Benzoic acid infrared spectrum

Fig. 5.2. Typical format, percentage transmittance (%T) versus wavenumber, for infrared spectra. This is a spectrum of benzoic acid.

Figure 6. Infrared absorption spectrum of benzoic acid, obtained in KBr pellet.

To a solution of 2.00 grams (0.00454 mole) of K[Cr(HO-A)2] in 200 ml. of water, cooled to 6° C., were added 12.8 grams of benzoyl chloride and a solution of 2.00 grams of potassium bicarbonate in 20 ml. of water. This mixture was stirred in an ice bath for 30 minutes and then for an additional hour out of the bath. The solution was acidified with concentrated nitric acid, and then filtered to remove benzoic acid. From the filtrate only starting material (infrared spectrum ) and its decomposition products could be isolated. 

The infrared spectrum of Figure 13.31 has no absorption in the 1600-1800-cm region, and so the unknown compound cannot contain a carbonyl (C=0) group. It cannot therefore be acetophenone or benzoic acid. 

FIGURE 2.46 The infrared spectrum of benzoic acid (Nujol mull, KBr plates). Dots indicate the Nujol (mineral oil) absorption bands (see Fig. 2.8). 

Interpret the principal peaks in the infrared spectrum of either triphenylmethanol or benzoic acid, depending on the procedure used in this experiment. 

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