13C NMR of carbonyl compounds. 3. Structure and dynamics of protonated enones and dienones

The unsaturated ketones $\text{1}$1 – $\text{10}$10 were protonated at low temperatures and studied by dynamic ¹³C NMR spectroscopy. Four interconverting stereoisomers were detected which differ in their conformation with respect to the CO and CC (enone) single bond.     

13C NMR study of the structures of some acyclic and cyclic ketene acetals

A ¹³C NMR study of the spatial structures of some acyclic and cyclic ketene acetals (for example, ketene dimethyl acetal and 2-methylene-1,3-dioxolane) has been carried out. The conclusions obtained are based on observation of the effect of structural changes on the ¹³C NMR chemical shift of the β carbon on the ketene moity. Since the extent of p-π conjugation and hence the ¹³C chemical shift of this carbon depend on the spatial orientation of the alkoxy groups about the O-C(sp²) bonds, the shift concerned may be used as a measure of the planarity of the system. The most stable retamers of ketene dimethyl acetal are s-cis,s-cis (planar) and s-cis,gauche (slightly nonplanar), in the order of decreasing stability. For ketene dialkyl acetals, the relative stability of the planar s-cis,s-cis form decreases with increasing bulkiness of the alkyl groups, but at least for primary and secondary alkyl groups, the s-cis,s-cis rotamer appears to be the most favored species. The conformations of 5- to 8-membered cyclic ketene acetals are discussed and compared with those of the corresponding cyclic vinyl ethers and hydrocarbons.     

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.     

The 13C NMR spectra of π-arenechromium carbonyl complexes

The ¹³C NMR spectra of π-arenechromium complexes XC₆H₅Cr(CO)₂L (where I, L  CO; II, L  PPh₃; X  aliphatic and aromatic substituents) were investigated. The effect of the nature of the substituent X on the chemical shifts of the carbon atoms of the aromatic ring in these complexes was analyzed.It was established that a correlation exists between δ(¹³C) and σ_R (Taft's constant) in complexes I, not only for C(4) nuclei but also for C(3) metal atoms, the difference being that the slopes of the corresponding curves are opposite.     

1H- und 13C-kernresonanzspektroskopische untersuchungen am pleiadien

The results of proton and carbon magnetic resonance studies on pleiadiene (1) are reported. Data are discussed with respect to the structure of 1. Proton resonance studies indicate for 1 a rather planar configuration. Bonding phenomena in the two six-membered rings are only small affected by the 1,8 bridging of the naphthalene. As nonalternant 14 π-electron system 1 shows a carbon-13 spectrum typical for such compounds. The carbon-13 chemical shifts are discussed in comparison to related hydrocarbons.     

1H- and 13C-NMR spectra of palladium and platinum meso-tetraphenylporphyrins

The ¹H- and ¹³C-NMR spectra of palladium and platinum mesotetraphenylporphyrins (TPP) are reported. PtTPP demonstrates spin-spin coupling between platinum and the pyrrole·β-protons and carbons. There is some evidence for spin-spin coupling between platinum and the pyrrole α-carbons. PdTPP and PtTPP also demonstrate upfield shifting of their pyrrole α-carbon ¹³C-resonances. Structural and electronic arguments are advanced to explain this behaviour.     

13C-{1H}-NMR-Spektroskopie von Polyacrylnitril

Ohne Zusammenfassung     

1H- and 13C-NMR study of rotational isomerism in N-vinyltetrazoles

The ¹H- and ¹³C-NMR spectral parameters of N-vinyltetrazoles have been analyzed. It has been found that rotational isomerism is inherent to 1- and 2-vinyltetrazoles. A quantitative estimate of the ratio of rotational isomers has been made. In the case of 1-vinyltetrazoles, introduction of a substituent to the 5-position in the tetrazole ring stabilizes the trans-orientation of the vinyl group relative to the substituent, while in the case of 2-vinyltetrazoles the presence of a substituent in the 5-position of the ring essentially does not affect the conformer population.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1662–1667, December, 1989.     

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.     

Synthesis and 1H, 13C and 15N NMR characterisation of substituted Pyrazolo[4,3-c]quinolines and related compounds

A wide range of novel and known alkyl substituted pyrazolo[4,3-c]quinolines and related compounds were synthesized. Some of these compounds can undergo tautomerism and differences have been noted in the structural assignments already published. For each of these compounds, a complete assignment was made using ¹H, ¹³C and ¹⁵N one- and two-dimensional NMR measurements, including NOESY, COSY, ¹H-¹³C HSQC and ¹H-¹³C HMBC. ¹H-¹⁵N HMBC NMR has proved crucial in determining the relevant tautomeric and protonated state of the compounds.     

O-17 NMR spectra of ring compounds. Correlation of 17O and 13C methyl substitution parameters

The ¹⁷O NMR spectra of 22 1,3-dioxanes, four exanes, four 4-heterooxanes, four tetrahydrofurans and four 1,3-dioxolanes have been recorded and methyl substitution parameters determined for the 1,3-dioxanes. The parameters, including γ_a, correlate linearly with corresponding ₁₃C parameters for methyloxanes.     

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.     

NMR study (1H, 13C and 29Si) of the methylallylsilanes

¹H, ¹³C and ²⁹Si NMR data for the compounds (CH₃)_xSi(CH₂CHCH₂)_4-x are reported. The ¹H resonances from the π system are indicative of the electron-supplying inductive effect (+I) of the (CH₃SiCH₂, moiety but the corresponding ¹³C_π chemical shifts seem to be influenced by a sterically induced polarization of the C-H bonds. The ¹³C_All, ¹³C_Me and ²⁹Si chemical shift data reveal an important neighbour anisotropy contribution originating from the π system. Ultraviolet study of the compounds mentioned above gives indication of a σ—π conjugation in accordance with PES and ab initio results [1—5]. The trend observed in the various coupling constants is too small to be Interpreted.     

1H and 13C nmr study of conformational and electronic structure of 1-vinylpyrroles

The ¹H and ¹³C NMR spectra of some 2-alkyl- and 2,3-dialkyl-1-vinylpyrroles as well as model 1-unsubstituted pyrroles were studied. Alkyi substituents affect electronic structures of the compounds through steric inhibition of p,π-conjugation and π-induction. Correlations of the ¹³C chemical shifts of the pyrrole ring carbon atoms with the total charge density (CNDO/2) of these atoms are established.     

13C-{1H} NMR spectra of episulphide copolymers

Ethylene sulphide-isobutylene sulphide and propylene sulphide-isobutylene sulphide copolymers have been prepared using anionic catalysts and investigated by ¹³C-{¹H} NMR spectroscopy. The carbon-13 NMR spectra are assigned in terms of diad and triad sequences. There is discussion of the effects of mono- or dimethyl substitution in the α, β, γ or δ positions on the chemical shift of the main chain carbon atoms. It has also been shown that for isobutylene sulphide, as for propylene sulphide, under the influence of an anionic catalyst, there is a normal ring opening only at the primary carbon atom.