Conformational behavior of some hydroxamic acids

Abstract

The conformational preferences of a few hydroxamic acids are investigated by the density functional B3LYP/6-311++G**//B3LYP16-31G* and semiempirical AM1 and PM3 methods in this work. It is found that both semiempirical methods give satisfactory results in comparison with sophisticated DFT and ab initio calculations, except for the activation barriers, which are overestimated. Of the two semiempirical methods, while the PM3 method gives better results for relative stabilities, AM1 geometries are in slightly better agreement with the experiments. The keto forms are found to be most stable and the reaction pathways for the interconversion between the keto and enol forms have been deduced. The effect of solvation on the reaction has also been investigated, as has the effect of methyl substitution at the carbon and nitrogen atoms. All the investigated acids exhibit N-acid behavior.

Density functional study of the intramolecular proton transfer and conformations in hydroxyaminosilanethione

“…This step involves unexpected barrier of 9.86 kcal/mol via TS6. This barrier value is in reverse with previously reported results for formohydroxamic acid [22]. Judging from the transition barriers it seems that the S2-TS4-1E is the slowest reaction step and it is endothermic with an energy barrier equal to 43.09 kcal/mol.…”

Keto–iminol tautomerism in acetohydroxamic and formohydroxamic acids

“…Low-quality calculations suggested that FHA exists preferentially as the 1E-keto isomer with OH bond in anti-orientation in the gas phase [21,25,28,32]. At the higher levels of theory, when more extended basis set and correlation energy were used, the 1Z-keto isomer with the OH bond involved in an intramolecular hydrogen bond, was predicted to be the most stable one.…”

“…A number of theoretical calculations were performed related to the structural analysis of FHA [21][22][23][24][25][26][27][28][29][30][31][32][33] and AHA [34][35][36][37][38][39]. Low-quality calculations suggested that FHA exists preferentially as the 1E-keto isomer with OH bond in anti-orientation in the gas phase [21,25,28,32].…”

Hydroxamic Acids − An Intriguing Family of Enzyme Inhibitors and Biomedical Ligands

“…[50] The conformational preferences of some hydroxamic acids have recently been investigated by density functional and empirical methods. [51] Figure 5. Tautomeric forms of hydroxamic acids…”