NMR STUDIES OF VITRAIN, PYRIDIN-SOLUBLE AND-INSOLUBLE SOLIDS

Vitrain and its pyridin-extracted products （i. e. both the pyridin-soluble and-inso1ubleconstituents） were investigated by means of solid state 13C CPMAS and 1H CRAMPS NMRtechniques. From the measurements, twelve structural parameters of the carbon skeleton wereobtained and the size of aromatic clusters for each sample was estimated. It is shown that theaverage size of aromatic clusters in pyridin-soluble part of vitrain is relatively small, contain-ing only 2--3 aromatic rings, while that in pyridin-insoluble part is relatively high, contain-ing five fused aromatic rings and its carbon aromaticity is apparently higher than that ofthe pyridin-soluble constituents. Measurement of carbon (13C) and proton （1H） spin-latticerelaxation times （T1H and T1C） shows that the relaxation in vitrain is mainly caused by para-magnetic centers. Therefore, pyridin extracting process effectively takes away the paramagneticcenters in vitrain, hence the concentration of free radicals for both the pyridin-solubleand -insoluble constituents are decreased. However, the decrement for pyridin-soluble constit-uent is even larger than that of the insoluble one.