Quinoidal units

Carbonyl groups are present in units 31, 35, 48, 49, and 52 and also in cyclohexa-dienone and quinoid units (Figure 7.6). The total number of units with a carbonyl group in MWL has been determined to be = 20% or more in some studies [77]. Such a large number of carbonyl groups is, however, not compatible with results from NMR spectral examinations. Data given in Table 7.2 are to a large extent based on NMR spectral studies [74,78,80,92]. 

Ethylenic groups are present in units 47,48, and 51 and also in cyclohexadienone and quinoid units (Figure 7.6). It is difficult to determine the total number of ethylenic groups. Reported estimates suggest that there are 0.05-0.1 ethylenic groups/phenyl-propane units in softwood lignin [117]. 

The only transistor examples of higher-acenes based semiconductors are molecules containing an electron-rich acene unit and an electron-poor quinoid unit (4a-4c).[79] The packing influenced by this structure is such that acene units stack over... 

These compounds were assayed for antibiotic and cytotoxic activities and from them compound 202 was the only dimer that showed antibiotic activity against Gram positive bacteria its MICs on Bacillus subtilis and B. pumilus were 1-2 and 20 pg/ml, respectively. None of the dimers showed cytotoxic activity against the HeLa (cervix carcinoma) and Hep-2 (larynx carcinoma) cell lines at least at 20 pg/ml. These results support the fact that the additional double bond C-14(15) plays an important role for the antibiotic activity, as 202 was the only assayed dimer with a triterpene quinoid unit derived from netzahualcoyone skeleton, instead of pristimerin. 

Leucoemeraldine, which is an insulator with a large bandgap, showed an onset of n—n transition around 3 eV with a peak at 3.7—3.8 eV, whereas emeraldine base has a two principal absorptions (2 eV and 3.9 eV). However, overoxidized polyaniline exhibits intense absorption at 2.2 eV and a well-defined peak near 4 eV shown to be due to doubly charged bipolarons associated with a quinoid unit [164,227]. 

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