Anions, alkyl group stabilization

This can be circumvented by choosing alkyl groups with no P H, eg, methyl, neopentyl, trimethylsilylmethyl, phenyl and other aryl groups, and benzyl. The linear transition state for -elimination can also be made stericaHy impossible. The most successful technique for stabilization combines both principles. The pentahaptocyclopentadienyl ring anion (Cp) has six TT-electrons available to share with titanium. Biscyclopentadienyltitanium dichloride... 

Alkyl groups attached to pyridopyrimidines adjacent to a nitrogen are activated , i.e. they are readily deprotonated and react with electrophilic reagents as their anions, or resonance stabilized equivalents, e.g. (64). This ready deprotonation, of course, leads to facile exchange of the alkyl protons for deuterium (Sections 2.15.2.2.1, 2.15.4.2), but, in... 

Sn -I- 2RI R2Snl2 (where R is the alkyl group and I is the anion). Methyltin stabilizers are produced by direct synthesis in the United States. Dibutyltin dichloride is manufactured from crude tetrabutyltin and tin tetrachloride and is usually catalysed with aluminium trichloride (Blunden Evans, 1989 Gaver, 1997 Thoonen et al, 2001). 

Lithiation of alkyl groups is also possible and again a combination of donor chelation and polar stabilization of anionic character is required. Amides and carbamates can be lithiated a to the nitrogen. 

In 1996, Gratzel, Bonhote and coworkers published the synthesis and properties of ionic liquids with anions containing CF3- and other fluorinated alkyl groups [12]. These are usually highly hydrophobic melts with high stability (even under acidic conditions) against hydrolysis. 

An extensive study132 has been presented on the polarizability effects of alkyl groups in RX moieties (R = Me, Et, i-Pr and i-Bu X = CH2, S, SO2, O and N) in families of weak acids and on the stabilities of adjacent anions and radicals in DMSO solution. Some of the results related to the 9-(dialkylamino)fluorenes are given in Table 12. The increases in acidity are believed to be caused by the progressive increases in anion stabilizing... 

This is the case for secondary and tertiary alkyl bromides. If the stability is high, however, as, for example, with primary alkyl bromides, the organo nickel(III) complex is further reduced to an alkyl nickel(II) complex which loses the alkyl group in form of the alkyl anion. An electroinactive Ni(II) species remains. The number of regenerative cycles is consequently low. The structure of the ligand also influences the lifetime of the alkyl nickel(ni) complex thus, a less stable complex is formed in the case of [A,A -ethylene-bis(salicylidene-irainato)]nickel(II) ([Ni(salen)]) as compared with (5,5,7,12,12,14-hexamethyl-l,4,8,ll-tetraazacyclo-tetradecane)nickel(II) ([Ni(teta)] ), and hence the former complex favors the radical pathway even with primary alkyl halides. 

Some interesting results have recently become available for the effects of a range of n-alkyl triethyl ammonium bromides upon the mechanical stability of natural rubber latex. The number of carbon atoms in the alkyl group varied from 6 to 18. Figure 6 summarises the results. It is usually believed that the addition of cationic surfactants to an anionic latex such as natural rubber latex invariably leads to a reduction in colloid stability, the effect being attributed to adsorption of the cations with consequent partial neutralisation of the particle charge and reduction of the counterion cloud surrounding the particles. 

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