crystalline-amorphous interfacial, and amorphous components. The mass fractions of the crystalline, interfacial, and amorphous components are finally determined to be 0.42, 0.30, and 0.28, respectively. In the crystalline region, different molecular mobilities along the methylene sequence are suggested through the difference in T1C value for the constituting carbons. More detailed molecular motion in the crystalline region has been characterized by the analysis of the 13 C chemical shift anisotropy (CSA) in terms of the two-site exchange model. 13 C CSA spectra of the individual carbons are successfully recorded by using the two-dimensional switching angle sample spinning technique. The CSA spectrum of the carbonyl carbon exhibit that the carbonyl carbon is almost in the rigid state or undergoes the jump motion around the molecular chain axis with a jump angle less than 30°. In contrast, methylene carbons exhibit almost axially symmetric CSA spectra, suggesting the rapid jump motions around the molecular chain axis with a jump angle of 60-90°. Further narrowed CSA spectra, which are still axially symmetric, are observed for the methylene carbons not directly attached to the ester group, suggesting the existence of additional enhanced jump motion around the C-C bonds. Such enhanced molecular motions of the methylene sequence may be due to the distorted nonplanar zigzag chain conformation of PCL in the crystalline region.

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Section: Resultsmentioning

confidence: 89%

One- and Two-Dimensional Solid-State¹³C NMR Analyses of the Solid Structure and Molecular Motion of Poly(ε-caprolactone) Isothermally Crystallized from the Melt

Kaji

Horii

1997

Macromolecules

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“…Due to the diamagnetism of the surrounding electrons a nucleus will be partly "shielded" from the external field. In order to obtain the absolute scale for the order parameters, a knowledge of the diagonal elements of iT is required, which is, analogous to the case of the magnetic susceptibility, a complicated solid state problem (Hohener 1978). The difference in chemical shift between the nematic and the isotropic phase can be evaluated analogously to (9.33) for the magnetic anisotropy, giving (9.44) For proton NMR the effect of the chemical shift is small, and in the case of liquid crystals not visible due to the dipolar coupling.…”

Section: Nuclear Magnetic Resonancementioning

confidence: 99%

Thermotropic Liquid Crystals, Fundamentals

Vertogen¹,

Jeu

1988

Springer Series in Chemical Physics

578

332

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“…Although these methods are said to produce "liquid-like" spectra, an important difference between liquid and CP/MAS solid state nmr spectra is that dynamic averaging due to internal rotation or inversion is often absent in the solid. There have been several examples of such "freezing" of internal rotation (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). A frequently cited example is 1,4-dimethoxybenzene ( 2 , 3 , 6 , 15).…”

Section: Introductionmentioning

confidence: 99%

A carbon-13 CP/MAS nuclear magnetic resonance study of several 1,4-disubstituted benzenes in the solid state

Penner¹,

Wasylishen²

1989

Can. J. Chem.

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The carbon-13 chemical shifts of several 1,4-disubstituted benzenes in the solid state are reported. At least one of the substituents is unsymmetrical and in most cases this leads to different 13C chemical shifts of C-2 and C-6 and in some cases to different shifts for C-3 and C-5. The 13c chemical shifts observed in the solid state are compared with those measured in solution and, where possible, with those obtained in low temperature solution studies where internal rotation of the unsymmetrical substituent is slow on the I3C chemical shift time scale. Agreement between the chemical shifts observed in the solid state and solution is excellent. The potential application of CP/MAS nuclear magnetic resonance in deducing the conformation of benzene derivatives with two unsymmetrical substituents is discussed.

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13C shielding tensors in p-alkoxybenzenes

Cited by 14 publications

References 12 publications

One- and Two-Dimensional Solid-State¹³C NMR Analyses of the Solid Structure and Molecular Motion of Poly(ε-caprolactone) Isothermally Crystallized from the Melt

One- and Two-Dimensional Solid-State¹³C NMR Analyses of the Solid Structure and Molecular Motion of Poly(ε-caprolactone) Isothermally Crystallized from the Melt

Thermotropic Liquid Crystals, Fundamentals

A carbon-13 CP/MAS nuclear magnetic resonance study of several 1,4-disubstituted benzenes in the solid state

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13C shielding tensors in p-alkoxybenzenes

Cited by 14 publications

References 12 publications

One- and Two-Dimensional Solid-State 13C NMR Analyses of the Solid Structure and Molecular Motion of Poly(ε-caprolactone) Isothermally Crystallized from the Melt

One- and Two-Dimensional Solid-State 13C NMR Analyses of the Solid Structure and Molecular Motion of Poly(ε-caprolactone) Isothermally Crystallized from the Melt

Thermotropic Liquid Crystals, Fundamentals

A carbon-13 CP/MAS nuclear magnetic resonance study of several 1,4-disubstituted benzenes in the solid state

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Product

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About

One- and Two-Dimensional Solid-State¹³C NMR Analyses of the Solid Structure and Molecular Motion of Poly(ε-caprolactone) Isothermally Crystallized from the Melt

One- and Two-Dimensional Solid-State¹³C NMR Analyses of the Solid Structure and Molecular Motion of Poly(ε-caprolactone) Isothermally Crystallized from the Melt