Infrared Correlation Tables

Unless otherwise noted, all art on this page is Cengage Learning 2014. 

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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. 

Useful Integrals 2 Thermodynamic Properties of Various Substances 3 Character Tables 4 Infrared Correlation Tables 5 Nuclear Properties... 

K. Nakamoto. Infrared Spectra of Inornanie and Ciiordiruitum Compounda, 2ful edn., Wiley, New York. 1970,. 338 pp (Sec also / Am. Chem. Soc. 79, 4904-8 (1957) for detailed correlation table.)... 

A full revision has been made to the appendices and some of those used in the Fourth Edition have now been incorporated into the main text where appropriate. At the same time other tables have been extended to include more organic compounds and additional appendices include correlation tables for infrared, absorption characteristics for ultraviolet/visible, and additional statistical tables, along with the essential up-dated atomic weights. 

Carboxylic acids The smallest carboxylic acid, formic acid, can be measured using infrared spectroscopy (Table 11.2), since it has characteristic absorption bands. As discussed earlier and seen in Fig. 11.33b, mass spectrometry with chemical ionization using SiF5 also revealed HCOOH in an indoor environment (Huey et al., 1998). However, since the sensitivity in these initial studies was about two orders of magnitude less than that for HN03, the detection limit may be about the same as that for FTIR and TDLS. Formic and acetic acids have been monitored continuously from aircraft (Chapman et al., 1995) and their surface flux determined by eddy correlation (Shaw et al., 1998) using atmospheric pressure ionization mass spectrometry. Detection limits are about 30 ppt. 

The following table presents a correlation between common chromophoric functional groups and the expected absorptions from ultraviolet spectrophotometry.13 Although not as informative as infrared correlations, UV can often provide valuable qualitative information. 

Ceo has four infrared allowed vibrations, all of which belong to the Ti representation. The correlation table (Table 1) lists the possible splitting in various point groups describing the molecule when the icosahedral symmetry is lost. Since the LUMO of the molecule which accommodates the extra electrons in the anions, is also a tiu orbital, the same correlations hold for the electrons as well. The resulting schemes are shown in Fig. 3 for different occupation numbers 0-6 [29]. These schemes are based on the calculations of Auerbach et al. [7] for isolated anions with correlations between electrons neglected. This calculation resulted in low-spin states for all ions which, because of the full occupation of the lowest levels, are not subject to further IT activity. 

A typical application area of expert systems and their supporting technologies is spectroscopy. Since spectra require interpretation, they are ideally suited for automated analysis with or without the aid of a spectroscopist. Particularly vibrational spectra, like infrared spectra, are subject to interpretation with rules and experience. A series of monographs and correlation tables exist for the interpretation of vibrational spectra [7-10]. The relationship between frequency characteristics and structural features is rather complicated, and the number of known correlations between... 

Neural networks have been applied to infrared spectrum interpreting systems in many variations and applications. Anand introduced a neural network approach to analyze the presence of amino acids in protein molecules with a reliability of nearly 90% [37]. Robb used a linear neural network model for interpreting infrared spectra in routine analysis purposes with a similar performance [38]. Ehrentreich et al. used a counterpropagation (CPG) network based on a strategy of Novic and Zupan to model the correlation of structures and infrared spectra [39]. Penchev and colleagues compared three types of spectral features derived from infrared peak tables for their ability to be used in automatic classification of infrared spectra [40]. 

G. Socrates, Infrared Characteristic Group Frequencies. 2nd Ed. Chichester Wiley, 1994. A comprehensive reference of correlation tables. 

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. 

As most polymers are organically based, the spectral assignments made for organic molecules in Chapter 4 are helpful when interpreting the infrared spectra of polymers. A useful correlation table for polymers is shown in Figure 6.1. 

Figure 6.1 Correlation table for the infrared bands of polymers. Reprinted from Polymer Synthesis and Characterization A Laboratory Manual, Sandler, S. R., Karo, W., Bones-teel, J. and Pearce, E. M., Figure 14.1, p. 99, Copyright (1998), with permission from...

The major infrared modes of poly(m-isoprene) observed in Figure 6.4 are listed in Table SAQ 6.1. These assignments are made as a result of consultation with the correlation table shown in Figure 6.1. 

Data on absorption patterns of selected functional groups are collected in tables called correlation tables. Table 11.3 gives the characteristic infrared absorptions for the types of bonds and functional groups we deal with most often. Appendix 4 contains a more comprehensive correlation table. In these tables, we refer to the intensity of a particular absorption as strong (s), medium (m), or weak (w). 

If the diamine portion of the polyurethane is desired, the solution is extracted with several 25 ml portions of diethyl ether. These are combined, the ether removed, and the spectrum of the diamines can then be identified from reterence infrared spectra and correlation tables. The solution is then neutralized and acidified slightly with nitric or hydrochloric acid and the glycols remaining in solution from saponification of a polyester foam must be steam-distilled to effect recovery. 

The reader is certainly familiar with the traditional group-frequency approach generally used in the past 50 years for the chemical application of the infrared spectra (Section 3.4). Correlation tables and books have been written which discuss group-frequency correlations and provide the way to carry out a chemical diagnosis from the vibrational spectrum (so far, the infrared spectra have enjoyed great popularity the reader is advised to extend their interest to the very useful and easily available Raman spectra). 

FIGURE 14.34 A correlation table for assigning infrared spectra. Tables like this are useful in trying to identify molecules from their vibrational spectrum. 

As in the case of infrared absorption spectroscopy, the bands in a Raman spectrum can be assigned through the use of group frequency correlation tables. Significant insight can be obtained from the compilations of functional group vibrational frequencies associated with infrared absorption spectroscopy, but... 

This correlation ubie predicts that the molecular vibrations of TXntS chain will split into two due 10 the inteimoiccular interactkms one is infrared active and the other is Raman active. Therefore we may not expect any band splitting in the infrared spectra as well as in the Raman spectra, but mutual exclusion should be observed as a slight band gap between the frequencies of the infrared and Raman bands. On the other hand, if the space group is P2,-Cj or Pl-C then all the intramolecular vibrations should be split into two bands due to the coupling effect of a symmetry reduction in the molecular chain at a site (site symmetry Cl) and inteimoiccular correlation of the adjacent two chains. The correlation table should become as follows. 

I would like to present some ideas on band contours and types of vibrations that I think may be of help to the spectroscopist unfamiliar with some of the more theoretical aspects of infrared spectroscopy. In addition, I would like to compare the concept of group frequencies to a concept of infrared theory termed correlation tables. These correlation tables, I think, can be as useful in some infrared analyses as the concept of group frequencies. To present these ideas in a short time, I shall specifically discuss only one series of compounds, namely, the series CHa—CFa, CHa—CF2CI, CHa—CFCI2, and CHa—CCla. First, let me introduce the concept of a species of vibration, limiting the discussion specifically to the species of vibrations of CHa—CFa and CHa—CCla. 

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