4- Fluorostyrenes

A theoretical investigation of the use of NMR lineshape second moments in determining elastomer chain configurations has been undertaken. Monte Carlo chains have been generated by computer using a modified rotational isomeric state (RIS) theory in which parameters have been included which simulate bulk uniaxial deformation. The behavior of the model for a hypothetical poly(methylene) system and for a real poly(p-fluorostyrene) system has been examined. Excluded volume effects are described. Initial experimental approaches are discussed. 

The algorithm also incorporates tacticity control for vinyl chains. The random number generator is used to choose between d- and l-versions of the transformation matrix. A single parameter controls the relative probability of d- and l-residues. The poly(p-fluorostyrene) results presented here are for atactic (stereochemically irregular) chains. 

A preferable system is poly(p-fluorostyrene) doped into poly(styrene). Since rotations about the 1,4 phenyl axis do not alter the position of the fluorine, the F spin may be regarded as being at the end of a long "bond" to the backbone carbon. In standard RIS theory, this polymer would be treated with dyad statistical weights to automatically take into account conformations of the vinyl monomer unit which are excluded on steric grounds. We have found it more convenient to retain the monad statistical weight structure employed for the poly(methylene) calculations. The calculations reproduce the experimental unperturbed dimensions quite well when a reasonable set of hard sphere exclusion distances is employed. 

Figure 5. ORTEP computer plot showing the positions of the fluorine atoms of the first 50 backbone carbons of a poly(p-fluorostyrene) chain. The excluded volumes used in the calculation keep the fluorines well separated.

Figure 7. Average values of for poly(p-fluorostyrene) chains of 200 backbone atoms, 100 chains per point. In this calculation, the fluorines are at their correct locations on the sidegroups.

Primary and secondary alkylzinc iodides and benzylic zinc halides also undergo Ni-catalyzed reactions with various primary alkyl iodides and bromides.407-409 According to the procedure by Knochel and co-workers, the transformations with alkylzinc iodides, which are less reactive than the corresponding dialkylzincs, require the presence of two additives Bu4NI and 4-fluorostyrene (Scheme 155).407,408... 

Fluorostyrene 99% from Aldrich Chemical Company, Inc., is used as obtained. 

N-Methylpyrrolidinone 2-Pyrrolidinone, 1-methyl- (8,9) (872-50-4) p-Fluorostyrene Styrene, p-fluoro- (8) Benzene, 1-ethenyl-4-fluoro- (9) (405-99-2)... 

Knochel and co-workers developed the Ni(acac)3-catalyzed cross-coupling reaction between polyfunctional primary iodoalkanes and a variety of primary diorganozinc compounds in the presence of w-trifluoromethylstyrene as a promoter. " The addition of this unsaturated promoter is required in order to coordinate to the nickel center and remove electron density from the metal atom, to facilitate the reductive elimination step. " " The scope of the reaction is extended, when Ni(acac)2 is used in the presence of BU4NI and fluorostyrene (Scheme With these... 

When DISN reacts with electron-rich styrenes such as p-methoxystyrene, good yields of reduced pyrazines 117, often accompanied by their oxidized forms, are obtained. However, reaction with electron-deficient styrenes like p-fluorostyrene give the 2-amino-3-(2-arylaziridin-l-yl)maleonitriles (118) (72JA3242 84JOC813). 

Similarly, decreasing the electron density on the metal will enhance its willingness to undergo reductive elimination and become more electron rich. A typical demonstration of this tendency is the nickel catalyzed coupling of sp3 hybridized carbon atoms. Here, if a nickel-phosphine catalyst is used, the catalytic cycle is very slow, due to disfavoured reductive elimination. The use of additives that deplete the electron density of the nickel atom through coordination (e.g. fluorostyrenes) leads to a marked increase of the turnover frequency.18... 

Fig. 4. Melting temperatures of crystalline styrene//>-fluorostyrene copolymers I, crystallites with threefold helix II, crystallites with fourfold helix (from Natta, G., etal. J. Polymer Sci. 51, 527 (1961))...

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