If you had taken an IR spectrum of the crude product (before extraction with NaO

Question

If you had taken an IR spectrum of the crude product (before extraction with NaOH), would you be able to determine whether your reaction had worked as expected? Explain. (Hint: Examine the IR spectra of pure bromobenzene and benzoic acid: how are they different?) If you had taken an IR spectrum of the crude product (before extraction with NaOH), would you be able to determine whether your reaction had worked as expected? Explain. (Hint: Examine the IR spectra of pure bromobenzene and benzoic acid: how are they different?) If you had taken an IR spectrum of the crude product (before extraction with NaOH), would you be able to determine whether your reaction had worked as expected? Explain. (Hint: Examine the IR spectra of pure bromobenzene and benzoic acid: how are they different?)

Explanation / Answer

Yes we can determine whether the reaction has worked as expected if we take the IR spectrum of the crude product.

During the Grignard synthesis bromobenzene is converted to benzoic acid in two steps. The unwanted products are benzene (if moisture is present), biphenyl etc.

Since the IR spectrum of bromobenzene, benzene and biphenyl are different from the IR spectrum of the desired product (benzoic acid) we can easily determine by IR spectrum.

If the product (benzoic acid) is formed, we will observe the following distinct peaks in the IR spectrum

1. A peak in the range of 2500 - 3300 cm-1 due to carboxylic -OH group.

2. A peak at around 1670 cm-1 due to carbonyl (-C=O) group.

3. A peak at around 1290 cm-1 due to the presence of -OH group.

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