Hydrogen migrations fluorination

A fluorine-hydrogen migration is typical for the reactions of aldehydes branched at the carbon atom a to the formyl group. Comparable amounts of 1,1 -difluoroalkanes and 1,2-difluoroalkanes together with bis(l -fluoroalkyl) ethers are obtained [169] (equation 84). 

Fig. 5 shows experimental charge distributions determined for polyvinylene fluoride and polytrifluoroethylene. These show rather effectively the large net migration of electron densities from carbon and hydrogen to fluorine. 

It is presumed that the barrier-to-1,2-fluorine migration in the singlet nitrene substantially exceeds the analogous barrier-to-hydrogen shift. This difference allows a portion of the nascent singlet nitrene to relax to the lower energy triplet in the matrix. 

The reaction of 5-bromo-2-furoic acid with the sulfur tetrafluoridc/hydrogen fluoride system proceeds under mild conditions and results not only in conversion of the carboxylic acid group but also in addition of two fluorines and replacement or migration of bromine a 1 3.5 mixture of 2,2,5-trifluoro-5-(trifluoromethyl)-2.5-dihydrofuran (10) and 2-(bromodifluoromethyl)-2,5.5-trifluoro-2,5-dihydrofuran (11) is obtained.153... 

The infrared spectrum of the tetrafluoropropene suggested the structure CF2H—CH=CF2, which would be formed by migration of hydrogen but not fluorine atoms. The opening up of the excited ring to give the biradical with CH2 in the central position is thermodynamically favored over that with CH2 in the terminal positions. 

When there is a hydrogen or perfluoroalkyl substituent on the alk-l-ene chain, Lewis acid catalyzed migration of the C = C bond to the 3-position can proceed to minimize the number of alkenic fluorine atoms,3 as illustrated by the isomerizations of 4//-perfluorobut-l-ene (3),8 4//-perfluoro(5-methylhex-l -enc) (5),18 perfluoro(4-methylpent-2-ene) (7),14 and perfluoro(3-methylcyclopentene) (9).2 3... 

In contrast to hydrocarbon radicals where hydrogen atom migration is common, fluorine atom migration is rare.105 Pcrfluoroalkyl radical disproportionation is as yet unknown and cannot... 

In radical rearrangements, the migrating groups are those that can accommodate electrons in a tt system (vinyl, aryl, carbonyl) or atoms that can expand their valence shell, i.e., all halogens but fluorine. Hydrogen and alkyl do not migrate to... 

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