D. Nicole

Sequence distribution of the methyl methacrylate-ethyl acrylate copolymer by 13C n.m.r. spectroscopy

Abstract A method for characterizing triad and pentad distribution by 13 C n.m.r. spectroscopy has been developed and applied for an acrylate-methacrylate copolymer for which the chemical shifts of the homopolymers were sufficiently separated to observe mixed sequences up to pentads. Calculation of the intensity was performed applying Markov-Bernoulli statistics while the chemical shift for each sequence was calculated by a separately developed incremental method. Based on these data, the carbonyl signal was simulated yielding very good agreement at the triad level and satisfactory agreement at the pentad level.

Analysis of β-CH2 signals in the 13C NMR spectra of the methyl methacrylate–ethyl acrylate copolymer as a tool for microstructure determination

The incremental method of the chemical shift calculation in the 13C NMR spectra of the methyl methacrylate–ethyl acrylate copolymer, PMMA/EA, has been applied to the β-CH2 carbons. A positive simulation of the DEPT sub-spectrum shows that it is possible to determine in this way the distribution of configurational-compositional tetrads providing a tool for microstructure analysis of acrylic copolymers.

Chemical structure changes in coals after low-temperature oxidation and demineralization by acid treatment as revealed by high resolution solid state 13C NMR

13C CP/MAS NMR has been used for characterization of chemical structure changes in coals after low-temperature oxidation and prolonged demineralization by acid treatment. In both cases the changes take place mainly in the aliphatic part of coal molecules.

Performance indices for coal liquefaction solvents

Abstract Most coal liquefaction processes are based on the thermal cleavage of activated bonds giving reactive carbon and oxygen radicals which abstract hydrogen atoms from the donor solvent. The role of oil is approximated in this study by using a simple standard reaction. A series of five representative solvents react with phenyl and phenyloxy radicals generated by thermolysis of benzoyl peroxide at 87 °C in tetrachloroethylene. The n.m.r. analysis of the reacting mixture defines four performance indices, i.e. the hydrogen-donor, the efficiency, the recycle and the scavenger indices, which characterize the ability of these solvents as efficient recycle oils in coal liquefaction processes. 9,10-dihydrophenanthrene proves to be by far the most appropriate solvent for this purpose.

Coal liquefaction solvents: An n.m.r. analysis of a recycle oil over successive passes

Abstract Recycle distillates from a coal liquefaction continuous pilot plant, which used prehydrogenated anthracene oil as a start-up solvent and up to seven successive passes over an operation time of 800 h, were analysed by 13 C and 1 H n.m.r. to give average structure and molecular parameters. The fraction of donatable hydrogen steadily decreased in the successive recycle solvents, by ≈ 3 wt% over each pass, as a result of a slow degradation of benzonaphthenic rings into saturates and alkyl-substituted aromatics or five-membered hydroaromatics.

La mutarotation du β-D-fructose en milieu acide dans le dimethylsulfoxyde

Abstract The proton and solvent catalyzed rate constants of furanose formation are 2 to 3-fold greater than those of pyranose formation. The activation and thermodynamic parameters are calculated.

Computer aided analysis of carbon-13 nuclear magnetic resonance spectra of multicomponent mixtures. Part 2. Determination of the content of alkadienes in a light gasoline

A method for the computer aided analysis of 13C nuclear magnetic resonance spectra of multicomponent mixtures has been applied to determine the content of polymerizable compounds, especially alkadienes, in light gasolines derived from the steam cracking process of crude oil. The results obtained are in good agreement with those provided by gas chromatography–mass spectrometry.

The hydroxyl group protonation rates of α, β and γ-cyclodextrins in dimethyl sulphoxide

Abstract The mobility k of the hydroxylic protons of α, β and γ-cyclodextrins are in the order k OH (6)>k OH(2) >k OH(3)′) , thus revealing an instramolecular HO(2)…HO(3′) hydrogen-bond in which the OH(2) hydroxyl group is the donor.

Modelling of hydrogen transfer in coal hydroliquefaction: 5. The reaction of benzylphenylether with four hydroaromatic solvents at 300–450 °C

Abstract The variation of the performance indices of four hydroaromatic solvents: 9,10-dihydrophenanthrene (DHP), tetralin (T), indane (I) and 1,2,3,4-tetrahydroquinoline (THQ), when reacting with benzylphenylether, was studied from 300 °C to 450 °C. The results show that the addition reactions of benzyl radicals on the aromatic ring of the solvent decrease with temperature and lead to index values very close to unity at 400 °C for DHP. However, the degradation reactions of the solvents become very important at 450 °C, especially for THQ in the presence of phenoxy radicals. The classification of the solvents is thus modified as follows: DHP > T > THQ > I .

Hindered rotation around the aryl-to-nitrogen bond of n-acetyl, n-ethoxycarbonylmethyl-2-amino, 5-nitrothiophen

Abstract Two stereoisomers of the title compound are observed by H NMR at 10°. Their spectra coalesce at higher temperature (10°-90°). The equilibrium and rate constants K and k, strongly dependent on the solvent used (1,4-dioxane, tetrahydrofuran, acetone, chloroform); typical values for these parameters and the related thermodynamic functions are: K(25°)= 0.170; k(25°)=23.2s −1 ; ΔH R and ΔH ≠ =4.94 and 17.9 kcal.mol. −1 ; ΔS R and ΔS ≠ =13.1 and 7.7 e.u, in a 0.2 molar solution in 1,4-dioxane. The two isomers are shown to result from a hindered rotation around the aryl-to-nitrogen bond, presumably due to a direct resonance effect between the amide and nitro groups. The more abundant isomer was assigned a planar molecular structure in which the O atom of the amide group is close to the S atom of the thiophen ring, presumably on account of an electrostatic interaction between these two atoms which bear partial electrical charges of opposite sign.