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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.
An ylide (/ ˈ ɪ l aɪ d /) [1] or ylid (/ ˈ ɪ l ɪ d /) is a neutral dipolar molecule containing a formally negatively charged atom (usually a carbanion) directly attached to a heteroatom with a formal positive charge (usually nitrogen, phosphorus or sulfur), and in which both atoms have full octets of electrons.
The reaction mechanism of the Stevens rearrangement is one of the most controversial reaction mechanisms in organic chemistry. [4] Key in the reaction mechanism [5] [6] for the Stevens rearrangement (explained for the nitrogen reaction) is the formation of an ylide after deprotonation of the ammonium salt by a strong base.
In organic synthesis, PPTS is used as a weakly acidic catalyst, providing an organic soluble source of pyridinium (C 5 H 5 NH +) ions. For example, PPTS is used to deprotect silyl ethers or tetrahydropyranyl ethers when a substrate is unstable to stronger acid catalysts.
The free radical theory of aging states that organisms age because cells accumulate free radical damage over time. [1] A free radical is any atom or molecule that has a single unpaired electron in an outer shell. [2] While a few free radicals such as melanin are not chemically reactive, most biologically relevant free radicals are highly ...
The relative importance of the antioxidant and pro-oxidant activities of antioxidant vitamins is an area of current research, but vitamin C, for example, appears to have a mostly antioxidant action in the body. [7] [9] However, less data is available for other dietary antioxidants, such as polyphenol antioxidants, [10] zinc, [11] and vitamin E ...
The persistent radical effect (PRE) in chemistry describes and explains the selective product formation found in certain free-radical cross-reactions. In these type of reactions, different radicals compete in secondary reactions. The so-called persistent (long-lived) radicals do not self-terminate and only react in cross-couplings.
A free radical is formed from the carboxylic acid in an oxidative decarboxylation with silver salts and an oxidizing agent. The oxidizing agent (ammonium persulfate) oxidizes the Ag(+) to Ag(2+) under the acidic reaction conditions. This induces a hydrogen atom abstraction by the silver, followed by radical decarboxylation.