Structures of two isomeric hydroxamic acids: N-methyl-p-toluohydroxamic acid (MTH) and N-(4-methylphenyl)acetohydroxamic acid (MPA)

Abstract

. The hydroxamate group in each compound assumes the trans conformation as observed in other secondary hydroxamic acids. The interchange of the C and N substituents influences the planarity and dimensions (C---~O, C--N bonds) of the hydroxa, mate moiety. In MTH the hydroxamate group shows significant deviation from planarity; the r.m.s, deviation of the four atoms, @--N--O(H), is 0.094 A, whereas in MPA it is only 0.004A. This nonplanarity is due largely to out-of-plane bending at N, XN = 23"9 (1) °, as compared to XN = 0"1 ° for MPA. The phenyl ring in MPA is nearly coplanar with the hydroxamate plane (dihedral angle of 10.3°), but is significantly rotated from the hydroxamate plane in MTH (dihedral angle of 43.8°). Electronic differences in the two molecules are considered.

A Quantitative Treatment of Dephosphorylation by an Amphiphilic Hydroxamate Ion. The Role of Micellar Charge

“…The E - and Z -isomers of hydroxamates may have different nucleophilicities and basicities, which complicates comparisons of rate constants in different media, including micelles. Polar, hydroxylic solvents increase the Z : E ratio, as do micelles. , …”

“…Hydroxamate ions are α-effect nucleophiles; i.e., they are better nucleophiles than predicted by Bronsted relations between nucleophilicity and basicity. , However, hydroxamic acids and their anions, which are α-effect nucleophiles, exhibit amide-like geometrical isomerism and the E : Z ratio depends on structure, solvent composition, and incorporation in association colloids. , Insofar as E and Z isomers may differ in their nucleophilicities, this isomerism complicates analyses of relations between structure and reactivity.…”

“…Reactions of pNPDPP with 1a in water and 1c in comicelles with CTABr were analyzed by using eqs 1 and 2, and values of and were similar, based on V M in the range 0.14−0.3 M -1 , but this analysis neglected the geometrical isomerism of the hydroxamate ions. , In water 1a is an E − Z mixture, and the mole fraction of Z , χ Z = 0.31, but in micelles, regardless of charge, χ Z ≈ 1 for 1b , and probably also for 1c . (This point was not tested explicitly because the higher solubility of 1b was convenient for NMR work …”

On the reaction of bis(phosphothioyl)disul‐fanes with hydroxamic acids, part I: Ionic versus radical reaction pathways

“…2) with that of the corresponding N-methyl-4-methylbenzohydroxamic acid [18] and 1e (Fig. 1) revealed some significant differences in bond lengths.…”

DFT calculations on molecular structures, HOMO–LUMO study, reactivity descriptors and spectral analyses of newly synthesized diorganotin(IV) 2‐chloridophenylacetohydroxamate complexes

“…Nevertheless, the (N,O), (N,N), and bridging bis‐chelating modes forming metallocrowns are also known . The acetohydroxamic acid and a number of C‐ and N‐substituted hydroxamic acids studied by X‐ray crystallography have shown that the nature of the C‐ and N‐substituents influence the stability of the metal hydroxamato/imato complex . The hydroxamic acids with electron donating substituents (NH 2 , OH) at the aromatic ring form more stable complexes by increasing the localized negative charge on the coordinating oxygen atoms while those with electron withdrawing substituents (NO 2 , F, Cl) exhibit higher biological activity …”