Density functional theory calculations were applied to investigate 13C Chemical Shielding (CS) tensors in cryptolepine (1) and its sulfur (2) and oxygen (3) isosteres. The results showed that the CS of carbon nuclei in these compounds may be divided into three types. First, carbons type a, are those directly bonded to X (X=NH, S, O) and s33 shielding component of these carbons are deshielded in O isostere compared to N and S isosteres. The second group of carbons (b-carbons) is attached to α-carbons, in which s11 components of S isostere differs from O and N isosteres. The third carbon group, g-carbons are positioned at a distance of three interatomic bonds or greater away from X. The replacement of N by O or S in cryptolepine isosteres has negligible influence on all components of the later carbon type. The variations of CS components could be related to the inactivity of O isostere and broad spectrum activity of S isostere.

Yellowing of lignin-rich mechanical pulp is mainly attributed to light-induced changes in lignin structure. Hence, in this study the photodegradation of milled wood lignin (MWL) prepared from hardwood bleached chemimechanical pulp (BCMP) was investigated. The lignin preparation was then impregnated on Whatman filter paper and irradiated with UV light during 4 hour exposure time. Then, photodegraded lignin was recovered and characterized by 13C-NMR. Irradiation caused to b-O-4 bonds cleavage, increase in carboxylic and phenolic hydroxyl groups, decrease in methoxyl, primary and secondary hydroxyl group. The amount of b-b and b-5 condensation structures was increased during irradiation.

Stereoregularity and microstructure of polystyrene (PS) were investigated by split para carbon of the benzene ring demonstrated by 13C nuclear magnetic resonance (NMR) spectroscopy. Polystyrene was synthesized via bulk thermal polymerizations at 50, 150 and 250°C at low conversions. Assignment of all the peaks of para carbon in a triad sequence was achieved. Bernoullian statistics was applied for three PS samples and by comparing the experimental and theoretical results it is found that with increasing polymerization temperature the probability of meso is augmented. Furthermore, with increasing NMR acquisition temperature from 20 to 65°C, triad sequences were converted to pentad sequences which follow 1st-order Markov statistics. Finally, it is shown that different deuterated solvents and their mixtures affect peak resolution and splitting of syndiotactic and isotactic sequences. To investigate the effect of deuterated solvent, deuterated benzene and tetrahydrofuran (THF-d8) were also used and the spectra of polystyrene para aromatic carbon of benzene ring in these solvents were compared. There are three peak regions in CDCl3 at 20°C while, in THFd8, syndiotactic region is almost separated and isotactic region overlaps with the atactic region, and in C6D6 both syndiotactic and isotactic regions overlap. As a result, motions of racemic rich segments in THF-d8 are higher than those of meso and conversely the mobility of racemic rich segments in CDCl3 is lower than that of meso rich segments. In summary, in THF-d8 the upfield regions and in CDCl3 the downfield regions show better splitting.

Poly (p-methylstyrene) (Pp-MS) was synthesized at three different temperatures of 50, 150 and 250 °C via bulk thermal polymerization method. The assignment of all stereosequences at triad and pentad levels for two quaternary aromatic carbons and hexad level for methylene carbon was carried out by 13C liquid nuclear magnetic resonance spectroscopy (NMR) in deuterated chloroform at similar conditions. The probability of meso addition (P m) was calculated from second quaternary aromatic carbon and used to predict the relative intensities of methylene and first quaternary aromatic carbon by Bernoullian and first-order Markov statistical models. The results were compared with experimental data. It is shown that the Bernoullian statistics fit better than first-order Markov model for all three samples. The results indicate that P m increases by increasing polymerization temperature. The corresponding P m values determined for synthesized Pp-MSs at 50, 150 and 250oC were 0.383, 0.392 and 0.404, respectively. It was observed that higher resolutions and better splitting patterns were achievable by increasing the NMR acquisition temperature from 20 to 50oC. When temperature increased during NMR acquisition, the resolution improved for the first and second quaternary aromatic carbons and methylene carbon, though there was no splitting pattern observed for methyl carbon atom at the para-position of the aromatic ring.

Ziegler-Natta catalyst for propylene polymerization, which TiCl4 and di-alkyl phthalate were supported on MgCl2, was analyzed by solid state 13C NMR. It was confirmed that the spin-lattice relaxation time (“, relaxation time”,hereafter) of carbonyl group in phthalate was shortened with increasing measurement temperature as a general manner because of the enhancing of molecular mobility at high temperature. The degree of the relaxation period reduction with temperature was influenced by the alkyl group size in phthalate molecule,the larger alkyl group showed a greater shorting of the relaxation period. A short relaxation time should suggest a weak interaction between the phthalate molecule and the MgCl2 support surface. The change in catalytic performance was discussed by the active site formation mechanism involving the phthalate removal step.

We use the molecular dynamics-based method to predict the solid-state 13C NMR lineshape of a planar molecule in a nonspherical cage. Unlike linear molecules, three components of the chemical shielding tensor of a planar molecule are different which gives rise to a different lineshape and temperature dependence in the 13C NMR spectrum. We study the planar ethylene molecule in the oblate large cages of the structure I (sI) clathrate hydrate and extract the lineshapes from the angular distribution and dynamics at four temperatures (70, 150, 200, and 250 K) in the stability range of the hydrate. At low temperature, the C2H4 molecules have limited range of motion in the cages, but as the temperature is raised, they first gain greater rotational freedom about the molecular C=C axis, and then in other directions. These data allow for the calculation of the 13C NMR lineshapes of the C2H4 guests at each temperature.

1H, 13C, 15N and 17O NMR chemical shifts are used for the characterization of the intramolecular interactions in several nitramines of the Me2N-G-NO2 type. The charge of lone electron pair of the amino group in N,N-dimethylnitramine, N,N-dimethyl-2-nitroethenamine, N,N-dimethyl-p-nitroaniline, 4-nitro- b-dimethylaminostyrene, 4-N,N-dimethylamino-b-nitrostyrene, 4-(N,N-dimethylamino)-4’-nitrobiphenyl, and 4-(N,N-dimethylamino)-4’-nitrostilbene is transferred not only to the nitro oxygens, but also to the vinylene and benzene carbons of the G spacer and to N-methyl carbons as well. Decreased nuclear shielding is found to be qualitatively related to the decreased atomic charge around a nucleus. This finding was further verified and quantified by comparison of the NMR data with those obtained by ab initio quantum chemical calculations. 17O NMR chemical shift changes seem to be more significant when the interacting NMe2 and NO2 groups are separated by a short spacer. On the other hand, 15N NMR chemical shifts suggest that a decrease of the charge at the amino nitrogen is not related to the length of the spacer alone. A lack of the linear dependence between the 17Onitro and 15Namino chemical shifts suggests that the charge lost by the amino nitrogen was only partially gained by the oxygens in the nitro group. The increased shieldings of the aryl carbons in 4-(N, N-dimethylamino)-4’-nitrobiphenyl indicate that atoms of the p, p-biphenylene spacer also gain some charge originating from the amino nitrogen. 3 J H,H spin–spin coupling constant shows that among different vinylene compounds, the charge transfer to the nitro group is practically effective only in N,N-dimethyl-2-nitroethenamine where the bond between the vinylene carbons is significantly of low order by character. The calculated Natural Population Analysis (NPA) data confirms that except the nitro oxygens, other atoms that receive the negative charge lost by NMe2 in the compounds studied are the aryl and N-methyl carbons.