Factors affecting phenyl group

The (m) fraction is in the range 0.6-0.7 for polymerization at high monomer concentration in the temperature range —25 to 25°C [Resconi et al., 2000]. Substituents on the phenyl groups of the 2-phenylindene ligands, especially meta substituents, slow down the conformational interconversion, and this increases the isotacticity of the polymerization. Both steric and electronic factors operate to affect the interconversion of conformers. Bis(2-phenylin-dene)zirconium dichloride/MAO yields polypropene with (mmmm) = 0.33 for polymerization of liquid propene at 20°C. 3,5-Di-f-butyl and 3,5-difluoromethyl substituents increase (mmmm) above 0.70 [Lin and Waymouth, 2002 Wilmes et al., 2002a,b]. 

Surface Groups. Another factor affecting sorption characteristics is the chemical nature of the adsorbing surfaces. Solid sorbent surfaces may contain hydroxyl or phenyl groups, acid or base groups, or even reactive groups such as olefins. Polarities also... 

Robinson, 1969a). It is probable that the hydrophobic nature of the phenyl groups of p-nitrophenyl diphenyl phosphate results in deep penetration of the neutral ester in the Stern layer, thus shielding the phosphoryl group from nucleophilic attack. Unlike other reactions between nucleophiles and neutral substrates catalyzed by cationic micelles (Bunton and Robinson, 1968, 1969a) and the hydrolysis of dinitrophenyl phosphate dianions in the presence of cationic micelles (Bunton et al., 1968), the catalysis of the hydrolysis of -nitrophenyl diphenyl phosphate by CTAB arises from an increase in the activation entropy rather than from a decrease in the enthalpy of activation. The Arrhenius parameters for the micelle-catalyzed and inhibited reactions are most probably manifestations of the extensive solubilization of this substrate. However, these parameters can be composites of those for the micellar and non-micellar reactions and the eifects of temperature on the micelles themselves are not known. Interpretation of the factors which affect these parameters must therefore be carried out with caution. In addition, the inhibition of the micelle-catalyzed reactions by added electrolytes has been observed (Bunton and Robinson, 1969a Bunton et al., 1969, 1970) and, as in the cases of other anion-molecule reactions and the heterolysis of dinitrophenyl phosphate dianions, can be reasonably attributed to the exclusion of the nucleophile by the anion of the added salt. 

In a series of elegant experiments, Clair Collins (of Oak Ridge National Laboratory) has given us intimate details about the reaction the intermediacy of open carbonium ions, their approximate life-time, and the conformational factors that affect their chemistry. Collins, too, carried out deamination of optically active 2-amino-1,1-diphenyl-1-propanol, but his starting material was labeled stereospecifically (I) with carbon-14 in one of the phenyl groups. He resolved... 

Fluorine substitution is obviously valuable for improved enantioselection in the ammonium-catalyzed alkylation in the biphase system. However, it is not clear to estimate which factor, the electronic or steric effect, is more important in each reaction. The remarkable enhancement of both yield and enantioselectivity by the substitution of two phenyl groups on the 3- and 5-position of the phenyl group (R = Ph in 46b and R = 3,5-diphenyl in 46d in Table 5.5) suggests an importance of the steric effect and so the substitution of three fluorine atoms in 3,4,5-trifluoro compound (46e) may affect the enantioselection through the steric effect that arises from a Coulombic repulsion between the enolate anion of 47 and the lone pair electrons on fluorine atoms. The related non-spiro quaternary ammonium salt (53) is also usable for asymmetric alkylation of 47 [24]. 

Action of Alkyl, Aryl, or Fluoroalkyl Halides on Arsenic Compounds a. With R As to Produce Arsonium Derivatives. The reaction of alkyl halides with trialkylarsines to produce tetraalkylarsonium halides has been known for over 100 years (J). In general, alkyl bromides or iodides interact easily with trialkylarsines, although as more negative groups such as phenyl or trifluoromethyl are substituted for the alkyl groups on the arsine, ease of reaction decreases. There have been only a few attempts made to evaluate the factors affecting arsonium salt formation 157,158). 

Two main factors affect the chemoselectivity (i) coordination of N=CR to a metal and (ii) nature of the substituents. In the case of metal-free reactions, the DFT calculations predict that the DCA of nitfones to N=CCH=CH2 or N=CC=CH should occur exclusively at the C=C or C=C bond [47], Coordination of these nitriles to Pt(II) and, in particular, to Pt(IV), dramatically facilitates the DCA at the C=N bond relative to that at the C=C/C=C bond. However, the reaction at the CC bond still remains more preferable. At the same time, the DCA to phenyl-substituted nitrile in the model complexes frany-[PtCl2(L)(N=CCH=CHPh)] (L = NCCHCH2, NCMe) takes place already at the C=N bond [47, 51], Such a switch of the chemoselectivity is accounted for by (i) the steric repulsion between the bulky Ph groups and (ii) the loss of conjugation in phenylnitrone and phenylcyanoalkene upon formation of the TS. Both these effects are more important for the CC than for CN additions and disfavor the reaction along the former channel. 

If the model compound used for one tautomer is affected by a steric factor that distorts its pK value, the other being unaffected, then neither the correct tautomer ratio nor, sometimes, even which is the dominant tautomer can be deduced [2f]. This most commonly happens in crowded molecules, which should therefore be avoided. Peri interactions involving phenyl groups are one common source of trouble, illustrated by Katritzky and his collaborators inter alia with the contrast between 104 [46a] with a dihedral angle of 2.45° and 105 [46b] in which this has opened to 50.4°, with potentially severe effects on their mutual conjugation. Methyl is much harder in this respect than phenyl another such effect is exhibited by 106-108 whose pfC values, in 70% ethanol [47], demonstrate that 108 is no sort of model for 106 or 107 (Figure 12.12). 

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