Conundrums regarding 5–O–4- linkages in softwood MWLs

Abstract

Recent investigation of [alpha]-hydroxy 5–O–4-lignin model compounds by NMR indicates that the short-range 13C-1H correlations for the ring 2- and 6- carbons should be distinct in HSQC NMR spectra of softwood MWLs and possibly in guaiacyl-type synthetic lignins (DHPs). The levels of 5–O–4-type linkages have been reported to be on the order of 17% of C9 units for MWLs. A comparison of the aromatic spectral regions from the short-range 13C-1H correlation spectra of [alpha]-hydroxy 5–O–4- models and loblolly pine MWL suggests that 5–O–4- type units are either not present at the suggested levels or are not present with the a-hydroxy functionality. The HSQC NMR spectral data for a CAD–deficient pine MWL has interesting correlations in this region of interest potentially assignable to 5–O–4-units involving dihydroconiferyl alcohol and/or guaiacylpropane-1,3-diols.

Citation

Ralph, Sally. 2005. Conundrums regarding 5–O–4- linkages in softwood MWLs. 59th Appita Annual Conference and Exhibition : incorporating the 13th ISWFPC (International Symposium on Wood, Fibre and Pulping Chemistry) Auckland, New Zealand, 16-19 May 2005 : proceedings. Carlton, VIC : Appita, c2005: ISBN: 0958554897: pages 315-319.