Linear quinoid structure

Double-Bond Twisting Mechanism in Linear Quinoid Structure... 

PPS and PPO are polymers which behave differently due to the nature of the atom (S or O) between the rings and the geometric parameters. The inter-ring bondii s are not linear and the bond length C-S (1.75 A) is very different from that of C-O (1.36 A). In addition, conductivity after doping with AsFs is found to be s 2-3 S/cm for PPS and = 10 S/cm for PPO. A quinoid structure can be expected in these two cases, but its local extension is limited to one ring. 

The second redox process for both polytoluidines is dependent on the pH of the electrolytes. It is attributed to the conversion of the radical cation into a fully oxidized form of polytoluidines (complete quinoidal structure) as has been found for PANI [6]. This can be illustrated as given below. It is observed that a linear relationship between 1/2 of the second peak and the pH holds well for the pH —0.2 to 4.0 (Figure 13.9). 

Ouyang et al. have interpreted the changes observed in the Raman spectra as a change from a benzoid structure toward a quinoid structure of the PEDOT molecules due to a move from a coil structure toward an extended coil or linear structure of PEDOT chains. ... 

Lanata et al.109 have argued that molecules with quinoid ground states are particularly useful for the production of large linearities on account of the conjugation through the whole of the molecule. In certain cases, such as the merocyanine dyes in solution (see below in the section on open shell and ionic structures) the zwitterionic forms are more favourable. 

Polyphenyls show non-linear dependence of Amax on n. The Amax of para-polyphenyls varies approximately as the cube root of n11. The Amax of metapolyphenyls is nearly independent of n. This is because in meta-polyphenyls there is no resonance contribution from quinoid type of structures. Data on polyphenyls25 are given in Table 4 JO. 

Scheme 9 Two structurally different types of PANls obtained in typical enzymatic polymerization without template A ortho-, para-substituted branched structure and B benzenoid-quinoid linear structure...

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