1. (5 pts) Threonine is an essential amino acid, meaning that it must be consumed regularly. Two structures of threonine are represented in the box.
 

a. (4 pts) Assign absolute configurations to both chiral centers in both structures: Left structure: C-1:    S     C-2:     S     Right structure: C-1:    R     C-2:     S

b. (1 pt) What is the stereochemical relationship of the two structures to each other? Possible answers include: enantiomer    diastereomer      meso      same stereoisomer      Answer: diastereomer

2. (3 pts) Consider the three molecules in the box to the right. On the lines provided, indicate how many chiral centers are present in each molecule.