Draw all stereoisomers of 3-chloro-2-butanamine. Label each stereocenter with the appropriate R/S designation to show handedness. Indicate the relationship (enantiomers or diastereomers) between every possible pairing of compounds. Label each compound as chiral or achiral, and if there is a meso compound, label it as such.
One of these compounds has a specific rotation of -7.2°. Which compound might this be?
What do you expect the specific rotation of the remaining compounds to be?