Deprotonation of Amides and Polyfunctional Imides Probed by Heteronuclear NMR and Quantum Chemical Calculations

Abstract

The site of deprotonation of several types of amide acids (carboxylic amides and imides, sulfonamides, cyanamide, N‐hydroxyurea) has been investigated by quantum chemical calculations and heteronuclear NMR measurements. Relative energies of tautomeric ions deriving from protonation at the various sites were determined both in the gas phase and in water (by the IPCM continuum solvation method). NMR properties (nuclear shielding and electric field gradient) of the involved heteronuclei were calculated and compared with experimental 14N, 17O and 33S chemical shifts and relaxation rates. It is shown that the combination of theoretical and experimental tools allows a reliable prediction of spectral parameters and ultimately of the deprotonation site of polyfunctional acids.

Salts and Ionic Liquids of Resonance Stabilized Amides

“…178.6 ppm in diacetamide anion (H 3 C C O) 2 N − )42 and 14 N NMR spectrum (−128 ppm, cf. −140 ppm for sodium succinimide (H 2 C) 2 (CO) 2 N Na) 43. IR and Raman data are listed in Table 3.…”

“…À140 ppm for sodium succinimide (H 2 C) 2 (CO) 2 NNa). [43] IR and Raman data are listed in Table 3. Table 1.…”

Isomerical and structural determination of N-hydroxyurea: a matrix isolation and theoretical study

“…X-ray diffraction of crystals of HU [32][33][34] shows that the E-keto structure is the stable tautomer in the crystalline phase and all the atoms of the molecule, except the hydroxyl hydrogen, are coplanar. NMR studies of HU in water and deuterated dimethyl sulfoxide (DMSO-d 6 ) solutions 35,36 indicate that N-hydroxyurea in both solvents also exists in the E-keto form. However, IR spectra 37 suggest that HU in the solid-state exists in the keto form but in different solvents both keto and iminol tautomers are present.…”

Environmental risk assessment of commonly used anti-cancer drugs

“…As different from other ACDs, Ciclosporin, a polypeptide consisting of 11 amino acid moieties with their hydrophobic aliphatic groups, has a complex structure. Amino acids, possessing hydrophobic -R groups, are found in the interior part of the polypeptide where does not come into contact with water [28]. Ciclosporin has low water solubility (4.239x10 -5 ) due to the presence of hydrophobic CH3 and CH2 groups binding to amino acid units of polypeptide.…”