Variable-temperature Nuclear Magnetic Resonance Research Articles

Solution structure and dynamics of cyclic and acyclic cholinergic agonists

Two classes of nicotinic cholinergic agonists, which vary in flexibility and electronegativity, have been synthesized, and their structural and dynamic properties have been studied with nuclear magnetic resonance (NMR) spectroscopy. Although the compounds are chemically identical except for the presence or absence of one cyclicizing C--C bond, single channel recording and radioligand binding studies have shown that the cyclic compounds are considerably more potent than the acyclic derivatives (McGroddy, K.A., A.A. Carter, M.M. Tubbert, and R.E. Oswald. 1993. Biophys. J. 64:325-338). Using one- and two-dimensional NMR spectroscopy, we have shown that these molecules exist in two distinct stable conformers, which differ in the orientation of the amide bond. The cyclic 1,1-dimethyl-4-trifluoroacetyl-piperazinium iodide and its trifluoromethyl derivative compounds are symmetric, and the two conformers are of equal energy. The acyclic N,N,N,N'-tetramethyl-N'-acetylethylene-diamine iodide (TED) and its trifluoromethyl derivative derivatives, however, populate two energetically unequal solution conformations. Using variable temperature NMR spectroscopy on these molecules and their uncharged precursors, we have characterized the energetics of amide bond isomerization and have distinguished steric and electrostatic contributions to the equilibrium between the two conformers. The more populated TED conformer has the amide methyl group trans to the carbonyl oxygen, and it is stabilized by an electrostatic attraction between the partially negative carbonyl oxygen and the positively charged quaternary amine nitrogen. As discussed in the accompanying paper (McGroddy, K.A., A.A. Carter, M.M. Tubbert, and R.E. Oswald. 1993. Biophys. J. 64:325-338), the differences in the stable solution structures of the TED derivatives and their interconversion kinetics may be of biological significance.

Synthesis, characterisation and variable-temperature nuclear magnetic resonance of bis(bipyridine)ruthenium complexes containing dihydrazone ligands

A series of dihydrazone and substituted dihydrazone derivatives of biacetyl and of hydrazone and phenylhydrazone derivatives of 2-acetylpyridine bind to [Ru(bipy)2Cl2] to give [Ru(bipy)2(L–L)][PF6]2 complexes {bipy = 2,2′-bipyridine; L–L = biacetyl di(phenylhydrazone)1a, biacetyl di[methyl(phenyl)hydrazone]1b, biacetyl di(o-tolylhydrazone)1c, biacetyl di(dimethylhydrazone)1d, biacetyl dihydrazone 1e, biacetyl di(benzaldehyde azine)1f, 2-acetylpyridine phenylhydrazone 1g, or 2-acetylpyridine hydrazone 1h}. The structures of all complexes have been determined using IR, UV/VIS, NMR and microanalysis. The proton NMR spectra of 1a–1c show an unusual dependence on probe temperature with broadened aromatic resonances, sharpening at both high and low temperature in the case of 1b and 1c. No emission was observed for complexes with two hydrazone moieties, whereas it was observed for 1g and 1h with one hydrazone. The molecular structure of 1a has been determined and shows a hydrazone phenyl group lying over each of the bipyridyl rings: space group C2/c, a= 25.895(3), b= 10.505(1), c= 17.431(2)A, β= 106.03(2)° and Z= 4.

The structure and conformation of [1,1′-bipyrrolidine]-2,2′-dithione

The molecular structure of [1,1′-bipyrrolidine]-2,2′-dithione ( 1) has been determined by single-crystal X-ray crystallography. The compound crystallizes in the orthorhombic system: Pbca, a = 9.314(12), b = 13.213(2), c = 16.321(3) Å, V = 2008.4 Å 3, Z = 8, D c = 1.33 g cm −3, R = 0.042 for 2583 unique reflections and 140 variable parameters. The dihedral angle between the mean planes of the rings is 104.2(7)°. The conformations of the rings themselves are presented in terms of normalized linear combinations of the primitive envelope and twist forms. Certain bond distances are rationalized in terms of the screening of nuclear repulsion. The rorational barrier about the NN bond has been calculated from variable temperature nuclear magnetic resonance (NMR) measurements in deuterated toluene as 73 kJ mol −1. All measured parameters are contrasted with those found in the literature for the 2,2′-dioxo analogue ( 2), for which the rotational barrier has been determined in this work as 44 kJ mol −1.

Carnosol. Crystal structure, absolute configuration, and spectroscopic properties of a diterpene

The structure and absolute configuration of naturally occurring Carnosol have been investigated by X-ray analyses. Crystal data are: orthorhombic P21212;a=15.762(1),b=13.755(1),c=7.7747(7) A,Z=4,V=1688.2 A3, andR=0.031 (2569 reflections). The absolute configuration is established at a significance level better than 0.995 according to HamiltonsR-factor test and is in accordance with that predicted experimentally by chemically means. Correlation of the solid-state IR pattern of the regions sensitive to hydrogen bonding (CO and OH stretching bands) with the X-ray crystal structure is excellent and shows, that even weak inter- and intramolecular hydrogen bonds may be unambiguously identified by IR spectroscopy. The variable-temperature nuclear magnetic resonance studies (NMR) show that the twinning of the signals from the isopropyl methyl protons cannot be due to hindered rotation but can be ascribed magnetic nonequivalence induced by the chiral centers.

Cyclophanes. V. Synthesis and conformational analysis of novel heterocyclophanes containing 2,5-bis(5-oxazolyl)furan units.

Two novel heterocyclophanes, dioxazolo[32](2, 5)furanometacyclophane (5) and the higher homolog (6) possessing 2, 5-bis(5-oxazolyl)furan units, were synthesized by the one-pot coupling reaction of 1, 3-bis(2-isocyano-2-tosylethyl)benzene (3) with furan-2, 5-dicarbaldehyde (4). On the basis of the variable-temperature nuclear magnetic resonance (VT-NMR) spectra of 5, the conformations in solution both at room temperature and at -18°C could be assigned as a syn form, and the energy barrier (ΔG〓) for the conformational flipping at the coalescence temperature (Tc=12°C) was determined to be 58.0 kJ/mol, which is lower than that of dioxazolo[32]metacyclophane (1a). Therefore, it was suggested that the oxygen atom of 5 with its lone pair is less bulky with respect to the conformational change than the aromatic carbon-hydrogen bond of 1a.

ChemInform Abstract: Recent Developments in NMR Spectroscopy of Organometallic Compounds

Publisher Summary This chapter discusses the recent developments in nuclear magnetic resonance (NMR) spectroscopy of organometallic compounds. The experimental aspects and some results from multinuclear NMR spectroscopy and some examples from solid-state NMR spectroscopy are examined. Modern NMR spectrometers have powerful routines to modify the free induction decay and hence the resolution and signal/noise ratio. Homonuclear decoupling has long been established as a valuable tool in determining which nuclei are coupled. The Nuclear Overhauser Enhancement (NOE) is one of the most valuable tools in determining the connectivity among protons and, to a lesser extent, between protons and other nuclei. The sensitivity of an NMR experiment depends on the population difference among the energy levels. The Incredible Natural Abundurice Double Quantum Transfer Experiment (in adequate) pulse sequence was originally designed to detect 13 C – 13 C coupling without the confusion of the 13 C singlets due to the species without adjacent 13 C atoms. The normal π /2 pulse excites nuclei over a wide range of frequencies. Broadband decoupling has been applied for many years to obtain X-nuclei NMR spectra without 1 H coupling. Until very recently, variable-temperature solid-state NMR spectroscopy with magic angle spinning has been restricted close to room temperature because of the great difficulty of spinning the sample at high speed.

Structural studies of oxalohydroxamic acid by single crystal X-ray diffraction and spectroscopic methods

The structure of oxalohydroxamic acid has been investigated by X-ray and spectroscopic analyses. It has been shown that oxalohydroxamic acid exists in the oxamic form in the solid as well as in solution. The variable-temperature nuclear magnetic resonance (NMR) studies reveal an exchange of OH and NH protons, the exchange being faster at higher temperatures. The kinetic and the thermodynamic parameters such as the rate constant (K), the free energy of activation $(\Delta G^{\ddagger})$, and the energy of activation $(E_a)$ for the exchange process have been obtained. The compound crystallizes in the monoclinic space group $P2_1/c$ with a=5.208, b=3.864, $c=11.482 \AA$ ,$\beta = 111.45^0$, and Z=2. The structure was solved with MULTAN 80. The refinement by block diagonal least squares and Fourier methods provided R=0.035. There is strong hydrogen bonding between the molecules which form dimer

Cyclophanes. I. Preparations and conformational properties of dioxazolo[32]metacyclophane and related compounds.

The one-pot coupling reactions of bis (2-isocyano-2-tosylethyl) benzenes (5) with phthalaldehydes (11) afforded dioxazolo [32] cyclophanes (12a, 12d, 12e, 12f, and 12h), bis (naphth [2, 1-d] -oxazol-4-yl) benzenes (13a-c), and tetraoxazolo [34] parametacyclophane (14) as 1 : 1, 1 : 2, and 2 : 2 adducts, respectively. On the basis of the variable-temperature nuclear magnetic resonance (VT-NMR) spectra of dioxazolo [32] metacyclophane (12e), 12e in solution at room temperature exists in a syn form and the energy barrier to the conformational change (ΔG_??_) at the coalescence temperature (Tc = 38 °C) is determined to be 64.5 kJ/mol, which is higher than that of parent [32] metacyclophane (1). Therefore, it was suggested that the annelations of two oxazole rings to the two methylene bridges of 1 significantly affected the mobility of the benzene rings of 12e.

Utilization of protopine and related alkaloids. XVI. Nuclear magnetic resonance spectroscopy on the cycloadducts of anhydromethylberberines with dienophiles.

Proton assignments of the cycloadducts of anhydromethylberberines with dienophiles have been made by reference to the carbon-13 nulcear magnetic resonance spectra. The correlation between the molecular geometries and the proton chemical shifts is discussed on the basis of the variable-temperature nuclear magnetic resonance spectral data.

ChemInform Abstract: HIGH PRESSURE NMR KINETICS. 19. VARIABLE PRESSURE AND TEMPERATURE NUCLEAR MAGNETIC RESONANCE AND VISIBLE SPECTROPHOTOMETRIC STUDIES OF LANTHANIDE IONS IN DIMETHYLFORMAMIDE: SOLVATION AND SOLVENT EXCHANGE DYNAMICS

Chemischer InformationsdienstVolume 14, Issue 43 Physical Organic Chemistry ChemInform Abstract: HIGH PRESSURE NMR KINETICS. 19. VARIABLE PRESSURE AND TEMPERATURE NUCLEAR MAGNETIC RESONANCE AND VISIBLE SPECTROPHOTOMETRIC STUDIES OF LANTHANIDE IONS IN DIMETHYLFORMAMIDE: SOLVATION AND SOLVENT EXCHANGE DYNAMICS D. L. PISANIELLO, D. L. PISANIELLOSearch for more papers by this authorL. HELM, L. HELMSearch for more papers by this authorP. MEIER, P. MEIERSearch for more papers by this authorA. E. MERBACH, A. E. MERBACHSearch for more papers by this author D. L. PISANIELLO, D. L. PISANIELLOSearch for more papers by this authorL. HELM, L. HELMSearch for more papers by this authorP. MEIER, P. MEIERSearch for more papers by this authorA. E. MERBACH, A. E. MERBACHSearch for more papers by this author First published: October 25, 1983 https://doi.org/10.1002/chin.198343061AboutPDF 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 onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume14, Issue43October 25, 1983 RelatedInformation

High pressure NMR kinetics. 19. Variable pressure and temperature nuclear magnetic resonance and visible spectrophotometric studies of lanthanide ions in dimethylformamide: solvation and solvent exchange dynamics

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHigh pressure NMR kinetics. 19. Variable pressure and temperature nuclear magnetic resonance and visible spectrophotometric studies of lanthanide ions in dimethylformamide: solvation and solvent exchange dynamicsDino L. Pisaniello, Lothar Helm, Pierre Meier, and Andre E. MerbachCite this: J. Am. Chem. Soc. 1983, 105, 14, 4528–4536Publication Date (Print):July 1, 1983Publication History Published online1 May 2002Published inissue 1 July 1983https://doi.org/10.1021/ja00352a005RIGHTS & PERMISSIONSArticle Views169Altmetric-Citations64LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

ChemInform Abstract: CONFORMATIONS OF DIPHOSPHINOAMINES: VARIABLE‐TEMPERATURE NUCLEAR MAGNETIC RESONANCE AND X‐RAY CRYSTALLOGRAPHIC STUDIES

Chemischer InformationsdienstVolume 13, Issue 5 Physical Organic Chemistry ChemInform Abstract: CONFORMATIONS OF DIPHOSPHINOAMINES: VARIABLE-TEMPERATURE NUCLEAR MAGNETIC RESONANCE AND X-RAY CRYSTALLOGRAPHIC STUDIES R. KEAT, R. KEATSearch for more papers by this authorL. MANOJLOVIC-MUIR, L. MANOJLOVIC-MUIRSearch for more papers by this authorK. W. MUIR, K. W. MUIRSearch for more papers by this authorD. S. RYCROFT, D. S. RYCROFTSearch for more papers by this author R. KEAT, R. KEATSearch for more papers by this authorL. MANOJLOVIC-MUIR, L. MANOJLOVIC-MUIRSearch for more papers by this authorK. W. MUIR, K. W. MUIRSearch for more papers by this authorD. S. RYCROFT, D. S. RYCROFTSearch for more papers by this author First published: February 2, 1982 https://doi.org/10.1002/chin.198205066Read the full textAboutPDF 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 onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume13, Issue5February 2, 1982 RelatedInformation

ChemInform Abstract: EVIDENCE FOR FIVE‐COORDINATION IN TITANIUM(IV) COMPLEXES. A NUCLEAR MAGNETIC RESONANCE INVESTIGATION

Diketonato complexes of titanium(IV), (X3Ti(dik))2 (X = Cl, Br; dik = anions of dipivaloylmethane and benzoylacetone), of apparent five-coordinate stoichiometry have been prepared and investigated in nitrobenzene solutions using the variable temperature nuclear magnetic resonance technique. The nmr spectra reveal the existence of two equilibrium species; a five-coordinate X3Ti(dik) and a six-coordinate X2Ti(dik)2 complex. The data are interpreted in terms of a symmetric dissociation of the six-coordinate titanium(IV) dimer, (X3Ti(dik))2, into two five-coordinate monomers which then undergo a disproportionation reaction to the four-coordinate titanium tetrahalide and the six-coordinate X2Ti(dik)2 species.

Evidence for five-coordination in titanium(IV) complexes. A nuclear magnetic resonance investigation

Diketonato complexes of titanium(IV), (X3Ti(dik))2 (X = Cl, Br; dik = anions of dipivaloylmethane and benzoylacetone), of apparent five-coordinate stoichiometry have been prepared and investigated in nitrobenzene solutions using the variable temperature nuclear magnetic resonance technique. The nmr spectra reveal the existence of two equilibrium species; a five-coordinate X3Ti(dik) and a six-coordinate X2Ti(dik)2 complex. The data are interpreted in terms of a symmetric dissociation of the six-coordinate titanium(IV) dimer, (X3Ti(dik))2, into two five-coordinate monomers which then undergo a disproportionation reaction to the four-coordinate titanium tetrahalide and the six-coordinate X2Ti(dik)2 species.

Configurational rearrangements in cis-M(AA) 2X 2, cis-M(AA) 2XY, and 3. The cis-M(AA) 2X 2 system - diastereotopic probe on the terminal AA groups [1, 2

The series complexes Ti(dibm) 2X 2 [X = F, Cl, or Br; dibm = anion of diisobutyrylmethane], M(dibm) 2Cl 2 [M = Sn or Ge], and Ti(dpm) 2X 2 [X = F, Cl, or Br; dpm = anion of dipivaloylmethane] have been prepared and investigated by variable temperature nuclear magnetic resonance (NMR) spectroscopy. Except for Ti(dpm) 2F 2 and Ti(dpm) 2Cl 2, the above complexes have not been reported previously. NMR spectra indicate that these complexes possess the cis-diastereomeric configuration. Diastereotopic isopropyl methyl probes have been incorporated into the dibm ligand to follow the steric course of the configurational rearrangement taking place in these C 2-type complexes. The NMR spectra have been analyzed in terms of the permutational and topological and mechanistic analyses reported earlier. It is shown that the rearrangements can be rationalized in terms of the A 5 averaging set, and it is argued that the likely sole reaction pathway is a twist process about the two opposite C 3(i′) and C 3(‴) axes of the octahedral skeleton. Approximate rate constants for the configurational changes are reported: ligand labilization follows the order acac < dibm < dpm for the Ti(dik) 2Cl 2 complexes, and Cl < Br ∼ for the Ti(dibm) 2X 2 systems.

CYCLOPHANES VI. TEMPERATURE DEPENDENT CONFORMATIONS OF 3,6-DIKETO[8](1,4)NAPHTHALENEOPHANE AND 3,6-DIKETO[8] (2,5)FURANOPHANE

Abstract A temperature dependent conformational change in the aliphatic chain of 3,6-diketo[8]naphthalenophane is observed by variable temperature nuclear magnetic resonance spectroscopy; the energy of activation for the process is 9.4±0.2 Kcal/mole. For 3,6-diketo[8](2,5)furanophane the conformational change of the chain is more facile than that of the ring with a conservative upper limit for ring rotation of about 9.1 Kcal/mole.

Preparation and variable-temperature nuclear magnetic resonance studies of tris(diphenyltrifluoromethylphosphine)platinum(0)

Preparation and variable-temperature nuclear magnetic resonance studies of tris(diphenyltrifluoromethylphosphine)platinum(0)

Addition reactions of heterocyclic compounds. Part LIV. Rotational isomerism of 6-aralkyl-5-oxidovinylphenanthridiniums: an investigation by variable temperature nuclear magnetic resonance spectroscopy

5-Oxidovinylphenanthridiniums with 6-aryl substituents exhibit cis–trans and rotational isomerism. The nature of the species involved has been elucidated by variable temperature n.m.r. spectroscopy and by observation of the properties of related compounds.

Chemistry of methyltitanium trichloride. II. Variable-temperature nuclear magnetic resonance and infrared spectra of some complexes of Methyltitanium trichloride and of titanium tetrachloride with unsymmetrical bidentate ligands

Chemistry of methyltitanium trichloride. II. Variable-temperature nuclear magnetic resonance and infrared spectra of some complexes of Methyltitanium trichloride and of titanium tetrachloride with unsymmetrical bidentate ligands

The chemistry of methyltitanium trichloride. Part III. Oxidation of six-co-ordinate complexes of methyltitanium trichloride. Variable temperature nuclear magnetic resonance and infrared spectra of complexes of methoxytitanium trichloride with bidentate ligands

On oxidation, the pseudo-octahedral complexes of methyltitanium trichloride with symmetrical (X = Y) or unsymmetrical (X ≠ Y) substituted ethane ligands, TiCl3Me,XCH2CH2Y (X,Y = OMe, NMe2, or SMe), give the corresponding complexes of methoxytitanium trichloride, TiCl3OMe,XCH2CH2Y. Studies by variable-temperature n.m.r. spectroscopy indicate that most of the latter complexes are undergoing exchange between meridional and facial forms at room temperature. Electronic factors affecting the lability of the complexes of titanium(IV) in such exchange processes are discussed. In their i.r. spectra, the complexes of methoxytitanium trichloride all show strong bands ca. 1100 and 600 cm–1 which may be assigned to ν(C–O) and ν(Ti–O) respectively.