NMR Studies on the Occurrence of Spirodienone Structures in Lignins

Abstract

Abstract Spirodienone structures have been detected in spruce, birch, and kenaf lignin isolates. NMR signals corresponding to guaiacyl and syringyl spirodienones were fully identified and assigned based on 13C, QUAT, HSQC, HSQC‐TOCSY, and HMBC NMR data. Spruce lignin contains spirodienone structures of the guaiacyl type. Syringyl spirodienones dominate in kenaf and birch lignins. Each type of spirodienone was found to be present in two different stereoisomeric forms, with one of the isomers being more prevalent. Signal integrations indicate that about three spirodienones per 100 phenylpropanoid units are present in the spruce and birch lignins and about four in the kenaf lignin.