Carbon Atoms Of Methyl Groups Research Articles

DETERMINATION OF WOOD COMPOSITION USING SOLID-STATE 13C NMR SPECTROSCOPY

In recent years, solid-state 13C NMR spectroscopy using the technique of cross-polarization (CP) and sample rotation at a magic angle (MAS) has been widely used in the analysis of plant materials, including wood. Knowledge of the composition, structure and behavior of wood components under various conditions is of great importance, since the properties of wood materials depend on this. In this work, differences in the composition of wood belonging to various tree species growing in central Russia (spruce, aspen, birch, oak, linden, pine, poplar and larch) were revealed using CP MAS 13C NMR spectroscopy. The assignment of various peaks in CP MAS 13C NMR spectra to the main components of wood was carried out. It was shown that cellulose is present in its amorphous and crystalline forms, the presence of lignin was unambiguously confirmed by the signals of aromatic carbon atoms, and hemicelluloses were detected by the signals from the carbon atoms of methyl groups of acetylxylose and L-rhamnose. According to the integral intensities, the total ratio of cellulose and hemicelluloses to lignin was determined: the largest amount of lignin was found in coniferous wood (spruce, larch and pine), and the smallest amount of lignin was detected in deciduous species (aspen, oak, linden, birch and poplar).

CP MAS 13C NMR SPECTROSCOPY IN DETERMINATION OF SPECIFIC DIFFERENCES IN COMPOSITION OF WOOD

In recent years solid-state 13C NMR spectroscopy using the technique of cross-polarization (CP) and sample rotation at a magic angle (MAS) has been used in the analysis of plant materials, including wood. Knowledge of the composition, structure and behavior of wood components in different conditions is of great importance, since the properties of wood materials depend on this. In this work differences in the composition of various tree species wood in central Russia (birch, aspen, spruce, and larch) were revealed using CP MAS 13C NMR spectroscopy. Assignment of various peaks in CP MAS 13C NMR spectra with the main components of wood was carried out. It was shown that cellulose is presented in amorphous and crystalline forms, the presence of lignin is unambiguously confirmed by signals of aromatic carbon atoms, and hemicellulose is detected by signals from carbon atoms of methyl groups of acetylxylose and L-rhamnose. According to the integral intensities, the total proportion of cellulose and hemicellulose in relation to lignin was determined: the largest amount of lignin was found in coniferous wood (spruce, larch), and the smallest amount of lignin was detected in deciduous species (aspen and birch).

Investigating the electronic structure of tetramethylsilane by means of X-ray spectroscopy and theoretical calculations

The electronic structure of a tetramethylsilane molecule Si(CH3)4 is studied via X-ray fluorescence spectroscopy and simulations based on the density functional theory. An analysis of the molecular orbitals is conducted on the basis of the calculations, and a theoretical Si\({k_{{\beta _1}}}\) X-ray fluorescence spectrum is constructed that appears to be in good agreement with the experimental findings. The main types of chemical interactions between the silicon atoms and carbon atoms of methyl groups are revealed.

Modified (n, 0) BN nanotubes (n = 3–10) by acetic acids: DFT studies

Covalent additions of one acetic acid molecular group to the tips of eight (n, 0) boron nitride nanotubes (n=3–10) have been investigated by density functional theory (DFT) calculations. The results indicated that the properties of pristine and modified models detect almost similar effects by widening the nanotubes. The values of dipole moments and energy gaps have been increased for wider nanotubes. Comparing to the pristine models, the values of dipole moments and energy gaps show different properties for the models of two types of modifications. The values of binding energies have not been significantly changed for wider nanotubes. The atomic scale properties have been also investigated by computations of quadrupole coupling constants, in which the most significant effects of modifications have been observed for the atoms close to the modified regions. And finally, the properties for carbon atoms of methyl groups and oxygen atoms of carbonyl groups of the acetic acid molecular groups have been notably changed among the investigated modified BNNTs.

Crystal structure of volatile pyridine adducts of trimethylplatinum(IV) β-diketonates

The structures of volatile pyridine adducts of trimethylplatinum(IV) β-diketonates derived from acetylacetone (Hacac) and dipivaloylmethane (Hdpm) are studied for the first time. Their preparation is reported and the data of thermal studies obtained by the DTA technique are presented. The structures of the compounds in question comprise monomeric complexes. The platinum atom is coordinated to three carbon atoms of methyl groups, two oxygen atoms of β-diketone, and the nitrogen atom of the pyridine molecule. The (PtC3O2N) coordination core has the shape of a slightly distorted octahedron. The geometrical characteristics of the coordination cores are the following: in all complexes, the values of Pt-O, Pt-CMe, Pt-N bond lengths and O-Pt-O chelate angles fall within 2.122–2.146 A, 1.986–2.079 A, 2.131–2.186 A and 89.3–90.6° respectively.

NMR and semiempirical conformational analysis of the 2-aryl-1,3-dihydroxy-4,4,5,5-tetramethylimidazolidines

2-Aryl-1,3-dihydroxy-4,4,5,5-tetramethylimidazolidines (1) were synthesized and their 1H and 13C NMR spectra recorded. Quantum mechanical semiempirical calculations were also performed, for a better understanding of the signals recorded in the NMR spectra of imidazolidines. The conformation of the imidazolidine ring was initially studied for the 2-methyl-1,3-dihydroxy-4,4,5,5-tetramethylimidazolidine (2), used as a model molecule. The results of the calculations obtained for structure 2 showed that the methyl groups are located in axial and equatorial positions. At these positions, the methyl groups are affected by the magnetic anisotropic effects of carbon-nitrogen and carbon-carbon bonds of the imidazolinyl ring with different intensities. Semiempirical calculations for structure 2, suggested that the effect of the γ-oxygen on the carbon atoms of methyl groups (γ-effect) might lead to an alteration of the electronic charge density and consequently to a change in the diamagnetic shielding on these groups. These data were used for the analysis of the NMR spectra of compound 1. The diamagnetic shielding effects, estimated from the calculated electronic charge densities on the carbon atoms of methyl groups, are in agreement with the signals observed in the NMR spectra of compound 1. By combining the contribution of the anisotropic and γ-effects, it appears that the axial methyl groups are located relatively closer to the γ-oxygens in compounds 1.