th - 1987 - 51st ENC Conference
th - 1987 - 51st ENC Conference
th - 1987 - 51st ENC Conference
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MF33 - POSTERS<br />
INCREASED RESOLUTION FOR PROTON NMR SPECTRA OF SOLID MATERIALS<br />
Thomas G. Neiss and James E. Roberts<br />
Department of Chemistry #6<br />
Lehigh University<br />
Be<strong>th</strong>lehem, PA 18015<br />
Sophisticated multiple-pulse techniques must be used to<br />
obtain "high resolution" proton spectra of most solid<br />
materials, or a single broad peak is observed as a consequence<br />
of <strong>th</strong>e large homonuclear couplings of <strong>th</strong>e proton reservoir.<br />
When Magic Angle Sample Spinning (MASS) is included wi<strong>th</strong> <strong>th</strong>e<br />
multiple-pulse experiment, <strong>th</strong>e typical proton peak wid<strong>th</strong> is<br />
still between 1 and 2 ppm. When several isotropic chemical<br />
shifts are present, <strong>th</strong>e resulting spectrum is often not<br />
interpretable due to significant spectral overlap. Two more<br />
complicated experiments are available for increasing <strong>th</strong>e<br />
resolution obtained in proton NMR spectra of solid materials.<br />
Two-dimensional heteronuclear chemical shift correlation<br />
NMR has been applied to liquids to connect <strong>th</strong>e proton and<br />
carbon chemical shifts <strong>th</strong>rough J couplings. The J couplings<br />
in solids are usually not resolved. However, wi<strong>th</strong> appropriate<br />
implementation during MASS, <strong>th</strong>e 2-D experiment correlates <strong>th</strong>e<br />
proton and carbon chemical shifts, yielding better overall<br />
resolution in <strong>th</strong>e proton dimension, even <strong>th</strong>ough <strong>th</strong>e proton<br />
linewid<strong>th</strong>s are still 1 to 2 ppm.<br />
An alternative to <strong>th</strong>e full two dimensional technique<br />
utilizes selective coherence transfer to observe only specific<br />
spin systems in a one-dimensional experiment. The selective<br />
coherence transfer occurs <strong>th</strong>rough <strong>th</strong>e strong heteronuclear<br />
dipolar interaction between bonded spins, so some protons are<br />
not readily observed wi<strong>th</strong> <strong>th</strong>is technique. The gain in proton<br />
spectrum resolution is comparable to <strong>th</strong>at obtained wi<strong>th</strong><br />
two-dimensional chemical shift correlation, but data<br />
accumulation and processing takes less time. Al<strong>th</strong>ough several<br />
1-D selective experiments might be needed to fully<br />
characterize a molecule, it is still a viable approach in many<br />
situations.<br />
Acknowledgement is made to <strong>th</strong>e donors of <strong>th</strong>e Petroleum<br />
Research Fund for partial support of <strong>th</strong>is work. Supported by<br />
NSF-Solid State Chemistry program grant # DMR-8553275.<br />
Additional support <strong>th</strong>rough <strong>th</strong>e Presidential Young Investigator<br />
program was obtained from Cambridge Isotope Laboratories; Dory<br />
Scientific; General Electric Corporate Research and<br />
Development; General Electric NMR Instruments; IBM<br />
Instruments; Merck, Sharp and Dohme; and Monsanto Company.