Characteristic group absorptions

Table 14.1 Characteristic group Absorptions in IR spectra of organic molecules.

This section is concerned with a comprehensive look at these characteristic group absorptions and their relationship to molecular structure. As a major type or class of molecule or functional group is introduced in the succeeding sections, an example of an IR spectrum with the important peak assignments will be given. Spectra of common laboratory substances, representing... 

Assignments for C—H out-of-plane bending bands in the spectra of substituted benzenes appear in the chart of characteristic group absorptions (Appendix C). These assignments are usually reliable for alkyl-substituted benzenes, but caution must be observed in the interpretation of spectra when polar groups are attached directly to the ring, for example, in nitroben-zenes, aromatic acids, and esters or amides of aromatic acids. 

It is still necessary that an organic chemist understands a reasonable amount of theory and instrumentation in IR spectrometry. We believe that our coverage of characteristic group absorptions is useful, together with group-absorption charts, characteristic spectra, references, and Student Exercises. This chapter remains essentially the same except the Student Exercises at the end of the chapter. Most of the spectra have been redone. 

Some other characteristic group absorptions will now be summarized. The thiolester group in 4-amino-3-methyl-5-(methylthio)carbonyl-1,2,3-triazole (the 3-Me derivative of 18a) displayed two strong bands of equal intensity 1630 (C=0 stretching) and 900 (C—S stretching) cm". This and related examples are discussed in Refs. 69JCS(C)2379 and 72JCS(P1)461. The... 

---