Organic electroactive groups

Table 1, Organic Electroactive Groups on Mercury Electrodes...

In the following part of this paper I am going to present a system of organic electroactive groups or of substances which can be subjected to voltammetric analysis at solid electrodes forming thus a base for construction of electrochemical detectors in HPLC. Since electroactivity is the most important property of the substance to be studied and we are interested here only in the analytical properties, i.e. in the characteristical potentials (Ep or Ep and in the shape of the i - E or ip - E plot it will be not necessary to stress Adams observatlon[7] "Electrochemistry of organic oxidations is mainly the chemistry of follow-up reactions" (of course, similar ideas hold true with reductions). Nevertheless, electroactivity will be discussed here jointly with probable or proved interpretations of mechanisms. This is done in contrast to Bond s view[9] who considers interpretations of electrode processes and of their follow-up or preceding reaction useless in analytical chemistry. 

A Structural characteristic of conducting organic polymers is the conjugation of the chain-linked electroactive monomeric units, i.e. the monomers interact via a 7t-electron system. In this respect they are fundamentally different from redox polymers. Although redox polymers also contain electroactive groups, the polymer backbone is not conjugated. Consequently, and irrespective of their charge state, redox polymers are nonconductors. Their importance for electrochemistry lies mainly in their use as materials for modified el trodes. Redox polymers have been discussed in depth in the literature and will not be included in this review. 

Much more important is the polarographic behaviour of organic substances. This is based on the presence of electroactive groups, reducible or oxidizable at the dropping mercury electrode. The electroactive groups with examples from pharmaceutical chemistry are shown in Table 5J.lt should be emphasized that the aldehydic and ketonic groups. 

Organic Electroactive Polymer Research Group, Durham University, South road,... 

Although fatty acids and their salts are the classical materials for LB him formation, much activity has focused on the incorporation of electroactive groups into such long-chain compounds. Some examples are depicted in Figure 4. Charge-transfer materials, such as the Af-octadecylpyridinium-Ni(dmit)2 complex, are important organic conductors. These are formed from a variety of molecules, primarily aromatics that can behave as electron donors (D) and electron acceptors (A) [8]. Complete transfer of an electron from a donor to an acceptor molecule results in a system that is electrically insulating (e.g., the transfer of a valence electron in a Cl atom to a Na atom to form the compound NaCl). However, if the ratio of the number of donor molecules to the number of acceptor molecules differs from 1 1 (e.g., the stoichiometry is 1 2 or... 

Polarographic determination, by itself, is generally not specific for a particular organic compound. Usually the determination is, in practice, of a particular electroactive group and hence of a class of compounds. 

Various amphiphilic a- and jS-CyDs functionalized with alkyl chains at the primary hydroxy positions or modified on the secondary face form stable and well-organized monomolecular layers at the air-water interface [47, 48]. They can then be used for the preparation of L-B films on solid substrates. Electroactive CyDs persubstituted with electroactive groups, e.g. terathiafulvalene (TTF) moieties [49], were transferred as L-B films from the water surface with a transfer ratio of 1 to the solid substrate (Fig. 10.5.3). Charge-transfer interactions in the... 

The best result so far has been the synthesis of a CTC between TCNQ and DIP(S) with four alkyl chains [86], which has a respectable d.c. conductivity at room temperature (a = 0.7 0-1 cm-i). This solid phase undergoes a phase transformation at 123 C, and has a lamellar stmeture above this temperature, but with a lower electrical conductivity (a 10 O l cm-i) [87]. As shown in Fig. 7, the presumed structural organization is characterized by a stacking of the electroactive groups, which are called the cores, and their separation by alkane chains, as ocurs in the LB films (see next paragraph). 

Eor heterogeneous electron transfer, the use of ordered organic monolayers (self-assembled monolayers or SAMs) at electrode surfaces as blocking films either with electroactive species in the electrolyte [26] or with electroactive groups tethered at the opposite end of the blocking molecule from the covalent attachment end [27] has provided a method to study the effect of electrode-redox center distance and the effect of the electrode potential on the electron-transfer rate. 

Organic functional groups which are electroactive and the oxidations or reductions of which are the bases of the analytical determinations are listed... 

The organic layers obtained have been characterized by electrochemical techniques when the alkyl amines employed contained electroactive groups such as nitro groups, and also by X-Ray Photoelectron Spectroscopy... 

Many organic electrode processes require the adsorption of the electroactive species at the electrode surface before the electron transfer can occur. This adsorption may take the form of physical or reversible chemical adsorption, as has been commonly observed at a mercury/water interface, or it may take the form of irreversible, dissociative chemical adsorption where bond fracture occurs during the adsorption process and often leads to the complete destruction of the molecule. This latter t q)e of adsorption is particularly prevalent at metals in the platinum group and accounts for their activity as heterogeneous catalysts and as... 

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