Conjugate ions

In our previous treatment of the Kolthoff conjugates we concentrated more particularly on conjugate ion formation as the latter requires media of a relatively low dielectric constant (classes 4-8), one must also expect ion pairing hence the question arises of whether one has to deal with a conjugate ion pair, i.e., with hydrogen bonding, or with an ion pair with merely electrostatic... 

Various groups of workers have attempted to determine the k, by the use of common-ion salts so as to repress the dissociation of the ion-pairs at the growing end. In this context the two types of initiator pose different, but related, problems. If the initiator is a protonic acid AH, as in most of the stopped-flow experiments, the greatest part of the AH does not participate in the initiation (see Section 4.3.2). In these systems, therefore, conjugate ions A2H can be formed from the added salt Bs+A" and therefore the effective [A ] < [Bs+A ]0. In the usual plots [Equation (23) below] of kp (defined in Section 2.5.3) versus [Bs+A ]01/2 this uncertainty will not affect the intercept k, at [Bs+A ]0 1/2 = 0, but it will make the slope, from which the kp can be found, smaller, so that the resulting kp will be an underestimate. 

Attention should be paid to the fact that the electron motion from a donor to an acceptor or within spread-conjugated ion-radicals generates measurable electromagnetic radiation. In other words, there is one specific way to reveal intramolecular electron motion or intermolecular electron transfer in charge-transfer complexes. To probe electron transfer in this manner, the only fundamental requirements are that the molecule can be oriented in the external magnetic field. This takes place most easily if the species considered has a ground state dipole moment. On photoexcitation, there... 

The conversion of hydroxamic acids 589 to a, S-unsaturated amides 592 reported by Hoffmagn and Madan appears to be a first-order reaction of bis-anion 590 characterized by an intramolecular proton rearrangement to one of the anionic oxygen atoms to give conjugated ion 591 (equation 260). 

IV. Heterocyclic Analogs of Annulenes and Monocyclic Conjugated Ions. 354... 

The title compounds may be classified into two groups, viz., the hetero-substituted annulenes containing a type Y heteroatom, for example, pyridine and azete, and the derivatives of monocyclic conjugated ions with heteroatoms of type X (two 7r-electrons) or Z (zero 7r-electrons) (Table VI), such as pyrrole (42)-borole (98) or borirene (99)-2-azirine (100). 

Fig. 4.2 illustrates the first few members of the series of equilibria of conjugated ions. In cations, they are the equilibria between the allyl 4.11 and the cyclopropyl cation 4.12, the pentadienyl 4.13 and the cyclopentenyl cation 4.14, and the heptatrienyl 4.15 and cycloheptadienyl cation 4.16, In anions, they are between the allyl 4.17 and the cyclopropyl anion 4.18, the pentadienyl 4.19 and the cyclopentenyl anion 4.20, and the heptatrienyl 4.21 and cycloheptadienyl anion 4.22. There are heteroatom-containing analogues, with nitrogen and oxygen lone pairs rather than a carbanion centre, and the systems can again have substituents and fused rings. 

Electrocyclic opening and closing of some linearly conjugated ions... 

As to the tailor-made polymers, a more serious, perhaps intrinsic, cause is discussed (Haare et al. 1998). These polymeric cation radicals form ir-macrodimers according to usual equilibria 2M+ <=> (M)l+. The ir-dimerization inhibits the formation of high-spin states. Maybe other n-conjugated ion radicals with a much lower tendency to form ir-dimers, such as polymeric cation radicals based on p-phenylenediamine, are a promising way to construct intrachain ferromagnetic coupling in polymers. 

The common point of view, postulated by Mitchell, is that in energy-producing membranes H+ represents the conjugation ion . For the conjugation intermediate, biochemists upholding only the concept of energetic conjugation assumed the electrochemical potential (/ZII) produced due to difference in H+ concentrations on both sides of closed membrane. 

It should be pointed out that even if one starts with a single oxidation state of iron in the presence of hydrogen peroxide, both states are soon produced. The ferric ion can oxidize perhydroxyl radical (H02) and/or its conjugate ion (02 ), as well as hydrogen peroxide. The chemistry of iron(III) with hydrogen peroxide has been comprehensively reviewed by Brown, Jones and Suggett.28... 

Diels-Alder reactions are classified as [4 + 2] cycloadditions, and the reaction giving the cyclobutane would be a [2 + 2] cycloaddition. This classification is based on the number of electrons involved. Diels-Alder reactions are not the only [4 + 2] cycloadditions. Conjugated ions like allyl cations, allyl anions and pentadienyl cations are all capable of cycloadditions. Thus, an allyl cation can be a 2-electron component in a [4 + 2] cycloaddition, as in the reaction of the methallyl cation 6.2 derived from its iodide 6.1, with cyclo-pentadiene giving a seven-membered ring cation 6.3. The diene is the 4-electron component. The product eventually isolated is the alkene 6.4, as the result of the loss of the neighbouring proton, the usual fate of a tertiary cation. This cycloaddition is also called a [4 + 3] cycloaddition if you were to count the atoms, but this is a structural feature not an electronic feature. In this chapter it is the number of electrons that counts. 

This is more a solution process than a chemical reaction. In contrast, weak bases, like weak acids, react slightly with water to form ions. The reaction of ammonia with water, described earlier, is one example. Conjugate ions of molecular acids are also bases, as just described. Base strength determines the extent to which a base interacts with water to form ions. The stronger the base, the weaker its conjugate acid. 

In all the examples discussed above the conductive fillers have been inorganic materials. As noted in the previous section, it is possible to make conductive composites with organic metal fillers. The organic charge transfer (CT) salts are ionic materials which contain linear arrays of conjugated ions with strong overlap of the -electrons of adjacent ions. If charge transfer is complete and... 

Y ou already know that the conjugate base of a strong acid is extremely weak. The conjugate acid of a weak base, however, is relatively strong. Therefore, the conjugate ion from the weak base will hydrolyze to produce an acidic solution. The weaker the base, the stronger the conjugate acid will be. An example would be NH Cl. The NH ion, the cation from abase, hydrolyzes water as shown below ... 

For proteins containing more than one conjugated ion or molecule, their classification is usually based on the optically active moiety. 

The base peak (76) in the mass spectrum of chaetocin represents the favoured loss of sulphur and water and splitting in half to give the stabilized, conjugated ion. The structure of chaetocin, which was shown by labelling experiments to... 

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