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.     

Synthesis and spectral studies ofo-hydroxyacetophenone (N-benzoyl)glycyl hydrazone and some of its lanthanide(III) complexes

Summary o-Hydroxyacetophenone (N-benzoyl)glycyl hydrazone (o-HABzGH) has been characterized by i.r.,¹H n.m.r.,¹³C n.m.r. and mass spectral studies, and its complexes of the types [Ln(o-HABzGH)Cl₂(H₂O)₂]Cl and [Ln(o-HABzGH–2H)OH(H₂O)₃], where Ln=La, Pr, Nd, Sm and Eu, have been synthesized. The structures of the complexes have been studied by conductance, magnetic, electronic, i.r.,¹H n.m.r. and¹³C n.m.r. spectral techniques. The hypersensitive bands of the electronic spectra suggest coordination numbers six and seven around Nd^III in its adduct and neutral complexes respectively. I.r. and n.m.r. spectral data suggest a neutral bidentate behaviour for the ligand in the adducts and a dinegative tridentate nature in the neutral complexes.     

Five ingol esters and a 17-hydroxyingenol ester from the latex of Euphorbia Kamerunica. Assignment of esters using 13C.N.M.R. methods.

The structures of five ingol esters and a 17-hydroxyingenol ester from the latex of $\text{Euphorbia kamerunica}$ have been determined. The ¹³C n.m.r. spectra of these compounds have been assigned using 2D δ_C/δ_H correlations. The specific positions of attachment of esters have been assigned unambiguously using ¹³C n.m.r. methods including 2D long range δ_C/δ_H correlation.     

NMR-Untersuchungen an Dicyclopentadienderivaten. IV—1-Syn/anti-Epimere von endo-Dicyclopentadienderivaten

The syn/anti-arrangement of some substituents R in position 1 of endo-dicyclopentadiene derivatives is investigated by ¹H-and ¹³C n.m.r. spectroscopy. The HH-coupling constants of the epimeric alcohols 2 and 3 are determined by paramagnetic shift experiments [Eu(fod)₃] and the observed relative paramagnetic shifts ΔEu used for the determination of the configuration. The increasing steric compression in the syn-epimers is well reflected by the ¹H- and ¹³C n.m.r. chemical shifts.     

Complexation of palladium cyanide with imidazolidine-2-thione and its derivatives

Summary Pd(CN)₂ reacts with imidazolidine-2-thione (Imt), 1,3-diazinane-2-thione(Diaz), 1,3-diazipnane-2-thione (Diap) and their derivatives to yield complexes of stoichiometry [PdL₂(CN)₂] or [PdL(CN)₂] (L = Imt, Diaz or Diap and L = Imt having N-Me, Et or Pr substituents), which were characterized by elemental analysis, i.r., ¹H and ¹³C n.m.r. spectroscopy. Both mono- and bis ligand complexes are thought to be square planar with the monoligand binding to metal via sulphur (bridging) and the bis ligand via the monodentate thione group. The ¹³C enriched Pd(¹³CN)₂ complex was prepared and the ¹³C n.m.r. recorded. The C-2 resonance of ¹³C n.m.r. of Imt, Diaz or Diap complexes of the copper(I), silver(I), gold(I) and palladium(II) were compared.     

Trioxaphosphocanes-1,3,6,2, etude par R.M.N. (13C, 1H, 31P et stereochimie

The stereochemistry of several 2-R-1,3,6,2-trioxaphosphocanes (R = Cl, OCH₃, CH₃, N(CH₃)₃ has been investigated by ¹H, ¹³C and ³¹P n m r spectroscopy.     

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.     

Silver Cyanide Complexes of Heterocyclic Thiones

Silver(I) cyanide complexes of various thiones (imidazolidine-2-thione, diazinane-2-thione and their derivatives) have been prepared and characterized by elemental analysis, i.r. and n.m.r. (¹H, ¹³C, ¹⁵N and ¹⁰⁷Ag) spectroscopy. It appears from the i.r. data that six out of the ten complexes are nonionic [>C=S—Ag—CN] while the remaining four exist as ionic species [Ag(>C=S)₂]⁺[Ag(CN)₂]^– in the solid state. An upfield shift in the ¹³C-n.m.r. and downfield shifts in the ¹H-, ¹⁵N- and ¹⁰⁷Ag-n.m.r. spectra are consistent with the sulfur coordination to silver(I). The n.m.r. data shows that the [>C=S—AgCN] complexes are stable in solution and do not undergo redistribution.     

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.     

Complete assignment of the 13C n.m.r. spectrum of mutarotated D-ribose by integration and specific deuteration

The ¹³C n.m.r. spectrum of mutarotated D -ribose is completely assigned by using 2- and 3-deuterio-D -ribose as reference compounds. The signal intensities of the largely relaxed ¹³C n.m.r. spectrum are evaluated, and the equilibrium mixture of mutarotated D -ribose is found to consist of 6·1% α-furanose, 11·6% β-furanose, 20·3% α-pyranose and 62% β-pyranose.     

1H- und 13C-NMR-untersuchungen an dibromoxabicyclo[n.2.1]alkanen

The ¹H n.m.r. spectra of some dibromooxabicyclo[n.2.1]alkanes are discussed for the determination of the configuration and conformation. The ¹³C n.m.r. spectra confirm the observed stereochemistry. With increasing ring size the ¹³C n.m.r. chemical shifts of the hetero atom substituted C-atoms C-1 and C-2 move steadily to lower fields.     

Application of carbon-13 n.m.r. Spectroscopy to the structural investigation of ezomycins

Ezomycins A₁, A₂, B₁, B₂, C₁, C₂, D₁ and D₂, antifungal antibiotics, are anhydrooctose uronic acid nucleosides. Their novel structures were confirmed by studying their natural abundance ¹³C n.m.r. spectra in detail from gated proton-decoupled, long-range selective proton-decoupled and selective proton-decoupled spectra. The J(CH) value of the anomeric carbon signal (C-1″) supports the β-configuration.     

Nitrogen-15 n.m.r. studies of 13C, 15N labeled arginine

¹⁵N n.m.r. spectra of [¹³C-2, 3-¹⁵N₂-guanidino]arginine and [¹³C, ¹⁵N₂] urea were obtained in D₂O and H₂O at a variety of pH values both with and without proton decoupling. The effects of the proton exchange rate are readily observable in the proton coupled ¹⁵N spectra. When the guanidino group is deprotonated (pK = 12.5), the terminal nitrogens give a single resonance 6.6 ppm downfield of the protonated species, indicating a rapid tautomeric exchange. The observed NH and CN couplings are compared with calculated values, and good agreement is found for ¹J(CN) using a Blizzard–Santry type calculation. The ramifications of the proton exchange on ¹⁵N n.m.r. spectra of amino acids and peptides are discussed.     

NMR Studies of the Structures of Cyclic Phosphorus Compounds

Abstract

[RNPOCl]₃ (R = Ph, p-Tol, p-MeOC₆H₄) has been shown by ³¹P n.m.r. to consist mainly of the 2α, 4α, 6β(C₂) isomer (AB₂ spin system), along with small amounts of the symmetric (C₃) isomer (2α, 4α, 6α). The ³¹P shifts are almost independent of the nature of the group R. Confirmation of the ring structure requires the determination of J_BB which is achieved by second-order analysis of ¹³C or ¹H spectra. Similar techniques have been applied to the phosphorus-oxygen ring system [PhPO₂]₃. We have discovered a relationship between the orientation of N-phenyl substituents on cyclophosphazane ring systems and the ¹³C n.m.r. shifts of the ring carbons. In cyclodiphosphazanes the phenyl rings are coplanar with the P-N ring, whereas in cyclotriphosphazanes the phenyl rings are perpendicular to the P-N-P plane; the ¹³C shifts of the ortho and para carbons are quite different in these two situations, and we have used these shifts to obtain structural information on a number of cyclophosphazanes. Rotation of the ring about the C-N bond has also been studied by low-temperature n.m.r.     

Carbon-13 n.m.r. and CNDO/S study of 1,2-indandione and heterocyclic analogues

¹³C n.m.r. spectra are reported for 1,2-indandione, coumarandione and thionaphthenequinone in CDCl₃ solution and for isatin in dimethyl sulphoxide solution. The chemical shifts are assigned and discussed in connection with the influence of the heteroatom on the dicarbonyl group and the aromatic ring. The ¹³C shieldings have also been calculated by means of Pople's perturbation theory using CNDO/S wave functions.     

Schwefeldioxid als Ligand und Synthon. II. Synthese und Reaktionen der Trimethylsilyl-methansulfinsäure und ihrer Derivate

Sulfur Dioxide as Ligand and Synthon. II. Synthesis and Reaction of Trimethylsilyl Methane Sulfinic Acid and its Derivatives Synthesis and reaction of trimethylsilyl methane sulfinic acid and its derivatives, of the type Me₃SiCH₂S(O)? Y (Y = OH, OM, OR, NR₂) synthesized by insertion of SO₂ and R¹NSO, respectively, into Me₃SiCH₂MgCl are described. The compounds obtained are characterized by means of i.r., ¹H, ²⁹Si, and ¹³C n.m.r. spectroscopy.     

13C spin relaxation studies of the basic pancreatic trypsin inhibitor

The longitudinal ¹³C spin relaxation times T₁ and the ¹³C{¹H} nuclear Overhauser enhancement were measured in a concentrated aqueous solution of the basic pancreatic trypsin inhibitor. The correlation time for overall rotational motions of the basic pancreatic trypsin inhibitor molecules was found to be τ_R ≈ 2 × 10^?8 s. In connection with previous ¹H n.m.r. studies of intramolecular motions of the aromatics, we were particularly interested in the correlation times τ_G for intramolecular segmental motions of the aromatic rings. The present experiments revealed no manifestation of intramolecular motions of the aromatics, indicating that τ_G ? 2 × 10^?8 s for the aromatic ring carbon atoms. On the other hand, rapid segmental motions were evidenced for the peripheral carbon atoms of aliphatic amino acid sidechains. Comparison of the ¹H and ¹³C n.m.r. data on the basic pancreatic trypsin inhibitor indicates that the time scale of high resolution ¹H n.m.r. at high fields may in many instances be more appropriate for studies of the molecular dynamics in globular proteins than the time scale of spin relaxation measurements.     

Synthetic and structural aspects of hepta-coordinated semicarbazato complexes of oxotungsten(VI)

Summary The condensation of aldehydes and ketones, 2-pyridine carbaldehyde, 2-thiophene carbaldehyde, 2-furyl aldehyde, 3-indole carbaldehyde, 3-phenylpropane-1-one, 2-propanone, 4-methyl-2-pentane and 2-phenylethane-2-one, with semicarbazide hydrochloride yields the corresponding Schiff bases which, when subsequently reacted with tungsten oxotetrachloride, yield addition products of the type WOCl₄·L (L = ligand). The resulting complexes have been characterized by elemental analysis, molecular weight determination, and by conductivity and magnetic measurements. The bonding mode of the ligands with the metal atom is deduced on the basis of i.r.,¹H n.m.r. and¹³C n.m.r. spectral studies.     

Determination of ΔH≠ and ΔS≠ by simultaneous 1H and 13C dynamic n.m.r. studies: Importance of the accuracy of temperature measurement

From ΔG_Tc^≠ values obtained by ¹H and ¹³C dynamic nuclear magnetic resonance studies of the same dynamic process, it is possible to estimate ΔH^≠ and ΔS^≠. Nevertheless, the accuracy of the temperature measurement is a factor which limits the applicability of this method. A very simple procedure for calibrating the usual temperature sensors is described, which can be applied to all types of n.m.r. probes. By the use of this procedure it is possible to measure coalescence temperatures in ¹H and ¹³C n.m.r. with such an accuracy that ΔS^≠ can be effectively determined from the difference between ΔG_Tc^≠ values.     

13C NMR spectra of benzofuroxan and related compounds

The ¹³C n.m.r. spectrum of benzofuroxan at ?15°C is assigned on the basis of selective decoupling experiments and by comparison with the ¹³C chemical shifts of model compounds. The ¹³C spectra were also measured in trifluoroacetic acid as a solvent. From the temperature dependence of the ¹³C spectrum of benzofuroxan in CDCl₃, a barrier of 14·0 ± 0·2 kcal mol^?1 is obtained for the degenerate tautomerism in this compound.