Protonation and deprotonation of hydroxamic acids. An MO ab initio study

Ring‐substituted benzohydroxamic acids: 1H, 13C and 15N NMR spectra and NHOH proton exchange

“…Our calculations demonstrate that the benzohydroxamic acid and its ring-substituted derivatives are most stable in the Z-conformer of the hydroxamic form, which is in agreement with previous (ab initio for benzohydroxamic acid 33,34 and o-hydroxybenzohydroxamic acid 35 and semiempirical 36 ) results. The energy difference between the Z and E conformers in the gas phase is 17.2 kJ mol 1 (or 7.9 kJ mol 1 ;…”

“…52 -54 Our experiments and calculations may also contribute to the long-debated problem of hydroxamic acid protonation and subsequent hydrolysis. 55 Our ab initio calculations support the accepted opinion 34,56,57 that the preferred site of protonation is the carbonyl oxygen (Scheme 4).…”

“…34), which means that there is <0.1% of the E conformer. As seen in Table 6, the Z conformers of all studied meta-and para-substituted derivatives are 15.4-17.4 kJ mol 1 more stable than their E counterparts.…”

Keto–iminol tautomerism in acetohydroxamic and formohydroxamic acids

“…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].…”

Amide-imide tautomerism of acetohydroxamic acid in aqueous solution: quantum calculation and SMD simulations

“…Other studies on the isomers of hydroxamic acids have been performed in gas phase, with results varying depending on the level of calculation. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] The tautomeric equilibria of acetohydroxamic acid (AHA), of special importance in biochemistry, are very sensitive to the medium where the reactions occur. Therefore, AHA is an appropriate system for the study of the amide-imide tautomerization process via different mechanisms.…”