1H-Festkörper-NMR-Untersuchungen am synthetischen Pektolith Ca2NaHSi3O9

Solid-state ¹H N.M.R. Studies of Synthetic Pectolite Ca₂NaHSi₃O₉ A synthetic pectolite Ca₂NaHSi₃O₉ is studied by means of conventional ¹H pulse-fourier-transform wide line n.m.r. and methods of solid-state high-resolution ¹H n.m.r. (MREV8 multiple pulse technique, combined multiple pulse magic angle spinning experiments). The n.m.r. spectra consist of a dominant signal due to SiOH groups and a small signal which can be assigned to water molecules. The parameters of the ¹H n.m.r. spectra for the SiOH groups are discussed in comparison with the known structure of pectolite. It can be shown that the structural details for the proton of the SiOH groups are reflected by the ¹H n.m.r. spectra.     

Crystal and geometry‐optimized structure of an anthracene‐based Diels–Alder adduct

Computational calculations of an anthracene‐based Diels–Alder adduct, namely, 17‐ethyl‐1‐hydroxymethyl‐17‐azapentacyclo[6.6.5.0^2,7.0^9,14.0^15,19]nonadeca‐2,4,6,9,11,13‐hexaene‐16,18‐dione, C₂₁H₁₉NO₃, predicting density functional theory (DFT) optimized geometries in the gas phase are compared in terms of accuracy relative to the solid‐state crystal structure and computational cost. Crystal structure determination and Hirshfeld surface analysis of the racemic product reveal that the molecules are linked by O—H…O=C hydrogen bonds between the hydroxy and carbonyl groups, accounting for 9.5% of the intermolecular contacts, while H…H contacts represent 56.9% of the total. Boltzmann population analysis of computed relative rotamer abundances in the gas phase are based on lower‐level geometry optimization and thermochemical corrections coupled with higher‐level electronic energy calculations using the B2PLYP double‐hybrid functional. As expected, the choice of density functional has a greater effect than the basis set on accuracy for all levels of theory. For any given functional, increasing the basis set size did not always correlate with increasingly accurate structures. The hybrid functional B3LYP without dispersion correction routinely gave the closest approximations to the crystal structure where the B3LYP/aug‐cc‐pVDZ combination afforded the best structure (r.m.s. deviation = 0.1314 Å). However, the B3LYP/6‐31+G(d,p) level of theory represents the best compromise between accuracy (r.m.s. deviation = 0.1388 Å) and cost as it yielded appreciably accurate results in a fraction of the time compared to other method combinations.     

Hierarchical clustering of carbon-13 nulear magnetic resonance spectra

The problems of preprocessing of ¹³C-n.m.r. spectra for hierarchical clustering are discussed. Encoding of the spectra in nonequidistant intervals is proposed. To establish the optimal intervals, a Simplex method with variable-sized movements is used. The optimized parameter is the amount of information contained in the first two coordinates of the transforms, obtained by the application of principal component analysis to the ¹³C-n.m.r. spectra. The spectra encoded in optimized intervals are used for automated structure elucidation, based on a hierarchical organization of a collection of more than 2000 assigned¹³C-n.m.r. spectra. The hierarchical trees needed for the library search and prediction of some structural features were generated by a 3-distances clustering method. The retrieval and predictive abilities of the system are discussed.     

29Si-MAS-NMR-Untersuchungen an kristallinen Bleisilicaten

Si-M.A.S.-N.M.R. Investigations on Crystalline Lead Silicates The isotropic ²⁹Si-n.m.r. chemical shifts of ten crystalline lead silicates with molar ratio PbO:SiO₂ between 4:1 and 1:1 has been measured. Starting from the known anion constitution the respective ²⁹Si-n.m.r. signals were assigned to silicate structure units (Qⁿ groups). Decreasing ratio PbO:SiO₂ corresponds to significant low-field shifts of the ²⁹Si-n.m.r. signals of definite Qⁿ groups with constant n. This result is of importance to the future investigation of crystalline and vitreous lead silicates with unknown anion constitution.     

Carbon-13 n.m.r. studies of some saturated 1,2-oxazepine derivatives

The influence of incorporating an group, an oxygen atom and the fragment in a saturated 7-membered ring system on carbon-13 n.m.r. chemical shifts is examined, and also, the influence of the dioxolane ring moiety on the ¹³C chemical shifts in these ring systems. Substituent effects are generally additive except in cases where the ring is heavily substituted with methyl groups. A large upfield steric shift (γ effect) of 7–8 ppm is observed in two of the derivatives. An example of long range nonequivalence is also observed. Assignments of the ¹³C n.m.r. spectra have been made by comparison with model compounds, and from proton coupled ¹³C n.m.r. spectra. The synthesis of several new compounds is described.     

Solution <Superscript>1</Superscript>H n.m.r. of paramagnetic Co<Superscript>2+</Superscript>complexes with dioxobis(carboxymethyl)tetraazamacrocycles

Paramagnetic shifts in the ¹H n.m.r. spectra were observed for high-spin Co²⁺ complexes with 12--14-membered tetraazamacrocycles incorporating two amide groups and two pendant carboxymethyl groups. The pseudocontact term due to the dipolar interaction between the metal ion and the resonant protons was calculated on the basis of X-ray structures, and the Fermi contact term due to spin delocalization was determined. The ethylenediamine moiety of the ligand molecule is coordinated in an unsymmetric manner, even in solution, and internal motion (involving conformational change of the macrocyclic frame and exchange of coordinate bonds) is much slower than the n.m.r. observation frequency. In the 12-membered macrocyclic complex Co(L12), three of the eight CH₂ groups fix their orientation in the n.m.r. time scale; in Co(L13) only one CH₂ group fixes its orientation; in Co(L14) all CH₂ groups undergo a rapid reorientation. The facility in internal motion increases with the ring size, and shows a correlation with the chemical stabilities of these Co²⁺ complexes against oxidation; to atmospheric oxygen, Co²⁺(L12) is the most resistant and Co²⁺(L14) is the most susceptible.     

Characterization of the chemical structure of thermosetting resins by high-resolution solid-state carbon-13 nuclear magnetic resonance spectrometry

The combination of proton-dipolar decoupling, magic-angle spinning and cross-polarization techniques results in high-resolution ¹³C-nuclear magnetic resonance (n.m.r.) spectra of solid-state compounds. In homogeneous materials, using a relatively low external field and in the absence of motional line broadenings, the chemical structure of totally insoluble curec polymer resins can be estimated quantitatively, and the chemical mechanisms leading to their formation can be elucidated. The capability of high-resolution solid-state ¹³C-n.m.r. for solving such problems is illustrated by the example of the polystyrylpyridine system obtained by reaction of terephthalic aldehyde with pyridine. The decreasing amounts of aldehyde and methyl groups and the appearance of network crosslinkages were studied as a function of both the temperature and the duration of the curing treatment. The results are interpreted quantitatively in terms of two chemical mechanisms: first, the addition of a methyl group from the collidine molecule to the aldehyde function of terephthalic aldehyde followed by elimination of water; secondly, a cross-linking reaction consisting of the addition of a collidine methyl group to the double bonds formed in the first process. The high resolution of the ¹³C-n.m.. spectra also makes it possible to observe the different reactivities of the o- and p-methyl substituents of the collidine molecule. p-Methyl reactions occur only when most of the o-methyl functions have disappeared. Thus, high-resolution solid-state ¹³C-n.m.r. provides a precise characterization of the polystyrylpyridine resins in terms of both their quantitative chemical composition and their reaction mechanisms.     

Group contributions to the thermodynamic properties of non-ionic organic solutes in dilute aqueous solution

The thermodynamic properties G _h ^o,H _h ^o, and C _p,h ^oassociated with the transfer of non-ionic organic compounds from gas to dilute aqueous solution and the limiting partial molar properties C _p ^o ,2 and V₂ ² of these compounds in water are described through a simple scheme of group contributions. A distinction is made between groups made only of carbon and hydrogen, and functional groups i.e. groups containing at least one atom different from carbon and hydrogen. Each group is assigned a contribution, for each property, through a least squares procedure which utilizes only molecules containing at most one functional group. Finally, for compounds containing more than one functional group, correction parameters are evaluated as the differences between the experimental values and those calculated by means of the group contributions. The different behavior of hydrophilic compared with hydrophobic groups is discussed for the various properties. A rationale for the correction parameters, i.e. for the effects of the interactions among hydrophilic groups on the thermodynamic properties, is attempted.     

Borchelate und Bormetallchelate, 4. Mitt.

The i.r., u. v.,¹H n.m.r.,¹³C n.m.r., and¹¹B n.m.r. spectra of several substituted diphenylboron chelates derived from salicylaldehyde azomethines were compared with respect to the influence of the amine substituentR. O–B–N-6-ring constitution of the chelates29–32 [R=OH, NH₂, NHC₆H₅, N(CH₃)₂] can be deduced from the spectra.

Als 3. Mitt. gilt:F. Umland undE. Hohaus mit Beiträgen vonW. Riepe, K. Brodte, C. Schleyerbach undD. Szonn. Untersuchungen über borhaltige Ringsysteme vom Chelattyp. Forschungsbericht des Landes Nordrhein-Westfalen Nr. 2538. Opladen: Westdeutscher Verlag. 1976.     

Determination of Nucleic Acids Based on their Resonance Light Scattering Enhancement Effect on Metalloporphyrin Derivatives

A new method for the determination of nucleic acids at nanogram per mL level is proposed based on the enhanced resonance light scattering (RLS) signal resulting from the interaction of metalloporphyrins with nucleic acids. Under optimum conditions, the weak RLS signal of metalloporphyrin is enhanced by nucleic acids, and the enhanced RLS intensity is proportional to the concentration of nucleic acids. The detection limits of calf thymus DNA were 3.5ngmL^–1, 2.9ngmL^–1 and 1.0ngmL^–1 for three metalloporphyrins, respectively. Synthetic samples were determined with satisfactory results.     

The structure of α-(1,2-dithiole-3-ylidene) ketones and α-(1,2-dithiole-3-ylidene) aldehydes studied by means of n.m.r. spectroscopy

1H and ¹³C n.m.r. studies of a series of twelve 1,2-dithiole-3-ylidene ketones and aldehydes have shown that the geometry of the carbon backbone is the same as found in 1,6,6aλ⁴-trithiapentalenes. No evidence has been found which favours a bicyclic structure for the system. A linear correlation of observed ¹³C chemical shifts with calculated charge densities is found to be valid. The observations are in agreement with a structure which is a hybrid between a true ketonic structure and a true mesoionic structure. By using the difference in the ¹³C chemical shifts of ortho and meta carbon atoms in substituent phenyl groups it is possible to qualify the degree of coplanarity of the phenyl groups with the backbone of the molecule.     

Darstellung und spektroskopische Eigenschaften von Nitridophthalocyaninatorhenium(V)

Preparation and Spectroscopical Properties of Nitridophthalocyaninatorhenium(V) Nitridophthalocyaninatorhenium(V) ([ReNPc^2?]) is prepared by the reaction of dirheniumheptoxide with ammoniumiodide in molten 1,2-dicyano-benzene. The diamagnetic complex is chemically und thermically extremely stable. In the Uv-vis spectra the typical π-π*-transitions of the Pc^2? ligand are observed. Extra bands in the solid state spectrum are due to strong excitonic coupling of ca. 2.8 kK. In the resonance Raman spectra the intensity of the Re≡N stretching vibration (v(Re≡N)) at 969 cm^?1 is selectively enhanced by laser excitations above 19.0 kK. v(Re≡N) is a dominant m.i.r. absorption at 976 cm^?1.     

Temperature effects on 13C n.m.r. chemical shifts of normal alkanes and some line r and branched 1-alkenes

¹³C n.m.r. chemical shifts of a number of 1,1-disubstituted ethylenes are presented. Moreover, effects of changing temperatures on the ¹³C n.m.r. chemical shifts of some of these compounds as well as of three normal alkanes are given. These variations in chemical shifts are attributed to varying amounts of sterically induced shifts in the different conformational equilibria. In addition to the well-known 1,4 interaction between two alkyl groups shielding effects on the carbon atoms of the connecting bonds are also proposed. No definite explanation of this effect is presented at this time. It is further shown that no simple correlations exist between ¹³C n.m.r. chemical shifts and calculated total charge densities at this level. Instead, the experimental results in 1-alkenes are rationalized by assuming a linear dependence of the ¹³C n.m.r. chemical shifts of C-1 and C-2 via rehybridizations on changes in bond angles for small skeletal deformations caused by steric interactions. These changes in geometries, as well as conformational energies in three 1-alkenes, were calculated by means of VFF calculations. Finally. upfield shifts for both C-2 and C-4 are proposed for those conformations of 1-alkenes in which the C-3? C-4 group interacts with the p_z-orbital of C-2.     

Vinylierung und 91Zr-NMR-Spektren von Substituierten Zirconocendichloriden

Vinylation and ⁹¹Zr N.M.R. Spectra of substituted Zirconocene Dichlorides Substituted zirconocene dichlorides react with vinyl lithium with formation of zirconacyclopent-2-enes, Cp₂ZrCH = CHCH₂CH₂, or zirconocene butadiene complexes, Cp₂Zr(C₄H₆). The compounds obtained were characterized by their ¹H and ¹³C n.m.r. spectra. The ⁹¹Zr n.m.r. chemical shifts of substituted zirconocene dichlorides correlate with the bond angles Cp′? Zr? Cp′ and Cl? Zr? Cl respectively. They can be used to estimate the reaction behaviour of zirconocene dichlorides.     

Silver(I) complexes of thiourea

Ag^I complexes of thiourea (tu) having the general formula Ag(tu) _x NO₃ (x = 1–4) have been prepared and characterized by elemental analyses, i.r. and n.m.r. (¹H, ¹³C, ¹⁵N and ¹⁰⁷Ag) spectroscopy. Separate i.r. bands were observed for terminal and bridging tu ligands in the complexes. The Ag(tu)NO₃ complex is assumed to be polymeric with all tu groups in the bridging mode. A consistent upfield shift in the ¹³C-n.m.r. chemical shift is observed as the number of tu groups attached to Ag^I increases, whereas the opposite trend is observed for ¹H, ¹⁵N and ¹⁰⁷Ag chemical shifts.     

Spectroscopic,thermal and electrochemical characterization of synthesized divalent transition metal complexes with cysteine and 4-substituted thiosemicarbazides

Mixed ligand complexes of Co^II, Ni^II and Cu^II with cysteine and 4-substituted thiosemicarbazides (l ¹–l ³) have been synthesized. The elemental analyses, molar conductance, spectra [electronic, i.r., ¹H-n.m.r., mass] and thermal studies were used to characterize the isolated complexes. Cyclic voltammetry was used to study the electrochemical behaviour of the Ni^II complexes. The i.r. and ¹H-n.m.r. showed that cysteine is deprotonated in the complex and acts as a binegative ligand coordinating through thiol sulphur and COOH groups. Also, thiosemicarbazides act as a bidentate ligand, coordination via NH₂ and (C=S) groups. Square-planar geometry has been proposed for Co^II, Ni^II and Cu^II ternary complexes.     

Characterization and application of silylated substrates for the preconcentration of cations

Chelating functional groups immobilized on silica and controlled pore glass beads are used to preconcentrate cations from aqueous solution in the concentration region of ng ml^?1. The functional groups are chemically bonded to the substrates by silylation reagents which may be employed as received or further modified. For example, commercially available 1,2-diamines may be used or converted to the dithiocarbamate after immobilization. This report includes studies of ionic strength and sodium chloride effects on the recovery of transition metal ions. Batch extraction of transition metal ions is accomplished with silica as the substrate for solutions containing transition metal ions at μg ml^?1 concentrations. Column extraction of solutions pumped at 50 ml min^?1 is accomplished at concentrations of 25 ng ml^?1. Recovery is good in both cases. The cations were determined directly on pelletized substrates by x-ray fluorescence. However, the ions may be eluted from the substrate and determined by other methods. Examples of determinations of several cations in lake water and high-purity industrial water are given.     

Etude par RMN du Proton et du Carbone-13 de Pyrimidines Substituées. I—Effets de Substituant dans les Dérivés Méthylés et Aminés

Substituent effects of methyl and amino groups on the chemical shifts of pyrimidine have been investigated by ¹H and ¹³C n.m.r. and compared with similar data obtained for benzene and pyridine. Taking into account pairwise interactions, the chemical shifts calculated by using an additivity relationship are in very good agreement with the experimental results, except for some hindered pyrimidines. This study enabled us to assign the ¹³C n.m.r. spectra of some trisubstituted pyrimidines.     

Pteridine studies: III—13C n.m.r. data of pteridine,some of its derivatives and their covalent σ-adducts with ammonia and water

¹³C n.m.r. spectral data of pteridine and nineteen of its derivatives (containing one or more chloro, methylthio, methyl, t-butyl or phenyl substituents) are reported. The ¹³C n.m.r. spectrum of the title compound has been assigned conclusively. ¹³C n.m.r. substituent effects are shown to be very useful in discerning between 6- and 7-substituted pteridines. Additionally, the ¹³C n.m.r. spectra of several covalent amination products, i.e. the 3,4-dihydro-4- amino- and the 5,6,7,8-tetrahydro-6,7-diaminopteridine derivatives, formed by dissolving the appropriate pteridine in liquid ammonia, have been recorded. The ¹³C n.m.r. spectra of the corresponding covalent hydrates are also reported.