Experiment: Oxidation of Benzoin to Benzil The STANDARD IR spectrum of benzaldeh

Question

Experiment: Oxidation of Benzoin to Benzil

The STANDARD IR spectrum of benzaldehyde is the first image (or on the left) and the STANDARD IR spectrum of benzoin is the second image (or on the right).

The PRODUCT IR spectrum of benzoin is the first image (or on the left) and the PRODUCT IR spectrum of benzil is the second image (or on the right).

Does your IR data indicate that your benzoin product was pure? Briefly indicate if there were any issues.

Does your IR data indicate that your benzil product was pure? Briefly indicate if there were any issues.

169736/24 48 1201 65/3841 827 46/47 44 742.59133.10. 686.6637.88 3064 89/104,66 2819 93/97 80 2736.99 97.57 1653.00 89.82 1597.06170.31 1583 56/7047 14 56.26/75.05 1390.68/ 88.32 1309.67170.68 1166.93 71.38 1072 4219242 1022.2719 1.32

Explanation / Answer

The IR data reveals that the Benzoin is pure.

The peak at 3000 cm-1 of benzaldehyde is absent in benzoin and there is also an additional OH stretching at 3406 cm-1 in benzoin. Further, The C=O stretching is shifted in benzoin from 1697 cm-1 to 1678 cm-1. Hence, comparing the IR of both benzaldehyde and benzoin clearly indicates its purity.

However, the analysis of IR of Benzil creates suspicion about the purity of the compounds. The reasons are:

Although, there are three peaks corresponding to C=O and C=C stretching from 1577 to 1714 cm-1. These values should have been a little lesser maybe 1690 cm-1. The another major concern is the peak at 3404 cm-1. (The page is cut but it clearly shows and is unmistakebly due to OH, it's so broad that it can't be ignored).

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