Infrared spectroscopy base values

A 21.3-g sample of poly(hexamethylene adipamide) is found to contain 2.50 x 10-3 mol of carboxyl groups by both titration with base and infrared spectroscopy. From these data the polymer is calculated to have a number-average molecular weight of 8520. What assumption is made in the calculation How can one experimentally obtain the correct value of M ... 

The use of distribution coefficients or their simplified equivalents as p-values is not new and is based on sound chemical principles (19). Its particular value, however, is that it can be applied as a confirming means of identification where the component of concern is not available in sufficient quantity for the more common identification techniques such as infrared spectroscopy, elemental analysis, or physical property measurements (20). 

Corrosivity of used oils. The classical determination of TBN and TAN involves a titrimetric procedure, whereby the oil sample is dissolved in a particular solvent system and neutralized by strong acid or strong base (ASTM D664 or 2896), equivalent to (IP 171 or 276). TBN and TAN values do not correlate with corrosivity and the titrimetric analysis has a very limited ability to differentiate between acids of varying strengths. A quantitative differential infrared spectroscopy technique used to monitor the neutralization reaction is more meaningful, since the technique applies to reactions in hydrocarbon solvents. The classical reaction between corrosive acids and hard-core RMs results in formation of the metal salt of the acid and carbonic acid ... 

Osmium tetroxide reacts with CsF or RbF in water forming M2[0s04F2] H20 (M = Cs, Rb) which were characterized by elemental analysis, X-ray powder diffraction, infrared spectroscopy and thermogravimetric analysis [353]. Based on vibrational spectroscopy, the 0s04F22 anion is considered to possess a m-difluoro arrangement. Osmium Lm EXAFS data have been obtained for Cs2[0s04F2] giving values for the 0s=0 and Os—F bond distances [354]. 

Such twisted nematic phases are called induced cholesteric solutions and - as schematically outlined in Fig. 4.6-9 - enantiomers cause countercurrently twisted structures. As discussed by Korte and Schrader (1981) this effect offers the potential of sensitively characterizing the chirality of small amounts of optically active compounds. There are no restrictions as to the type of chirality, and the experiments can advantageously be based on infrared spectroscopy. The application of induced cholesteric solutions was later reviewed again by Solladie and Zimmermann (1984). The host phase is the more twisted the more of the optically active guest compound is dissolved. Quantifying the twist by the inverse pitch z and the concentration by the molar fraction x, the ability of a chiral. solute to twist a given nematic host phase is characterized by the helical twisting power (HTP Baessler and Labes, 1970). For small values of a this quantity P is defined by the relation... 

In early work (8) we used infrared spectroscopy coupled with attenuated total reflection optics. This work was done before the availability of infrared equipment based on Fourier transform methods. Due to their relative speed these methods now permit in situ, real time measurements with a resolution of 1 sec or less (9), and continue to yield valuable data, particularly in the hands of the Battelle group in a series of studies dating from 1979 (10). In our early infrared work we had to be content to rinse and dry the surface before obtaining the infrared reflection spectrum Nevertheless the values of surface concentration were remarkably close to those determined more recently. Infrared studies of proteins suffer generally from the fact that the main features of protein spectra are similar for all proteins and therefore it is difficult to distinguish one from another. 

There is a good agreement between the values of DA obtained in the different experiments demonstrating the advantage of solid state NMR well adapted to all the range of acetylation degrees (see Table 4,1), Infrared spectroscopy was also often used but it is more delicate to interpret due to the difficulty in adopting a convenient base line. This was also discussed previously for samples with different DAs [37],... 

There are several probe molecules for which infrared spectroscopy can differentiate between adsorption on Bronsted and Lewis acid sites and even estimate the amounts adsorbed. Pyridine is the most widely used because it gives well-resolved bands when protonated by Bronsted acid sites (e.g., 1540 and 1640 cm ) or when coordinated to Lewis acid sites (1450 and 1620 cm ). The values of extinction coefficients are available in the literature [121] for these bands, which makes possible semiquantitative measurements, separately, of Lewis and Bronsted sites. Ammonia, with a smaller kinetic diameter that enables it to reach more easily the acid sites in smaller pores, can also be used to distinguish betwen Bronsted and Lewis acid sites however, the use of ammonia is less reliable, mainly because the resulting IR bands overlap each other [122]. Another base that can distinguish between Bronsted and Lewis acid sites is quinoline because its size is greater than that of pyridine quinoline can also be used to differentiate between acid sites at the external surface and those in pores smaller than its kinetic diameter (6 A). Bronsted sites can be selectively measured with IR methods by using substituted pyridines as probe molecules [123]. 

The acid and base values of the surface functional groups of the samples were determined by Boehm s titration method [50]. To determine the acid value, O.lg of the sample was added to 100 ml of 0.1 M NaOH solution and the mixture was shaken for 24 h. The solution was then filtered through a membrane filter (pore size = 0.24 pm, nylon) and titrated with 0.1 M HCl. Likewise, the base value was determined by the reverse titration of the acid value. The specific surface areas (Sbet. [51]) of the samples were determined by gas adsorption. Physical adsorption of gases was used to characterize the CBs support, and the adsorbate used was N2 at 77 K with automated adsorption apparatus (Micromeritics, ASAP 2400). Prior to adsorption measurements, the samples were outgassed at 298 K for 6 h to obtain a residual pressure of less than 10 torr in high vacuum. To analyze the functional groups of CBs, the treated CBs were subjected to infrared (IR) spectroscopy (FTS-165 spectrometer, Bio-Rad Co.). 

Thirdly, in order to improve the dispersion of platinum catalysts deposited on carbon materials, the effects of surface plasma treatment of carbon blacks (CBs) were investigated. The surface characteristics of the CBs were determined by fourier transformed-infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), and Boehm s titration method. The electrochemical properties of the plasma-treated CBs-supported Pt (Pt/CBs) catalysts were analyzed by linear sweep voltammetry (LSV) experiments. From the results of FT-IR and acid-base values, N2-plasma treatment of the CBs at 300 W intensity led to a formation of a free radical on the CBs. The peak intensity increased with increase of the treatment time, due to the formation of new basic functional groups (such as C-N, C=N, -NHs, -NH, and =NH) by the free radical on the CBs. Accordingly, the basic values were enhanced by the basic functional groups. However, after a specific reaction time, Nz-plasma treatment could hardly influence on change of the surface functional groups of CBs, due to the disappearance of free radical. Consequently, it was found that optimal treatment time was 30 second for the best electro activity of Pt/CBs catalysts and the N2-plasma treated Pt/CBs possessed the better electrochemical properties than the pristine Pt/CBs. 

Using the information in the figure, the UV spectra of 18-20 may be predicted. For 18, the base value is 215 + 12 for a methyl on the P-carbon = 227 nm. For 19, the base value is 215 + 10 for a methyl on the a-carbon = 225 nm. Compound 20 is not conjugated, so it should show an absorption for the C=C at around 170-180 nm and an absorption for the C=0 at around 150-160 nm. It may be difficult to distinguish 18 from 19 by UV spectroscopy, but structure 20 is certainly ruled out. The inability to distinguish compounds that are very close in structure is a limitation of this method, but usually subtle differences will allow one to make a structure determination. Also remember that infrared spectroscopy and proton NMR spectroscopy (see Chapter 14) may be used. The chemical shifts in the NMR spectra and multiplicity of the methyl group on the alkene unit and the alkene protons themselves will be different for 18 when compared to 19 (see Chapter 14, Section 14.4.3) and this information is used to assist in the identification. 

---