Carbon chemical shifts temperature

The proton and carbon chemical shifts of twenty-one and twenty different anthocyanins are presented in Table FI. 4.4 and Table FI. 4.5, respectively. These anthocyanins are chosen to illustrate the chemical shifts of the majority of anthocyanin building blocks reported. The linkage positions of the various anthocyanin building blocks may be conspicuous through shift comparison. However, be aware of shift effects caused by variation in solvent, pigment concentration and temperature. Table FI.4.6 contains typical H- H coupling constants of the most common anthocyanidins. 

The C NMR spectrum of oxyphenbutazone in acetone-dg using TMS as an internal reference was obtained using a Jeol FX 100 MHz Spectrometer at an ambient temperature using 10 mm sample and is presented in Figure 4. The carbon chemical shift values are derived from the off-resonance spectrum and are listed below. The results are consistent with those reported earlier (5). 

Both were recorded over 5000 Hz range in DMSO-dg on FT 80, 80 MHz NMR spectrometer, using 10 ml sample tube, and tetramethylsllane as reference standard at ambient temperature. The carbon chemical shifts assigned on the basis of additivity principle and off-resonance splitting pattern are given in Table 3. 

Polyethylene Backbone and Side-Chain C-13 Chemical Shifts in ppm from TMS (+0.1) as a Function of Branch Length (y Carbon Chemical Shifts, which occur near 30.4 ppm, are not given because they are often obscured by the major 30 ppm resonance for the "n" equivalent, recurring methylene carbons). Sol vent 1,2,4-trichlorobenzene. Temperature 125°C. 

The numbers surrounding the structure are the carbon chemical shifts at -90°C a d indicates a doublet due to C-P coupling.) Account for the changes in the spectrum as the temperature is raised from -90 to 20.4°C. 

PDHS Structures in Solution. The determination of the chain conformation of polysilylenes in solution, particularly the conformations at temperatures just above or below the low-temperature thermochromic transition, is of great interest. NMR spectroscopy is one of the most useful techniques for probing chain conformation in solution (2i), and NMR is especially effective because of the large sensitivity of the carbon chemical shift to bond conformation (22). Silicon nuclei are also very sensitive to chain conformation, but a good correlation between silicon chemical shift and bond conformation has not been established yet. Unfortunately, both of these nuclei suffer from low sensitivity, primarily because of their low natural abundance. In contrast, protons have an essentially 100% natural abundance, but compared with the carbon or silicon chemical shift, the proton chemical shift is not very sensitive to bond conformation. Efforts to use NMR to probe the low-temperature dilute-solution conformation of the polysilylenes have been unsuccessful thus far. The diflSculty is that PDBS and PDHS precipitate from solution in 20-30 min after cooling through the thermochromic tran-... 

Dean et al. (65) have prepared organometallic mercury (2+) compounds of the type Hg2(AsF6)a Arene. The NMR spectra of these complexes exhibit averaged arene carbon signals due to rapid free-complexed arene exchange at NMR probe temperatures. On the basis of the variation of the aryl carbon chemical shift with the arene/Hg22 ratio for the system Hg2(AsFe)2-hexa-methylbenzene (HMB) the existence of the following two equilibria was determined ... 

Equilibrium isotope effects in 2-methyl-2-norbornyl cation have been investigated and it was inferred from the direction and the small size of temperature-dependent isotope effects on the carbon chemical shifts of 2-CDj-2-norbomyl cation (Lloyd, 1978) that the carbon spectrum is actually an averaged spectrum of three rapidly equilibrating isomeric cations. One tertiary cation [109] and two hypercoordinated cations [110] and [III] were estimated to have about the same energy and to be present in a ratio of about 70 25 5 at — 115°C. The equilibrium is nondegenerate and K is very large in favour of the tertiary cation [109] only small isotope effects are therefore observed. 

Synthesis and Properties.—Perhaps the most interesting new compound that might be included in this section is the non-ylidic F4S=CH2 (1)," a colourless, stable gas that boils at —19 °C and has been synthesized as shown. The carbon chemical shift of 43.9 p.p.m. is very different from that for phosphonium ylides, suggesting that there is little negative charge on the carbon atom in (1). Carbon is sp -hybridized and the barrier to rotation about the C=S bond (estimated bond order is 1.9) is greater than 25kcalmol" this precludes free rotation at room temperature. 

Section 15 14 The hydroxyl group of an alcohol has its O—H and C—O stretching vibrations at 3200-3650 and 1025-1200 cm respectively The chemical shift of the proton of an O—H group is variable (8 1-5) and depends on concentration temperature and solvent Oxygen deshields both the proton and the carbon of an H—C—O unit Typical... 

From the NMR data of the polymers and low-molecular models, it was inferred that the central C—H carbons in the aliphatic chain in polymer A undergo motions which do not involve the OCH2 carbons to a great extent. At ambiet temperatures, the chemical shift anisotropy of the 0(CH2)4 carbons of polymer A are partially averaged by molecular motion and move between lattice positions at a rate which is fast compared to the methylene chemical shift interaction. 

Lead-proton and lead-carbon coupling constant values have structural uses, as with tin. Lead chemical shifts are quite sensitive to temperature variations. 

Polymer Characterization. Proton NMR spectra at 300 MHz were obtained from a Varian HR-300 NMR spectrometer. Deutero-benzene and spectrograde carbon tetrachloride were used as solvents. The concentration of the polymer solutions was about 1-5%, Carbon-13 NMR spectra were obtained from a Varian CFT-20 NMR spectrometer, using deuterochloroform as the solvent for the polymers. The concentration of the solutions was about 5%. Chemical shifts in both proton and carbon-13 spectra were measured in ppm with respect to reference tetramethylsilane (TMS). All spectra were recorded at ambient temperature. 

The carbon-13 NMR spectrum of griseofulvin (Figure 3) was obtained at ambient temperature in DMSO-d containing TMS as internal reference utilizing Varian Associates XL-100-15 spectrometer equipped with Fourier accessories The system was locked to the deuterium resonance frequency of the solvent, and operated at a frequency of 25.2 MHz for carbon-13. The chemical shifts are reported ( c, ppm.) from the Internal standard TMS. 

A comparison of the carbon SSNMR spectra of the manufactured formulation to that of the equivalent physical mixture, both shown on the left of Fig. 10.25, shows no significant differences. The chemical shift and line shape differences between the top and bottom carbon spectra in the figure are minor and thus do not themselves prove an interaction between the API and excipients. Small spectral differences such as these may arise from minor fluctuations in sample temperature, for instance. One may, albeit incorrectly, conclude at this point that no drug-excipi-ent interactions exist. However, as we shall soon see, it is risky to make such conclusions based on the lack of an observed change. 

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