13C NMR measurements

When file polymerization is earned out in the same experimental conditions but without addition of p-TSA (S11CI2 2H20 = 0.4% mass, 180°C and 20 h), the resulting polymer is amorphous with Mw = 40,000 and a degree of racemization equal to 75% (determined from 13C NMR measurements). 

Talancon et al.40 investigated the effects of substituents on the ring-chain tautomerism of Schiff bases being derivatives of norephedrine on the basis of 1H and 13C NMR measurements [19]. 

Sibson, N. R., Mason, G. E, Shen, J. etal. In vivo 13C NMR measurement of neurotransmitter glutamate cycling, anaplerosis and TCA cycle flux in rat brain during [2-13C]glucose infusion. /. Neurochem. 76 975-978, 2001. 

Flash vacuum pyrolysis of tricyclo[7.1.0.04,6]deca-2,7-diene 544 is accompanied by a long cascade of rearrangements leading to various azulenes (equation 214)266. The structures of these products were determined by using the chlorine atoms as labels for the 13C NMR measurements. 

Dynamic 13C NMR measurements show that azocane exists at -112 °C as a 97 3 mixture of a boat-chair and a crown family conformation (AG° = 5 kJ mol-1, AG+44kJmol-1) (78JOC3021). From the NMR spectrum the barrier to ring inversion in the boat-chair is 31kJmol-1, but the barrier to pseudorotation is apparently too low for measurement. Likely candidates for the crown family and boat-chair conformations of azocane are the chair-chair (420), and the BC-1 (421), BC-3 (422) and BC-7 (423) conformations, respectively, but the precise position of the nitrogen atom is not known experimentally. JV-Methyl-and iV-chloro-azocane also have predominantly boat-chair conformations (75JOC369). 

C NMR Spectroscopy. 13C NMR measurements were carried out using a JEOL JMN-GSX 400 spectrometer for quantitative analysis in order to examine the amount of bound phenol in the phenolated SEL s. The analysis was conducted in DMSO-dg by using gated decoupling technique. 

In order to elucidate the conformational characterization of PLA/PLV blend samples obtained by using the four methods as mentioned above, solid-state 13C NMR measurements are made on the blend samples. 

This technique has been used to investigate the distribution of short-chain branches in LDPE and the relatively higher scission efficiency of ethyl branches would rationalize the yields with 13C NMR measurements of branch frequencies (2). 

It can no longer be claimed that dipole moments give reliable quantitative measures of conformational equilibria, and therefore the precise conformation of the perhydroquinazolines awaits low-temperature 13C-NMR measurements. However, for the di-H-axial conformation 332 to be predominant would be unique there is no evidence for any other hexahydropyrimidine existing even partially in such a conformation. 

The poly(ethylene-co-p-methylstyrene) with 10.9 mole % of p-methylstyrene shows a low melting point (76 °C) and very small crystallinity (5.4%), which implies the random distribution of p-methylstyrene along the polyethylene backbone [17]. The detailed sequence distribution can be quantitatively determined by 13C NMR measurements. 

C NMR measurements of 6-dimethylamino-6-methylfulvene, synthesized from 13C-7 labeled phenyldiazomethane via fulvenallene and ethynylcyclopentadiene, supported the proposed mechanism of the ring contraction of phenylcarbene to fulvenallene. The uniform distribution of 13C in the product fulvenallene may be explained in terms of a preequilibrium Before ring contraction, phenylcarbene, a bicyclic intermediate and cycloheptatrienylidene interconvert rapidly [406] ... 

The first measurements of pH-dependences of13C spectra of amino acids were carried out by INDOR spectroscopy [96]. Pulse Fourier transform 13C NMR measurements are less... 

The theory of terpene biosynthesis was confirmed by 13C NMR measurements on derivatives of the diterpenic compounds virescenoside A and B isolated from cultures of the mushroom Oospora virescens (Link) Wallr. inoculated with [l-13C]-acetate and [2-13C]-acetate [1010]. 

The literature on conductivity in poly(p-phenylene sulfide) is confused. According to Shacklette et al.74) heavy doping with AsF5 causes reduction of the polymer with the formation of fused benzothiophene structures which are responsible for conjugation. This would more properly place poly(p-phenylene sulfide) in the category of precursor polymers, discussed later. On the other hand, Friend and Giles 75) proposed an intrinsic conduction mechanism, based on optical measurements and Tsukamoto et al. 76) have presented XPS and 13C NMR measurements to support this view. 

Shine and co-workers239,240 have reported the synthesis and full NMR characterization of a series of alkoxysulfonium ion perchlorates including ions 85 derived from cis- and fraws-substituted cyclohexanols. The X-ray structural study of four salts showed that the orientation of the S O bond is always pseudoaxial. The optically active (—)-86 ion and similar systems have been synthesized.241 1H and 13C NMR measurements indicate that sulfur has a trigonal bipyramidal geometry due to the S—O intramolecular interaction in the axial position. 

Solid state 13C NMR measurements were performed on a JEOL GSX-270 spectrometer operating at 67.8 MHz equipped with a CP/MAS accessory. The field strength of the H decoupling was 1.2 mT, contact time 2 ms, repetition time 5s, and spectral width 27.0 kHz. 8K data points were used. Samples was placed in a cylindrical rotor and spun at about 4 kHz. The nC chemical shifts were calibrated indirectly through the adamantane peak(29.5 ppm relative to tetramethylsilane, TMS, (CH3)4Si). 

The dielectric relaxation exclusively reflects the amide group motions, starting at - 120 °C. So, the mechanical loss, E", occurring at a lower temperature originates from motions of the CH2 units, as evidenced by 13C NMR measurements (Sect. 6.2). Furthermore, these latter show that, at higher temperatures, the phenyl ring motions (oscillations then 7r-flips) are coupled to the amide group motions, in a way similar to that observed for poly(fere-phthalate) (Sect. 4). 

The dynamic mechanical results and the solid-state 13C NMR measurements lead to a deeper insight of the motions occurring below the glass transition temperature in the considered pure aryl-aliphatic epoxy networks, in particular those involved in the p transition of these systems, and the nature of their cooperativity. 

On another hand, dynamic computer modelling performed on isolated CMIMx chains [48] shows that conformational changes of MMA units are more difficult in the neighbourhood of CMI units. This result is confirmed by the 13C NMR measurements in solution [49] (reported in [1], Sect. 8.2). 

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