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Pyridinium refers to the cation [C 5 H 5 NH] +. It is the conjugate acid of pyridine . Many related cations are known involving substituted pyridines, e.g. picolines, lutidines, collidines.
For example, carbon monoxide is a very weak Brønsted–Lowry base but it forms a strong adduct with BF 3. In another comparison of Lewis and Brønsted–Lowry acidity by Brown and Kanner, [ 19 ] 2,6-di- t -butylpyridine reacts to form the hydrochloride salt with HCl but does not react with BF 3 .
Containing a pyridinium ion, pyridinium chloride has a pK a of approximately 5, slightly more acidic than that of typical amines. This is due to the hybridization of the nitrogen: the nitrogen is sp 2 hybridized and more electronegative than those nitrogens in ammonium cations, which are sp 3 hybridized. Hence they are stronger acids than ...
On the other hand, if a chemical is a weak acid its conjugate base will not necessarily be strong. Consider that ethanoate, the conjugate base of ethanoic acid, has a base splitting constant (Kb) of about 5.6 × 10 −10, making it a weak base. In order for a species to have a strong conjugate base it has to be a very weak acid, like water.
For this purpose, pyridine derivatives can be eliminated with good leaving groups using strong bases such as sodium and potassium tert-butoxide. The subsequent addition of a nucleophile to the triple bond has low selectivity, and the result is a mixture of the two possible adducts.
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The position of equilibrium varies from base to base when a weak base reacts with water. The further to the left it is, the weaker the base. [5] When there is a hydrogen ion gradient between two sides of the biological membrane, the concentration of some weak bases are focused on only one side of the membrane. [6]
Pyridinium chlorochromate in a vial. Pyridinium chlorochromate (PCC) is a yellow-orange salt with the formula [C 5 H 5 NH] + [CrO 3 Cl] −. It is a reagent in organic synthesis used primarily for oxidation of alcohols to form carbonyls. A variety of related compounds are known with similar reactivity.