Vibrational spectroscopy qualitative

Vibrational spectroscopy and in particular Raman spectroscopy is by far the most useful spectroscopic technique to qualitatively characterize polysulfide samples. The fundamental vibrations of the polysulfide dianions with between 4 and 8 atoms have been calculated by Steudel and Schuster [96] using force constants derived partly from the vibrational spectra of NayS4 and (NH4)2Ss and partly from cydo-Sg. It turned out that not only species of differing molecular size but also rotational isomers like Ss of either Cy or Cs symmetry can be recognized from pronounced differences in their spectra. The latter two anions are present, for instance, in NaySg (Cs) and KySg (Cy), respectively (see Table 2). 

The use of vibrational spectroscopy for the qualitative analysis of absorbed surface species is first considered, and a Table is then included which summarises a number of the key features of the various quantitative techniques. We then proceed to summarize these in groups depending not upon the probe used (as in the preceding chapters), but in terms of the signal emitted by the specimen which is used in each identification process. 

J.M. Chalmers and N.J. Everall, Qualitative and quantitative analysis of plastics, polymers and rubbers by vibrational spectroscopy. In N.J. Everall, J.M. Chalmers and P.R. Griffiths (Eds.), Vibrational Spectroscopy of Polymers Principles and Practice, Wiley, Chichester, 2007, pp. 1-67. 

In this section we give a simple and qualitative description of chemisorption in terms of molecular orbital theory. It should provide a feeling for why some atoms such as potassium or chlorine acquire positive or negative charge upon adsorption, while other atoms remain more or less neutral. We explain qualitatively why a molecule adsorbs associatively or dissociatively, and we discuss the role of the work function in dissociation. The text is meant to provide some elementary background for the chapters on photoemission, thermal desorption and vibrational spectroscopy. We avoid theoretical formulae and refer for thorough treatments of chemisorption to the literature [2,6-8],... 

The vibrational spectroscopy time scale (10-300 x 10 sec) is appropriate for the direct sampling of the fastest motion expected to occur in phospholipid acyl chains, namely trans-gauche isomerization. To date, most Raman ai)d FT-IR studies of phospholipid phase behavior and lipid/protein interaction have focused mainly on qualitative measures of acyl chain organization. For example, the... 

In this section, using purely qualitative symmetry arguments, we have discussed the kind of information regarding structure and bonding we can obtain from vibrational spectroscopy. Obviously, treatments of this kind have their limitations, such as their failure to make reliable assignments for the observed vibrational bands. To carry out this type of tasks with confidence, we need to make use of quantitative methods, which are beyond the scope of this book. 

The same subdivision is used in the qualitative discussion of ionic solvation energies, and it is found that the outer-sphere part is satisfactorily predicted by electrostatic continuum theories (as reviewed in Section III), whereas the inner-sphere part is best obtained by considering the distortion of individual bonds, using force constants from vibrational spectroscopy. 

Qualitative methods for the identification are given in Table 15. Quantitative methods are well documented. Sulfur compounds are readily studied by vibrational spectroscopy, both IR and Raman. The oxides and oxyanions have characteristic spectra in the IR while the sulfanes and cyc/o-sulfur compounds give strong Raman spectra as a result of their high polarizability. The only potentially useful NMR nucleus is S, which is quadrupolar and low in abundance (Table 2). In general, measurements of NMR... 

In its simplest application, solid-state NMR spectra can be used to qualitatively differentiate between polymorphs or solvates, much in the manner described for vibrational spectroscopy. When detailed assignments of solid-state spectra have been made, the technique can be used to deduce differences in molecular conformation, which cause crystallographic variations to exist. During the development of fosinopril sodium, a crystal structure was solved for the most stable phase, but no such structure could be obtained for its... 

Not surprisingly, vibrational spectra have proven to be an invaluable tool for experimental chemists in the characterization of transition metal and actinide sandwich compounds (98). Most known actinocenes have been characterized early on by vibrational spectroscopy (99). The IR and Raman spectra of thorocene and the IR spectra of protactinocene and uranocene were reported in the 1970s (100,101). However, normal coordinate analysis of these vibrational spectra is difficult because of the large number of vibrational modes involved. So far only a tentative assignment of the vibrational spectra of thorocene and uranocene, based on a qualitative group theory analysis, has been advanced (102). 

Infrared, and more recently Raman spectroscopy, have been widely used for the qualitative and quantitative characterization of polymorphic compounds of pharmaceutical interest (for the sake of brevity, the term polymorphism will encompass polymorphs, pseudo-polymorphs, hydrates, and solvates). Since solid-state vibrational spectroscopy can be used to probe the nature of polymorphism on the molecular level, these methods are particularly useful in instances where full crystallographic characterization of polymorphism was not found to be possible. 

Ab initio vibrational spectroscopy calculations have been able to provide dramatic improvements in interpretation of spectra, or yield qualitatively new insights in a number of intriguing cases. We mention here a single example, the work of A.T. Kowal [140], in sorting out the vibrational spectra of hydroxylamine and its and deuterium... 

The structures displayed in Tables 4.2 and 4.3, and discussed above, are usually qualitatively identified by vibrational spectroscopy using pattern recognition... 

Several recent overviews of principles and applications of Raman, FTIR, and HREELS spectroscopies are available in the literature [35-37, 124]. The use of all major surface and interface vibrational spectroscopies in adhesion studies has recently been reviewed [38]. Infrared spectroscopy is undoubtedly the most widely applied spectroscopic technique of all methods described in this chapter because so many different forms of the technique have been developed, each with its own specific applicability. Common to all vibrational techniques is the capability to detect functional groups, in contrast to the techniques discussed in Sec. III.A, which detect primarily elements. The techniques discussed here all are based in principle on the same mechanism, namely, when infrared radiation (or low-energy electrons as in HREELS) interacts with a sample, groups of atoms, not single elements, absorb energy at characteristic vibrations (frequencies). These absorptions are mainly used for qualitative identification of functional groups in the sample, but quantitative determinations are possible in many cases. 

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