1. what gaseous product evolved during the reaction and how is it formed (hint:

Question

1. what gaseous product evolved during the reaction and how is it formed (hint: an excess of BH4 is used so what else might it be able to react with)?

2. What absorption is diagnostic of benzophenone and not present in benzhydrol (give frequency and functional group); and what absorption is diagnostic of benzhydrol and not present in benzophenone

3. compare the IR spectra of the student products (posted to Blackboard) with the IR spectra of pure benzophenone and benhydrol samples shown below in Figure 2,3,4; do the student spectra show product? Are the student products very pure or is it a mixture of reactant and product? P.S Please refer Figure 1

4. comment on whether the product melted quickly (< 3 0C temperature range) or slowly (> 3 0C temperature range)? What does this observation tell you about the compound purity? P.S my melting point was range of 65~67

Figure 1

Explanation / Answer

Question 1

Likely H2 gas from the protic solvent (I can't tell which solvent you used from here)..

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Question 2

The absorption peak around ~1700 cm-1 . You can use the spectra provided to find the exact wavenumber if you wish. This peak is indicative of a C=O from the ketone in benzophenone. It is not observed in benzhydrol.

A broad intense peak in the 3200-3600 cm-1 region will be present in the IR spectrum of benzhydrol. It is indicative of an O-H stretch from the hydroxyl group. It is not present in benzophenone.

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Question 3

Figure 2 appears to be a pure sample of benzophenone. It does not show the broad O-H peak at 3200-3600 cm-1.

Figure 3 appears to be a pure sample of benzhydrol. It does not show the sharp C=O peak at ~1700 cm-1

Figure 4 appears to have some benzhydrol because of the labeled, small, broad peak around 3387 cm-1. There are other peaks at 2360 and 2341 cm-1 which do not appear in either spectrum, so there is likely a size product or another compound.

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Question 4

If your melting temperature was between 65-67 oC then that is good. A pure compound has a small melting range of 1-2 oC, which is what you have. If it were impure, the range would be higher.

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