Ion-dipole interactions of macrocyclic ethers using13C dipole-dipole relaxation time measurements. Part XI: The complexation of 1,4,7,10,13,16-hexaoxa-2,6-dioxocyclooctadecane with Ca2+ in CD3OH

The association constants,K _a, of Ca²⁺ complexes with the nonequivalent binding site macrocycle,1,4,7,10,13,16-hexaoxa-2,6-dioxocyclooctadecane, were determined in CD₃OH solution using¹³C dipole-dipole relaxation time,T ₁ ^DD , studies. The measurements ofT ₁ ^DD of the macrocyclic backbone for different stoichiometries (n:m) of complex formation were conducted under extreme narrowing experimental NMR conditions. The general equilibria given with 1/K _a[L ₀] ^n+m–1 = (1-nP) ⁿ (1-mP) ^m /P was used for identical cation and macrocyclic ether-ester concentrations in CD₃OH and the association constants found were comparatively small depending on the cyclic ether-ester segments. The logK _a values varied from 1.09 to 0.231 for 1 :1 and from 2.43 to 3.61 for 1 : 2 and from 2.29 to 4.24 for 2 : 1 ligand to cation complex stoichiometries.Presented at the Sixth International Seminar on Inclusion Compounds, Istanbul, Turkey, 27–31 August, 1995.     

A technique for the quantitative measurements of signal intensities in cellulose-based transformer insulators by13C CPMAS NMR

A full investigation of the¹³C CPMAS relaxation times for samples of virgin and aged insulation paper material has revealed the quantitative aspects of the CPMAS technique. We observe, as have others, that the peak due to methyloxy carbon C₆ in the solid-state spectrum is reduced in intensity, compared with the other peaks, by ca. 7%. This is a direct result of the difference in relaxation times for the different carbon nuclei. It is shown that simplifying assumptions concerning the relative magnitude of the relaxation times used in the analysis of cross-polarization dynamics are not valid in these materials. In particular, the¹³C spin-lattice relaxation time in the rotating frame (¹³C T₁     

Solid-state C NMR and SAXS characterization of the amorphous phase in low-molecular weight poly(ethylene oxide)s

Low-molecular weight poly(ethylene oxide)s (PEO) with extended, once or twice folded chains (as characterized by SAXS), were investigated by solid-state ¹³C NMR spectra measured under conditions to detect only the signal of the narrow line component. The direct detection and integrated intensities of the signals from hydroxy-terminated chain-end units in these spectra confirm that the narrow line component corresponds to the noncrystalline (amorphous) phase. The NMR line of PEO carbons adjacent to the hydroxy end-groups was used as an intensity standard to obtain information on the mean number of carbons per chain contributing to the amorphous phase. Assuming that amorphous phase is formed by chain ends (cilia) and folds it follows from the spectra that the length of folds is 6-7 monomer units; cilia are 2-3 monomer units long.     

Microstructure of poly(methyl methacrylate-co-isopropyl acrylate) studied by 13C NMR

The distribution of configurational–compositional sequences of poly(methyl methacrylate-co-isopropyl acrylate) (PMMA/iPrA) has been determined from the carbonyl and β-CH₂ signals in the 100?MHz ¹³C NMR spectra of the copolymer. The carbonyl signal provided information on configurational–compositional sequences up to heptads, whereas β-CH₂ signals offered complementary information on even sequences up to hexads. The assignment of the sequences to the respective signals was based on a comparison with the spectra of respective homopolymers, that is, PMMA and PiPrA followed by a computer simulation applying an incremental calculation of chemical shifts of the individual sequences.     

Polymer chain conformation of copolymers with different monomer size: C NMR spectroscopy and MALS study

Copolymer composition, distribution and molecular size of the comonomer influence the final properties of polymer materials. Such influence can be followed from the effect on the chain conformation in solution determined from the scaling law between radius of gyration and molecular weight.     

13C NMR spectra and the structure of dithizone

The structural characteristics of dithizone in the solid state and in solution were studied by a high-resolution¹³C NMR method. A highly symmetrical structure of dithizone was established in the crystalline state, and it was suggested that it exhibits dual behavior in complexation reactions with metal ions.V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 117975 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 113–117, January, 1992.     

Oxidation of C-labeled ethyl linoleate monitored and quantitatively analyzed by C NMR

The oxidation of ¹³C-labeled ethyl linoleate (¹³C-EL), a model compound for alkyd resins, was investigated by ¹³C NMR in the presence of Co(II)-2-ethylhexanoate (Co-EH), Mn(acac)₃ (acac = acetylacetonate), and Mn(acac)₃ in combination with 2,2′-bipyridine (bpy), respectively. The use of ¹³C-EL allows us, in an unprecedented way, to reveal the individual evolution of hydroperoxides (ROOH) and peroxy (ROOR) links by ¹³C NMR and to quantify the oxidation intermediates during the oxidation. Mn(acac)₃ appeared to be less effective in decomposing ROOH than Co-EH and the Mn(acac)₃/bpy combination. Quantitative analyses were attempted for a few major ¹³C peaks.     

Analysis of F and C NMR spectra of tetrafluorophthalic anhydride and its derivatives

¹⁹F and ¹³C NMR spectra of perfluorinated compounds (i.e., tetrafluorophthalic anhydride, its hydroxyl- and amino-derivatives, N-pentafluorophenyltetrafluorophthalimide, and hexafluoroindan-1,3-dione) were analysed. Different signals in NMR spectra were assigned based on the analysis of spin-spin coupling constants. All assignments made were further confirmed by density functional theory (DFT) calculations of ¹³C chemical shifts and J_C,F coupling constants.     

Discrepancy in infrared measurement results of carbon monoxide in nitrogen mixtures due to variations of the 13C/12C isotope ratio

Significant errors in the non-dispersive infrared (NDIR) analyses of carbon monoxide (CO) can be made when the ¹³C/¹²C isotope ratio in the sample and the calibrant differ significantly. This paper shows that variations in the ¹³C/¹²C isotope ratio of 5×10⁻² mol/mol CO in nitrogen mixtures on three different NDIR CO analysers may lead to serious deviations in the instrument response, whereas the instrument response using GC-TCD is unaffected. The observed deviations in the assigned amount-of-substance fraction CO for a ¹³C depleted mixture vary from +2 to −5% relative to the gravimetric amount-of-substance fraction for different NDIR analysers. A GC-MS method has been developed to perform a pre-screening of the isotopic composition of CO in nitrogen mixtures. This method proved to be an adequate tool to measure differences in the ¹³C/¹²C ratio. Based on the GC-MS results a suitable measurement technique can be selected, or information about a possible error in NDIR analysis can be given to the producer or user of the calibration gas mixture. Presented at 3. International Gas Analysis Symposium, October 6–8, 2004, in Amsterdam     

Correlation between the synthetic origin of methamphetamine samples and their 15N and 13C stable isotope ratios

The active ingredient of ecstasy, N-methyl-3,4-methyldioxyphenylisopropylamine (MDMA) can be manufactured by a number of easy routes from simple precursors. We have synthesised 45 samples of MDMA following the five most common routes using N-precursors from 12 different origins and three different precursors for the aromatic moiety. The ¹³C and ¹⁵N contents of both the precursors and the MDMA samples derived therefrom were measured by isotope ratio mass spectrometry coupled to an elemental analyser (EA-IRMS). We show that within-pathway correlation between the ¹⁵N content of the precursor and that of the derived MDMA can be strong but that no general pattern of correlation can be defined. Rather, it is evident that the δ¹⁵N values of MDMA are strongly influenced by a combination of the δ¹⁵N values of the source of nitrogen used, the route by which the MDMA is synthesised, and the experimental conditions employed. Multivariate analysis (PCA) based on the δ¹⁵N values of the synthetic MDMA and of the δ¹⁵N and δ¹³C values of the N-precursors leads to good discrimination between the majority of the reaction conditions tested.     

Structural Study of Methyl Acrylate in a Nematic Liquid Crystal by 1H NMR with 13C Satellites

The molecular structure and conformation of methyl acrylate have been determined by analyzing the ¹H NMR spectrum with ¹³C satellites of the molecules dissolved in the liquid crystal ZLI 1132. In the structural analysis, direct coupling constants have been corrected for molecular vibrations and converted to those in the r structure. The correlation between reorientational motion and internal rotation has been taken into account by using the mean external potential described in terms of bond interaction tensors. The potential for the internal rotation about the bond has been represented as V() = (V ₁/2) (1 – cos ) + (V ₂/2)(1 – cos 2), where is zero for the s-cis configuration, and the determined values of V ₁ and V ₂ are 2.7(1) and 8.4(13) kJ mol^–1, respectively. The relative abundance of the s-cis conformer, 76(1)%, agrees with a gas-phase value, 67(11)%, determined by electron diffraction within experimental errors.     

NMR spectroscopic study of the (Z)/(E)-isomerism of 1-aryl-3-arylamino-2-propen-1-ones in solution and in the crystalline state

Summary ¹H,¹³C, and CP/MAS¹³C NMR spectra of sixp-substituted 1-aryl-3-arylamino-2-propen-1-ones in solution and in the solid state are reported and discussed. In the proteon-accepting solvent dimethylsulfoxide, electronegative substituents shift the isomeric equilibrium to the (E)-isomer. Bulky substituents promote crystallization of the (Z)-form.

---

NMR-Spektroskopische Untersuchung der (Z)/(E)-Isomerie von 1-Aryl-3-arylamino-2-propen-1-onen in Lösung und im Kristallzustand (Kurze Mitt.)

Zusammenfassung ¹H-,¹³C- und CP/MAS-¹³C-NMR Spektren von sechsp-substituierten 1-Aryl-3-arylamino-2-propen-1-onen in gelöstem und festem Zustand werden berichtet und diskutiert. In protonenakzeptierendem Dimethylsulfoxid verschieben elektronegative Substituenten das Gleichgewicht zum (E)-Isomer. Große Substituenten begünstigen die Kristallisation in der (Z)-Form.

     

Studies on the phase structure of ethylene‐vinyl acetate copolymers by solid‐state 1H and 13C NMR

The phase structure of a series of ethylene‐vinyl acetate copolymers has been investigated by solid‐state wide‐line ¹H NMR and solid‐state high‐resolution ¹³C NMR spectroscopy. Not only the degree of crystallinity but the relative contents of the monoclinic and orthorhombic crystals within the crystalline region varied with the vinyl acetate (VA) content. Biexponential ¹³C NMR spin–lattice relaxation behavior was observed for the crystalline region of all samples. The component with longer ¹³C NMR spin–lattice relaxation time (T₁) was attributed to the internal part of the crystalline region, whereas the component with shorter ¹³C NMR T₁ to the mobile crystalline component was located between the noncrystalline region and the internal part of the crystalline region. The content of the mobile crystalline component relative to the internal part of the crystalline region increased with the VA content, showing that the ¹³C NMR spin–lattice relaxation behavior is closely related to the crystalline structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2199–2207, 2002     

A C and N experimental NMR and theoretical study of the structure of linear primary aliphatic amines and ammonium salts: from C1 to C18

Eighteen aliphatic linear amines, from methylamine to stearylamine, have been experimentally studied by NMR and theoretically calculated at the GIAO/B3LYP/6-311++G(d,p) level. A partial exploration of their conformation has been carried out, mainly to determine the effect on the chemical shifts. In solution and for neutral amines, ¹⁵N chemical shifts indicate a mixture of two conformations. In the solid state (CPMAS NMR) only the subset of solid amines has been studied (from C14 to C18). The ¹⁵N signals of the corresponding ammonium salts in the solid state depend on the counteranions, Cl⁻ and CF₃CO₂⁻, a result that is theoretically proven.     

Selective paramagnetic relaxation reagents (SPRR). Study of line broadening effect of Cu2+ ions on the13C-NMR spectral lines of N-containing molecules

Summary The selective line broadening effect of the paramagnetic Cu²⁺ on the¹³C-NMR linewidths of nitrogen compounds has been studied. It operates through electron-nuclear hyperfine coupling, however, chemical exchange processes also contribute significantly. The observed selective broadenings make possible the assignments of carbon atoms one or two bonds away from a basic nitrogen (earlier assignment of quinidine has been modified), the determination of likely metal binding sites of a complex and the relative basicity of different nitrogen atoms of the same molecule. The broadenings depend also on the spatial vicinity of the Cu²⁺ ion and the interacting nuclei. While its main advantage is simplicity, the main drawback is that it is limited to molecules capable to form complexes with Cu²⁺ ion.

---

Selektive paramagnetische Relaxationsreagenzien (SPRR). Untersuchung des Linienverbreiterungs-effekts von Cu²⁺-Ionen auf die¹³C-NMR-Signale in N-Verbindungen

Zusammenfassung Es wurde der selektive Verbreiterungseffekt von paramagnetischen Cu²⁺-Ionen auf¹³C-NMR-Linienbreiten von Stickstoff-Verbindungen untersucht. Diese Verbreiterung erfolgt durch Elektron-Kern-Hyperfeinkopplung, allerdings liefern auch chemische Austauschprozesse signifikante Beiträge. Die beobachteten Verbreiterungen erlauben die Zuordnung von Kohlenstoffatomen, die eine oder zwei Bindungen vom basischen Stickstoffatom entfernt sind (die frühere Zuordnung für Chinidin mußte modifiziert werden). Außerdem können die Koordinationsstellen festgestellt und eine relative Basizitätszuordnung von verschiedenen Stickstoffatomen innerhalb eines Moleküls getroffen werden. Die Verbreiterungen hängen auch von der räumlichen Nachbarschaft der Cu²⁺-Ionen und dem in Wechselwirkung befindlichen Kern ab. Der Hauptvorteil ist die Einfachheit der Methode, der Hauptnachteil liegt in der Limitierung der Methode auf Moleküle, die mit Cu²⁺ Komplexe bilden können.

     

N-Oxides of polychloropyridines.13C NMR study

The effect ofN-oxidation of a series of polychloropyridines on¹³C NMR parameters has been studied. It has been established that inN-oxides of polychloropyridines an electric field through-space effect of theN-oxide group predominates in the shielding of the -carbon atom compared to the other carbon atoms. A linear correlation between¹³C NMR chemical shifts and total charge densities calculated by the MNDO method for the carbon atoms ofN-oxides of polychloropyridines has been found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2425–2428, December, 1995.The authors are grateful to V. V. Kolchanov for help in the synthesis of compounds under study.     

13C NMR Spectra of 6-Hydroximinosteroids of the Stigmastane Series

¹³ C NMR spectra were studied and signals of C atoms were assigned for 6-keto- and 6-hydroximinosteroids 1-10.     

High-Resolution Solid-State NMR Characterization of Morphology in Annealed Polylactic Acid

Single-pulse ¹³C NMR spectra and spin-lattice relaxation times T₁(¹H), detected indirectly via ¹³C carbons, and T₁(¹³C) were measured at 31°C for virgin pelletized and annealed polylactic acid (PLA) samples using the magic-angle spinning technique. The structural relaxation resulting in more regular crystals with narrower conformation distribution and increase in the lamellae thickness and crystallinity brought about by annealing at 100°C was deduced from the narrowing of the ¹³C NMR lines and proton spin-lattice relaxation times T₁(¹H). The spin-lattice relaxation times T₁(¹³C) related to the respective carbons of the α-polymorph of PLA are also discussed in the study.     

13C NMR spectra of azolopyridines and their quaternary salts

¹³ C NMR spectra of some azole series have been investigated: 2-pyridylbenzimidazoles, 2-pyridylimidazo [4,5-b]-pyridines, 2-pyridylimidazo[4,5-c]-pyridines, analogous oxazole compounds, as well as their mono- and bisquaternary salts. Some problems, related to the structure of these compounds in solution, have been discussed.V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow 117975. Torino University, Italy. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 866–872, April, 1992.