GROUP-FREQUENCY CHARTS, references

As stated in Sec. II-6(A), Muller and co-workers reviewed the vibrational spectra of thio and seleno compounds of transition-metal ions. The group frequency chart of sulfur compounds shown in Fig. 11-22 is based on the literature appearing in this book. For individual compounds, only references are cited [S ] (n = 3 6) (939), (940), S7 (941), S (942), H2S3.4 (943),... 

The value of infrared spectrometry as a means of identification of unknown compounds and to investigate structural features is immense. Spectra are used in an empirical manner by comparison of samples with known materials and by reference to charts of group frequencies. A simplified correlation chart is shown in Table 9.8. The interpretation of infrared spectra is best considered by discussing the prominent features of a representative series of compounds. 

Although the IR spectrum is characteristic of the entire molecule, it is true that certain groups of atoms give rise to bands at or near the same frequency regardless of the structure of the rest of the molecule. It is the persistence of these characteristic bands that permits the chemist to obtain useful structural information by simple inspection and reference to generalized charts of characteristic group frequencies. We shall rely heavily on these characteristic group frequencies. 

For an unknown compound without a reference standard, important structural information can be obtained from the IR spectrum. Fig. 9 is a simplified illustration of the correlation between the absorption frequency incm and the functional groups (a more comprehensive description of this type of correlation chart is given in Ref. ). By observing the presence or absence of certain group frequencies, related to common functional groups such as -OH, -NH2, -CH3, -C=0, -CN, -C-O-C, -COOH, etc., the gross structural features of an unknown compound can be quickly determined. 

To extract structural information from infrared spectra, you must be familiar with the frequencies at which various functional groups absorb. You may consult infrared correlation tables, which provide as much infonnation as is known about where the various functional groups absorb. The references listed at the end of this chapter contain extensive series of correlation tables. Sometimes the absorption information is presented in the form of a chart called a correlation chart. Table 2.3 is a simplified correlation table a more detailed chart appears in Appendix 1. 

More recently, the fundamental frequencies of all types of phosphate ions, such as metaphosphates, pyrophosphates, hypo-phosphites, etc., have been studied by several groups of workers, notably by Corbridge [31,32], by Lecomte [33,34] and by Tsuboi [42]. Their findings have been condensed in the form of a correlation chart for phosphorus oxyacids by Corbridge [32], and sufficient data are now available to enable most of the individual types to be differentiated. These absorptions Jiave already been discussed in Chapter 18, to which further reference should be made. The spectra of some phosphate high polymers in molten, glaceous and crystalline states have been reported by Dues and Gehrke [35]. 

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