Base dissociation constants nitrogen bases

Table 8.3 lists the base dissociation constants for several weak bases at 25°C. Nitrogen-containing compounds are Bronsted-Lowry bases, because the lone pair of electrons on a nitrogen atom can bond with H+ from water. The steps for solving problems that involve weak bases are similar to the steps you learned for solving problems that involve weak acids. 

Delphonine shows an unusually high basic dissociation constant, and that of aconine is only a little less. In the case of tertiary vinyl cyclic amines, which prove to be unexpectedly strong bases, Adams and Mahan suggested that they exist in solution as equilibrium mixtures consisting of the tertiary unsaturated base and a quaternary arrangement in which the double bond has moved to the nitrogen, which may be represented thus —. . . +. . . +... 

A highly interesting and often overlooked aspect of this structure proof was brought out by the titrimetric measurements on nucleosides and their free bases by Levene, Bass, and Simms.1M They reasoned, quite justifiably, that uracil should possess two acidic dissociation constants, because of the presence of two potentially dissociable protons in the molecule. (At that time, the problem as to the position of attachment of the carbohydrate to the nitrogenous base had essentially been diminished to a choice between positions 1 and 6.) They demonstrated in an early paper109(a) that uracil possesses two acidic dissociation constants (9.28 and 18.66). If the sugar radical were substituted on position 6 of uridine, both of the dissociation constants of uracil should be demonstrable in uridine whereas, if substitution by the sugar were on position 1, only one of these pKa values should be observable. 

These chelating agents have frequently been used as probes for the interactions taking place at the catalytic site. Vallee and co-workers (133,232,233,246-248) have utilized the optical rotatory dispersion curves of the complexes, whereas Yonetani (97,120) and Sigman (249) have studied the changes in the absorption spectrum. By the latter method dissociation constants have been measured for a number of binary substrate and inhibitor complexes as well as some ternary inhibitor complexes. The interaction of LADH and a spin-labeled analog of 1,10-phenanthroline has also been studied (141)-Heterocyclic nitrogen bases such as imidazole have been found (244, 60-252) to form both binary complexes with LADH and ternary... 

Most plant alkaloids are derivatives of tertiary amines, while others contain primary, secondary or quarternary nitrogen. The basicity of individual alkaloids varies considerably, depending on which of the four types is represented. The pK values (dissociation constants) lie in the range of 10-12 for very weak bases (e.g. purines), of 7-10 for weak bases (e.g. Cinchona alkaloids) anti of 3-7 for medium-strength bases (e.g. Opium alkaloidvSh... 

The dissociation constant of amiloride. .. from aqueous titration (18) indicates that amiloride is a moderately strong organic base with a pKa of approximately 8.7 at 25 °C (amidino nitrogen). The pKa of amiloride. .. has also been determined using gas-phase proton affinities, enthalpies of solution and semi-empirical calculations (25,26). These theoretically derived pKa values agree well with the experimentally determined value of pKa = 8.7."... 

This book contains values of dissociation constants for organic bases In aqueous solution. The bases are arranged under the headings aliphatic, allcyclic, aromatic, heterocyclic, natural products, dyes and indicators, substances lacking a basic nitrogen atom, and miscellaneous. Accompanying the data entry for each base is the temperature, method of measurement, formula, assessment of the measurement, and the appropriate reference. There are 3790 data entries in this book. Also see item [73]. 

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