Temperature vs. shift

Fluorine has a high NMR sensitivity and, having similar chemical properties to protons, fluorine-substituted compounds are used widely in the pharmaceutical and medical industries. In addition to many studies carried out in the gas phase, the temperature dependence of the chemical shifts of liquid-state hexafluorobenzene, 1,4-ditrifluoromethylbenzene (DTFMB), 1,4-dibromo-tetrafluorobenzene (DBTFB) and CFCI3 have been measured.Plots of chemical shift vs. temperature were highly linear for hexafluorobenzene (0.0022 ppm K from 280 to 340 K) and CFCI3 (0.0048 ppm K from 220 to... 

Several details can be read from these three-dimensional pictures. Here we will consider an interesting point in the diagram of the frequency shift vs. temperature. For the three samples, the V - T diagrams are shown in Fig. 18. 

The pro jLle of chemical shifts vs. temperature of each modified base In tRNA shown In Fig. 3. The major changes as compared... 

Fig. 5. Isomer shift vs. temperature for SmB. Typical values measured for ionic Sm and Sm compounds are also shown. (After Cohen et al. 1970.)...

Thus, larger-scale cooperative chain motions can be observed using this technique. A Tj vs. temperature plot is generally analogous to a curve with the lower time values and minima shifted to lower temperatures (Fig. 4). In the case of rapid motions (to2i 4 1), Tj is identical to Tt and, assuming a single correlation time, both relaxation times are equal to 1/5 Ctc (Eqs. (15) and (19)). 

ZnO bulk sample [43], Spectra are shifted for clarity, (b) Phonon-mode frequencies vs. temperature as determined from the Raman data in Fig. 3.11a. The solid lines are model approximations according to (3.22). Excitation with Nd YAG-laser line A = 532 nm and laser power P 60 mW... 

An additional relaxation can be detected in plots of the loss tangent as a function of temperature for 2,6-T-2P-43, not shown. The relaxation occurred at 60°C (11 Hz) in the first examination of this sample. A weak ah relaxation can be detected in the loss modulus vs. temperature plots in Figure 13, but the process is more readily apparent in the tan(8) data. Upon retesting of this sample, the h dispersion was shifted to 71 °C. The activation energy for the ah relaxation did not change significantly with thermal history and was extremely weak or undetectable in 2,6-T-2P samples which contained less than 43 wt% hard segments. 

Figure 4. Tan vs. temperature curves at 3.5 Hz for the diblocks and homopolymers. The scale on the ordinate corresponds to the bottom curve only, the other curves have been shifted upwards for clarity. The two arrows along the temperature scale indicate the polybutadiene (—82°C) and polyisoprene (—49°C) transitions.

Figure 7 Absorption frequency (Q-branch) vs. temperature for the CO asymmetric stretch of W(CO)6 in the gas phase. A representative error bar is shown. Extrapolation to 450 K (internal vibrational temperature following relaxation of the 2000 cm-1 CO stretch) yields a temperature-dependent shift of 1.1 cm" 1 from the peak position at 326 K, the initial sample temperature.

For this purpose, the dynamic mechanical properties of a series of 25/75 in situ SIM IPNs have been investigated (Figure 5). With 1% OcSn, the tan 8 vs temperature curve shows a classical shape, as for in situ SEQ IPNs and corroborates the kinetic results two separated transitions, broadened and damped, exist (10). The lower transition corresponding to the polyurethane phase, is shifted... 

Figure 2.36 shows the rate of oxidation vs temperature for propene. We have seen that the minimum in this figure is related to the shifting of the R + O2 equilibrium back towards reactants and an alternative mechanism for alkyl oxidation. As the temperature is increased further, the break down of large hydrocarbon radicals becomes very rapid and the main propagating species are H, Ci and C2 radicals. Hydrogen atoms play an increasingly important role in the overall combustion process and therefore... 

Fig. 1. Examples of anomalies in electrochemical interface characteristics in the vicinity of Tc-(a) Current vs. temperature dependence for proton discharge on YBa2(Cuo.9Pdo,i)07 (rc = 90 K) in HC104-5.5H20 [134]. (b) Shift of impedance minima under magnetic field for Ag/Ag reaction at the YBCO/RbAg4ls interface [147] magnetic field strength 0 (1), 1 T (2). (c) Cdi vs. temperature dependences for TBCCO rc = 119 K (1) and glassy carbon (2) measured in a butyronitrile-dichloroethane quasi-Uquid solution at potentials —2.5 and —3 V (vs. Ag), respectively. Supporting electrolyte is 0.1 M tributylammonium perchlorate (TBAP) [153].

Plots of the flux of butane (Fig. 9.24), propane and ethane versus temperature exhibit a (weak) maximum which values shifts from 440 K for n-butane to 350 K for ethane at 100 kPa. This maximum depends on the (partial) pressure of the gas (e.g. for n-butane at 8 kPa pressure the maximum is situated at about 390 K). Similar maxima are found [72,74] in the curves of H2 and CO2 vs temperature as shown in Fig. 9.25 and are also reported by Kapteyn for n-butane [88,89]. 

FIGURE 7 Isomer shift vs. Pauling electronegativity for anhydrous ferrous halides. The IS values are corrected for the effects of temperature, assuming no intrinsic thermal contribution. The uncertainty limits are represented by the size of the dots. 

Figure 2. Viscosity vs. temperature for the pure PPO polymers of various molecular weights and the master curve for the system superimposed onto the curve for the pure polymer by vertical shifting...

The plot of shift vs T- (fig. 4, Table V) is strictly linear with an extrapolated intercept at T - -=() of zero within experimental error. The difference between this result and that reported by Edelstein et al. (5), appears to arise entirely from uncertainty in measurement of the temperature. In the earlier work the uncertainty in the temperature at both the high and low extremes was +3.0°C while in this study it is +0.3°C. In fact, if one takes into account the reported error in the temperature measurements in the earlier work, the data can be fitted with a straight line which intercepts zero at T 1=0. (Fig. 5). 

The temperature dependence of the unsubstituted ring proton resonances are linear functions of T 1 and the slopes of shift vs. T-- - are identical within experimental error to that of uranocene (fig. 7, Table V). The slight difference in intercepts at T-1=0 undoubtedly result from using the proton resonance of cycloocta-tetraene dianion as a diamagnetic reference for all the compounds. 

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