Theoretical, Structural, Vibrational, NMR, and Thermal Evidence of the Inter- versus Intramolecular Hydrogen Bonding in Oxamides and Thiooxamides

Abstract

This contribution describes the study of hydrogen bonding in secondary oxamides, monothiooxamides, and dithiooxamides by ab initio calculations, X-ray diffractions, NMR spectra, thermal analysis, and variabletemperature infrared and Raman spectroscopy. The results can all be interpreted as a function of the change in the strength and the nature of the hydrogen bonding by substituting oxygen for sulfur in the series CH 3 -HNCOCONHCH 3 , CH 3 HNCSCONHCH 3 , CH 3 HNCSCSNHCH 3 and by changing the steric influence of the alkyl group in a series of oxamides (RHNCOCNHR; R ) CH 3 , C 2 H 5 , iC 3 H 7 , tC 4 H 9 ).

New bis-oxalamides from trans-1,2-diaminocyclohexane

“…Experimental and theoretical studies have demonstrated that intramolecular hydrogen bonds in oxalamides determine their geometry and conformation whereas intermolecular hydrogen bonds increase their stability. [1][2][3] Due to these interactions, oxalamides are applied in diverse areas such as artificial receptors for biological recognition, 4 in engineering and crystal design 5 and in organogels formation. 6 Recently, oxalamide derivatives were identified as HIV-1 inhibitors.…”

Oxalamides as a hydrogen bonding motif in thermoplastic elastomers

“…The ability of the oxalamide group to form intramolecular hydrogen bonds has been confirmed by spectroscopic methods like NMR and also X-ray diffraction 95,[97][98][99][100][101] .…”

“…This clearly indicates that the hydrogen bonds are bifurcated exhibiting weak intramolecular and stronger intermolecular hydrogen bonds. Moreover, infrared spectra of oxalamides dissolved in CH 2 Cl 2 at high dilution revealed the presence of hydrogen bonds indicating intramolecular hydrogen bonding 98 . The intra-and intermolecular hydrogen bond interactions also depend highly on substituents.…”

“…Energy calculations showed that the intermolecular N-H···O=C hydrogen bond formed by two amide groups in NMA is about 30 % stronger than that involving two oxalamide groups 95,98 . Moreover, the cooperative energy effects generated by formation of multiple hydrogen bonds are almost negligible for oxalamides while these account for about ∼17 % in amides.…”

“…It was shown for N,N'-butyl substituted oxalamides (C 4 H 9 , i-C 4 H 9 , s-C 4 H 9 and t-C 4 H 9 ) that the intramolecular hydrogen bonding character of the oxalamide increases with the amount of methyl groups on the α-carbon due to steric hindrance. It appeared that the hydrogen bonding in the t-C 4 H 9 derivative was almost exclusively intramolecular 98 .…”