Органиқалық қосылыстардағы 1,2-қайта орналасу реакциясы

Organic chemical reaction
A 1,2 rearrangement or 1,2 migration or 1,2 shift or Whitmore 1,2 shift is an organic reaction where a substituent moves from one atom to another atom in a chemical compound. In a 1,2 shift the movement involves two adjacent atoms but moves over larger distances are possible. In the example below the substituent R moves from carbon atom C2 to C3. The rearrangement is intramolecular and the starting compound and reaction product are structural isomers. The 1,2 rearrangement belongs to a broad class of chemical reactions called rearrangement reactions. A rearrangement involving a hydrogen atom is called a 1,2 hydride shift. If the substituent being rearranged is an alkyl group, it is named according to the alkyl group's anion: i. e. 1,2 methanide shift, 1,2 ethanide shift, etc.

The first radical 1,2 rearrangement reported by Heinrich Otto Wieland in 1911 was the conversion of bis(triphenylmethyl)peroxide 1 to the tetraphenylethane 2. The reaction proceeds through the triphenylmethoxyl radical A, a rearrangement to diphenylphenoxymethyl C and its dimerization. It is unclear to this day whether in this rearrangement the cyclohexadienyl radical intermediate B is a transition state or a reactive intermediate as it (or any other such species) has thus far eluded detection by ESR spectroscopy. An example of a less common radical 1,2 shift can be found in the gas phase pyrolysis of certain polycyclic aromatic compounds. The energy required in an aryl radical for the 1,2 shift can be high (up to 60 kcal/mol or 250 kJ/mol) but much less than that required for a proton abstraction to an aryne (82 kcal/mol or 340 kJ/mol). In alkene radicals proton abstraction to an alkyne is preferred.