Question

6)Draw perspective formulas for the acetonide formed from the meso and racemic hydrobenzoin (use models or PC Spartan if necessary to visualize these compounds).

7)Based on your structures in question 6.

a)How many H NMR signals should be observed for the benzyl hydrogens for the meso and racemic acetonide? Explain your answer

b)How many H NMR signals should be observed for the methyl groups for the meso and racemic acetonide? Explain your answer.

c)Explain how H NMR can be used to establish the stereochemistry of the hydrobenzoin (meso or racemic) - formed in the reduction of benzil with NaBH₄.                

Answer 1

a) Both meso and racemic have single peak for benzyl hydrogen.

b) One H NMR signals observed for the methyl groups for the meso and racemic acetonide

c) The NMR of these two samples will be very similar. It is often useful to make a derivative of the compound that will have a distinct NMR. In this case, making the acetonide (an acetal) of the hydrobenzoin may help us to distinguish between these samples using NMR.