Group frequency charts

Vibrational spectra of phosphorus compounds have been reviewed extensively [1702-1705]. Figure 2.70 shows a group frequency chart based on these review articles. 

Compounds of sulfur and selenium are of great interest for spectroscopists because of their unusual structures and strong Raman bands involving S—S or Se—Se bonds. Steudel and co-workers have made an extensive study on vibrational spectra of these compounds. Figure 2.76 shows a group frequency chart for sulfur compounds. 

The vibrational spectra of nitrogen oxides and phosphorus compoundshave been reviewed. Figure 11-21 shows a group frequency chart based on these reviews. Appendix VI also gives group frequency chart for KPH), i (PO), and f(PX) (X a halogen). 

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 data cited in this book were used in the preparation of the following group frequency charts. Each section of Part III gives a number of group frequencies that are not included here. For the physical meaning of group frequency, see Sec. 1-17. 

Socrates G 1994 Infrared Characteristic Group Frequencies Tables and Charts 2nd edn (Chichester Wiley)... 

G. Socrates, Infrared and Raman Characteristic Group Frequencies Tables and Charts, 3rd ed., Wiley, Chichester, 2001, p. 142. 

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. 

Socrates G, Infrared Characteristic Group Frequencies, Tables and Charts, 2nd edn, Chichester, WUey, 1997. 

Limitations to the Use of Correlation Charts The unambiguous establishment of the identity or the structure of a compound is seldom possible from correlation charts alone. Uncertainties frequently arise from overlapping group frequencies, spectral variations as a function of the physical stale of the sample (that is. whether it is a solution, a mull, in a pelleted form, and so forth), and instrumental limitations. 

Figure 8.10. ( Next two pages). Correlation chart of group frequencies. Courtesy of Dow Chemical Company.

The interpretation of infrared spectra requires practice, but the task is eased with the help of correlation charts of group frequencies [2, 3]. Such a chart is shown in Figure 8.10, pp. 118-19. Other charts are available that document group frequencies in the near infrared and the far infrared. 

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