ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full... more
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full... more
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
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High-frequency (125 MHz) high-resolution 13 C NMR spectra of polybutadiene with varying amounts of 1,2 units were studied. Methine and methylene subspectra were separated using DEPT (Distortionless Enhancement by Polarization Transfer)... more
High-frequency (125 MHz) high-resolution 13 C NMR spectra of polybutadiene with varying amounts of 1,2 units were studied. Methine and methylene subspectra were separated using DEPT (Distortionless Enhancement by Polarization Transfer) techniques. Comparison of the NMR spectra of polyalkenamers, linear polybutadiene, and related structures made it possible to calculate the substitution parameters for the carbons that are up to four bonds away from the branching junction. The assignment of 13 C NMR signals to aliphatic carbons incorporated into the diads or triads of 1,2 or 1,4-units was made.
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A classification of the chemical structure fragments in the ethylene-propylene copolymer chain and the corresponding signals in the 13 C NMR spectrum of this copolymer is proposed. Within the framework of this classification, the... more
A classification of the chemical structure fragments in the ethylene-propylene copolymer chain and the corresponding signals in the 13 C NMR spectrum of this copolymer is proposed. Within the framework of this classification, the positions of signals due to methylene and methine carbon atoms observed in the NMR spectra of the copolymer agree with the spectra calculated by the proposed additive scheme. The values of additive increments of the chemical shifts of resonant carbon atoms in various structural fragments were determined from the results of high- resolution 13 C NMR measurements, including experiments in the DEPT mode.
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Ethylene-propylene-d 6 and ethylene-d4-propylene copolymers were synthesized over a vanadium catalyst. Subspectra for each individual nondeuterated monomer unit in the copolymers were obtained by DEPT editing high-resolution 13 C NMR... more
Ethylene-propylene-d 6 and ethylene-d4-propylene copolymers were synthesized over a vanadium catalyst. Subspectra for each individual nondeuterated monomer unit in the copolymers were obtained by DEPT editing high-resolution 13 C NMR spectra. The subspectra revealed in detail pronounced deuterium isotope effects on carbon resonances. A study of the isotope effects showed that the resulting isotope shifts or split-tings in the initial carbon signals depend on different alignments of asymmetrical propylene units with the macromolecular chain. A comparison of isotopic displacements of split NMR signals allowed the influence of deuterium substitution in the copolymer along the chain over a distance up to five bonds from the resonating carbon atom to be successively estimated. The obtained values of isotopic displacements and their analysis unequivocally confirmed the previous thorough signal assignment for the 13 C NMR spectrum of the ethylene-propylene copolymer. The influence of isoto...
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The paper reports on a measurement of the chemical-shift tensor for 47Ti and 49Ti in TiO2 single crystals (rutile and anatase). The nature of the chemical shift anisotropy is discussed.
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13 C MAS NMR spectrum of polycrystalline [Rh(Acac)(CO)2] (1) displays separate signals from all 7 carbon atoms: 2 doublets from CO ligand carbons along with 5 singlets from Acac carbons. GIPAW calculation of 13 C shielding tensor values... more
13 C MAS NMR spectrum of polycrystalline [Rh(Acac)(CO)2] (1) displays separate signals from all 7 carbon atoms: 2 doublets from CO ligand carbons along with 5 singlets from Acac carbons. GIPAW calculation of 13 C shielding tensor values also revealed nonequivalence of all carbon atoms in molecule 1 in the anisotropic medium of the crystal lattice. Apparently, the C2v symmetry of molecule 1 is broken owing to the asymmetry of its contacts to the neighboring molecules. For example, the contacts O···H–C of two CO ligands of molecule 1 to the CH group of the closest molecule in the adjacent stack are markedly different: the distances OH are 2.72 and 4.38 Å, OC are 3.65 and 5.00 Å, the angles OHC are 164.9° and 126.4°.
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Titanium‐based Ziegler–Natta catalysts for the polymerization of buta‐1,3‐diene give linear trimers of butadiene among other by‐products. A combination of 1H and 13C NMR, DEPT and 2D‐INADEQUATE gives exhaustive assignments of their 13C... more
Titanium‐based Ziegler–Natta catalysts for the polymerization of buta‐1,3‐diene give linear trimers of butadiene among other by‐products. A combination of 1H and 13C NMR, DEPT and 2D‐INADEQUATE gives exhaustive assignments of their 13C NMR spectra and affords their structures. All these trimers are dodeca‐2,4,6,10‐tetraenes which have an isolated cis double bond. The internal double bond of the conjugated triad has a trans configuration in each isomer, and the trimers differ only in the outer double bonds. The 13C NMR spectra of the timers reveal that the signal position of the carbon involved in the conjugated double bond series is mainly controlled by the configuration of the adjacent double bond and, to a lesser extent, by the geometry of its own double bond. The oligomers studied serve as models for polyacetylene. Some reassignments in the spectra of oligomers of terminal acetylenes are proposed.
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The 13C NMR spectra of models for the initial and terminal monomeric unit diads of polybutadiene are interpreted. The models are C10H18, diolefins, separated from the mixture of oligomers which are formed in the reaction of buta‐1,3‐diene... more
The 13C NMR spectra of models for the initial and terminal monomeric unit diads of polybutadiene are interpreted. The models are C10H18, diolefins, separated from the mixture of oligomers which are formed in the reaction of buta‐1,3‐diene with ethyllithium and a proton donor. A version of the INADEQUATE pulse sequence with DEPT polarization transfer and a selective DANTE read pulse is described and used for assignment.
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ABSTRACT Triple-rhodium quantum effects in the HMQC spectra of [Rh6(C0)15L][L = MeCN, I, PBun3, P(0Ph)3, P(4-XC6H4)3; X = H. 0Me, F] modulate the intensity and position of the correlations in the rhodium dimension; cross peaks are... more
ABSTRACT Triple-rhodium quantum effects in the HMQC spectra of [Rh6(C0)15L][L = MeCN, I, PBun3, P(0Ph)3, P(4-XC6H4)3; X = H. 0Me, F] modulate the intensity and position of the correlations in the rhodium dimension; cross peaks are displaced from the true chemical shift, additional cross peaks are seen, and the intensity of the coherences varies as a function of the mixing time and coupling constant, going to zero at the conventional valueof 1/(2J).
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A series of substituted hexarhodium carbonyl clusters [Rh6(CO)15L] (L = PR3 (R = alkyl, aryl), P(OPh)3, NCMe, I−) has been studied by variable temperature and two-dimensional, X-{103Rh}, (X = 13C, 31P) HMQC and 13C EXSY NMR spectroscopy... more
A series of substituted hexarhodium carbonyl clusters [Rh6(CO)15L] (L = PR3 (R = alkyl, aryl), P(OPh)3, NCMe, I−) has been studied by variable temperature and two-dimensional, X-{103Rh}, (X = 13C, 31P) HMQC and 13C EXSY NMR spectroscopy in solution. At low temperatures, the spectra are consistent with retention of the solid state structure. Different localised exchanges of terminal (COt) and face-bridging (COfb) CO's are found to occur over different atoms of the Rh6-octahedron at higher temperatures and the different pathways of the exchanges are discussed. When L = PR3 (R = alkyl, aryl), the lowest energy scrambling surprisingly involves exchange of COt and COfb, associated with the substituted rhodium (text-decoration:underline'S-type), with concomitant exchange of L between the two terminal sites on the substituted rhodium, followed by other localised stereospecific exchanges involving CO's associated with unsubstituted rhodium atoms (text-decoration:underline'U-type). For the other substituted clusters (L = P(OPh)3, NCMe, I−), only text-decoration:underline'U-type exchanges are observed. The kinetics of these exchanges are reported at different temperatures and for the text-decoration:underline'S-type exchange mechanism, the rate is found to vary with the nature of PR3.