The product from your reaction has a sharp melting point, ...

[Medesa]

The product from your reaction has a sharp melting point, indicating that it is either meso-hydrobenzoin or a racemic mixture of the (1R, 2R) and (1S, 2S) enantiomers. Why is it not possible that your product is either the (1R, 2R) or the (1S, 2S) pure enantiomer?

Question 2

Explain why the vapor pressure of 4-chlorobenzaldehyde is greater than that of the alcohol.

[dlook33]

Answer to Question 1

It is a fundamental principle of chemistry that if you begin with no optical activity you must end up with no optical activity, assuming the sample size is large enough. In this experiment, one student started with benzil, which is achiral and therefore, by definition, optically inactive. The other student began with a racemic mixture of benzoin, which also has a net optical rotation of zero. Because sodium borohydride and isopropanol are also achiral, one cannot expect to make an excess of one of the two enantiomeric hydrobenzoins.

Answer to Question 2

Considering that the mass and overall shape of these two molecules are very similar, the reason the alcohol has a lower vapor pressure is due to the greater intermolecular forces between alcohols relative to aldehydes. Alcohols can hydrogen bond (a special type of dipole-dipole interaction) whereas aldehydes cannot