Phosphonium and ammonium ions

Overall, there is no large difference in activity between lipophilic phosphonium and ammonium ions, although the phosphonium ions appear to be more active in locations close to the polymer backbone. 

The information includes location of double bonds In fatty acids, indentlficatlon of components in complex lipids, determination of compositions of anionic and cationic surfactants, and identification of long-chained alkyl substituents on phosphonium and ammonium ions. 

Electropositive leaving groups such as phosphonium and ammonium ions [ROP+(Ph)3, RN+R3] can have favourable dipolar interactions in the transition state and therefore reaction rates can be enhanoed. Similarly, the use of a neutral nucleophile such as ammonia or hydrazine will reverse the polarity of the forming bond in the transition state, giving rise to favourable polar interactions with neighbouring electronegative substituents. 

For the above reasons nitrogen forms many compounds of types not formed by other elements of this group, and for this reason we deal separately with the stereochemistry of this element. For example, the only compounds of N and P which are structurally similar are the molecules in which the elements are 3-covalent and the phosphonium and ammonium ions. There are no nitrogen analogues of the phosphorus pentahalides, and there is little resemblance between the oxygen compounds of the two elements. Monatomic ions of nitrogen and phosphorus are known only in the solid state, in the salt-like nitrides and phosphides of the more electropositive elements. The multiple-bonded azide ion, N3, is peculiar to nitrogen. 

Addition of water (36) or alcohols (37—39) direcdy to butadiene at 40—100°C produces the corresponding unsaturated alcohols or ethers. Acidic ion exchangers have been used to catalyze these reactions. The yields for these latter reactions are generally very low because of unfavorable thermodynamics. At 50°C addition of acetic acid to butadiene produces the expected butenyl acetate with 60—100% selectivity at butadiene conversions of 50%. The catalysts are ion-exchange resins modified with quaternary ammonium, quaternary phosphonium, and ammonium substituted ferrocenyl ions (40). Addition of amines yields unsaturated alkyl amines. The reaction can be catalyzed by homogeneous catalysts such as Rh[P(C(5H5)3]3Q (41) or heterogeneous catalysts such as MgO and other solid bases (42). 

Onium ions are cationic species with expanded valencies. The most important onium ions relevant to cationic polymerizations are oxonium, sulfo-nium, ammonium, and phosphonium ions. Ammonium, phosphonium, and sulfonium ions are tetrahedral with angles of approximately 109.5° between substituents. These species may be chiral if all... 

Retention of the terminal amine also allows the potential for further modification of the peptide with sensitivity-enhancing molecules such as the C-5 alkyl quaternary ammonium activated ester developed in this laboratory (Figure 5). N-terminal derivatisation of peptides with fixed-charge compounds including quaternary amines, phosphonium and pyridinium ions have already been shown to simplify the daughter-ion spectra of peptides produced by high-energy collision-induced... 

Three issues need to be addressed in connection with oxonium ylide mechanisms. The first question concerns the existence of oxonium ylides. Whereas sulfonium, phosphonium, and ammonium ylides are well known, oxonium ylides have not been isolated. Secondly, if they exist, will they undergo Stevens rearrangement, or decompose via other routes Finally, is the zeolite conjugate base sufficiently basic to abstract a proton from oxonium ions to form an ylide ... 

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