To determine the content of trans-gauche-trans (TGT) conformation in poly(ethylene glycol) (PEG) 1H-NMR spectra were measured with tris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-1,4,6-octanedinato)europium(III) [Eu(fod)3] as a shift reagent. As a result the peaks assigned to the ethylene protons in the polymeric segments separated from those assigned to four ethylene protons as the “near-end” groups, and the singlet peak in the former at the lowest field was assigned to the TGT conformation of the COCCOC sequence. It was confirmed that the conformation of the polymeric segments in PEG complexed with Eu(fod)3 remained unchanged with benzene-d6 content as the solvent. The concentration of TGT conformation increased with the number-average molecular weight (Mn): it increased rapidly until about 70% at Mn = 1500. 相似文献
The aromatic 1H- and 13C-NMR. spectra of some metal complexes of o, o′-dihydroxyazobenzenes are shown to be useful in distinguishing the two possible isomers (acolar and discolar) stemming from the non equivalence of the two ligating azo nitrogen atoms. The ortho aromatic carbon atoms, C(6) and C(12) experience relatively large upfield shifts between 12.8 and 15.7 ppm when the adjacent nitrogen atom is coordinated. The protons attached to these carbon atoms are shifted downfield. The values nJ (15N, 13C) for the ligand 2,2′-dihydroxy-3-methyl-4′-chloro-5-(t-butyl)-15N-azobenzene are reported. 相似文献
The conformation of diethylacetamide, (C2H5)2 CHCONH2, and dipropylacetamide, (C3H7)3 CHCONH2, in solution in CDCl3, are studied from NMR spectra observed in the presence of europium and ytterbium chelates, Eu (fod)3 and Yb (fod)3. The 1H and 13C induced shifts are interpreted using classical energy calculations, they are found to reflect a mixture of two or three conformations. The crystalline conformation observed in derivatives of these compounds is found to be identical to the most probable one in solution. 相似文献
The excitation energy transfer (EET) pathways in the sensitization luminescence of EuIII and the excitation energy migration between the different ligands in [Eu(fod)3dpbt] [where fod=6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione and dpbt=2-(N,N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine], exhibiting well-separated fluorescence excitation and phosphorescence bands of the different ligands, were investigated by using time-resolved luminescence spectroscopy for the first time. The data clearly revealed that upon the excitation of dpbt, the sensitization luminescence of EuIII in [Eu(fod)3dpbt] was dominated by the singlet EET pathway, whereas the triplet EET pathway involving T1(dpbt) was inefficient. The energy migration from T1(dpbt) to T1(fod) in [Eu(fod)3dpbt] was not observed. Moreover, upon the excitation of fod, a singlet EET pathway for the sensitization of EuIII luminescence, including the energy migration from S1(fod) to S1(dpbt) was revealed, in addition to the triplet EET pathway involving T1(fod). Under the excitation of dpbt at 410 nm, [Eu(fod)3dpbt] exhibited an absolute quantum yield for EuIII luminescence of 0.59 at 298 K. This work provides a solid and elegant example for the concept that singlet EET pathway could dominate the sensitization luminescence of EuIII in some complexes. 相似文献
It is shown that the complexation of the (R)-MTPA (α-methoxy-α-trifluoromethyl-α-phenylacetic acid) ester of cis-4-tert-butylcyclohexanol with Eu(fod)3 is very similar to that of the corresponding trans-ester and ketones with Eu(fod)3. Further evidence is provided that the MTPA moiety exists as two different rotamers. The LIS technique, used as a tool for structure and conformation elucidation, was found by means of a Monte Carlo error analysis not to be dependent on small experimental errors. 相似文献
A mixture of stereoisomers of 2,4-dimethoxybicyclo[3.3.1]nonan-9-one was prepared, separated by column chromatography and characterized by 60 MHz 1H NMR spectroscopy using Eu(fod)3. A double chair conformation with axial methoxyl groups is established for (1R,2S,4R,5S)-2,4-dimethoxybicyclo[3.3.1]-nonan-9-one on the basis of the J(12), J(2,H-3 exo) and J(2,3 endo) values and the chemical shifts for H-2(4). The conformation of some related compounds is subsequently inferred. 相似文献
The conformation of dipropylacetic, diethylacetic and dimethylacetic acids, (Cn,H2n+1)2— CHCOOH, n = 1–3, in solution in CDCl3, are studied from NMR spectra observed in the presence of europium and ytterbrium chelates, Eu(fod)3 and Yb(fod)3. The 1H and 13C spectra are very similar to those observed for corresponding primary amides previously studied. Molecular conformations in solution are found to be the same for both acids and amides. 相似文献
A new method of conformational analysis has been developed, in which energy minimization calculations are combined with lanthanide-induced shift data. First, exhaustive energy calculations are carried out on the free molecules in order to determine the conformations of lowest energy. Then, the coordinates of all low energy conformations or pairs of conformations are used in the pseudocontact shift equation for lanthanide-induced shifts in order to find which of the theoretically obtained conformation(s) gives the best agreement with experiment. The molecules complexed to the lanthanide shift reagent were N,N-diisopropylformamide (DIPF) and N,N-diisopropylacetamide (DIPA). Two different lanthanide shift reagents were used, Eu(fod)3
1 Fod is the anion of 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione-d27.
and Pr(fod)3, in order to check the validity of the method. Proton magnetic resonance spectra were taken at 6 °C in carbon tetrachloride solution. The principal conformation found was different for each amide. DIPF was found to exist as a mixture of I (39 mol%) and II (61 mol%) with Eu(fod)3, and a mixture of I (37%) and II (63%) with Pr(fod)3. DIPA was found to exist as a mixture of I (79%) and IV (21%) with Eu(fod)3 and a mixture of I (87%) and IV (13%) with Pr(fod)3. For both molecules, the two conformations of lowest computed energy were also the pair which gave the best fit to the lanthanide shift reagent data. The location of the principal magnetic axis of the complex was found to lie between 0° and 14° from the lanthanide atom–oxygen atom bond axis. The technique of combining lanthanide shift reagent data with energy calculations shows great promise in conformational analysis. 相似文献
The effect of the electronic excitation of the -diketonate Eu(fod)3 (fod is 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyloctanedione-3,5) on complexation with 1,10-phenanthroline (phen) in benzene solutions was studied. The excitation of the f–f transitions of Eu3+ increased the stability of the Eu(fod)3 · phen complex, thus providing direct evidence for the involvement of the 4f shell of Eu3+ in chemical bonding. The thermodynamic parameters of complexation were determined. The temperature quenching of Eu(fod)3 · phen luminescence was studied. 相似文献
Eu(fod)3 shift reagent was used to simplify PMR spectra from isomeric mono-, di and trimethoxybenzaldehydes. Deshielding gradients, obtained by plotting induced shift vs. molar ratio of [Eu(fod)3]/[substrate] made it possible to assign methoxyl proton signals to the correct positional substituent in polymethoxylated benzaldehydes. Anomalous upfield shifts for the aldehydic protons of 2,6-dimethoxy- and 2,4,6-trimethoxybenzaldehyde were observed with Eu(fod)3 Various instances of long-range (5J) proton coupling between the aldehydic proton and a meta-proton provide insight to the geometry of the substrate in the complexed state with Eu(fod)3. Di- and trimethoxybenzaldehydes are important precursors for the synthesis of the correspondingly methoxylated amphetamines which are of pharmacological and forensic interest because of abuse and illicit manufacture. 相似文献
The study of the 1H n.m.r. spectra of a series of 2-alkylidenehydrazono-3-methyl-2,3-dihydrobenzothiazoles in the presence of Eu(fod)3 shows that the site of coordination of the lanthanide complex at the two nitrogen atoms of these azines varies as a function of either steric or polar factors. The use of Eu(fod)3 also makes it possible to determine the Z or E configuration of these compounds, as well as their isomer ratio in different solvents. 相似文献
The equimolar mixtures of typical lanthanide shift reagents such as Eu(fod)3, Pr(fod)3 or Yb(fod)3 with silver trifluoroacetate, previously used to induce paramagnetic shifts in the 1H NMR spectra of alkenes, have been successfully applied to simple aromatic hydrocarbons such as benzene, toluene, ethylbenzene and xylenes. In benzene and p-xylene the signals of all the aromatic protons are shifted identically. In other substituted benzenes the magnitude of the induced shift depends on the distance between the proton and the substituents. In addition, the different behaviour of the signals of the methyl groups in meta-and para-xylene on the addition of the complex shift reagent allows the quantitative analysis of the two xylenes in their mixtures. 相似文献
Lanthanide induced shifts using Yb(fod)3 and Pr(fod)3 were used for the signal assignments of the 13C spectra of the 1,4-benzodiazepines diazepam, desmethyldiazepam, prazepam and flurazepam, and for characterizing their solution conformation with respect to the substituents at N-1 and C-5. The phenyl substituent at C-5 is found to be nearly coplanar with the π-bond between C-5 and N-4, and the substituents at N-1 seem to be orientated towards the carbonyl group with dihedral angles of either 60° or 120° between the bonds N-1 and C-2 and C-12 and C-13. The metal ions seem to bind to O-2 with metal-oxygen distances between 0.19 and 0.26 nm and bond angles between 117° and 167°. Contact shifts induced by Pr(fod)3 are slightly larger than obtained for Yb(fod)3, whereas the latter reagent causes a stronger broadening. 相似文献
The proton magnetic resonance spectrum of 4-t-butyl-5,6-dihydro-4H-pyran has been analyzed with the aid of the paramagnetic shift reagent Eu(fod)3. All hydrogen-hydrogen spin-spin coupling constants are reported and a conformation is suggested which is consistent with these data. 相似文献
The synthesis of the lanthanide chelates of α′-(trifluoromethyl)polyfluoroalkyl β-diketones Ln {CF3CF2[CF2OCF(CF3)]n COCHCOC(CH3)3}3 [ 1 , n=1; Ln=Eu (1a) , Pr (1b) , Nd (1c) , Sm (1d) , Gd (1e) , Tb (1f) , Dy (1g) , Er (1h). 2 , n=2; Ln=Eu (2a) , Pr (2b) , Nd (2c) , Sm (2d) , Gd (2e) , Tb (2f) , Dy (2g) and Er (2h) ] was reported and the 1H NMR shift properties were studied using alcohol, ketone, ether and amine as substrates. Compounds 1a, 1b, 2a and 2b induce shifts similar to that induced by Ln(fod)3 (Ln=Eu, Pr). However compounds 1a and 2a are superior to Eu(fod)3, because their 1H signal shifts to higher field in the presence of substrate than that of Eu(fod)3, does. For example, Δh for 1a and 2a is close to zero ppm in the presence of alcohol. A very satisfactory first order spectra can be obtained using 1a, 2a, 1b and 2b as 1H NMR shift reagents. 1c, 1f, 1g, 2c, 2f and 2g produce upfield shifts, and 1h and 2h produce downfield shifts. 1c and 2c induce shifts smaller than that of 1b and 2b , whereas 1f, 1g, 1h, 2f, 2g and 2h induce very large shifts. 相似文献
The effect of deuteration of dimethyl sulfoxide on the fluorescence quantum yield, temperature quenching of fluorescence, and its complexation with tris(heptafluorodimethyloctanedionato)europium(III) (Eu(fod)3) in the ground and excited states was studied. It was found that excitation of f–ftransitions in Eu(III) increases the stability of Eu(fod)3complexes with sulfoxides but has a very insignificantly influence on isotope effects. The deuterium effect is displayed to a small extent in altering the quantum yield and is accompanied by a decrease in the efficiency of temperature quenching of Eu(fod)*3fluorescence. 相似文献
At 160 K, the glucopyranosyl ring in 1,6‐dichloro‐1,6‐dideoxy‐β‐d ‐fructofuranosyl 4‐chloro‐4‐deoxy‐α‐d ‐glucopyranoside monohydrate, C12H19Cl3O8·H2O, has a near ideal 4C1 chair conformation, while the fructofuranosyl ring has a 4T3 conformation. The conformation of the sugar molecule is quite different to that of sucralose, particularly in the conformation about the glycosidic linkage, which affects the observed pattern of intramolecular hydrogen bonds. A complex series of intermolecular hydrogen bonds links the sugar and water molecules into an infinite three‐dimensional framework. 相似文献
Polyaromatic ether-ketone resins with potentially open structures which are possibly useful as membranes were prepared from diphenyl ethers with alkyl substitutions in the ortho positions and isophthaloyl or terephthaloyl chloride by Friedel–Craft-type polymerization. These polymers are soluble in such solvents as DMF, DMA, and CHCl3, and can be cast into colorless transparent films. 相似文献