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1 2008

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Zjawiska dysocjacji i asocjacji towarzyszące reakcjom przeniesienia protonu między C-kwasami i zasadami organicznymi w rozpuszczalnikach aprotonowych

Nowak I., Binkowska I., Stańczyk-Dunaj M., Jarczewski A.

Wiadomości Chemiczne

2008

[Z] 62, 1-2

67-95

The proton transfer reactions in solutions have attracted the attention of a number of laboratories for many years. These processes seem to be quite simple as they proceed without perturbation of bounding electrons and have low steric demands what enables study of their mechanism. However, many factors influences the mechanisms of these reactions. Among them and not the trifling ones, are dissociation-association effects accompanying them. The definition, behavior and reactivity of carbon acids (C-acids) depending on the type of electron withdrawing group are given [1-57]. Also the values of dissociation constants of C-acids in protic and aprotic solvents are collated in Tables 4, 5 and 7 [11, 38, 49]. The nature of products, free ions and ion pairs, of proton transfer reactions of various C-acids and strong organic bases are carefully discussed. Also their spectral characteristics are given. The equilibria and the possible routes between the substrates and the products of these reactions are also shown [58-66]. The reasons of the homoconjugation effects as a result of an association of the ionic products of the proton transfer reactions in different solvents are discussed in the context of their solvation abilities [67-86]. The formation constants of the homoconjugation complexes of amidine and guanidine bases in relation to their pK? values are quoted in Table 6 [87-95]. The nature of heteroconjugation complexes formed as the result of hydrogen bonding of different entities in the system of proton transfer reactions is discussed [96-116]. The pK? values of a number of C-acids, derivatives of nitromethane, measured in acetonitrile by potentiometric method, are given in Table 7. The pK? values of these derivatives measured in DMSO/H2O systems are compared with those obtained in acetonitrile [18, 38]. The general view of these problems is discussed and carefully reviewed.