The chemistry of N,N′-dimethylformamidine. III. Tautomerism and hindered rotation

1978 ◽  
Vol 56 (11) ◽  
pp. 1470-1476 ◽  
Author(s):  
James D. Halliday ◽  
E. Allan Symons ◽  
Patrick E. Bindner
Keyword(s):  
Acid Catalysis ◽  
Proton Nmr ◽  
Cyclic Dimer ◽  
Acidic Media ◽  
Hindered Rotation ◽  
Temperature Range ◽  
Infrared Studies ◽  
Cis Isomer ◽  
Hydrogen Bonded

Proton nmr and infrared studies of neat N,N′-dimethylformamidine (DMFA) have shown that the cis isomer 1 is present exclusively and that it undergoes tautomerism. At 25 °C, ktaut = 8.2 × 102 s−1, Ea = 41.5 ± 1.5 kJ mol−1, ΔH≠ = 39.1 ± 1.5 kJ mol−1, and ΔS≠ =−57.5 ± 5.0 J mol−1 K−1. The tautomerism is proposed to occur through a hydrogen-bonded cyclic dimer. The effects of solvent on the tautomeric rate in DMFA have also been investigated for CD3NH2 and CDCl3 solutions.Potassium N,N′-dimethylformamidide (PDMFA) in CD3NH2 does not exhibit hindered rotation about the single C—N bond on the nmr lime scale over the temperature range −56 to 25 °C. However, protonated DMFA undergoes hindered rotation about this bond in highly acidic media (97 wt.% H2SO4 at 25 °C, krot = 0.16 × 102 s−1, Ea = 35.4 ± 0.8 kJ mol−1). The acid catalysis is interpreted as occurring through formation of the diprotonated species. The two nitrogens in protonated DMFA have different base strengths.

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

Molecules ◽  
2021 ◽  
Vol 26 (4) ◽  
pp. 926
Author(s):  
Malose J. Mphahlele ◽  
Eugene E. Onwu ◽  
Marole M. Maluleka
Keyword(s):  
Density Functional Theory ◽  
Solid State ◽  
Hydrogen Bonds ◽  
Density Functional ◽  
Tetrahedral Geometry ◽  
Hindered Rotation ◽  
Hydrogen Bond Acceptor ◽  
Functional Theory ◽  
Vis Spectroscopy ◽  
Hydrogen Bonded

The conformations of the title compounds were determined in solution (NMR and UV-Vis spectroscopy) and in the solid state (FT-IR and XRD), complemented with density functional theory (DFT) in the gas phase. The nonequivalence of the amide protons of these compounds due to the hindered rotation of the C(O)–NH2 single bond resulted in two distinct resonances of different chemical shift values in the aromatic region of their 1H-NMR spectra. Intramolecular hydrogen bonding interactions between the carbonyl oxygen and the sulfonamide hydrogen atom were observed in the solution phase and solid state. XRD confirmed the ability of the amide moiety of this class of compounds to function as a hydrogen bond acceptor to form a six-membered hydrogen bonded ring and a donor simultaneously to form intermolecular hydrogen bonded complexes of the type N–H···O=S. The distorted tetrahedral geometry of the sulfur atom resulted in a deviation of the sulfonamide moiety from co-planarity of the anthranilamide scaffold, and this geometry enabled oxygen atoms to form hydrogen bonds in higher dimensions.

Hydrogen-Bonded Cyclic Dimer Formation in Temperature-Induced Reversal of Tautomerism of Salicylideneanilines

2009 ◽  
Vol 113 (9) ◽  
pp. 1822-1826 ◽  
Author(s):  
Toshikatsu Fujiwara ◽  
Jun Harada ◽  
Keiichiro Ogawa
Keyword(s):  
Cyclic Dimer ◽  
Dimer Formation ◽  
Hydrogen Bonded

scholarly journals Corrosion Inhibition of Titanium in Acidic Media Containing Fluoride with Bixin

2009 ◽  
Vol 6 (4) ◽  
pp. 975-978 ◽  
Author(s):  
Jinendra Singh Chauhan ◽  
D. K. Gupta
Keyword(s):  
Corrosion Inhibitor ◽  
Sulphuric Acid ◽  
Corrosion Inhibition ◽  
Electrochemical Methods ◽  
Great Efficiency ◽  
Acidic Media ◽  
Temperature Range ◽  
Hcl Solution

The bixin in acidic media were tested for corrosion inhibition of Ti in 0.5 N sulphuric acid and 0.1 N HCl solution at 30 to 40 °C temperature range by electrochemical methods. It reveals that bixin works as a corrosion inhibitor in halide media and protect the metals from the corrosion with great efficiency

Hydrogen bonding in enantiomeric versus racemic mono-carboxylic acids; a case study of 2-phenoxypropionic acid

2003 ◽  
Vol 59 (1) ◽  
pp. 132-140 ◽  
Author(s):  
Henning Osholm Sørensen ◽  
Sine Larsen
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Crystal Structures ◽  
Carboxylic Acids ◽  
Crystal Packing ◽  
Cyclic Dimer ◽  
Optically Pure ◽  
Pure Enantiomer ◽  
Hydrogen Bonded

The structural and thermodynamic backgrounds for the crystallization behaviour of racemates have been investigated using 2-phenoxypropionic acid (PPA) as an example. The racemate of PPA behaves normally and forms a racemic compound that has a higher melting point and is denser than the enantiomer. Low-temperature crystal structures of the pure enantiomer, the enantiomer cocrystallized with n-alkanes and the racemic acid showed that hydrogen-bonded dimers that form over crystallographic symmetry elements exist in all but the structure of the pure enantiomer. A database search for optically pure chiral mono-carboxylic acids revealed that the hydrogen-bonded cyclic dimer is the most prevalent hydrogen-bond motif in chiral mono-carboxylic acids. The conformation of PPA depends on the hydrogen-bond motif; the antiplanar conformation relative to the ether group is associated with a catemer hydrogen-bonding motif, whereas the more abundant synplanar conformation is found in crystals that contain cyclic dimers. Other intermolecular interactions that involve the substituent of the carboxylic group were identified in the crystals that contain the cyclic dimer. This result shows how important the nature of the substituent is for the crystal packing. The differences in crystal packing have been related to differences in melting enthalpy and entropy between the racemic and enantiomeric acids. In a comparison with the equivalent 2-(4-chlorophenoxy)-propionic acids, the differences between the crystal structures of the chloro and the unsubstituted acid have been identified and related to thermodynamic data.

The reaction of trimethylamine in liquid hydrogen sulphide: an electrical conductivity study

1983 ◽  
Vol 61 (6) ◽  
pp. 1142-1145 ◽  
Author(s):  
James D. Halliday ◽  
Patrick E. Bindner
Keyword(s):  
Electrical Conductivity ◽  
Dielectric Constant ◽  
Hydrogen Sulphide ◽  
Liquid Hydrogen ◽  
Weak Electrolyte ◽  
Temperature Range ◽  
Conductance Data ◽  
Brønsted Base ◽  
Electrical Conductivity Study ◽  
Hydrogen Bonded

The electrical conductivity of trimethylamine solutions (2.26 × 10−4 to 2.89 × 10−1 mol L−1) in liquid hydrogen sulphide over the temperature range −72.5 °C to +25.0 °C has been measured. The data indicate that the trimethylamine behaves as a Brønsted base in liquid hydrogen sulphide [1] and is protonated to form trimethylammonium hydrogensulphide. The latter[Formula: see text]behaves as a normal weak electrolyte in a solvent of low to medium dielectric constant [Formula: see text]. The conductance data as a function of temperature also show that trimethylamine exists both as a hydrogen bonded complex with H2S and as an unassociated molecule in liquid H2S.

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