Search results
Results from the WOW.Com Content Network
Pyridine N-oxide is five orders of magnitude less basic than pyridine: the pK a of protonated pyridine-N-oxide is 0.8. [7] Protonated derivatives are isolable, e.g., [C 5 H 5 NOH]Cl. [3] Further demonstrating its (feeble) basicity, pyridine-N-oxide also serves as a ligand in coordination chemistry.
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 ...
Structure of pyridine N-oxide. Oxidation of pyridine occurs at nitrogen to give pyridine N-oxide. The oxidation can be achieved with peracids: [94] C 5 H 5 N + RCO 3 H → C 5 H 5 NO + RCO 2 H. Some electrophilic substitutions on the pyridine are usefully effected using pyridine N-oxide followed by deoxygenation. Addition of oxygen suppresses ...
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.
This reaction is similar to nucleophilic aliphatic substitution where the reactant is a nucleophile rather than an electrophile. The four possible electrophilic aliphatic substitution reaction mechanisms are S E 1, S E 2(front), S E 2(back) and S E i (Substitution Electrophilic), which are also similar to the nucleophile counterparts S N 1 and ...
The partial rate factor of electrophilic aromatic substitution on fluorobenzene is often larger than one at the para position, making it an activating group. [11] Conversely, it is moderately deactivated at the ortho and meta positions, due to the proximity of these positions to the electronegative fluoro substituent.
If there is steric crowding on the substrate near the leaving group, such as at a tertiary carbon center, the substitution will involve an S N 1 rather than an S N 2. [2] Nucleophilic acyl substitution mechanism. Other types of nucleophilic substitution include, nucleophilic acyl substitution, and nucleophilic aromatic substitution. Acyl ...
The direct amination of pyridine with sodium amide can take place in liquid ammonia or an aprotic solvent such as xylene is commonly used. Following the addition elimination mechanism first a nucleophilic NH 2 − is added while a hydride (H −) is leaving. The reaction formally is a nucleophilic substitution of hydrogen S N H.