Oxidation of 1,3-butadiene over Pd/C and Pd-Te/C catalysts in polar media

The oxidation of 1,3-butadiene over the Pd/C and Pd-Te/C heterogeneous catalysts occurs in organic solvents containing water at a temperature of 100°C and an oxygen partial pressure of $P_{\left[ {O_2 } \right]} = 4$ atm. Crotonaldehyde dominates among the three major products of oxidation over the Pd catalyst. The introduction of Te into the catalyst increases the methyl vinyl ketone yield, the furan yield being the lowest in all cases. X-ray photoelectron spectroscopy (XPS) showed that the active catalyst components can be in a partially oxidized state, particularly after storing the catalysts in air. Additional hydrogen treatment results in almost complete reduction of the active components to metals and enhances the catalytic activity. It is supposed that the oxidation of 1,3-butadiene over the Pd-Te catalysts proceeds via the activation of dioxygen over the Pd⁰ sites, with oxidized Pd and Te participating in subsequent chemical transformations.     

Copolymerization of 1,3-butadiene and styrene with a neodymium catalyst

Homo- and copolymerization of butadiene and styrene in the presence of the catalyst system Nd(octanoate)₃/CCl₄/Al(iBu)₃ (iBu: isobutyl) were investigated at 60°C in heptane as solvent. The initiating catalyst system is very effective in the polymerization of butadiene. However, the presented copolymerization of butadiene and styrene is only practicable when using a special addition order of the catalyst components and a prescribed ageing phase. Copolymers obtained from various monomer feed ratios were characterized by ¹H and ¹³C NMR spectroscopy and gel-permeation chromatography (GPC). The copolymer characteristics especially microstructure, molar mass and molar-mass distribution (MMD) are strongly dependent on the composition of the monomer mixture.     

Ethylene‐norbornene copolymers prepared with metallocene‐ based catalysts: new sequence assignments by 13C NMR

A series of ethylene‐norbornene copolymers were synthesized in the presence of zirconocenes with different symmetries and ligand patterns and at different norbornene (N)/ethylene (E) mole ratios. Copolymers were characterized by ¹³C NMR spectroscopy; Inadequate NMR sequences were used also. The comparison of ¹³C NMR spectra of copolymers prepared with different norbornene content and the correlation between ¹³C NMR chemical shifts and conformational structures of the chain on the basis of molecular mechanics calculations were performed. Preliminary assignments were revised and new comonomer sequences such as ENNE which contain meso and racemo NN dyads were assigned.     

DFT-GIAO-NBO and 13C NMR study of the delta-syn-axial effect in 2,4-disubstituted adamantanes

Six groups of diastereomeric 2,4-disubstituted adamantanes were studied with DFT-GIAO-NBO (natural orbital analysis) methods. The calculated (13)C chemical shifts reproduce well the experimental data. It was found that among all diastereomers, those bearing substituents in delta-syn-axial positions showed the largest overall deshielding, i.e. the sum of all (13)C chemical shifts [Sigmadelta((13)C)] was the greatest and also had the highest delocalization contribution to the molecular energy evaluated with NBO. The higher delocalization energy is proposed to be the origin of the deshielding delta-syn-axial effect.     

A 13C NMR study of the dynamic structure of the thiourea-ferrocene inclusion compound

¹³C NMR anisotropic chemical shielding spectra of the thiourea-ferrocene inclusion compound were measured between 125 and 294 K. The orientations and dynamic behaviour of ferrocene molecules trapped in the channels are discussed.     

A study of sesquiterpene lactones by13C NMR spectroscopy. I.13C NMR spectra of badkhyzin and its derivatives

The¹³C NMR spectra of badkhyzin and its derivatives have been studied.     

N-Oxides of polychloropyridines.13C NMR study

The effect ofN-oxidation of a series of polychloropyridines on¹³C NMR parameters has been studied. It has been established that inN-oxides of polychloropyridines an electric field through-space effect of theN-oxide group predominates in the shielding of the -carbon atom compared to the other carbon atoms. A linear correlation between¹³C NMR chemical shifts and total charge densities calculated by the MNDO method for the carbon atoms ofN-oxides of polychloropyridines has been found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2425–2428, December, 1995.The authors are grateful to V. V. Kolchanov for help in the synthesis of compounds under study.     

13C NMR spectra and the structure of dithizone

The structural characteristics of dithizone in the solid state and in solution were studied by a high-resolution¹³C NMR method. A highly symmetrical structure of dithizone was established in the crystalline state, and it was suggested that it exhibits dual behavior in complexation reactions with metal ions.V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 117975 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 113–117, January, 1992.     

The assignment of the 1H and the 13C NMR chemical shifts of N-phenyl-2,4-dimethylbuta-1,3-diene-1,4-sultam

The assignment of the signals in the ¹³C and ¹H NMR spectra of N-phenyl-2,4-dimethylbuta-1,3-diene-1,4-sultam is difficult for the signal pairs C-2 and C-4, C-1 and C-3, (C-1)? H, (C-2)? CH₃ and (C-4)? CH₃. The ¹³C NMR spectrum recorded under gated decoupling conditions provide long-range couplings which make possible an unambiguous assignment of the ¹³C NMR signal pairs. Application of the ¹H CW off-resonance decoupling technique in recording the ¹³C NMR spectra enables the assignment information from the ¹³C NMR spectrum to be transferred to the ¹H NMR spectrum.     

Polymerization and copolymerization of 2-phthalimidomethyll 1,3-butadiene. II. Kinetic study of the polymerization of 1,3-butadiene and of the copolymerization of 1,3-butadiene with 2-phthalimidomethyl 1,3-butadiene initiated by bis-(η3-allyl nickel trifluoroacetate)

The kinetics of the polymerization of 1,3-butadiene initiated by bis(η³-allyl nickel trifluoroacetate) prepared in benzene was studied in methylene chloride at 40°C. The reaction is first order with respect to the monomer, second order with respect to the catalyst in contrast to the case in which solvent is benzene. We have shown that the presence of a polar molecule (fe, N-methyl phthalimide) decreases the overall rate of polymerization. The apparent reactivity ratios for the system 2-phthalimidomethyl 1,3-butadiene (1)-1,3-butadiene (2) are r₁ = 0.65 ± 0.006 and r₂ = 0.48 ± 0.015.     

1 H and 13 C NMR spectra and structure of 2-trichloromethyl-4-methylene-1,3-dioxolanes

The ¹H and ¹³C NMR spectra of a number of 5-substituted 2-trichloromethyl-4-methylene-1,3-dioxolanes were studied. It was observed that the exocyclic double bond is in effective conjugation with the 3–0 ring atom. The configuration of the substituents was established, and a conformational model of these heterocycles of the envelope type with the 1–0 atom deviating from the plane in which the remaining ring atoms are situated is proposed. The applicability of the ¹³C NMR spectra for the determination of the configuration of the compounds is demonstrated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1176–1180, September, 1976.     

13C and1H NMR spectra and structure of 2-aryl-1,3-dibenzoyl-1,3-diazabicyclo[3.3.1]nonanes

Conclusion ¹³C and¹H NMR spectroscopy was used to determine the structures of 2-aryl-1,3-dibenzoyl-1, 3-diazabicyclo[3.3.1]nonanes and 2-aryl-1-benzyl-3-benzoyl-1,3-diazabicyclo[3.3.1]nonane. These compounds were found to exist predominantly in the boat-chair conformation (boat for the diaza ring), while the 2-aryl substituents occupy the exo or endo position.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1023–1028, May, 1988.     

Coisotactic shift contributions in 13C NMR spectra of propylene/butene-1 copolymers

Coisotactic shift contributions caused by sterically crowded isotactic side-chain alkyl groups are proposed for peak assignments of isotactic propylene/butene-1 copolymers. Previously disputed analyses of methine triads and PB tetrads of backbone methylene carbons (α,α′-CH₂) have been verified using first-order Markovian distribution theory. Coisotactic shift contributions also account for the reverse order of the propylene-centered triads from that predicted by the Grant-Paul equation.     

A study of sesquiterpene lactones by13C NMR spectroscopy. II.13C NMR spectra of alkhanin,acetylartemisin, and tauremisin

The¹³C NMR spectra of alkhanin, acetylartemisin, and tauremisin have been studied.     

A 13C NMR study of the structure of sulfur-stabilized carbanions

The structure of the lithium and potassium salts of φSCH₃,φSOCH₃,φSO₂CH₃,φSO(NCH₃)CH₃ has been studied by ¹³C NMR in different solvents. The results show that the metalated carbon is nearly pyramidal in and nearly planar in φSOCH₂^?M⁺, whatever the solvent are cation are φSO₂CH₂^? φSCH₂^?M⁺ and φSO(NCH₃)CH₂^?M⁺ are in an intermediate hydridization state, cation and solvent dependent. For the sulfoxide, a four-center chelate is proposed, stable to strong solvating agents and only disrupted by cryptands. It is very likely responsible for the planar configuration of the anionic carbon.The low temperature study of φSOCH₂Li shows the existence of aggregates in THF. HMPA or external lithium salts disrupt these associations, giving rise to other species.The ¹³C NMR parameters of the whole series of sulfur-stabilized carbanions are quite consistent with the date reported for phosphorous and arsenic ylids: the

coupling constants appear to be a good probe of the geometry of the anionic carbon, whereas the chemical shifts are rather insensitive to its hybridization state.     

Quantum chemical study of the structure of tricyclic saturated hexafluoro-1,3-butadiene dimers

Results of a quantum-chemical study of the molecular structure of dimerization products of saturated 1,3-butadiene and hexafluoro-1,3-butadiene (tricyclo[3.3.0.0^2.6]octane, dodecafluorotricyclo[4.2.0.0^2.5]octane (I), and dodecafluorotricyclo[3.3.0.0^2.6]octane (II)) are presented. The calculated symmetry of the molecule of I in vacuum (C ₂) differs from its symmetry in the single crystal (C _b , XRD). The most stable of dimers (II) contains C-C bonds with a length of up to 1.573 Å and a four-atom cycle with angles of 82.3°.     

Comparison of the electrophilic and free-radical addition of halogens with hexafluoro-1,3-butadiene and 1,3-butadiene

Ionic and photochemical reaction of chlorine (Cl₂), bromine (Br₂) and iodine monochloride (ICl) to hexafluoro-1,3-butadiene (1) and 1,3-butadiene (2) were carried out under conditions that would provide product distributions under controlled ionic or free-radical conditions. Product distributions for ionic reaction of Cl₂ and Br₂ with 1 are similar and suggest a weakly-bridged halonium ion species. Theoretical calculations support weakly-bridged chloronium and bromonium ions for both dienes 1 and 2. There are more of the 1,4-dihalo-2-butene products from ionic halogenation of 1 than 2 which correlates with the greater charge density on carbon-4 of halonium ions from 1. Ionic and free-radical reactions of ICl with 1 give 8 and 2% of 3-chloro-4-iodohexafluoro-1-butene and 4-chloro-3-iodohexafluoro-1-butene, respectively. The minor cis-1,4-dihalo-2-butene products from 1 and 2 are reported when formed.