Carbon-fluorine bond, cyclopropane

The strength of the carbon-carbon bond adjacent to a difluoromethylene group IS hardly affected by the presence of fluorine on the cyclopropyl ring When heated, 2,2 difluoromethylenecyclopropane undergoes methylene-cyclopropane rearrangement [/2 ] Under kinetic control, 2,2 difluoro 1 methylenecyclopropane and (difluoromethylene)cyclopropane are formed in a 2 1 ratio, although the latter IS slightly more stable [129] (equation 27)... 

There are molecules containing two sp3 carbon atoms where four contacts are possible. Consider, for instance, a cyclopropane ring bearing two fluorine (black circles) and two hydroxy substituents (white circles) and consider the formation of O-H - F hydrogen bonds. There are two possible isomers, the meso and the d, 1 (Scheme 3.8), the second one being of C2 symmetry. 

Unfortunately, structures of monosubstituted cyclic hydrocarbons which would allow a systematic correlation between C—F bond distances and ring size have not been reported in the literature. Some polyfluorinated and the perfluorinated cyclopropanes were studied by MW and ED and the C—F bond lengths are listed in Table 14. If only one fluorine is bonded to a ring carbon atom, the C—F bonds are long ca 137 to 139 pm), very similar to that in fluoromethane [139.1(1) pm]. An unexpected result is that the cis standing bonds... 

Considerably less work has been done on the kinetic aspects of the radiolysis of fluorine compounds than on other halogen compounds. With °Co y-radiation, perfluoromethane produces perfluoroethane , and perfluoroethane produces (refs. 351, 352) a mixture of perfluoromethane, -propane, -butane, -cyclopropane, and -acetylene. Similar radiolysis studies on perfluorocyclobutane , perfluoro-cyclohexane and other perfluoro-compounds show that the dominant process is one of rupture of the carbon-carbon bond with the formation of a variety of perfluoro-compounds as products. 

The formally rhodium(I) complex [RhCl(C2F4) (PPh3)2 ] has the structure shown in D.XI 113>. The fluorine atoms are bent back from the metal atom suggesting a change towards sp3 in hybridization of the carbon atoms (as required in a cyclopropane structure) and the C=C bond is lengthened somewhat. Rh(I) is a ds ion so would be expected to favour planar co-ordination. In the complex co-ordination is far from planar being distorted towards tetrahedral, so suggesting an oxidation state other than +1. 

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