13C13C spin spin coupling constants in azulenes

[4-¹³C]- Azulene and [4-¹³C]-4-methylazulene have been synthesized. The ¹³C¹³C spin coupling constants have been measured and interpreted in terms of πMO theory.     

Natural abundance 13C13C coupling constants observed via double quantum coherence. The two-dimensional ‘inadequate’ experiment for 13C NMR spectral analysis of erythronolide - B

A one- and a two-dimensional INADEQUATE NMR experiment afforded one-bond ¹³C¹³C coupling constants at natural abundance and total unambiguous signal assignment for erythronolide-B (1). ¹³C¹³C coupling constants at natural abundance and total unambiguous signal assignment for erythronolide-B (1).     

13C NMR of pterocarpans

¹³CNMR spectra of eight pterocarpans are reported Assignments are based on multiplicities and second-order features in off-resonance decoupled spectra and on chemical shifts in model compounds. Comparison of the degree of long-range (C, H) coupling in ¹H-coupled spectra is found useful     

57Fe NMR Chemical shifts and 57fe, 13C coupling constants in α-ferrocenyl carbocations. Direct metal participation in the stabilization of metallocenyl carbocations

The ¹³C{⁵⁷Fe} double resonance method has been used to investigate ⁵⁷Fe-enriched samples of ferrocene derivatives, α-ferrocenyl carbocations and carbonyl complexes with various σ- and π-hydrocarbon ligands. In the α-ferrocenyl carbocations the ⁵⁷Fe resonances span a 1200 ppm range, being a sensitive tool of direct iron participation in the stabilization. The ⁵⁷Fe resonances in the carbocations [FcCH₂][HSO₄] (I), [FcCHMe][HSO₄] (II), [FcCHPh][HSO₄] (III), [FcCHC₅H₄ Mn(CO)₃][CF₃CO₂] (IV), [(Fc)₂CH][BF₄] (V), [FcCHC₅H₄RuC₅Hs][BF₄] (VI) and [FcCMe₂][HSO₄] (VII), ?523.6, ?219.3, 221.0, 368.7, 699.0, 405.0 and 288.5 ppm, respectively, relative to ferrocene, are interpreted in terms of rehybridization of the iron non-bonding d orbitals (shielding effect and the electron withdrawing effect of the substituent in the cyclic ligand (deshielding effect). The role of rehybridization of non-bonding iron orbitals in the low-frequency shift of the ⁵⁷Fe resonances, in addition to that in the previously investigated complex [(C₅H₅)₂FeH][BF₃OH] (?1109.3 ppm), has been demonstrated for bridge-substituted [3]ferrocenophanes, whose ring tilting induces a low-frequency shift of up to 340 ppm relative to their unbridged analogues.The ¹³C NMR spectra of carbocations V and VI reveal a temperature dependence due to the rotation around the C(1)C_α exocyclic bonds. In carbocation VI the ruthenium atom effectively competes with the iron atom to bond with C_α whereas in carbocation V two equivalent metal atoms possess the same ability for such bonding; as a result, complex V has a more pronounced “carbenium ion” nature than IV and VI, as indicated by the relative positions of the ¹³C_α resonances in carbocations IV, V and VI: δ 122.4, 147.2 and 116.9 ppm, respectively.The values of ⁵⁷Fe, ¹³C coupling constants for α-ferrocenyl carbocations exclude Fe-C_α σ-bonding and support a structure in which the iron atom is π-bonded with six carbon atoms of a fulvenoid ligand. According to the data on ⁵⁷Fe resonances and ⁵⁷Fe, ¹³C coupling constants in α-ferrocenyl carbocations the strength of FeC_α bonding is markedly influenced by the electronic effect of the substituent at C_α, being even lower in carbocation I than that of Fe-cyclopentadienyl carbon atoms.     

14N and 13C NMR of tautomeric systems of hydroxy-pyridines

¹⁴N NMR is shown to be an efficient method of investigation of the tautomeric equilibria in hydroxy-and related substituted pyridines. Large relative ¹⁴N chemical shifts within tautomeric pairs estimated from N-Me and O-Me derivatives make possible quantitative determinations of the equilibria. Qualitative conclusions may be drawn from ¹⁴N line widths as well as from ¹³C and proton chemical shifts.     

13C NMR of some insect attractants and related compounds

Ten insect attractants, a number of intermediates in their synthesis and some related compounds were characterized by their 13C NMR spectra. The chemical shifts of the allylic carbon atoms allowed neat distinction between E and Z isomers of alkenic compounds.     

13C NMR spectrum of coumarin

Summary The positions of the signals from the C₃, C₅, C₆, and C₇ carbon atoms in the¹³C NMR spectrum of coumarin have been established with the aid of information obtained from the¹³C NMR spectra of [3-D]-, [4-D]-, and 7-methoxycoumarins and by the use of an additive calculation based on the increments of the methoxy group in the¹³C NMR spectrum of anisole.M. V. Lomonosov Moscow State University Scientific-Research Institute of Pharmacology, Academy of Medical Sciences of the USSR. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 458–462, July–August, 1975.     

13C NMR spectroscopy of cyclopentenpoliols

The ¹³C NMR spectral parameters of eleven cyclopentenpoliols are discussed. Chemical shift criteria to distinguish isomeric 3' and 4' monodeoxy eucommiols have been clearly established.     

Fourier 13C NMR and PMR including 13C satellites of oriented cyanopropyne

Fourier ¹³C and proton NMR spectra of cyanopropyne partially oriented by a nematic phase have been recorded and interpreted. It is shown that more accurate measurements are obtained much more rapidly by observing ¹³C satellites by Fourier PMR than by direct observation of the ¹³C spectrum. The geometry has been extracted from direct couplings; a small but systematic discrepancy with microwave spectroscopy is observed for the carboncarbon bond lengths.     

Computer-assisted determination of carbon connectivity patterns based on natural abundance one-bond 13C13C coupling constants: terpenes

With the help of the interactive computer program CABSA the carbon connectivity pattern of representative known terpenes was established by measuring the one-bond ¹³C¹³C coupling constants in the presence of the signals of molecules containing one ¹³C isotope.     

1H and13C NMR spectra of biologically active compounds

The¹H and¹³C NMR spectra of diols of the hexachlorobicycloheptene and-heptadiene series, and also of the diacetates and sulfites corresponding to them, have been investigated. Criteria for the stereochemical assignment of the compounds mentioned on the basis of chemical shifts and spin-spin coupling constants have been determined.Institute of Chemistry, Bashkir Branch, USSR Academy of Sciences, Ufa. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 439–443, May–June, 1988.     

13C NMR spectra of η3 -allylmanganesetetracarbonyl compounds; structural implications

The ¹³C NMR spectra of η³-allylmanganese tetracarbonyl complexes are consistent with an overall C_s, symmetry and involving a σ_v plane in the Mn(CO)₄ fragment. A dynamic carbonyl interchange process was looked for but the results are inconclusive, however the barrier for this process is certainly greater than 42 kJ/mol. This observation suggests an octahedral type geometry rather than a square pyramid type configuration.     

13C NMR spectra of some furocoumarins

¹³C NMR spectra of some naturally occurring furocoumarins and derivatives have been examined. The assignment of chemical shifts for all the C atoms has been achieved by using techniques recently reported by Bose et al.     

29Si and 13C NMR spectra of permethylpolysilanes

²⁹Si, ¹³C and ¹H NMR spectra are reported for the series of linear permethylpolysilanes Me(SiMe₂)_nMe where n = 1 to 6, for the cyclic permethylpolysilanes (Me₂Si)_n where n = 5 to 8, and for a few related compounds. For linear polysilanes the ²⁹Si and ¹³C chemical shifts can be accurately calculated from simple additivity relationships based on the number of silicon atoms in α, β, γ and δ positions. Adjacent (α) silicon atoms lead to upfield shifts in the ²⁹Si and ¹³C resonances, whereas more remote silicon atoms lead to downfield shifts. The ²⁹Si chemical shifts of the polysilane chains are linearly related to the ¹³C shifts of the carbon atoms attached to the silicon. The ²⁹Si and ¹³C resonances of the cyclic silanes deviate from this relationship. Ring current effects arising from σ delocalization are suggested as an explanation for the deviations. Proton-coupled ²⁹Si NMR spectra are reported for Me₃SiSiMe₃ and for (Me₂Si)_n, n = 5 to 7.     

Natural abundance 13C - 13C coupling constants observed via double quantum coherence. Structural elucidation by the one- and the two-dimensional NMR experiements of velloziolone,a new seco-diterpene.

With the help of Natural Abundance ¹³C - ¹³C Coupling Constants, observed via double quantum coherence, the structural determination of VELLOZIOLONE (1), a new diterpene, has been carried out.     

13C Pulse fourier transform NMR of menthol stereoisomers and related compounds

¹³C NMR spectra of menthol stereoisomers have been determined. The correlations of chemical shifts of these ring carbons with those of stereoisomeric 2-isopropylcyclohexanols are examined. Observed chemical shifts of 1-Me carbons are compared with those predicted from the chemical shifts of stereoisomeric 1-methyl-4-t-butylcyclohexanes. ¹³C NMR spectra of menthyl acetates, and cis and trans p -menthanes have also been examined.