Spectroscopic, DFT, and XRD Studies of Hydrogen Bonds in N-Unsubstituted 2-Aminobenzamides

Abstract

The structures of the mono- and the dihalogenated N-unsubstituted 2-aminobenzamides were characterized by means of the spectroscopic (1H-NMR, UV-Vis, FT-IR, and FT-Raman) and X-ray crystallographic techniques complemented with a density functional theory (DFT) method. The hindered rotation of the C(O)–NH2 single bond resulted in non-equivalence of the amide protons and therefore two distinct resonances of different chemical shift values in the 1H-NMR spectra of these compounds were observed. 2-Amino-5-bromobenzamide (ABB) as a model confirmed the presence of strong intramolecular hydrogen bonds between oxygen and the amine hydrogen. However, intramolecular hydrogen bonding between the carbonyl oxygen and the amine protons was not observed in the solution phase due to a rapid exchange of these two protons with the solvent and fast rotation of the Ar–NH2 single bond. XRD also revealed the ability of the amide unit of these compounds to function as a hydrogen bond donor and acceptor simultaneously to form strong intermolecular hydrogen bonding between oxygen of one molecule and the NH moiety of the amine or amide group of the other molecule and between the amine nitrogen and the amide hydrogen of different molecules. DFT calculations using the B3LYP/6-311++G(d,p) basis set revealed that the conformer (A) with oxygen and 2-amine on the same side predominates possibly due to the formation of a six-membered intramolecular ring, which is assisted by hydrogen bonding as observed in the single crystal XRD structure.

Spectroscopic, X-ray Diffraction and Density Functional Theory Study of Intra- and Intermolecular Hydrogen Bonds in Ortho-(4-tolylsulfonamido)benzamides

“…The strong charge transfer interaction through the π-conjugated system led to substantial ground state donor-acceptor mixing and the appearance of a charge transfer band in the electron absorption spectrum. A partial double bond character for the C-N bond of primary amides is always invoked to account for the hindered rotation [24], and is therefore the cause of the nonequivalence of the resonances for the amide hydrogen atoms observed in their 1 H-NMR spectra [13,15]. Although the resonance interaction model provides a convenient explanation for the stabilization of the amino-carbonyl moiety, the changes in electron population and structure on rotation were previously found not to be in accord with an electron donation from the amino group to the carbonyl oxygen of formamide [26].…”

Theoretical Investigation of the Formation Mechanism of NH3 and HCN during Pyrrole Pyrolysis: The Effect of H2O

“…The equilibrium geometries of the reactants, intermediates, transition states, and products were optimized by employing B3LYP/6-31G(d,p). DFT is a computational method that derives the properties of a system based on the electron density of the system [31,32]. The B3LYP functional with a 6-31G(d,p) basis set has been proven to be an appropriate choice for modeling organic species [31,33].…”

Physico-Mechanical, Morphological Properties of Polyvinyl Alcohol/Palm Kernel Shell/Coconut Kernel Shell Elastomeric Polymer Nanocomposites

“…Palm kernel shell and coconut kernel shell powder is introduced into the polymer matrix according to the suggested ratio in Table 1. The experimental conditions as listed in Table 1 were selected based on the optimum conditions from previous researchers [7][8][9]. The solutions were then poured into a mold and dried at 40 o C for 1 days before being demoulded.…”