Lanthanide-induced Shifts Research Articles

Conformational analysis. Part 6. A lanthanide-induced shift nuclear magnetic resonance investigation of steric effects in mesitaldehyde and 2,4,6-trimethylacetophenone

A lanthanide-induced shift (L.I.S.) n.m.r. Investigation of the structures in solution of mesitaldehyde (1) and 2,4,6-trimethylacetophenone (2) has been performed. The use of the crystal structure geometry of the mesitaldehyde–perchloric acid complex was unsatisfactory and no reasonable fit to the L.I.S. Data was achieved. In contrast, use of a model geometry in which steric relaxation (of the methyl groups) was allowed gave good agreement. The formyl group is co-planar with the benzene ring, but the CCC angles to the adjacent methyl groups are increased (to 126°) to relieve steric interactions. In contrast, in (2) the acetyl group has a dihedral of 60–90° with the aromatic ring whilst the methyl CCC angles are unaffected. The lanthanum(III) diamagnetic complexation shifts further illustrate the lack of conjugation of the carbonyl group with the aromatic ring in (2) compared with (1).

The complexation of calcium(II) and lanthanide(III) cations with the phosphate substitute (carboxymethoxy)succinate (CMOS), as studied by magnetic resonance spectroscopy

AbstractThe complexation of trisodium (carboxymethoxy)succinate (Na3CMOS) with calcium(II) and with lanthanide(III) cations has been studied using NMR spectroscopy. Structural information has been obtained from lanthanide‐induced shifts (LIS), T1 relaxation rate enhancements and vicinal 1H coupling constants. CMOS forms 1:1 and 1:2 complexes in which it mainly acts as a tetradentate ligand via the three carboxylate groups and the ether oxygen. LIS measurements on non‐racemic mixtures of Na3CMOS indicate self‐association of the Ln(III) complexes at [CMOS]0 > 0.01 M.

Preparation and photochemical behaviour of 2,3,4,5,6-pentafluorophenylazo-benzene and - 4′-metoxybenzene

Pentafluoronitrosobenzene reacts readily with aniline and with p-methoxyaniline to give the corresponding 2,3,4,5,- 6-pentafluoroazobenzenes (1a and 1b) in good yield. Minor components detected by n.m.r, spectroscopy in the analytically pure products are shown by a combination of lanthanide-induced shift studies and photochemical reactions to be the cis -azo compounds these cis -azo compounds are unusually stable in the dark, with half lives ranging from 19h to > 100 days at room temperature.

Structural information from chemical shifts in lanthanide complexes

The relationship between lanthanide-induced shifts and molecular structure and the assumptions necessary for its ready application is reexamined. A method is presented for extracting the structural information contained in lanthanide-induced shifts of the axially symmetric type. The new method requires data on at least two nuclei within the same ligand in complexes with at least two lanthanides. It eliminates the requirement to know or make assumptions regarding the lanthanide crystal field coefficients. The application of the method demonstrates that some peculiarities in data correlations, interpreted earlier in terms of structural changes along the lanthanide series, are due to variations in the crystal field coefficients.

The Conformations of Several 1-Phenylethyl and 1-Phenylpropyl Aryl Sulfoxides. Evidence for Attractive Aryl/Aryl Interaction

Abstract The conformations of the diastereoisomers of 1-phenylethyl phenyl (1), 1-phenylethyl p-tolyl (2), 1-phenylpropyl phenyl sulfoxides (3) were studied by NMR spectroscopy, largely by means of the computer simulation of the lanthanoid-induced shifts. It has been suggested that the rotamer in which the aromatic group (Ar) is 4C_6H_5CH(R)–SO–Ar& 1:R=& &CH_3,& Ar=&C_6H_5 & 2:& &CH_3,& &C_6H_4CH_3(p) & 3:& &C_2H_5,& &C_6H_5 gauche to the phenyl (Ph) and anti to the alkyl (R) group is most populated in the conformational equilibria of (RS/SR)-1, 2, 3, and (RR/SS)-3. For (RR/SS)-1 and 2, on the other hand, the most important contributor has been suggested to be the rotamer in which Ar is flanked by Ph and R. The results have been discussed in the light of the presence of attractive interactions between relevant groups.

Structure elucidation with lanthanide-induced shifts. 15. Blocking groups for polyfunctional compounds

This article assesses the effectiveness of silyl ethers as blocking groups for hydroxyl groups in shift reagent work. The chemical preparation and study of derivatives of a series of monofunctional alcohols was undertaken to analyze the molecular structure with lanthanide shift reagents (LSR). Evaluation of derivatives of primary, secondary, and tertiary alcohols were undertaken. Results indicated that the effectiveness at preventing coordination with LSR and the remarkable ease with which this blocking group can be introduced and removed combine to make tert-butyldimethylsilyl ethers the derivatives of choice for shift reagent studies. Results demonstrate that tert-butyldimethylsilyl ethers allow, for the first time, the use of lanthanide shift reagents for reliable and accurate structure evaluation of polyfunctional organic compounds.

ChemInform Abstract: TEMPERATURE DEPENDENCE OF THE LANTHANIDE‐INDUCED SHIFTS, STRUCTURE, AND DYNAMICS OF ADDUCTS OF QUINUCLIDINE AND LN(FOD)3 CHELATES AS STUDIED BY VARIABLE‐TEMPERATURE NMR SHIFT AND RELAXATION MEASUREMENTS

Chemischer InformationsdienstVolume 13, Issue 27 Organoelement Compounds ChemInform Abstract: TEMPERATURE DEPENDENCE OF THE LANTHANIDE-INDUCED SHIFTS, STRUCTURE, AND DYNAMICS OF ADDUCTS OF QUINUCLIDINE AND LN(FOD)3 CHELATES AS STUDIED BY VARIABLE-TEMPERATURE NMR SHIFT AND RELAXATION MEASUREMENTS W. M. M. J. BOVEE, W. M. M. J. BOVEESearch for more papers by this authorJ. H. ALBERTS, J. H. ALBERTSSearch for more papers by this authorJ. A. PETERS, J. A. PETERSSearch for more papers by this authorJ. SMIDT, J. SMIDTSearch for more papers by this author W. M. M. J. BOVEE, W. M. M. J. BOVEESearch for more papers by this authorJ. H. ALBERTS, J. H. ALBERTSSearch for more papers by this authorJ. A. PETERS, J. A. PETERSSearch for more papers by this authorJ. SMIDT, J. SMIDTSearch for more papers by this author First published: July 6, 1982 https://doi.org/10.1002/chin.198227248AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume13, Issue27July 6, 1982 RelatedInformation

ChemInform Abstract: SYNTHESIS OF PYRIDYLALLYLAMINES RELATED TO ZIMELIDINE AND THEIR INHIBITION OF NEURONAL MONOAMINE UPTAKE

AbstractAnaloga des Antidepressivums Zimelidin (I) werden dargestellt.

Structure elucidation with lanthanide-induced shifts. 11. Analysis of alkyl-substituted benzonitriles

The 1H NMR spectra for a series of alkyl-substituted benzonitriles were investigated in the presence of Eu(fod) 3. The experimental lanthanide-induced shifts (LIS) were determined for the 1:1 complexes, and the structures of the complexes were evaluated by comparison of the experimental LIS with values predicted with the pseudocontact equation. The contribution to the observed LIS from contact shifts and complex formation shifts is shown to be small, and excellent structure fits are obtained. The correct structure of a compound can be reliably selected from several possibilities, even if only one of the structural alternatives is available for experimental study.

Temperature dependence of the lanthanide-induced shifts, structure, and dynamics of adducts of quinuclidine and Ln(fod)3 chelates as studied by variable-temperature NMR shift and relaxation measurements

Temperature dependence of the lanthanide-induced shifts, structure, and dynamics of adducts of quinuclidine and Ln(fod)3 chelates as studied by variable-temperature NMR shift and relaxation measurements

Conformational analysis-V.: A lanthanide induced shift (L.I.S.) N.M.R. investigation of conformational isomerism in aromatic aldehydes and ketones

An L.I.S. N.M.R. investigation of conformational isomerism in meta-nitrobenzaldehyde and furan- and thiophene-3-aldehydes, and of the conformation of acetophenone has been carried out. With the diamagnetic (complexation) contributions to the observed shifts removed by means of experiments with La (fod) 3 and the application of our previously-described lanthanide ion complexing model, the pseudo-contact shifts have been used to obtain the precise conformational preferences of the aldehydes. They exist to the extent of 45%, 100% and 80% respectively in the O - trans conformation, findings which are good agreement with the previously-reported values. The L.I.S.'s for acetophenone are in best agreement with a planar molecule, although the definition is not as good in this case. These examples suggest that the L.I.S. technique is of general applicability in the determination of conformer populations and the conformations of aromatic aldehydes and ketones.

Conformational analysis—III: A lanthanide induced shift (LIS) NMR investigation of benzaldehyde, and thiophen- and furan-2-aldehyde

A rigorous error analysis of LIS is described which avoids the use of any normalising atom. This analysis is used to investigate the LIS of benzaldehyde and thiophen- and furan-2-aldehyde. The non pseudo-contact components of the Yb(fod) 3 induced shifts are isolated and found to be appreciable at the carbonyl carbon and the ortho and para carbons. Estimation of the diamagnetic contribution to these shifts with La(fod) 3 allows a precise analysis of the 1H and 13C LiS of these aldehydes without the need to invoke any contact shifts. The lanthanide-complex geometry found is essentially one-site, i.e. 100% population on the unhindered exo side of the carbonyl. The lanthanide is in the molecular plane of the aldehydes with Ln O and Ln.O.C. parameters of ca 2.5A˚and 140°, respectively. This procedure also gives the percent population of the O-cis conformer of furfural as ca 70–75% in CDCl 3 solution.

Conformational analysis—IV: A lanthanide induced shift (LIS) NMR investigation of the conformation and relative conformer energies of trans and cis 2-decalone

The solution conformation of trans-2-decalone and the conformational population of cis-2-decalone has been determined by LIS analysis. The angle of pucker (α) of the ketone ring in trans-2-decalone is 51 ± 2°, identical to that of cyclohexanone, but different from that determined for substituted decalones in the solid state, in which significant flattening of the ring occurs. The steroidal conformer of cis-2-decalone, when the latter is complexed to Yb(fod) 3 in CDCl 3, found to be preferred over the non-steroidal conformer by a ratio of 55:45, in contrast to the preference reported from the low temperature 13C NMR spectrum for the non complexed ketone in CH 2Cl 2. The two determinations can be combined to give the enthalpy difference in favor of the non-steroidal conformer of ca 0.8 kcal mole −1.

Tetrahydroisoxazolo[2,3-d][1,4]benzodiazepinone ring system: synthesis, stereochemistry, and conformation

Reaction of 7-chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one 4-oxide (diazepam 4-oxide) with acrylic esters produces annelated substituted isoxazolidines : 1,3-dipolar cycloaddition is regiospecific, the adducts with methyl crotonate showing a ‘reverse’ direction of addition, in comparison with the ‘normal’ products of the reaction between diazepam 4-oxide and acrylic or methacrylic esters. Structures and conformations of cycloadducts have been assigned by means of 1H n.m.r. spectroscopy, largely by the computer simulation of the lanthanide-induced shifts and broadenings of the n.m.r. spectral lines: a small increase in the conformational rigidity of the seven-membered ring is observed, on going from diazepam to the previously unknown isoxazolobenzodiazepinones. Their structural assignments are supported by the results of catalytic hydrogenation (Raney nickel).

Synthesis of pyridylallylamines related to zimelidine and their inhibition of neuronal monoamine uptake.

Analogues of the antidepressant agent zimelidine [6, (Z)-3-(4-bromophenyl)-N,N-dimethyl-3-(3-pyridyl)allylamine], a selective inhibitor of neuronal 5-hydroxytryptamine reuptake, were synthesized by several routes with the aim of obtaining compounds having a cis configuration (with respect to pyridyl and allylamine). Two methods utilized suitably substituted benzoylpyridines as starting materials. In two other routes, the bromine in 6 was either directly displaced (CN) or converted via the corresponding lithio derivative to H, Cl, I, Me, SiMe3, and SMe. The configurations were determined by UV, 1H NMR, and lanthanide-induced shifts in 1H NMR. The compounds were evaluated as uptake inhibitors by measuring the accumulation of [3H]noradrenaline and 5-hydroxy[14C]tryptamine in mouse brain slices (in vitro and in vivo). Para substitution favored 5-hydroxytryptamine activity and ortho substitution favored NA activity in the cis series. The in vitro effect on 5-hydroxytryptamine was rather insensitive to variations in the para substituent, whereas pronounced effects in vivo were observed only with Cl, Br (6), and I.

The 13C NMR of olefins complexed with a binuclear Ag(I)–Yb(III) chelate

AbstractThe effect of silver ion complexation on the 13C NMR of several rigid olefin structures has been determined. The silver ion induced chemical shifts (AgIS) are not amenable to easy interpretation. Addition of Yb(fod)3 forms binuclear Ag–Yb complexes with the olefin. Lanthanide induced shifts (LIS) fall off rationally with distance from the site of complexation and the averaged position of the lanthanide. The complexes may be used as probes of olefin stereochemistry.

Solvent- and lanthanide-induced shifts in the exact solution of three-proton systems: Case study of 2-t-Butyl-2-cyano-3-phenylcyclobutanone

An exact analysis was carried out for 1H NMR experimental spectra of the three protons attached to the four-membered ring of the title compound in various solvents (carbon tetrachloride, chloroform- d, benzene- d 6, acetone- d 6, all at 60 MHz, and chloroform- d at 80 MHz), then in presence of lanthanide-shift reagents Eu(fod) 3 · d 27 and Pr(fod) 3. Among the four, six, and in some cases eight real frequency solutions, only one is related unequivocally to the true spectral parameters obtained in CDCl 3 (at 60 MHz) δ H 1 = 4.41 ppm, δ H 2 = 3.81 ppm, δ H 3 = 3.44 ppm, J gem = −18.24 Hz, J cis = 10.07 Hz, J trans = 11.14 Hz. We propose that whenever one encounters possible alternatives for the choice of a true solution, the exact analysis of the solvent or lanthanide-induced-shift spectra represents a valid competing approach to the tickling technique.

Structure elucidation with lanthanide-induced shifts. 10. Generation of atomic coordinates: empirical force field calculations vs. other methods

Structure elucidation with lanthanide-induced shifts. 10. Generation of atomic coordinates: empirical force field calculations vs. other methods

Potential causes of erroneous results of analysis of lanthanide-induced shifts: contamination of Ln(fod)3 NMR shift reagents with Ln(fod)3.Mfod and self-association of Ln(fod)3

Potential causes of erroneous results of analysis of lanthanide-induced shifts: contamination of Ln(fod)3 NMR shift reagents with Ln(fod)3.Mfod and self-association of Ln(fod)3

Advanced nuclear magnetic resonance lanthanide probe analyses of short-range conformational interrelations controlling ribonucleic acid structures.

An advanced method was developed for lanthanide-probe analyses of the conformations of flexible biomolecules such as nucleotides. The new method is to determine structure parameters (such as internal-rotation angles) and population parameters for local conformational equilibria of flexible sites, together with standard deviations of these parameters. As the prominent advantage of this method, the interrelations among local conformations of flexible sites may be quantitatively elucidated from the experimental data of lanthanide-induced shifts and relaxations and vicinal coupling constants. As a structural unit of ribonucleic acids, the molecular conformations and conformational equilibria of uridine 3'-monophosphate in aqueous solution were analyzed. The stable local conformers about the C3'-O3' bond are the G+ (phi' = 281 +/- 11 degrees) and G- (phi' = 211 +/- 8 degrees) forms. The internal rotation about the C3'-O3' bond and the ribose-ring puckering are interrelated; 97 +/- 5% of the C3'-endo ribose ring is associated with the G- form while 70 +/- 22% o the C2'-endo ribose ring is associated with the G+ form. An interdependency also exists between the internal rotation about the C4'-C5' bond and the ribose-ring puckering. These short-range conformational interrelations are probably important in controlling the dynamic aspects of ribonucleic acid structures.