NMR-Untersuchungen an Dicyclopentadienderivaten: III—Stereochemische Zuordnung von überbrückten endo-Dicyclopentadienderivaten und deren Wagner-Meerwein-Umlagerungs-produkten mit Hilfe der NMR-Spektroskopie

The ¹H n.m.r. spectra of some substituted oxa- and azatetracycloundecanes are studied and selected examples analysed in detail with the aid of spin-spin decoupling and Eu(fod)₃ paramagnetic shift experiments. From the quoted ¹³C n.m.r. spectra the carbon resonances are assigned, using known substituent effects and paramagnetic shift values. The determined paramagnetic shift parameters ΔEu are discussed in respect of their contact and pseudocontact contributions.     

NMR-Untersuchungen an Dicyclopentadienderivaten: II.—13C-NMR: γ-gauche-Effekt in Abhängigkeit von der exo/endo-Isomerie an Dicyclopentadien diolen

The ¹³C FT n.m.r. spectra of some exo- and endo-dihydro- and tetrahydrodicyclopentadiene-9,10-diols(exo/exo or endo/endo) are studied and the chemical shifts of the C-atoms are assigned by application of Eu(fod)₃ paramagnetic shift investigations and additional chemical shift parameters. Thus relatively strong γ-effects up to 12,8 ppm were observed for the C-atoms 4, 5, 7, 9, 10 and 1, 3, dependent on the exo/endo configuration of the OH-groups and the attached 5-ring, giving an interesting insight into the gemetry of these norbornane systems.     

Influence of chemical exchange on the temperature dependence of Eu(fod)3-induced shifts

Temperature dependences of the paramagnetic shifts induced by Eu(fod)₃ in ¹H NMR spectra of ethylene oxide in carbon disulphide solution are obtained in the temperature range from +40 to ? 100°C at 100 MHz and from +30 to ?60°C at 60 MHz. The influence of chemical exchange leads to a decrease of the observed paramagnetic shifts with decreasing temperature. It is shown that a modified Swift and Connick equation can be used to describe the observed dependences. Upper limits of the mean lifetimes of the Eu(fod)₃-ethylene oxide adduct are τ_p < 1·7 × 10^?8 s at 14 °C and τ_p < 1 × 10^?8 s at 20 °C, respectively. The corresponding activation energy is equal to V_a = 13·7 kcal/mol.     

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.     

A 13C n.m.r. study of the charge-transfer complexes between o-chloranil and some aromatic electron donors

The ¹³C n.m.r. spectra of complexes between o-chloranil and aromatic electron donors were studied. Complexation leads to a general diamagnetic shift of the ¹³C n.m.r. signals for the acceptor (o-chloranil), but for signals from the ¹³C nuclei in the donors both diamagnetic and paramagnetic shifts are found. These phenomena are thought to be the result of competing anisotropy and charge-migration effects. Charge migration in o-chloranil complexes appears to be more important than in corresponding 1,3,5-trinitrobenzene complexes.     

NMR–Untersuchungen an Dicyclopentadienderivaten: I—1H-NMR: Anwendung von paramagnetischen Verschiebungsreagenzien (Eu(fod)3) zur Vereinfachung der Spektren exo/endo-isomerer Diole

The determination of the stereochemistry of a series of exo/endo-isomeric dihydro- and tetrahydro-dicyclopentadiene-9.10-diols (exo/exo or endo/endo), using Eu(fod)₃ for separation of the signals in their ¹H n.m.r. spectra, is discussed in detail. The paramagnetic shift values ΔEu determined for half-molar ratios Eu(fod)₃/diol allow an unambiguous stereochemical assignment of the diols with regard to exo/endo isomerism. The ΔEu quantities are correlated with the distance H_i…O-atom (R_i).     

13C n.m.r. spectra of some thiobenzamides. Correlation between 13C and 1H n.m.r. spectra and signal assignments of syn and anti CH2 groups

¹³C n.m.r. spectra of a series of N,N-disubstituted thioamides have been recorded and signal assignments were performed. Separate signals are observed for methylene groups fixed on the nitrogen atom. Since the carbon atom syn to the thiocarbonyl sulfur resonates at higher field than the anti carbon, the syn-anti assignment in ¹H n.m.r. is easily obtained by selective double irradiation. This method, which is rapid and reliable, affords a rather general solution to the interesting problem of resonance assignments in tertiary amides and thioamides (and in analogous molecules such as oximes and nitrosamines).     

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.     

Mixed ligand gold(I) complexes with phosphines and selenourea

A series of mixed ligand Au^I complexes with selenourea (Seu) and various phosphines, [R₃PAuSeu]Cl, have been prepared and characterized by elemental analysis, i.r. and n.m.r. methods. A decrease in the i.r. frequency of the C=Se mode of Seu upon complexation is indicative of Au^I binding via a selenone group. An upfield shift in the ¹³C-n.m.r. for the C=Se resonance of Seu, and downfield shifts in ³¹P-n.m.r., for the R₃P moiety are consistent with selenium coordination to Au^I.     

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.     

Gold(I) complexes with selenones and triphenylphosphine as ligands

A number of mixed ligand complexes of gold(I) with various selenones and Ph₃P, [Ph₃PAuSe=C<]Cl have been prepared and characterized by elemental analyses, i.r. and n.m.r. methods. A decrease in the i.r. frequency of the C=Se mode of selenones upon complexation is indicative of gold(I) binding viaa selenone group. An upfield shift in the ¹³ C-n.m.r. for the C=Se resonance of selenones and downfield shifts in ³¹P-n.m.r. for the Ph₃P moiety are consistent with the selenium coordination to gold(I). Available data in the literature suggest that P–Au–Se type complexes are usually linear.     

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.     

A 13C NMR study of actinomycin D and related model peptides

¹³C n.m.r. pulsed Fourier transform spectra were measured and interpreted for actinomycin D and for two related peptide derivatives: BOC-Pro-Sar-OCH₃ and BOC-Sar-Meval-OCH₃. Actinomycin D, specifically enriched with ¹³C in the chromophoric C-methyl and in the peptide N-methyl carbons, was produced biosynthetically. Enrichment of specific N-methyl carbons in the model peptides was effected synthetically. Spectral assignments relied on the use of the enriched samples and particularly on off-resonance and selective low power ¹H decoupling experiments. Poor correlation was observed between some of the ¹³C chemical shifts in the model compounds and those of the analogous carbons in actinomycin D. Ten of our ¹³C assignments for actinomycin D differ from those published by Hollstein, Breitmaier and Jung.     

13C-NMR-spektroskopische und stereochemische Untersuchungen: XI—Konformationen von Bicyclo[3.3.1]nonanen und ihre Unterscheidbarkeit durch lanthanideninduzierte Verschiebungen

The ¹³C chemical shifts of bicyclo[3.3.1]nonane and of the corresponding 9-hydroxy- and 9-oxo- derivatives are compared with chemical shifts calculated on the basis of stereospecific shift increments. These results as well as the ¹H n.m.r. spectrum of the ketone indicate a predominant chair-chair conformation CC. A low temperature ¹³C n.m.r. study as well as an analysis of the temperature dependence of ¹³C chemical shifts in bicyclo[3.3.1]nonane furnish a limit for the free energy difference between CC and BC conformations of ΔG ≧ 5,85 kJ mol^?1. The distinction between CC, BC and BB provides a test for the applicability of lanthanide-induced ¹H and ¹³C shifts for the assignment of flexible geometries. The typical occurrence of several and/or flat minima in the LIS geometry analysis allows only the exclusion of boat–boat conformations.     

13C NMR spectroscopy of polycyclic aromatics. VIII—amino derivatives of quinoline,isoquinoline, acenaphthene and fluoranthene

Complete assignments of the ¹³C n.m.r. spectra have been made for 5-aminoquinoline, 5-aminoisoquinoline, 5-aminoacenaphthene and 3-aminofluoranthene. Substituent-induced shifts are compared with those of the structurally related 1-aminonaphthalene. Some deviations within the series can be interpreted in terms of an increase of the exocyclic peri angle. An analysis of the ¹H n.m.r. spectrum of 3-aminofluoranthene is also given.     

Carbon-13 nuclear magnetic resonance spectra: III—2-heteroadamantanes

The ¹³C n.m.r. spectra of some 2-heteroadamantanes and 1-substituted 2-heteroadamantanes are reported. The influences of the heteroatoms in the adamantane framework, and those of the substituents attached to it, on the ¹³C chemical shifts of the adamantane carbons are investigated and compared with related compounds such as the corresponding heterocyclohexane derivatives and 2-mono- and 2,2-disubstituted adamantanes. The nonadditivity of the substituent effects for 1-substituted 2-heteroadamantanes, especially for the geminally substituted carbons, is substantially confirmed. In addition, the influences of a missing CH₂ group and of NCH₃ carbons upon the ¹³C chemical shifts of the carbons in the adamantane system are described.     

Complexation of (trimethylphosphine)gold(I) with Selenones

Mixed ligand complexes of gold(I) with various selenones and Me₃P, [Me₃PAuSe=C<]Cl, have been prepared and characterized by elemental analyses, i.r. and n.m.r. methods. A decrease in the i.r. frequency of the >C=Se mode of selenones upon complexation is indicative of selenone binding to gold(I) via a selenone group. An upfield shift in ¹³C-n.m.r. for the >C=Se resonance of selenones and downfield shifts in ³¹P-n.m.r. for Me₃P moiety are consistent with the selenium coordination to gold(I). The steric effect as well as the basicity of Me₃PAu⁺ plays a significant role in bonding with Se-containing ligands compared to the Et₃PAu⁺ and Ph₃PAu⁺ complexes.     

Benzofurobenzthiazole: VI—1H- und 13C-NMR-Spektren von 2-Aminobenzofuro[2,3-f] benzthiazol und 2-Aminobenzofuro[2,3-e]benzthiazol im Vergleich mit Dibenzofuran und 2-Aminobenzthiazol

Cyclization of 3-dibenzofurylthiourea under the conditions of the Hugershoff reaction gives the linear structure 1. ¹H n.m.r. and ¹³C n.m.r. spectra of the two isomeric aminobenzofurobenzothiazoles (1 and 3), recorded at 220 MHz, 60 MHz and 22,62 MHz respectively, were used as aids for the structure determination. The magnetic parameters were obtained partly by first-order analysis and partly by simulation of spectra using LAOCOON 3. The assignments were made by comparing the chemical shifts and coupling constants with those of the parent compounds dibenzofuran (4a) and 2-aminobenzothiazole (5c). In so far as the assignments of ¹H n.m.r. and ¹³C n.m.r. frequencies of the parent compounds themselves were unknown or supported by analogy only, they have been determined using experimental criteria such as deuterium substitution and investigation of changes in chemical shifts caused by derivation.     

Carbon-13 isotope effect on proton decoupled 13C and 31P n.m.r. spectra of bis(diphenylphosphino)acetylene

High resolution proton decoupled ¹³C and ³¹P n.m.r. spectra of bis(diphenylphosphino)acetylene in (CD₃)₂SO and CDCl₃ are analysed as ABX spectra to give the relative chemical shifts of the ¹³C and ³¹P nuclei as well as the spin–spin coupling constants ³J(PP) and ⁿJ(PC). The differences in ³¹P shieldings are due to secondary ¹³C isotope effects which have been observed to be negligible over more than two bonds.