Question

1. Could you predict the sign of the rotation for the benzamide derivative of (-)-sec-butylamine? Explain.

2. How would you separate (+)- or (-)-tartaric acid from meso-tartaric acid? How would you separate (+) and (-)-tartaric acid?

Answer 1

1)You cannot determine the rotation for this compound. You need to use the formula for specific rotation which asks for information that is not present in thsi question. the only thing you can derive from this information is that its levoratory, which is shows from the negative sign in from of the name of the compound. there is no relation between S, and R and the specific rotation.

2)A common way of separation of enantiomers uses the conversion into diastereomers, that are not mirror images of each other. The following example demonstrates this principle. The two enantiomers 1-phenylethylamine (S-(-), R-(+)) are separated using (L)-(+)-tartaric acid (also known as the (R,R)-form) as resolving agent. The two salts formed possess different cation ions are therefore not enantiomers of each other anymore. The (S)-(1)-phenylethyl ammonium-(R,R)-tartrate salt crystallizes faster than the (R)-(1)-phenylethyl ammonium-(R,R)-tartrate salt.