Hexadecane spectra

After extraction, samples to be analyzed are dissolved in a solvent, commonly acetonitrile, heptane, hexadecane, or water. A scan of the pure solvent in the sample cell, typically made of quartz (Figure 14.3 [A]), is first obtained. The dissolved sample is placed in the sample cell, which is placed in the sample compartment of the instrument, and a spectrum is obtained. 

The first practical example of an on-line SFC-1 NMR separation was recorded by Dorn and co-workers [16] (Figure 7.2.14). Since up to 90% of a fuel is aliphatic, SFC-NMR on-line analysis is the matter of choice for separation and identification. Figure 7.2.14 shows a fuel mixture of isooctane, n-hexane, -nonane, dodecane, and n-hexadecane, separated by SFC and detected by on-line NMR spectroscopy. The SFC separation was accomplished with a flow rate of 2.0ml/min, a C18 250 x 4.6 mm column, operated at an isobaric pressure of 100 bar and a temperature of 323 K, using CO2 with 1% (w/w) CD3CN as solvent. Each NMR spectrum consists of 20 co-added transients at an acquisition time of 1 s per transient. The total separation occurred within 5 min. The first eluting isooctane can be easily identified by the methylene-to-... 

Figure 1 shows the spectrum obtained for n-perdeutero decane solubilized in the lamellar phase of water and C E. a comparison with the spectrum of n-perdeutero hexadecane (Fig. la) from the preliminary investigations by Ward at al (3) is instructive. In both cases, the spectrum may be simulated by a number of overlapping spectra corresponding to half the number of carbon atoms in the solubilized chain. 

The interpretation of mass spectra and the validity of the above rules may be demonstrated by examining the spectra of several compounds. Returning to the spectrum of n-hexadecane shown in figure 9.51, it will be seen that it is characterized by a small parent peak (Rule 1) and clusters of peaks 14 mass units (CH2) apart. The largest peak in each cluster is the most... 

If the density p and ratio of specific heats y are known, measurements of A(0(i) can be used to obtain /3t- The ratio of specific heats for the case where t << 10" sec can be obtained from the Rayleigh-Brillouin spectrum of the fluid. The intensity of the central peak owing to the thermal expansion divided by the intensity of the two Brillouin peaks is equal to y — 1 (6). For n-hexadecane at 120°G (shown in Figure 1), this ratio yields y = 1.227. The density is 0.7036 (7). The Brillouin splitting is measured to be 0.131 cm" The isothermal compressibility is calculated to be 1.6 X 10" cm /dyn in good agreement with the directly measured value of (7). 

Figure 6. Depolarized (Ihv) Rayhigh-Brillouiri spectrum of n-hexadecane at 65°C...

Figure 4.1 Inversion-recovery proton-decoupled CNMR spectra of n-hexadecane. t is the variable waiting time between the n and njl pulses. Note that the methyl resonance at the right recovers its equilibrium magnetisation (top spectrum) more slowly than the tall resonance arising from the eight central methylene carbons.

The UV spectrum of o-quinone has an intense absorbance band in the region 380-390 nm [53]. An increase in absorbance at 380 nm is observed in the course of QHP thermal decomposition (Figure 5.1, curve 3). The kinetics of QHP decay in hexadecane solutions during NO bubbling at 295 K is described by a second-order equation [50]. The following scheme has been proposed for explanation of the kinetics ... 

FIG. 15 Water-hexadecane system (Table 2). DSC-ENDO spectra of the upper isotropic phase of biphasic samples with increasing water concentration of the sample as a whole. Curve 1 Ctoi = 0.372, the first appearance of a birefiingent liquid crystalline lens. Curve 2 Ct = 0.388. Curve 3 Ct = 0.419. Curve 4 Melting endotherms of the Uquid crystalline bottom mesophase of a sample with Ct , = 0.419. AH and AHb are the thermal contributions of the n-hexanol and the water-K-oleate-hexanol mixture, respectively. (From Ref. 23.) Curve 5 DSC-ENDO spectrum of the ternary mixture n-hexanol-K-oleate-water. The proportions between surfactant and cosurfactant are the same as those used to formulate the four-component W/O microemulsions. 

A similar effect can also be observed with some organic surface species, where the pKa of the surface-bound molecule leads to a characteristic acquisition of surface charge at a particular pH (17), Such an effect is particularly useful in cases such as that displayed in Figure 1, where a species with a moderate pKa (-COOH-terminated hexadecane thiol) can be readily distinguished from a species that only dissociates under extreme conditions (methyl-terminated hexadecane thiol). In order to exploit this effect, however, the chemical species to be distinguished must display appropriate dissociative behavior, which is, of course, not necessarily the case. The convenient spectrum of isoelectric points that can be used for identification purposes in oxide systems (15) is not mirrored in the organic world, where amphoteric behavior is the exception rather than the rule. 

Figure 5.13 Monomer fluorescence spectrum of pyrene in (a) hexadecane and in (b) CTAB showing the Ham effect on the vibronic band intensities. From Dorrance and Hunter [116] with permission.

Figure 7.17 Dielectric relaxation spectrum of a 21 kDa triblock copolymer (58 g/1 in hexadecane) in which the central 3 kDa is the type-A c -polyisoprene and the two terminal ends are 8 kDa dielectrically inert polybutadienes, using original measurements by Adachi, et al.(2). The high- and low-frequency features are here interpreted as segmental motion and whole-chain reorientation, respectively.

The surface conductance can dramatically alter the shape of the dynamic mobility spectrum. This is illustrated by Figure 4.8, which shows the dynamic mobility measurements on a 5 vol.% hexadecane emulsion stabilized with 1 mM SDS over a range of electrolyte concentrations [2]. At the lowest salt concentration (1 mM NaCl) the magnitudes show an increase with frequency and the argument displays a phase... 

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