Coulometric determination of the moisture content, using modified Fischer reagent with epichlorohydrin

Application of a coulometric method of water titration in the medium of a modified Fischer reagent in which epichlorohydrin is used to shift the equilibrium of sulfur dioxide oxidation by iodine was experimentally substantiated.     

Stéréochimie en pentacoordination. Apport des réactifs inducteurs de déplacement chimique à l'etude de spirophosphoranes à liaison P?H

The NMR spectra of eight spirophosphoranes bearing a P? H bond have been recorded in the presence of europium NMR shift reagent. The spectra are simplified by addition of the europium chelate. The observed displacements in the proton NMR lines allow the assignment of the endo and exo signals in some cases. By addition of the NMR shift reagent, one observes a displacement in the phosphite-spirophosphorane equilibrium in some cases.     

The structure of polymer-supported triphenylphosphine ditriflate: a potentially useful reagent in organic synthesis

The structure of a polymer-supported version of the Hendrickson "POP" reagent, prepared by the reaction of polymer-supported triphenylphosphine oxide 1 with triflic anhydride, is established as an equilibrium mixture of polymer-supported triphenylphosphine ditriflate 3 (delta 79.4 ppm) and polymer-supported phosphonium anhydride 4 (delta 73.3 ppm). The (31)P NMR chemical shift reported previously for 3 is shown to be incorrect.     

NMR位移试剂Eu(fod)~4^-对锍盐^1H和^1^3C NMR的影响

合成了八种新的四氟硼酸二甲基苯基锍，用元素分析和核磁共振对其结构进行了表征。研究了以CDCl~3为溶剂，NMR位移试剂Eu(fod)~4^-对所合成锍盐的^1H和^1^3C NMR的影响。结果表明，Eu(fod)~4^-是一个对锍盐非常有效的位移试剂，且Eu(fod)~4^-对二甲基苯基锍盐之甲基的^1H和^1^3C NMR的位移呈线性关系。     

Aggregation of meso-tetra-(p-sulphonatophenyl)porphine and its cu(II) and zn(II) complexes in aqueous solution

The aggregation of meso-tetra(p-sulphonatophenyl)porphine, an analytical reagent for the determination of metals at low concentration, has been studied over a wide concentration range by both spectrophotometric and (1)H NMR methods. Up to a concentration of about 3 x 10(-4)M, the experimental data were satisfactorily accounted for by a monomer-dimer equilibrium. At higher concentrations, the best fit of the chemical shift data required postulation of a tetramer. Analysis of the experimental data for the Zn(II) complex indicated the occurrence of dimerization at higher concentrations.     

Shift reagent spectra. The automatic determination of relative bound shifts and the automatic assignment of signals in the parent spectrum. Effects of concentration,temperature and solvent on relative bound shifts

In the use of a shift reagent as an aid in the structural elucidation of organic compounds, it is shown that accurate measurements of the shift reagent and substrate concentrations are not needed to determine the relative bound shifts of the substrate and the chemical shifts of the free substrate spectrum with good precision. This is possible whenever the induced shift ratios of nuclei of a given molecule are independent of the shift reagent concentration. This independence has been verified for all the monofunctional compounds described in this paper. The effect of absolute substrate concentration, solvent, temperature and the presence of water on the relative bound shifts is studied using the eight methyl group signals of β-amyrin. The method is demonstrated by its use for structural determinations in the ketoandrostane series.     

Tautomerism of anthraquinones: X. Quinizarin boron complex

Products of reactions of hydroxyanthraquinones with boric acid exist as equilibrium mixtures of tautomeric boron complexes and boric acid esters in which one or two boron atoms are not coordinated to carbonyl groups. Tautomerism is responsible for the appearance of several π_l,π bands in the electronic absorption spectra and considerable differences in the data obtained by different authors. Boron-containing quinizarin derivatives have mostly 1,10-quinoid structures. The use of quinizarin as an analytical reagent for the determination of boron is based on replacement of tautomeric equilibria due to complex formation rather than on coordination-induced red shift of the absorption maximum.     

Nuclear magnetic resonance spectra of psychotherapeutic agents. V*—conformational analysis of 1,3,4,5-tetrahydro-2H-1,5-benzodiazepin-2-ones

The conformational analysis of biologically active lofendazam (7-chloro-5-phenyl-1,3,4,5-tetrahydro-2H-1,5-benzodiazepin-2-one) is carried out by means of lanthanide shift reagent assisted ¹H NMR spectroscopy: the lanthanide induced shift computer simulation suggests that in deuteriochloroform the heterocyclic ring of lofendazam assumes a cycloheptene-like chair conformation, where 1-N moves away from trigonal stereochemistry to a very flattened pyramidal structure. At room temperature the conformational equilibrium is markedly shifted (85%) towards the conformer showing pseudoaxial H-1 and 5-Ph. The remarkable influence of steric requirements in controlling conformation, and the importance of 3- and/or 4-methyl groups in hindering the ring inversion at room temperature, have been verified by conformational analysis of suitable analogous 1,3,4,5-tetraydro-2H-1,5-benzodiazepin-2-ones.     

Nuclear magnetic resonance of 1,4-benzodiazepines. II Stereochemistry of 1,3-dihydro-2H-1,4-benzodiazepin-2-ones by lanthanide shift reagents

The sterochemistry of some 1,3-dihydro-2H-1,4-benxodiazepin-2-ones, employed as psychotherapeutic agents, is deduced by proton magnetic resonance using the paramagnetic shift reagent Eu(fod)₃. the lanthanide induced shifts are computer simulated on the basis of the geometric parameters of the protons in different model structures, having intermediate conformations between a cycloheptadiene- and a cyclohepatatriene-like system. N-Desmethyldiazepam shows a conformational equilibrium between two pseudoboat forms, while the 1-alkyl substituted derivatives exist, at room temperature, in olny one boat cycloheptatriene-like conformation.     

The protonated 4,4'-diaminotriphenylmethyl cation as a reagent and cyclohexanone as an absorbant for sulphur dioxide determination

Protonated 4,4'-diaminotriphenylmethyl cation, DATM, has been investigated as a colorimetric reagent for the determination of sulphur dioxide. The bisulphite addition compound with formaldehyde alkylates a primary arylamine group in the protonated reagent to re-establish resonance, and hence produces a colour that is proportional in intensity to the concentration of either bisulphite or formaldehyde (the other being in excess). The large bathochromic spectral shift results in a negligible blank correction. Cyclohexanone in aqueous solution has been found to stabilize bisulphite solutions for up to 6 hr. The stabilization by cyclohexanone has been compared with stabilization by tetrachloromercurate(II). The Beer-Lambert law is obeyed with good precision for both sulphite and formaldehyde determination.     

Wasserstoff/Deuterium-Isotopeneffekte bei Europium-Verschiebungsexperimenten and Allencarbonsäureestern

Hydrogen/Deuterium Isotope Effects on Europium Induced Chemical Shifts of Allenic Esters It is shown by ¹H-NMR. experiments, that in the presence of europium shift reagents, mixtures of allenic esters and their partially deuterated counterparts give rise to α-, β-, γ, and δ-H/D isotope effects (cf. Table and Fig. as well as formula 6 for assignment). The measured effects (0.4 to 2.2%) are mainly attributable to C, H/C, D bond length differences which influence the complexation constant between the shift reagent and the substrate as well as the s-cis/s-trans conformational equilibrium of the allenic esters.     

A novel method for correlation of substituent constants in some aromatic esters using the shift reagent Eu(fod)3

The lanthanide induced chemical shifts of the ester methyl group were studied in eighteen m-, and p-substituted aromatic methyl esters with varying amounts of added shift reagent, Eu(fod)₃. Each time the lanthanide induced shift (LIS) was plotted against the molar ratio of shift reagent (SR)/substrate and a straight line was obtained upto one mole ratio of added shift reagent. The slopes of these plots correlated well with the Hammett's σ constants and yield a value of ?4.95 for the reaction constant ?. The method is therefore one of the simplest ways of correlating the substituent constants in aromatic esters.     

Applications of rare earth complexes as nmr shift reagents in elucidating the structure of organic molecules

The present state of affairs concerning shift reagents is reviewed and some new data on lanthanide-1,10-phenanthroline and lanthanide-2,2'-dipyridyl systems are presented. The use of Pr(TTA)₃ as an NMR shift reagent for benzylic systems has been reviewed and it is concluded that this complex possesses useful properties as a “two-way” shift reagent. Both high field and low field shifts for benzylic protons have been observed.     

The tautomerism of 6-hydroxy-, 6-amino- and 6-acylamino-7-azaindolines

The lactam-lactim tautomerism of 6-hydroxy-7-azaindolines and amino-imine tautomerism of 6-amino- and 6-acylamino-7-azaindolines has been studied by IR and UV spectroscopy. It is shown that the lactam-lactim tautomeric equilibrium of 6-hydroxy-7-azaindolines in contrast to the other analogous N-heteroaromatic compounds is not completely shifted for the lactam. The commensurable amounts of both tautomeric forms can be observed in the solutions of 6-hydroxy-7-azaindolines and it is possible to elucidate the influence of the solvent polarity upon the lactam-lactim tautomeric equilibrium. The tautomeric equilibrium of 6-amino- and 6-acylamino-7-azaindolines is practically completely shifted for the amino form, and even acylation with p-toluene-sulfonic acid does not result in a noticeable shift of the tautomeric equilibrium for the amino form in contrast to the other N-heterocyclic amines.     

Microwave spectroscopy and nuclear magnetic resonance study of the molecular geometry of 2-fluorophenylisocyanate

Analysis of the microwave spectra of the vibrational ground state of 2-fluorophenyl-isocyanate in the gaseous state shows the existence of a single planar cis conformer. Rotational spectra of the excited torsional states out of the plane and spectra of in-plane vibrations have also been studied. MINDO III type theoretical calculations corroborate the experimental results. Similarly, the configuration of 2-fluorophenylisocyanate in the liquid phase has been studied by NMR using the chemical shift reagent, Eu(fod)₃. Induced paramagnetic shifts have been measured on the ¹³C spectra, for different quantities of the reagent. The results clearly show a higher paramagnetic shift for the carbon bonded to the fluorine atom than for the other nuclei of the aromatic cycle (with the exception of the quaternary carbon), indicating the probable presence of the cis isomer.     

Structure elucidation with lanthanide-induced shifts 5. Evaluation of the binding ability of various functional groups

The equilibrium binding constants have been evaluated for the association in CCl₄ of the lanthanide shift reagent. Eu(fod)₃, with a series of adamantane derivatives containing a variety of different functional groups. It is shown that if steric effects are held constant the binding abilities of the adamantane derivatives exhibit a good correlation with the proton affinities of the methyl analogs containing the same functional groups. The results permit the prediction of binding strength of other functional groups with Eu(dpm)₃ as well as with Eu(fod)₃ and thus can be of great assistance in planning and interpreting the results of experiments with lanthanide shift reagents.Part 4:D. J. Raber, M. D. Johnston, jr., C. M. Campbell, C. M. Janks, andP. Sutton, Org. Mag. Res.11, 323 (1978).     

DFTMP, an NMR reagent for assessing the near-neutral pH of biological samples

A new NMR chemical shift standard and pH indicator, difluorotrimethylsilanylphosphonic acid (DFTMP), is described, and the utility of this reagent is demonstrated for in situ determination of pH in complex biofluids. The pH dependence of this reagent allows accurate in situ determination of aqueous solution pH to within an RMSE of 0.02 pH units over a pH range of 5 to 8. Advantages of this reagent over previously described pH-sensitive components include (1) lack of metal binding affinity, (2) minimal disturbance of endogenous spectral regions, and (3) the potential to function as a multinuclear pH indicator and chemical shift reference point for 19F, 1H, and 31P nuclei. This reagent will be generally useful for NMR experiments on biological systems where the pH needs to be accurately measured at the moment of data acquisition.     

Shift reagent 1H NMR study of methoxycoumarins

The complete assignment of the proton chemical shifts of coumarin ( 1 ), all monomethoxy derivatives and the six possible dimethoxyl substituted compounds at the aromatic ring was achieved at 60 MHz in a quantitative study utilizing Pr(fod)₃ as the shift reagent. It was found that in addition to the complexation at the lactone carbonyl a second interaction of the lanthanide shift reagent occurs when two methoxyl groups are found in an ortho distribution. The results are discussed in comparison to data published for flavones in the presence of Pr(fod)₃ shift reagent.     

o-(Pentafluorobenzyloxycarbonyl)benzoyl chloride: a novel electrophoric derivatisation reagent for amino compounds designed for negative ion chemical ionisation mass spectrometry

The synthesis of a novel electrophoric derivatisation reagent, o-(pentafluorobenzyloxycarbonyl)benzoyl chloride, is described. The reagent was tested against selected primary and secondary amino compounds as analytical targets. The derivatives exhibit excellent mass spectral properties under negative ion chemical ionisation (NICI), i.e. reduced fragmentation and thus high ion current for the targeted m/z during analysis. Since the reagent bears a pentafluorobenzyl ester group, resulting mass NICI mass spectra were expectedly dominated by dissociative resonance electron capture typically observed with these compounds. The reagent is suitable for detecting volatile primary and secondary amines with high sensitivity. Background is reduced by a shift in detected m/z and retention time, as demonstrated for the analysis of the drug methylphenidate from human plasma.     

Colour change and tautomerism of some azo-indicators on complex formation with cyclodextrins

Complex formation of methyl orange and some other azobenzene derivatives with cyclodextrins has been studied in acidic and alkaline solutions by a spectrophotometric method. A correlation has been established between the stability constants of the complexes, the spectral changes accompanying complex formation and a tautomeric equilibrium between protonation on the azo and dimethylamino group. Our own results have been compared with some literature data, and equilibrium constants for the tautomeric rearrangement have been calculated. It has been demonstrated that the significant colour changes observed with the protonated forms only (and not with the corresponding bases) is really caused by a shift of the tautomeric equilibrium.