Nitrenium ions solvolysis

In addition to solvolysis and nitrenium ion formation, Af-aLkoxy-A-chloroamides (2) also undergo bimolecular reactions with nucleophiles at nitrogen. Not only is the configuration destabilized by the anomeric effect, it also parallels that of a-halo ketones, where halogen on an sp carbon is activated towards reactions by the adjacent carbonyl. This rate-enhancing effect on 8 /2 processes at carbon is well-known, and has been attributed to conjugation of the p-orbital on carbon with the carbonyl jr-bond in the S 2 transition state stabilization of ionic character at the central carbon as outlined by Pross as weU as electrostatic attraction to the carbonyl carbon. The transition states are also affected by the nature of the nucleophile. ... 

Other evidence advanced in favor of alkyl nitrenium ions came from Ag+ promoted isomerization and solvolysis of various cyclic and bicyclic A-chloroamines (e.g., A representative example is shown in Figure 13.12. It was argued... 

The formation of the parent amine 23 in these solvolysis reactions was considered to be the most dehnitive evidence for formation of a discrete nitrenium ion. Gassman and Cryberg" postulated the following, (a) Initial Cl—N bond heterolysis would occur adiabatic ally, generating the singlet nitrenium ion 21. (b) The triplet... 

Effects of the aryl substituents X on knuc for alcohols and H2O were different from those expected for arylcarbenium ions, but were very similar to those deduced for from azide-clock experiments on similarly substituted nitrenium ions generated by solvolysis reactions in... 

The formation of a covalent bond to the nitrenium nitrogen atom by an oxygen-centered nucleophile is not a favorable reaction on the basis of HSAB and would in many cases be a futile reaction in that the arylhydroxylamine (or arylhydroxamic acid) compound or its 0-ester is regenerated. Hydration of a primary arylnitrenium ion at the nitrogen results in an arylhydroxylamine (or arylhydroxamic acid) compound. However, experimental observations suggest that this is a minor reaction in many cases (53, 82). The formation of arylhydroxylamine or arylhydroxamic acid compounds in reactions of analogous O-esters is most often the result of solvolysis of the ester and not the result of hydration of the nitrenium ion at nitrogen. 

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