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.     

Benzo- and indolo-quinolizine derivatives XI—The configurational and conformational study of 1,2,3,4,4a,6,7,8,9,13b-decahydro-9aH-pyrido[1,2-f]phenanthridine isomers by 270 MHz 1H n.m.r.

The preferred conformations of the four isomers of 1,2,3,4,4a,6,7,8,9,13b-decahydro-9aH-pyrido[1,2-f] phenanthridine have been determined by 270 MHz ¹H n.m.r. and i.r. spectroscopy. N.m.r. assignments are based on the specific chemical shifts of the protons adjacent to the nitrogen atom, their geminal coupling constants and on the shifts induced by the C? C bonds and by the benzene nucleus. Specifically deuterated derivatives and double resonance experiments confirm the assignments unequivocally. These data are completed by solvent and temperature studies.     

NMR-daten substituierter 1,2-diphospholane sowie des 1,5-diphosphabicyclo[3.3.0]octans und seiner p-derivate

The structures of 1- and 2-substituted 1,2-diphospholanes and of 1,5-diphosphabicyclo[3.3.0]octane and its P-derivatives are elucidated, using their ¹³C and ¹³P-n.m.r. spectra. In case of the latter compounds the ³¹P-chemical shifts indicate an additional, sterically caused, interaction of the phosphorus atoms. Within the limits of n.m.r. sensitivity all compounds are sterically uniform.     

Conformational analysis of the dibenzo [a,g]-quinolizidines by spectroscopic means. II—The use of high resolution 270 MHz proton magnetic resonance

The 270 MHz ¹H n.m.r. spectra of some model tetrahydroprotoberberines have been analysed and the dependence of the chemical shifts and the geminal and interbenzylic coupling constants on the conformation examined. Their use for conformational analysis was illustrated on two 8-methyl substituted epimers.     

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 n.m.r. spectra of rotameric dimethyl 1-isopropyldibenzo[b,e]bicyclo[2.2.2]octatriene-7,8-dicarboxylate: Non-equivalency of carbons along the rotational axis

¹³C n.m.r. spectra of dimethyl 1-isopropyldibenzo[b,e]bicyclo[2.2.2]octatriene-7,8-dicarboxylate disclose the existence of both dl and meso isomers, whereas ¹H n.m.r. spectra were interpreted by the sole existence of the former. Characteristic chemical shifts for the rotamers were found, among others, for carbons along the rotational axis. The non-equivalence is most probably attributed to the difference in geometry about the carbons in question. An unusual fact was also that the more compressed methyl carbon of the isopropyl group gives a signal at higher field.     

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.     

Carbon-13 n.m.r. spectra of 2,3-dimethylenebicyclo[2.2.1]heptanes and 2,3-dimethylene-7-oxabicyclo[2.2.1]heptanes

The ¹³C n.m.r. spectra of 11 derivatives of 2,3-dimethylenenorbornane, 1–11, of 5 derivatives of 2,3-dimethylene-7-oxanorbornane, 12–16, and of 2,3,5,6-tetramethylene-7-oxanorbornane (17) have been measured and the chemical shifts have been assigned. The effects of 1-methyl, 5-hydroxy, 5-acetoxy, 5-para-bromobenzenesulphonyloxy and 5-keto substituents on the olefinic carbons of the s-cis-butadiene group are compared with the same substituent effects reported for model compounds. Apparent linear correlations between the reciprocals of the V←N transition energies of the butadiene chromophores and the differences of the chemical shifts ΔδC between the quaternary and methylene olefinic carbons are found for the dienes 1–3, 12–14, butadiene and 2,3-dimethylbutadiene. The ΔδC of the olefinic carbons of the tetraene 17 also falls on the correlation line if the average of the two absorption hands at 250 and 228 nm is taken for the V←N transition energy of this compound. The chemical shift of the carbon of the methano bridge H₂C-7 is almost insensitive to the presence of one or two methylene groups at C-2,3, in contrast with the downfield shift of 10–14 ppm observed when an endocyclic double bond is introduced into the norbornane skeleton.     

Structural studies by 1H and 13C dynamic n.m.r.: Part III alternative protonation sites in carbonyl conjugated enamines of the type R1?C(O)?CH?CH?NR2R3

¹³C magnetic resonance spectra of several enamino ketones with secondary and tertiary amino groups were obtained for trifluoroacetic acid solutions. In both series O-protonation is predominant and the chemical shifts are related to the electron density changes with respect to the parent base. The spectra of the tertiary compounds are interpreted in terms of slow rotation around the C–1? C–2 and C–3? N bonds discernible at room temperature. O-protonated forms of the secondary enamino ketones undergo further reaction on C–2 yielding pyridinium salts. The mechanism of formation of the quaternary salts is interpreted and the additivity parameters of the ¹³C n.m.r. chemical shifts in the pyridinium ions is briefly discussed.     

Proton n.m.r. spectra of furo[3,2-c] and furo[2,3-c]thiapyrylium cations,compared with their thieno homologues. Correlations between chemical shifts and charge densities from CNDO/2 and PPP calculations

Significant variations of thiapyrylium chemical shifts, by comparison with their thienohomologues, are shown by ¹H n.m.r. spectra of furo[3,2-c]thiapyrylium and furo[2,3-c]thiapyrylium perchlorates. The observed changes can be ascribed to a different distribution of the electron charge (mainly caused by participation of the 3d orbitals of sulphur in the thienohomologues) and to a different contribution of the ring current; this is shown by MO calculations performed by the CNDO/2 and the coupled Hartree–Fock methods, respectively.     

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.     

1H N.m.r. Chemical shifts and hydrogen exchange rates oftrans-[Co(en)2XY]n+ complexes in liquid ammonia

Summary ¹H n.m.r. spectra of coordinated ethylenediamine HN< hydrogens for 23trans-[Co(en)₂XY]ⁿ⁺ complexes and¹H-²H exchange rates for some selected compounds are reported in the solvent liquid ammonia. Assignments are presented for asymmetric complexes. These are based on the chemical shift order of the symmetric complexes. The assignments are confirmed by independent experimental findings including the effect of specific ion-association and the observed exchange rates. The exchange rates follow the relation k_obsd=k⁰+k¹ [N²H₄ClO₄]^–1, illustrative of general base-catalysis; in this case rate-determining proton abstraction by N²H₃ and N²H ₂ ^– , respectively. Chemical shifts and exchange rates in liquid ammonia follow the published order of the aqueous parameters.     

1H NMR spectra of the 2-trifluoroacetyl derivatives of benzo[b]furan and benzo[b]thiophene

The ¹H NMR spectra of the 2-trifluoroacetyl derivatives of benzo[b]furan and benzo[b]thiophene were recorded at 200MHz in two solvents, chloroform and acetone. A long-range coupling constant, 5J(HF), between the fluorine nuclei of the trifluoroacetyl group and H-3, of a value higher than 1 Hz, was measured. From the comparison of the ¹H chemical shifts of, and the solvent effects on, the trifluoroacetyl compounds and those of the corresponding 2-acetyl derivatives, and on the basis of an empirical interpretation of the ⁵J(HF) coupling constant, a predominant Z conformation was tentatively assigned to these derivatives.     

Carbon-13 NMR spectra of some phenanthrene derivatives from Aristolochia indica and their analogues

¹³C NMR spectra of compounds related to aristolochic acid and aristololactam, the constituents of Aristolochia indica, have been studied to determine the chemical shifts and coupling constants of polysubstituted phenanthrenes. Selective ¹H decoupling and long-range couplings were utilized for the assignments. Substituent-induced chemical shifts and also the effects on coupling constants could be deduced in some cases. Anion formation was found to be particularly helpful in the interpretation of the spectra of carboxylic compounds. Shift assignments of some structurally related compounds could also be made.     

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.     

Cage compounds IV. 1H and 13C NMR study of 3,6-epoxypentacyclo-[6.2.2.02,7.04,10.05,9]dodecane and 3,6-epoxypentacyclo-[6.2.1.02,7.04,10.05,9]undecane

The complete ¹H and ¹³C NMR assignments for 3,6-epoxypentacyclo[6.2.2.0^2,7.0^4,10.0^5,9]dodecane and 3,6-epoxypentacyclo[6.2.1.0^2,7.0^4,10.0^5,9]undecane are reported. The difference between the ¹H and ¹³C chemical shifts and one-bond proton-carbon coupling constants of these two compounds are adequately explained by the difference in the hybridization of the C? H bonds.     

Carbon-13 NMR spectroscopy of hop bitter substances

The ¹³C NMR spectra of the most important hop bitter substances are analysed. All individual carbon atoms are assigned, except the oxygen bonded sp² carbon atoms. Most assignments are made partly by comparison with analogous compounds and partly by reference to literature data. Cross-correlations with the ¹H NMR shifts are made for two main products and confirm the correctness of the assignments. All data are in agreement with the known structures.     

13C NMR spectra of thiophenes. III—Bromothiophenes

The ¹³C NMR spectra of all bromo substituted thiophenes have been obtained at 15·085 MHz. ¹³C signal assignments for monobromothiophenes have been confirmed by comparison with the spectra of their partially deuteriated derivatives; a revision is made for the assignment in 3-bromothiophene. The substituent effect of bromine is generally additive for the ¹³C chemical shifts. The substituent effect on various types of ¹³C, ¹H coupling constants is also obtained and discussed.     

Furopyridines. XI. 13C NMR Spectra of 2- or 3-Substituted Furo[2,3-b]-, Furo[3,2-b]-, Furo[2,3-c]- and Furo[3,2-c]pyridine

The ¹³C nmr spectra of 2- or 3-monosubstituted furo[2,3-b]- 1a-1j , furo[3,2-b]- 2a-2j , furo[2,3-c]- 3a-3j and furo[3,2-c]pyridine derivatives 4a-4j are reported. Effects by change in annelation and substituent effects on ¹³C chemical shifts and carbon-proton coupling constants are discussed. The spectra of benzo[b]furan derivatives 5a-5j having the corresponding substituent are also reported for comparison.     

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.