Substituted ammonium cations

In initial work, a total of 17 different ILs were evaluated by the solvation parameter model [8]. Ten of these ILs were comprised of imidazolium or pyrolidinium cations paired with different anions. Many of these compounds represent the traditional class of IL solvents that have been used extensively in organic synthesis reactions or in other analytical uses. The remaining seven ILs consisted of substituted ammonium cations that have proven to be successful analyte matrices in matrix-assisted laser desorption ionization (MALDI) mass spectrometry [11]. 

The thermodynamic stability of could clearly influence the position of this equilibrium. The importance of this effect is shown by the work of Reidel and Charles (23) who prepared salts of [(BTFA)4Eu] with 15 different substituted ammonium cations and observed a more than threefold change in laser threshold at 0°C. on going from piperi-dinium through quinolinium. The increase in threshold roughly parallels an increase in the pKb of the amine from which the cation is derived for those compounds with other than quaternary ammonium ions, and for the quinolinium salt these workers showed that the extent of dissociation to tris chelate is about 40%, as compared with 10% or less for the piperidinium compound. 

In dipolar aprotic solvents partially substituted ammonium cations, i nH4 nN , can form internal hydrogen bonds with small anions, " thus increasing their association. PhHgNPic is more associated than i NPic in and its low A° suggests that two dissociation equilibria... 

Anticipating here results to be discussed in 4, in which it is found that substituted ammonium cations do not produce noticeable polarisation of the negative ionised groups of colloids of acidic nature, it seems that explanation 1 comes nearest to the truth (see p. 309). 

Fig. 26. Reversal of charge spectra of egg lecithin (R.H.N > 20000) with substituted ammonium cations.

A Theoretical Study of Complexes of Crown Ethers with Substituted Ammonium Cations... 

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