Question

In synthesizing benzilic acid from benzil, the resulting IR peaks were less intense than expected in the final product. Why might this be?

Answer 1

OH OH OH OK C-C IHC1 0 KOH C-C Benzil Benzilic acid Potassium salt of Benzilic acid

In the spectrum of benzilic acid, the intense and sharp peak at 3425.69 cm^-1 is due to the hydroxyl group corresponding to O-H stretching.The broad peak centered at 3063.06 cm^-1 is due to C-H stretching in aromatic ring. the less intense weak bands at 2841.24 and 2804.59 cm^-1 are attributed to the O-H stretching of the carboxylic acid arising as a result of intramolecular hydrogen bonding. The 1963.60 and 1886.44 cm^-1 peaks signify the overtones that support the presence of the phenyl ring and are main reason for the weak less intense spectra. Due to the interaction of the solvent (DMF) on the surface of the benzilic acid crystal, the C=O stretching has shifted to 1645.33 cm^-1 . The C=C stretching vibrations of the aromatic ring are observed at three envelopes occurring at 1489.10, 1469.81 and 1442.80 cm^-1. The peaks at 1388.79 and 1338 cm^-1 correspond to O-H in plane bending. The C-O stretching of the alcohol occurs at 1163.11 and 1053.17 cm^-1; and an intense band at 702.11 cm^-1 is due to the C-H out of plane bending