1H-NMR spectra of the following lignin model substances have been analyzed: cinnamaldehyde, 2-methoxycinnamaldehyde, 3-methoxycinnamaldehyde, 4-methoxycinnamaldehyde, 3,4-dimethoxycinnamaldehyde, 3-methoxy-4-hydroxycinnamaldehyde and 3,4,5-trimethoxycinnamaldehyde. From the NMR spectra analysis it follows that the studied compounds exist in solutions as trans isomers. Theoretical (PCILO) calculations in agreement with the NMR data have shown that the more stable conformer has trans orientation of C=O group with respect to the double bond of the conjugated side chain.
Electronic spectra of seven hydroxy and methoxy substituted flavones as well as nine hydroxy and methoxy substituted flavoneles have been studied experimentally and theoretically with the use of the semiempirical SCF LCI PPP method. The same method has been applied to electronic spectra of some model compounds of lignin of stilbene and coumarone type. The calculated excitation energies agree well with the observed ones. Results of our experimental and theoretical studies of electronic spectra of basic chromophoric structural units of lignin are summarized from the viewpoint of their contribution to color of lignin.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.