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The protonation of isobutene in the formation of a carbocation: (CH 3) 2 C=CH 2 + HBF 4 ⇌ (CH 3) 3 C + + BF − 4; The protonation of ammonia in the formation of ammonium chloride from ammonia and hydrogen chloride: NH 3 + HCl → NH 4 Cl; Protonation is a fundamental chemical reaction and is a step in many stoichiometric and catalytic processes.
Two common modes of Lewis acid catalysis in reactions with polar mechanisms. In reactions with polar mechanisms, Lewis acid catalysis often involves binding of the catalyst to Lewis basic heteroatoms and withdrawing electron density, which in turn facilitates heterolytic bond cleavage (in the case of Friedel-Crafts reaction) or directly activates the substrate toward nucleophilic attack (in ...
Most fundamental reactivity of bicarbonate/carbonato complexes is their interconversion. This acid-base reaction has been examined mainly for unimolecular complexes. Such reactions are molecular versions of the familiar reaction of acids with carbonate minerals. Protonation of carbonato complexes gives the corresponding bicarbonate.
It is well-known that Lewis acids and bases can influence carbonyl activity by either protonation of the oxygen or de-protonation of a beta-site to influence electrophilicity at the carbon. In the former case, there is a stabilization effect and priming for a potential leaving group by providing an equilibrium between a formal positive charge ...
However, as ethers show similar basicity as alcohols (pK a of approximately 16), the equilibrium of protonation lies on the side of the unprotonated ether and cleavage is usually very slow at room temperature. Ethers can be cleaved by strongly basic agents, e.g. organolithium compounds.
In pure compounds, reactivity is regulated by the physical properties of the sample. For instance, grinding a sample to a higher specific surface area increases its reactivity. In impure compounds, the reactivity is also affected by the inclusion of contaminants. In crystalline compounds, the crystalline form can also affect reactivity. However ...
In organic chemistry, steric effects are nearly universal and affect the rates and activation energies of most chemical reactions to varying degrees. In biochemistry, steric effects are often exploited in naturally occurring molecules such as enzymes , where the catalytic site may be buried within a large protein structure.
The protonation of substituted aniline is inhibited by steric hindrance. When protonated, the nitrogen in the amino group changes its orbital hybridization from sp 2 to sp 3, becoming non-planar. This leads to steric hindrance between the ortho-substituted group and the hydrogen atom of the amino group, reducing the stability of the conjugate ...