Correlation Charts and Tables

FIGURE 2.6 A comparison of the shapes of the absorption bands for the O—H and N—H groups. 

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. 

9 HOW TO APPROACH THE ANALYSIS OF A SPECTRUM (OR WHAT YOU CAN TELL AT A GLANCE) 

When analyzing the spectrum of an unknown, concentrate your first efforts on determining the presence (or absence) of a few major functional groups. The C=0, O—H, N—H, C—O, C=C, C=C, C=N, and NO2 peaks are the most conspicuous and give immediate structural information if they are present. Do not try to make a detailed analysis of the C—H absorptions near 3000 cm almost all compounds have these absorptions. Do not worry about subtleties of the exact environment in which the functional group is found. Following is a major checklist of the important gross features. 

Is a carbonyl group present The C=0 group gives rise to a strong absorption in the region 1820-1660 cm The peak is often the strongest in the spectrum and of medium width. You 

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CO Alcohols, ethers, esters, carboxylic acids, anhydrides 1300-1000 s 47, 50, 62,64, and 73 

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The band positions for all the major structural bonding types have been determined and correlation charts and tables are available which give the ranges within which particular bonding types have been observed to absorb. A simpli-... 

The chemical shift is used to identify functional groups and to aid in determining structural arrangements of groups. These applications arc based on empirical correlations between structure and shift. A number of correlation charts and tables " have been published, two ol which are. shown in Figure 19-17 and Table 19-2. Keep in mind that the c.Kaci values for 8 may depend t)n the nature of the solvent as scll as on the concen-... 

B. Fourier Transform Spectrometers 25 Preparation of Samples for Infrared Spectroscopy 26 What to Look for When Examining Infrared Spectra 26 Correlation Charts and Tables 28... 

Charts and tables may be found in handbooks (Perry, 1997), or in specialised publications. The tables are more accurate than small-scale diagrams. All these representations have been obtained with great effort by combining experimental data and correlation methods. In the computer simulation era charts and tables might be seen as obsolete. To answer this issue we should take into account the followings ... 

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. 

Charts, correlations, and tables in the sources cited earlier relate capital costs to various parameters characteristic of the equipment to be evaluated. Table B.2 lists typical parameters used to correlate equipment costs for common types of process equipment. Figure B.3 is an example of such correlations for the cost of heat exchangers as a function of exchanger area. These forms of cost curves generally appear as nearly straight lines on log-log plots, indicating a power-law relationship between capital cost and capacity, with exponents typically ranging from 0.5 to 0.8. 

Attempt to identify the unknown labeled with a letter by matching the spectrum with a spectrum from the IR spectral library. First, take a preliminary look at the spectrum to check for obvious signs of the various functional groups (refer to Table 8.1 or a correlation chart). This will help reduce the number of possibilities. Report your decision regarding its identity to your instructor and justify your decision. 

Compact information storage and retrieval. A good correlation leads to compact storage of information in the form of equations and coefficient values, which is more convenient for rapid retrieval than tables of numbers or charts and graphs. This property, which is valuable in a forward search from substance to property, is even more valuable in a reverse search from property to substances. 

Similarly, one can calculate the correlation chart for the six Cl atoms as illustrated in Table 1-13. For the six Cl atoms, activity is demonstrated for 2Ag,2Bu,2E2g,2Eiu, Au, Bg, E2u and E g totaling 18 DOF. Summarizing the modes for LaCF we obtain... 

From the outset, it was clear that Si MASNMR resonances were, to some degree, structure-sensitive. The correlation charts of Lippmaa et al (5.9) and our own (7, 10) show a range of values at which a 2 si nucleus in a particular environemnt (Si(0Al) (OSi) with n = 0, 1, 2, 3> or k) was expected to resonate his point emerges clearly from Table 1. In this respect MASNMR is similar to IR, UV and Raman and solution NMR spectroscopies for which there are comparable charts that are constructed, as in 29sI MASNMR, solid-state spectroscopy, largely on the basis of accumulated practical experience, rather than on theoretical calculations. ... 

Table 10.1 Correlation Chart in the mid-infrared between functional groups and absorption bands 4000 3500 3000 2500 2000 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900 800 700...

Three tables containing the dissociation constants of more than 1050 phenols, organic acids and organic bases were added. Correlation charts for I.R., Far I.R. and N.M.R. were also included. 

Most chemical shifts have 8 values between 0 and 15. A small 8 value represents a small downfield shift, and vice versa. A simplified correlation chart for proton chemical shift values is shown in Table 2 [37]. 

Several very useful infrared correlation charts appear in the Handbook of Biochemistry (Sober, 1968, pp. J-4-J-12), and a typical correlation chart for the region from 700 to 300 cm taken from the same source, is presented in Table 1.2. Correlations for the 4505-450 cm region are also given in Chapter 6. 

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