title: Spectroscopic, DFT, and XRD Studies of Hydrogen Bonds in N-Unsubstituted 2-Aminobenzamides.
abstract: The structures of the mono- and the dihalogenatedN-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.
authors.affiliation: Department of Chemistry, College of Science, Engineering and Technology, University of South Africa, Private Bag X06, Florida 1710, South Africa. mphahmj@unisa.ac.za.
authors.forename: Malose Jack
authors.initials: MJ
authors.lastname: Mphahlele
authors.affiliation: Department of Chemistry, College of Science, Engineering and Technology, University of South Africa, Private Bag X06, Florida 1710, South Africa. malulmm@unisa.ac.za.
authors.forename: Marole Maria
authors.initials: MM
authors.lastname: Maluleka
authors.affiliation: Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius, Reduit 80837, Mauritius. lyd.rhyman@gmail.com.
authors.forename: Lydia
authors.initials: L
authors.lastname: Rhyman
authors.affiliation: Department of Chemistry, College of Science, Engineering and Technology, University of South Africa, Private Bag X06, Florida 1710, South Africa. p.ramasami@uom.ac.mu.
authors.forename: Ponnadurai
authors.initials: P
authors.lastname: Ramasami
authors.affiliation: Department of Chemistry, University of Limpopo, Private Bag X1106, Sovenga 0727, South Africa. Richard.Mampa@ul.ac.za.
authors.forename: Richard Mokome
authors.initials: RM
authors.lastname: Mampa
mesh_terms: D000588:Amines / Q000737:chemistry*; D001549:Benzamides / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006219:Halogens / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D011522:Protons; D011789:Quantum Theory; D012996:Solutions; D013057:Spectrum Analysis / Q000379:methods
chemical_list: D000588:Amines; D001549:Benzamides; D006219:Halogens; D011522:Protons; D012996:Solutions
keywords: 1H-NMR spectra; DFT; XRD; halogenated 2-aminobenzamides; vibrational spectra