P-31 NMR-SPECTROSCOPY IN WOOD CHEMISTRY .7. STUDIES TOWARD ELUCIDATING THE PHOSPHORUS RELAXATION MECHANISM OF PHOSPHITYLATED LIGNINS

Two-dimensional P-31 NMR spectroscopic techniques have been used for c larifying the assignments of one-dimensional P-31 NMR spectra of ligni ns phosphitylated with 1,3,2-dioxaphospholanyl chloride. Extensive evi dence was obtained confirming the absence of P-31-P-31 and P-31-H-1, t hrough-bond and through-space couplings from within a P-31 NMR spectru m of phosphitylated lignin. All signals in such spectra are clear sing lets arising in their respective positions in accordance with earlier reports on model compounds and lignins. Detailed measurements of the p hosphorus spin-lattice and spin-spin relaxation times at various stati c magnetic fields and temperatures, allowed the detailed analysis of t he spin relaxation mechanism of P-31 nuclei to be made. The predominan t spin relaxation mechanism of phosphorus in phosphitylated lignins wa s thus found to be due to chemical shift anisotropy. Comparison of exp erimental spin relaxation data with theoretical models permitted the r otational correlation times of the phosphorus nuclei to be evaluated. These were found to be within the range of 0.5 - 1.0 x 10(-9) s.