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Pyridine-N-oxides bind to metals through the oxygen. According to X-ray crystallography, the M-O-N angle is approximately 130° in many of these complexes. As reflected by the pKa of 0.79 for C 5 H 5 NOH +, pyridine N-oxides are weakly basic ligands. Their complexes are generally high spin, hence they are kinetically labile.
Pyridine-N-oxide is the heterocyclic compound with the formula C 5 H 5 NO. This colourless, hygroscopic solid is the product of the oxidation of pyridine . It was originally prepared using peroxyacids as the oxidising agent.
With secondary amines and not primary amines the Zincke reaction takes on a different shape forming so-called Zincke aldehydes in which the pyridine ring is ring-opened with the terminal iminium group hydrolyzed to an aldehyde: [4] Zincke aldehydes. This variation has been applied in the synthesis of novel indoles: [11] Zincke aldehydes Kearney ...
Transition metal pyridine complexes encompass many coordination complexes that contain pyridine as a ligand. Most examples are mixed-ligand complexes. Most examples are mixed-ligand complexes. Many variants of pyridine are also known to coordinate to metal ions, such as the methylpyridines, quinolines, and more complex rings.
Pyridine-borane (C 5 H 5 NBH 3, melting point 10–11 °C) is a mild reducing agent. structure of the Crabtree's catalyst. Transition metal pyridine complexes are numerous. [108] [109] Typical octahedral complexes have the stoichiometry MCl 2 (py) 4 and MCl 3 (py) 3. Octahedral homoleptic complexes of the type M(py) + 6 are rare or tend to ...
Compared to benzene, the rate of electrophilic substitution on pyridine is much slower, due to the higher electronegativity of the nitrogen atom. Additionally, the nitrogen in pyridine easily gets a positive charge either by protonation (from nitration or sulfonation) or Lewis acids (such as AlCl 3) used to catalyze the reaction. This makes the ...
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The inductive and resonance properties compete with each other but the resonance effect dominates for purposes of directing the sites of reactivity. For nitration, for example, fluorine directs strongly to the para position because the ortho position is inductively deactivated (86% para, 13% ortho, 0.6% meta).