Salt adduct

The 13C NMR spectrum for Experiment II appeared to consist of two sets of resonances that corresponded to Pyroglu. We speculate this is due to a Pyroglu-prolinol salt adduct. 

Phosphorus ylides have been reviewed and an intermediate betaine lithium salt adduct (stabilized by complexation with lithium ions and by the chelating effect of pyridyl ligands) has been observed spectroscopically for the first time during the course of a Wittig reaction. ... 

Spectroscopic evidence for formation of a betaine lithium salt adduct during the course of a Wittig reaction has been reported for the first time. The ylide Ph3P=CH2 formed oxaphosphetane (71) on treatment with 2,2 -dipyridyl ketone at -60 °C in... 

The ion formation may occur in the bulk solution before the electrospray process takes place or in the gas phase by protonation or salt adduct formation, or by an electrochemical redox reaction. Polar compounds already exist in solution as ions therefore, the task of the electrospray is to separate them from their counterions. This is the case of many inorganic and organic species and all those compounds that show acidic or basic properties. Proteins, peptides, nucleotides, and many other bio- and pharmaceutical analytes are typical examples of substances that can be detected as proto-nated or deprotonated species. 

Measurement of ionization potentials has shown that 2,4,6-triphenylpyrylium salts undergo a thermal reduction in the mass spectrometer giving the corresponding free radicals. Steric properties preclude dimerization (74OMS(9)80>. This type of reduction appears to be largely independent of the nature of the anion the bromide and iodide salts behave identically. However, in the case of the tetrafluoroborate salt, adduct formation between a cation and a fluoride ion gave a minor peak. Anomalous behaviour is displayed by the perchlorates the anion effects oxidation of the cation upon evaporation giving a base peak which corresponds to [M + 0-H]+. 

The data thus provided good evidence for the existence of preponderantly 1 1 sucrose-alkali metal salt adduct in aqueous solutions of low to moderate concentration of salt. Similar studies of n-fructose with alkali metal salts have given identical results. 0 In anhydrous ethanolic media,10 potassium acetate and methyl j3-D-glucopyranoside have been shown polarimetrically to combine in the ratio of 1 1. This ratio is also found in the adduct isolated. 

Application of Job s principle00 to aqueous solutions of sucrose and alkaline-earth metal salts (magnesium sulfate, calcium acetate, and barium chloride), whose combined concentration was 1 M, gave curves of Aa against concentration that exhibited two maxima, one at 0.5 M sucrose and the other at 0.66 M sucrose. These observations suggest that both 1 1 and 2 1 carbohydrate-salt adducts can exist in solution. 

The epoxy-phosphonium salt adduct would then be vulnerable to attack by another epoxy molecule resulting in the formation of an oxonium ion (Eq. (26)) or it reacts with the anhydride to form a special monoester with hydroxy groups (Eq. (27)). 

In addition, on reacting Na2Cr(CO)s with t-Bu2Si(OTf)2 in THF, similarly to equation 18, the salt adduct (CO)5Cr=Si(Bu-t)2 Na(OTf).2THF was obtained with an... 

A final lmM HEPES, pH 7.2 wash is performed to remove contaminants such as salts and detergent, which may interfere with interpretation of spectra. Formation of salt adducts creates additional peaks with a mass shift of 22 and 38 Da for sodium and potassium, respectively, which can affect the sensitivity of the assay. Detergents generate a series of low molecular weight peaks, which can complicate analysis and decrease the specific signal. 

It has been pointed out previously that silylation of ylides leads to stabilized products and that this is only one example of the very general phenomenon of carbanion stabilization through silicon (34, 61, 72). This effect was also found for arsenic ylides (34, 73), and is the basis for the preparation of other compounds of this series. The influence of silicon is by no means solely an electronic effect. In many cases, where alkylsilyl substituents are introduced, a steric effect may well dominate, which may reduce lattice energies for salts in transylidation reactions, preventing intermolecular contacts in decomposition processes, and rendering the formation of salt adducts unfavorable. This steric effect is reduced to a minimum, but not eliminated, if simple SiH3 groups are employed (61). Even then, however, a pronounced silicon effect is found, which must be based on electronic influences (49, 60, 61). 

In contrast, Sr(NCS)2(HMPA) and SrIjIHMPA) were not prepared by dissolution of their respective anhydrous salts by base, but rather by reaction of NH4X (X = SCN or 1) with Sr metal in the presence of base. The main advantage of this method is that it yields anhydrous compounds. In addition, this method is useful in the preparation of salt adducts when the dissolution method fails for kinetic reasons (i.e., when the metal coordination sites of [MX2l are inaccessible to the base). 

Grierson, D. S., Harris, M., Husson, H. P. Synthesis and chemistry of 5,6-dihydropyridinium salt adducts. Synthons for general electrophilic and nucleophilic substitution of the piperidine ring system. J. Am. Chem. Soc. 1980,102, 1064-1082. 

Carbonyl compounds are capable of undergoing another completely different sort of reaction, in which the carbonyl oxygen is replaced, not by a heteroatom as we saw above, but by an sp carbon atom. When triphenylphosphine is treated with a secondary aliphatic halide, a normal substitution reaction occurs, resulting in the replacement of the halide by the phosphorus compound. This phosphonium salt adduct may then be treated with a very strong base, such as phenyllithium, to produce an ylid. An ylid is a compound in which there is a positive charge adjacent to a negative charge. Write down this reaction sequence. 

Due to the hyperconjugative effect of the alkyl groups, which change the electrophilic character of the cyanide carbon atom, the addition of another cyanide molecule in the presence of an acid is hindered."9,142 Furthermore, the formation of stable salt adducts as intermediates during acid catalysis prevents the cyclotrimerization.143 144... 

---