E.p.r. and ENDOR studies of Argonne Premium coals doped with nitroxide spin probes
✍ Scribed by Janina Goslar; Lowell D. Kispert
- Publisher
- Elsevier Science
- Year
- 1990
- Tongue
- English
- Weight
- 708 KB
- Volume
- 69
- Category
- Article
- ISSN
- 0016-2361
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✦ Synopsis
E.p.r. and ENDOR measurements of five Argonne Premium Coal Samples (APCS) varying in rank from low-volatile (Pocahontas, No. 5) to lignite (Beulah-Zap, No. 8) either undoped or doped with nitroxide spin probes and a series of nitroxide radicals are reported. For the first time proton hyperline coupling constants have been deduced from ENDOR studies of tempamine, DCT-tempamine and a carboxaldimine nitroxide radical in toluene solution at 185 K. Proton matrix ENDOR signals at the free proton frequency and a broad ENDOR signal were observed for all undoped APCS, except for a sample of Beulah-Zap in which no proton ENDOR lines were observed. For the spin probe doped Beulah-Zap, Blind Canyon and Illinois No. 6, the ENDOR spectrum consisted of the lines observed for the undoped coal, and two pairs of proton ENDOR lines with hyperline couplings of 3.6 MHz and 0.18 MHz. The lines with the coupling of 3.6 MHz are due to nitroxide radicals, assigned by similarity to the ENDOR results of the nitroxide spin probes in toluene solution at 120 K.
The existence of the second pair of lines with hyperhne coupling constant 0.18 MHz was assumed to be due to the interaction of surrounding matrix coal protons with the nitroxide species, substantiating an earlier report of hydrogen bonding to the nitroxide spin probe.