1, 1-Difluoroethylene

Addition ofGrignard reagents to 1,1-difluoroethylene yields an acetylide anion which can be subsequently trapped with electrophiles. 

The molecule tran5 -l,2-difluoroethylene, in Figure 4.18(h), belongs to the C2 , point group in which none of the translational symmetry species is totally symmetric therefore the molecule has no dipole moment. Arguments using bond moments would reach the same conclusion. 

The reaction of dihalocarbenes with isoprene yields exclusively the 1,2- (or 3,4-) addition product, eg, dichlorocarbene CI2C and isoprene react to give l,l-dichloro-2-methyl-2-vinylcyclopropane (63). The evidence for the presence of any 1,4 or much 3,4 addition is inconclusive (64). The cycloaddition reaction of l,l-dichloro-2,2-difluoroethylene to isoprene yields 1,2- and 3,4-cycloaddition products in a ratio of 5.4 1 (65). The main product is l,l-dichloro-2,2-difluoro-3-isopropenylcyclobutane, and the side product is l,l-dichloro-2,2-difluoro-3-methyl-3-vinylcyclobutane. When the dichlorocarbene is generated from CHCl plus aqueous base with a tertiary amine as a phase-transfer catalyst, the addition has a high selectivity that increases (for a series of diolefins) with a decrease in activity (66) (see Catalysis, phase-TRANSFEr). For isoprene, both mono-(l,2-) and diadducts (1,2- and 3,4-) could be obtained in various ratios depending on which amine is used. 

Treatment of glyoxal with sulfur tetrafluoride in the presence of sodium fluoride results iii the formation of difluoroethylene glycol orthosulfite [174] (equation 89) Similarly, perfluonnated 1,2-diketones react with sulfur tetrafluonde to give tetraoxyspirosulfuranes as the only products Thus, perfluorobiacetyl gives a ciystalhne product, perfluorobutylene glycol 2,3 orthosulfite [175] (equation 89)... 

Ozonuies (1,2,4-trioxolanes) are generally obtained by the reaction of fluoroalkenes with ozone Thus, vmyl fluonde is oxidized to monofluoroozomde and formyl fluonde [23] (equation 15) The same ozomde is formed by ozonolysis of a mixture of cis 1,2-difluoroethylene with ethylene [24]... 

CIS- And trans-1,2-difluoroethylene are oxidized by ozone stereoselectively to a mixture of the corresponding epoxides and ozonides with formyl fluoride The composition of the mixture depends on the solvent used [25] (equation 16)... 

Early attempts to metalate 1,1-difluoroethylene with -butyllithium in tetra-hydrofuran or diethyl ether were unsuccessful. Another example whereby the course of the reaction may be altered by substitution of rec-butyllithium in place of n-butyllithium is the metalation of 1,1 -difluoroethylene [60] (equation 26)... 

With a difluoroethylene containing hydrogen and chlonne, where both groups can be replaced by lithium, a mixture of two organolithium compounds is formed in a 2 1 ratio, indicating a more facile replacement of chlorine [63] (equation 30)... 

Olefins with strained, relatively weak n-bonds form cycLobutanes under rather mild conditions [96] (equations 35 and 36). By contrast, cw-l-methylcyclooctene hardly reacts with I,I-dicholo-2,2-difluoroethylene after 15 days at 150 °C, and norbornene gives only a 9% yield of cycloadduct after 3 days at 120 [96]... 

Nonfluonnated allenes also readily react with fluoroalkenes to give diverse fluonnated alkylidenecyclobutanes [727, 12S, 129, 130] (equations 55 and 56), except for tetramelhylallene, which rearranges to 2,4-dimethyl 1,3-pentadiene under the reaction conditions prior to cycloaddition (equation 57) Systematic studies of l,l-dichloro-2,2-difluoroethylene additions to alkyl-substituted allenes establish a two-step, diradical process for alkylidenecyclobutane formation [131, 132, 133]... 

Fluorinaied dienophiles. Although ethylene reacts with butadiene to give a 99 98% yield of a Diels-Alder adduct [63], tetrattuoroethylene and 1,1-dichloro-2,2-difluoroethylene prefer to react with 1,3-butadiene via a [2+2] pathway to form almost exclusively cyclobutane adducts [61, 64] (equation 61). This obvious difference in the behavior of hydrocarbon ethylenes and fluorocarbon ethylenes is believed to result not from a lack of reactivity of the latter species toward [2+4] cycloadditions but rather from the fact that the rate of nonconcerted cyclobutane formation is greatly enhanced [65]... 

Current option 136, 214 density matrix 263 l,2-dichloro-l,2-difluoroethane 24 dichloroethane 239, 242 dielectric constant 239 diffuse functions 99 difluoroethylene 45 dihedral angles 290 valid range 288 n,n-dimethylformamide 105 dipole moment 20... 

A variety of electronic effects control the relative energies of the disubstituted benzenes. For the difluorobenzenes, the meta and para isomers are of comparable energy the ortho isomer is clearly less stable. This is most likely due to the electrostatic repulsions of the two C-F bond dipoles which are aligned in the same direction. This is just like the difluoroethylenes where the 1,2-cis isomer is much less stable than the 1,1-isomer.poj. he dihydroxybenzenes. 

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