Dehydrogenation polymers (DHPs or synthetic lignins) were synthesized from coniferyl alcohol by enzymatic oxidation in the presence of ascorbic acid to study the potential effects of an antioxidant upon their structure. Specific interunit substructures (beta-O-4', beta-beta', and beta-5') were quantified by C-13 NMR, which showed how ascorbic acid altered their amounts compared with control syntheses without this antioxidant, especially by increasing the amount of beta-O-4' substructures. The effect of ascorbic acid increased with its concentration. Surprisingly, no influence on the sizes of the synthetic lignins, as determined by size exclusion chromatography, was observed. The chemistry of this antioxidant effect during dehydrogenative polymerization and the potential biological significance (cell wall lignification) of these observations are discussed.