The Brønsted Acid/Base Character of Hydroxylamines, Oximes and Hydroxamic Acids

Abstract

A summary is presented for hydroxylamines, oximes, and hydroxamic acids, of their gas phase Bronsted acidities and basicities, acidities in DMSO solvent, and aqueous solution acidities and basicities. The gas phase experiemtnal values are supplemented with computational values. An analysis of structural effects on the acid/base values is presented. Introduction Hydroxylamines Oximes Hydroxamic Acids Final Comparisons Acknowledgment

Electrospray Ionization (ESI) Fragmentations and Dimethyldioxirane Reactivities of Three Diverse Lactams Having Full, Half, and Zero Resonance Energies

“…Such negative evidence is not, of course, very strong. While N-hydroxylamines are typically five orders of magnitude weaker bases than the corresponding amines, 57 simple N-hydroxyamino acids are zwitterionic. 58 The product ( 16 ) would appear to be kinetically-determined (relative to 17 ).…”

Blue Light Photocatalytic Glycosylation without Electrophilic Additives

“…38,44 The part of the reaction manifold that affords substitution with overall retention of configuration is best interpreted as taking place via solvent-separated ion triplets rather than via equilibration of the donor configuration followed by concerted displacement as no evidence was found for donor anomerization in these reactions. The root cause of the observed acceleration of reaction rate by the 4 Å MS is presumably associated with their basic character 45 and the relative acidity 46 of the hydroxylamine Tempol.…”

“…The hexafluorophosphate counterion is not considered to intervene directly in the reaction mechanism except for providing charge stabilization consistent with studies on the influence of a variety of counterions on the stereoselectivity of glycosylation reactions. , The part of the reaction manifold that affords substitution with overall retention of configuration is best interpreted as taking place via solvent-separated ion triplets rather than via equilibration of the donor configuration followed by concerted displacement, as no evidence was found for donor anomerization in these reactions. The root cause of the observed acceleration of reaction rate by the 4 Å MS is presumably associated with their basic character and the relative acidity of the hydroxylamine Tempol.…”

Synthesis of N,N,O-Trisubstituted Hydroxylamines by Stepwise Reduction and Substitution of O-Acyl N,N-Disubstituted Hydroxylamines

“…The hydroxylamine moiety is an interesting functional group with the potential to enrich compound collections, in which it is currently under-represented, by increasing the fraction of sp 3 -hybridized atoms (Fsp 3 ) without the synthetic complication of an additional stereogenic center. This is because the low basicity of the hydroxylamine function (p K a hydroxylamine in water = 5.93) , and the modest barrier to inversion (∼15 kcal·mol –1 ) − together ensure that at physiological pH the pyramidal nitrogen is not protonated in aqueous solution and undergoes rapid inversion of configuration. As such, hydroxylamines carrying two different nitrogen substituents can be considered as surrogates of chiral alcohols and ethers that avoid the need for asymmetric synthesis.…”