Ammonium concerted mechanism

Several detailed reaction paths have been proposed for the addition process (117). The most powerful acylating agent present is the proton-ated lactam (XXIX), p. 437, and the strongest nucleophile is the neutral amine group so that the fastest addition should be reaction (92). Since the equilibrium (91) results in a low concentration of lactam cations and neutral amine groups, most amine groups are present as ammonium ions or undissociated salt (—COONH3—). Therefore, a two-step or concerted mechanism could also be operative in which the iVI-protonation of the lactam by an ammonium ion is accompanied or followed by acylation of the amine and intramolecular proton transfer [220], viz. 

Removal of the acyl functions is typically accomplished, with concentrated ammonium hydroxide or aqueous sodium hydroxide. Further, the benzoyl group on the base may be selectively removed (leaving behind a benzoylated sugar) under neutral conditions by use of hydrazine hydrate (NH2NH2 0.5 H2O). This preference for the base benzoyl function is accounted for by a concerted mechanism ... 

The addition of HC1 to 3-hexyne shows an unexpectedly different picture. The rate law is rather complicated and the reaction is accelerated by addition of chloride ion (as tetramethylammonium chloride). The product distribution ranges from that shown under 5 of Table 2 to the almost exclusive formation of ammonium chloride. The postulated mechanism excludes the formation of vinyl cations intermediates and indicates a concerted transition state for the reaction of type 16. 

The first mechanism to be classified, the bimolecular elimination (E2), was suggested to account for the Hofmann degradation (1), p. 163, of quaternary ammonium hydroxides to olefins and tertiary amines. A single-step reaction between the substrate and a base is involved and the Q-H and C -X bonds break and the Ca-Q double bond forms in a concerted fashion, viz-... 

There has been debate over the mechanism through the years, with some contesting that the reaction took place via a concerted [3 + 21-cycloaddition mechanism (depicted in reaction of 23 and 24). Koldobskii and co-workers suggested that dialkyl ammonium azide (a practically unionized salt based on electrochemical measurements) underwent Diels-Alder type cycloadditions to yield tetrazoles. In addition, a modest solvent... 

Several parameters can govern the storage mechanism in the EDLC for PILs according to the electrolytes/material couple. First, a reduction of the ammonium cation in the presence of an activated carbon electrode is presumably linked to electronic transfer kinetics. Reactions in which electron and proton transfer is performed have been described either by two distinct steps. Electron Proton Transfer or Proton Electron Transfer (EPT or PET), or in the same concerted step. Concerted Proton Electron Transfer (CPET) [140-142]. Contrary to simple proton or electron transfer, CPET is more complicated and the coupling at the activated carbon /molecule (cation) interface influences the process both thermodynamically and kinetically. 

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