Nuclear magnetic resonance study of exchanging systems—IV : Complete line shape analysis of nitrogen inversion of ethylenimine by the density matrix method

An NMR spectrum of completely dehydrated ethylenimine 1 in liquid phase was found to show well resolved multiplets for the aziridine ring protons at room temperature. The computer analysis was made to determine the NMR parameters. Temperature dependent NMR spectra show that the nitrogen inversion of 1 is slow enough in the NMR time scale at room temperature. In order to obtain the kinetic parameters of this inversion, the complete line shape analysis for the NMR spectra of 1 as an AA′BB′C spin system was performed using the density matrix method, and fitting the calculated spectra with the observed at various temperatures. The activation parameters are obtained as follows: Ea = 15·9±0·4 Kcal/mole Δ^≠ = 17·1±0·8 Kcal/mole ΔH^≠ = 15·3±0·4 Kcal/mole at 25·° ΔS^≠ = ?6·2+-1·2 e.u. Some discussion is made about the activation parameters of the nitrogen inversion of various aziridines.     

A study of imidazole by the proton magnetic resonance method

The concentration dependence of the chemical shifts of the protons of imidazole in six polar organic solvents and water has been studied. In aqueous solutions an exchange of the NH protons between the imidazole and the water molecules takes place. In organic solvents, the position and half-width of the NH line of imidazole depend on the concentration. With an increase in the concentration, this line shifts in the downfield direction. The shift (1 ppm for a solution of imidazole in DMSO) may be due to the formation of an ordinary hydrogen bond (> NH N ) between the imidazole molecules.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 6, pp. 810–813, June, 1970.     

Nuclear magnetic resonance of psychotherapeutic agents. IV—conformational analysis of 2,3-dihydro-1H-1,4-benzodiazepines

The lanthanide shift reagent (LSR)/¹H NMR study of some 7-chloro-5-phenyl-2,3-dihydro-1 H-1, 4-benzodiazepines shows that these compounds exist in CDCI₃ solution as two pseudo-boat conformers, rapidly interconverting at room temperature. Computer simulated lanthanide induced shifts (LIS) are consistent with LSR complexation by the imine nitrogen atom. The lanthanide shifts the conformational equilibrium towards conformer (a), with a pseudoequatorial 1-substituent: this effect may be the result of the greater basicity of 4-N when the 1-N lone pair is pseudoaxially directed, thus permitting an extended electron delocalization from 1- to 4-N through the fused benzene ring. The detection of H-9/1-Me through space spin-spin coupling in medazepam (7-chloro-1-methyl-5-phenyl-2,3-dihydro-1H-1,4-benzodiazepine) supports the observed higher availability of conformer (a) to LSR. A LIS computer calculation to predict the population ratio results in reasonable agreement with the conformational changes based on the response of ³J(HH) to lanthanide addition. The electronic and steric effects which determine the greater stability of conformer (a) may be effective in the drug-receptor interaction.     

Equation-of-motion coupled-cluster method for the study of shape resonance

The equation-of-motion coupled-cluster method (EOM-CC) is applied for the first time to calculate the energy and width of a shape resonance in an electron-molecule scattering. The procedure is based on inclusion of complex absorbing potential with EOM-CC theory. We have applied this method to investigate the shape resonance in e(-)N(2), e(-)CO, and e(-)C(2)H(2).     

Nuclear magnetic resonance spectroscopic method for the estimation of competitive equilibrium constants

A nuclear magnetic resonance method is described which yields precise estimates of competitive equilibrium constants for systems in which two or more complexing agents compete for common species. Chemical-shift data under rapid exchange conditions are required, but neither analytical not equilibrium concentrations are needed. The method is demonstrated by estimating equilibria of proton exchange between aniline and pyridinium ion, proton exchange between triethylamine and diisopropylammonium ion, and cyclohexaamylose exchange between m- and p-hydroxybenzoic acids. The precisions of the equilibrium constants are similar to or better than those obtained from classical methods and are relatively free from interferences.     

Nuclear magnetic resonance analysis of trace sulfur mustard chemicals in the environmental samples

Nuclear magnetic resonance （NMR） technique was used to screen and identify trace sulfur mustard chemicals in the organic and aqueous waste samples. 1H-NMR and one dimensional total correlation spectroscopy （1D TOCSY） were used for non-destructive screening analysis of the original samples. 1D TOCSY-TOCSY and 1D TOCSY incorporated with a chemical shift selective filter （1D CSSF-TOCSY） were applied in screening the contained sulfur mustard related compounds in the unknown samples. In order to meet the criteria for 1H-NMR data presentation, sample pretreatment technologies including liquid-liquid extraction, solvent exchange and solid phase extraction were used to eliminate the interference of the target resonances. Bis（2-chloroethyl） sulfide, 1, 3-Bis（vinylthio）propane and 1,3-Bis（2-hydroxyethylsulfonyl） propane were identified based on 1HNMR spectra comparison. The results were in good agreement with the list of spiking chemicals. The analytical strategies of this work can provide reference for the 1H-NMR analysis of the trace chemical warfare related compounds in official OPCW proficiency test. © 2023, Youke Publishing Co.,Ltd. All rights reserved.     

Nuclear magnetic resonance spectroscopic analysis of ethyl ester yield in the transesterification of vegetable oil: an accurate method for a truly quantitative analysis

Biodiesel has recently gained importance as an alternative to fossil diesel. However, the development of more efficient biodiesel formation processes still depends on the use of fast and accurate analytical techniques to evaluate the conversion degree of the transesterification reaction. Nuclear magnetic resonance (NMR) spectroscopy has been used for this purpose, but some experimental details still need to be addressed. Therefore, in this communication, the experimental conditions for a truly quantitative NMR analysis of biodiesel formation are presented. The longitudinal relaxation time (T₁), which is the determining factor for quantitative analysis, was measured using an inversion‐recovery method, and a maximum value of 2.35 s was obtained for a biodiesel sample. A linear determination coefficient of r² = 0.99 was obtained when a time delay between pulses longer than 5T₁ =15 s was used, whereas strong deviations were observed when using shorter delays. Copyright © 2012 John Wiley & Sons, Ltd.