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Based in the infrared spectrum diagram for benzoic acid, only some of the most prominent peaks for particular bond vibrations are discussed, particularly if benzoic acid has a functional group with a particular characteristic wavenumber peak.
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When analyzing an IR spectrum, it is helpful to overlay the diagram below onto the spectrum with our mind to help recognize functional groups. Figure 1. Group frequency and fingerprint regions of the mid-infrared spectrum. The region of the infrared spectrum from 1200 to 700 cm-1 is called the fingerprint region.
Table of Characteristic IR Absorptions m=medium, w=weak, s=strong, n=narrow, b=broad, sh=sharp ... frequency, cm –1 bond functional group 3640–3610 (s, sh) O–H stretch, free hydroxyl alcohols, phenols 3500–3200 (s,b) O–H stretch, H–bonded alcohols, phenols 3400–3250 (m) N–H stretch 1˚, 2˚ amines, amides 3300–2500 (m) O–H ...
IR Tables, UCSC Table 1. Characteristic IR Absorption Peaks of Functional Groups* Vibration Position (cm-1) Intensity* Notes Alkanes C-H stretch 2990 – 2850 m to s Alkenes =C-H stretch 3100 – 3000 m C=C stretch 1680 – 1620 (sat.) ... Carboxylic Acids** O-H stretch 3200 – 2500 br, m to w C=O stretch 1725 – 1700 (sat.)
By learning where characteristic functional-group absorptions occur, it’s possible to get structural information from IR spectra. Table 12.1 lists the characteristic IR bands of some common functional groups.
individual functional groups may fall outside the quoted ranges. This is to be expected for several reasons: the influences of other functional groups within a molecule, the impact of preferred spatial orientations, and environ-mental effects (chemical and physical interactions) on the molecule. The preferred format for presenting spectral ...
