Guaiacyl units

It weis found that hardwood lignins yielded both guaiacyl and syringyl units on oxidation, whereas softwood lignins yielded only guaiacyl units. Hibbert and co-workers (20), (21) distinguished perennial plant lignins... 

Polyacylhydrazones Having Guaiacyl Units with Alkylene Groups... 

Polyacylhydrazones [X] having two guaiacyl units with the alkylene groups in each repeating unit were synthesized using vanillin and dibromoalkanes as starting materials as shown in Scheme 5 (10). 

The only very slight photochromic behaviour obtained upon irradiation of bleached aspen CTMP may be due to the presence of syringyl instead of guaiacyl units in hardwood lignin. These structures are less able to form orr/to-quinones during irradiation than softwood pulps (8). 

The guaiacyl unit, derived from the trans-coniferyl alcohol, abundantly present in softwoods... 

The syringyl unit, derived from the frans-sinapyl alcohol, which is present with the guaiacyl unit in hardwoods... 

Fig. 8-10. Example of the reactions of a guaiacyl unit with chlorine dioxide and chlorine (Hardell and Lindgren, 1975).

The lignin content can be estimated from the spectrum by measuring the fractional area, A, of a band of signals between chemical shifts of 141 and 159 parts per million (ppm) relative to the total area of the spectrum. This band is assigned to C-3 and C-4 of guaiacyl units or C-3 and C-5 of syringyl units the fact that it is associated with just two carbon atoms of each structural unit means that the method can be used for both softwoods and hardwoods. 

Aromatic protons in guaiacyl units (a sharp peak at <> 6 99 has about the same intensity... 

---