Question

4000 4000 3600 3600 3200 3200 3022.55 2918.40 2858.60+ 2800 2300 2727.444 2400 2400 2000 2000 1917 31- 1800 1800 1853.65 --- 1801.57 1737.92 1718.63 1701.27 - 1631683 1602.90 1589.40 1560.46 1535,3945 31512 24- 1494.882 1600 1600 1452 45 1400 1375.29- 1400 1307.78- 1238.34 1200 -- 1190.12 1105.04 1138.04 1107.18- 1200 1091.75-- S 1 074.39 1000 31031.05 958.65 941.29- 1000 1/cm 800 810.13 1/cm 800 CA

I performed a Friedel-Crafts acylation with toluene and benzoyl chloride as the reactants and aluminum chloride as the catalyst. The product was expected to be a mixture of para- and ortho-isomers of methylbenzophenone. This is the IR spectrum of the product that I obtained. I am trying to figure out if I obtained methylbenzophenone based on this spectrum. Please be detailed as to why it is or is not methylbenzophenone and if not, what else it could be! Thanks!

Answer 1

IR Spectrum is a useful tool to predict the formation of a new bond.

The usual observed vibrational frequency of C=O is 1725-1700 cm-1 and that of C- Cl bond is around 700 cm-1. But the peak of the C-Cl bond is missing in the spectrum.

Since a peak appears around 1737.97 cm-1, we can assume the formation of a product, i.e, C=O frequency may have shifted from 1725-1700 cm-1 to 1737-97 cm-1. In order to confirm the formation of the product, you have to check the IR Spectrum of Benzoyl chloride and compare the C=O frequency with the product to know the shift in frequency.

If the product is not formed it may be the IR of the starting material Benzoyl chloride.