A potentiometric study of cationic heteroconjugation equilibria in systems with substituted pyridine N-oxides in nitrobenzene

Ab Initio Study of the Energetics of Protonation and Homocomplexed Cation Formation in Systems with Pyridine and Its Derivatives

“…Acid-base equilibria set up in nonaqueous media in systems containing heterocyclic bases such as amines [1][2][3][4][5] (pyridine and substituted pyridines) and amine N-oxides 4,[6][7][8][9][10][11][12][13][14][15][16][17] (pyridine Noxide and its derivatives) have been systematically studied in our laboratory. Our interest was focused not only on acid dissociation [1][2][3][4][5][6][7][8][9][10][11][12][13] of protonated pyridine and pyridine N-oxide, as well as their derivatives, but also on consecutive acid-base reactions 18 occurring in media of limited capability to exchange proton (polar aprotic and medium polar amphiprotic solvents), referred to as cationic homoconjugation: [1][2][3][4][5][6][7][8][9][10][11][12][13] In the preliminary step, the above equilibria were systematically surveyed in the BH + /B systems of substituted pyridine N-oxides in nonaqueous media, as well as ...…”

Potentiometric studies of cationic heteroconjugation equilibria in systems involving free and protonated pyridine derivatives in dimethyl sulfoxide

“…For instance, no relationship could be established between cationic standard heteroconjugation constants and solvent basicities, which is characteristic for substituted pyridine N -oxides. (17) Furthermore, in the case of the (OHO) + bridges, the cationic standard heteroconjugation constant values increase with increasing acceptor basicity and decrease with proton donor basicity, (18)(19)(20)(21) a regularity not observed in the case of the (NHN) + bridges. Another feature influencing the tendency towards cationic heteroconjugation in the systems with the N -oxides is the capacity of the constituents to form hydrogen bonds, as defined by the arithmetic mean of their cationic standard homoconjugation constant values.…”

“…Also, the (OHO) + bridges, where different amine N -oxides are bound together with a hydrogen bond, turned out to be less stable. (18)(19)(20)(21) However, it should be emphasised that analysing cationic standard heteroconjugation constants determined in non-aqueous media in systems involving organic N -bases is not straightforward for two reasons. First, there were many methods employed to study the equilibria considered.…”

A study of the tendency of organic bases towards cationic heteroconjugation in polar non-aqueous solvents

“…In the [OHO] ϩ systems, the constant values have been found to increase with increasing proton acceptor basicity and decreasing basicity of the proton donor. 28, 29 Another factor affecting the tendency towards cationic heteroconjugation in the [OHO] ϩ systems was their capacity for hydrogen bonding. 30 Having in hand experimental data concerning the [OHO] ϩ bridges, we have recently embarked on issues of cationic heteroconjugation equilibria set up in non-aqueous solvents in [NHN] ϩ and [NHO] ϩ -[OHN] ϩ systems.…”