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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.
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.
Radical dimerization of pyridine with elemental sodium or Raney nickel selectively yields 4,4'-bipyridine, [98] or 2,2'-bipyridine, [99] which are important precursor reagents in the chemical industry. One of the name reactions involving free radicals is the Minisci reaction.
However, a few examples exist of a stepwise mechanism for the catalyst-free 1,3-dipolar cycloaddition reactions of thiocarbonyl ylides, [6] and nitrile oxides [7] The generic mechanism of a 1,3-dipolar cycloaddition between a dipole and a dipolarophile to give a five-membered heterocycle, through a six-electron transition state.
Radical elimination can be viewed as the reverse of radical addition. In radical elimination, an unstable radical compound breaks down into a spin-paired molecule and a new radical compound. Shown below is an example of a radical elimination reaction, where a benzoyloxy radical breaks down into a phenyl radical and a carbon dioxide molecule. [7]
Basic aromatic compounds get protonated and form aromatic cations (e.g. pyridinium) under acidic conditions. Typical examples of basic aromatic rings are pyridine or quinoline. Several rings contain basic as well as non-basic nitrogen atoms, e.g. imidazole and purine.
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Structures and names of common heterocyclic compounds Pyridine, a heterocyclic compound. A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). [1]