Hughes, CD
1993
Measurement of C-13 Chemical-Shift Anisotropy in Coal
Orendt, A.M.; Solum, M.S.; Sethi, N.K.; Hughes, C.D.; Pugmire, R.J. and Grant, D.M.
Magnetic Resonance of Carbonaceous Solids, Advances in Chemistry Series #229, 22:419-439, 1993. Funded by US Department of Energy, Basic Energy Services and ACERC.
The methods of available in NMR spectroscopy to obtain the principal values of the chemical-shift tensor are discussed. Applications to coal and to compounds with model structures that might be important in coal are presented. The composition of aromatic carbons in coal as determined by chemical-shift powder patterns is compared to results obtained by cross-polarization with magic-angle spinning and dipolar dephasing.
Chemical-Shift-Chemical-Shift Correlation Spectroscopy in Powdered Solids
Hughes, C.D.; Sherwood, M.H.; Alderman, D.W. and Grant, D.M.
Journal of Magnetic Resonance, 102:58-72, 1993. Funded by US Department of Energy.
Sample reorientation during the mixing time of a two-dimensional NMR exchange experiment allows the measurement of chemical-shift tensors in powdered samples whose one-dimensional powder patterns are too complex to reliably analyze. This technique has the advantages that the chemical-shift anisotropy has an unscaled representation, the artifacts caused by cross polarization, spin relaxation, and partial sample orientation can be accounted for, the experiment is relatively easy to perform, and no spinning sidebands interfere. The method is useful for sorting out the principal values of overlapping chemical-shift tensors.
1992
Carbon-13 Chemical Shift Tensors in Aromatic Compounds. 3. Phenanthrene and Triphenylene
Soderquist, A.; Hughes, C.D.; Horton, W.J.; Facelli, J.C. and Grant, D.M.
Journal of American Chemistry Society, 114(8):2826-2832, 1992. Funded by National Institutes of Health and US Department of Energy.
Measurements of the principal values of the C-13 chemical shift tensor are presented for the three carbons in triphenylene and for three different alpha-carbons in phenanthrene. The measurements in triphenylene were made in natural abundance samples at room temperature, while the phenanthrene tensors were obtained from selectively labeled compounds (99% C-13) at low temperatures (~25 K). The principal values of the shift tensors were oriented in the molecular fram using ab initio LORG calculations. The steric compression at C4 in phenanthrene and in corresponding positions in triphenylene is manifested in a sizable upfield shift in the alpha33 component relative to the corresponding alpha33 values at C1 and C9 in phenanthrene. The upfield shift in alpha33 is mainly responsible for the well-known upfield shift of the isotropic chemical shifts of such sterically perturbed carbons. In phenanthrene C9 exhibits a unique a22 value reflecting the greater localization of pi-electrons in the C9-C10 bond. This localization of the pi-electrons at the C9-C10 bond in the central ring of phenanthrene also corresponds with the most likely ordering of electrons described by the various Kekulé structures in phenanthrene. The analysis of the C-13 chemical shieldings of the bridgehead carbons in triphenylene provides significant experimental information on bonding between rings in polycyclic aromatic compounds. The results confirm that the electronic structure of triphenylene is best described by three fairly isolated benzene rings linked by C-C bonds of essentially single bond character. Similarly in phenanthrene, the bonding structure that correlates the shielding information may be characterized by the dominance of two benzene rings comprising the biphenyl moiety. A strong C9-C10 pi-bond with only limited pi-electron character n the C8a-C9 and C10-C10a bonds is indicated by both the experimental and theoretical results.
Chemical Shift-Chemical Shift Correlation Spectroscopy in Powdered Solids
Hughes, C.D.; Sherwood, M.H.; Alderman, D.W. and Grant, D.M.
Fifth Coal Chemistry Conference and Workshop, Rockford, IL, June 1992. Funded by US Department of Energy.
Sample reorientation during the mixing time of a two-dimensional NMR exchange experiment allows the measurements of chemical shift tensors in powdered samples whose one-dimensional powder patterns are too complex to reliably analyze. This technique has the advantages that the chemical shift anisotropy has an unscaled representation, the artifacts caused by cross polarization, spin relaxation and partial sample orientation can be accounted for, the experiment is relatively easy to perform, and no spinning sidebands interfere. The method is useful for sorting out the principal values of overlapping chemical shift tensors.
1991
Measurement of C-13 Chemical Shielding Anisotropy in Coal
Orendt, A.M.; Solum, M.S.; Sethi, N.K.; Hughes, C.D.; Pugmire, R.J. and Grant, D.M.
Magnetic Resonance of Solid Carbonaceous Fuels, ACS Symposium Series, (R.E. Botto and Y. Sanada, eds.), 1991 (in press). Funded by US Department of Energy and ACERC.
The methods available in nuclear magnetic resonance to obtain the principal values of the shielding tensor are discussed. Applications to coal and to compounds that model structures that might be important in coal are presented. The composition of aromatic carbons in coal as determined by chemical shielding powder patterns is compared to results obtained by cross polarization with magic angle spinning (CP/MAS) and dipolar dephasing (DD).
1990
Measurement of C-13 Chemical Shielding Anisotropy in Coal
Orendt, A.M.; Solum, M.S.; Sethi, N.K.; Hughes, C.D.; Pugmire, R.J. and Grant, D.M.
Magnetic Resonance of Solid Carbonaceous Fuels, ACS Symposium Series, Botto, R.E. and Sanada, Y., Editors, 1990 (In press). Funded by ACERC and US Department of Energy.
The methods available in nuclear magnetic resonance to obtain the principal values of the shielding tensor are discussed. Applications to coal and to compounds that model structures that might be important in coal are presented. The composition of aromatic carbons in coal as determined by chemical shielding powder patterns is compared to results obtained by cross polarization with magic angle spinning (CP/MAS) and dipolar dephasing (DD).
1989
Polyethylene Crystallinity From Static, Solid-State NMR Spectra
Hughes, C.D.; Sethi, N.K.; Baltisberger, J.H. and Grant, D.M.
Macromolecules, 22, 2551, 1989. Funded by US Department of Energy.
A new method for determining the crystallinity of linear polyethylene (LPE) utilizing static, solid state C-13 Nuclear Magnetic Resonance (NMR) spectroscopy and computer lineshape simulation is described. Good agreement between the crystallinity measured by this method and a standard method was found. The computer simulation of the experimental spectrum also reflects the degree of gauche and trans chain conformations in the amorphous region of the sample.
Hughes, CD
1993
Measurement of C-13 Chemical-Shift Anisotropy in Coal
Orendt, A.M.; Solum, M.S.; Sethi, N.K.; Hughes, C.D.; Pugmire, R.J. and Grant, D.M.
Magnetic Resonance of Carbonaceous Solids, Advances in Chemistry Series #229, 22:419-439, 1993. Funded by US Department of Energy, Basic Energy Services and ACERC.
The methods of available in NMR spectroscopy to obtain the principal values of the chemical-shift tensor are discussed. Applications to coal and to compounds with model structures that might be important in coal are presented. The composition of aromatic carbons in coal as determined by chemical-shift powder patterns is compared to results obtained by cross-polarization with magic-angle spinning and dipolar dephasing.
Chemical-Shift-Chemical-Shift Correlation Spectroscopy in Powdered Solids
Hughes, C.D.; Sherwood, M.H.; Alderman, D.W. and Grant, D.M.
Journal of Magnetic Resonance, 102:58-72, 1993. Funded by US Department of Energy.
Sample reorientation during the mixing time of a two-dimensional NMR exchange experiment allows the measurement of chemical-shift tensors in powdered samples whose one-dimensional powder patterns are too complex to reliably analyze. This technique has the advantages that the chemical-shift anisotropy has an unscaled representation, the artifacts caused by cross polarization, spin relaxation, and partial sample orientation can be accounted for, the experiment is relatively easy to perform, and no spinning sidebands interfere. The method is useful for sorting out the principal values of overlapping chemical-shift tensors.
1992
Carbon-13 Chemical Shift Tensors in Aromatic Compounds. 3. Phenanthrene and Triphenylene
Soderquist, A.; Hughes, C.D.; Horton, W.J.; Facelli, J.C. and Grant, D.M.
Journal of American Chemistry Society, 114(8):2826-2832, 1992. Funded by National Institutes of Health and US Department of Energy.
Measurements of the principal values of the C-13 chemical shift tensor are presented for the three carbons in triphenylene and for three different alpha-carbons in phenanthrene. The measurements in triphenylene were made in natural abundance samples at room temperature, while the phenanthrene tensors were obtained from selectively labeled compounds (99% C-13) at low temperatures (~25 K). The principal values of the shift tensors were oriented in the molecular fram using ab initio LORG calculations. The steric compression at C4 in phenanthrene and in corresponding positions in triphenylene is manifested in a sizable upfield shift in the alpha33 component relative to the corresponding alpha33 values at C1 and C9 in phenanthrene. The upfield shift in alpha33 is mainly responsible for the well-known upfield shift of the isotropic chemical shifts of such sterically perturbed carbons. In phenanthrene C9 exhibits a unique a22 value reflecting the greater localization of pi-electrons in the C9-C10 bond. This localization of the pi-electrons at the C9-C10 bond in the central ring of phenanthrene also corresponds with the most likely ordering of electrons described by the various Kekulé structures in phenanthrene. The analysis of the C-13 chemical shieldings of the bridgehead carbons in triphenylene provides significant experimental information on bonding between rings in polycyclic aromatic compounds. The results confirm that the electronic structure of triphenylene is best described by three fairly isolated benzene rings linked by C-C bonds of essentially single bond character. Similarly in phenanthrene, the bonding structure that correlates the shielding information may be characterized by the dominance of two benzene rings comprising the biphenyl moiety. A strong C9-C10 pi-bond with only limited pi-electron character n the C8a-C9 and C10-C10a bonds is indicated by both the experimental and theoretical results.
Chemical Shift-Chemical Shift Correlation Spectroscopy in Powdered Solids
Hughes, C.D.; Sherwood, M.H.; Alderman, D.W. and Grant, D.M.
Fifth Coal Chemistry Conference and Workshop, Rockford, IL, June 1992. Funded by US Department of Energy.
Sample reorientation during the mixing time of a two-dimensional NMR exchange experiment allows the measurements of chemical shift tensors in powdered samples whose one-dimensional powder patterns are too complex to reliably analyze. This technique has the advantages that the chemical shift anisotropy has an unscaled representation, the artifacts caused by cross polarization, spin relaxation and partial sample orientation can be accounted for, the experiment is relatively easy to perform, and no spinning sidebands interfere. The method is useful for sorting out the principal values of overlapping chemical shift tensors.
1991
Measurement of C-13 Chemical Shielding Anisotropy in Coal
Orendt, A.M.; Solum, M.S.; Sethi, N.K.; Hughes, C.D.; Pugmire, R.J. and Grant, D.M.
Magnetic Resonance of Solid Carbonaceous Fuels, ACS Symposium Series, (R.E. Botto and Y. Sanada, eds.), 1991 (in press). Funded by US Department of Energy and ACERC.
The methods available in nuclear magnetic resonance to obtain the principal values of the shielding tensor are discussed. Applications to coal and to compounds that model structures that might be important in coal are presented. The composition of aromatic carbons in coal as determined by chemical shielding powder patterns is compared to results obtained by cross polarization with magic angle spinning (CP/MAS) and dipolar dephasing (DD).
1990
Measurement of C-13 Chemical Shielding Anisotropy in Coal
Orendt, A.M.; Solum, M.S.; Sethi, N.K.; Hughes, C.D.; Pugmire, R.J. and Grant, D.M.
Magnetic Resonance of Solid Carbonaceous Fuels, ACS Symposium Series, Botto, R.E. and Sanada, Y., Editors, 1990 (In press). Funded by ACERC and US Department of Energy.
The methods available in nuclear magnetic resonance to obtain the principal values of the shielding tensor are discussed. Applications to coal and to compounds that model structures that might be important in coal are presented. The composition of aromatic carbons in coal as determined by chemical shielding powder patterns is compared to results obtained by cross polarization with magic angle spinning (CP/MAS) and dipolar dephasing (DD).
1989
Polyethylene Crystallinity From Static, Solid-State NMR Spectra
Hughes, C.D.; Sethi, N.K.; Baltisberger, J.H. and Grant, D.M.
Macromolecules, 22, 2551, 1989. Funded by US Department of Energy.
A new method for determining the crystallinity of linear polyethylene (LPE) utilizing static, solid state C-13 Nuclear Magnetic Resonance (NMR) spectroscopy and computer lineshape simulation is described. Good agreement between the crystallinity measured by this method and a standard method was found. The computer simulation of the experimental spectrum also reflects the degree of gauche and trans chain conformations in the amorphous region of the sample.