Question

Draw Fischer projections for all 2-ketopentoses. Which are D-2-ketopentoses, which are L-2-ketopentoses, and which are enantiomers?

Short answer

Answer: There are two D-2-ketopentoses: D-erythro-2-ketopentose and D-threo-2-ketopentose. The enantiomers for these D-2-ketopentoses are L-erythro-2-ketopentose and L-threo-2-ketopentose, respectively.

Step-by-step solution

Draw Fischer projections for all possible 2-ketopentoses

First, let's draw the Fischer projections for all possible 2-ketopentoses. Since there are two chiral centers (carbon atoms 3 and 4), there will be 2^2 = 4 possible stereoisomers. 1. D-erythro-2-ketopentose: - Carbon 3: OH group to the right - Carbon 4: OH group to the right  2. L-erythro-2-ketopentose: - Carbon 3: OH group to the left - Carbon 4: OH group to the left  3. D-threo-2-ketopentose: - Carbon 3: OH group to the right - Carbon 4: OH group to the left  4. L-threo-2-ketopentose: - Carbon 3: OH group to the left - Carbon 4: OH group to the right 

Identify D-2-ketopentoses and L-2-ketopentoses

To identify if the molecule is a D-2-ketopentose or an L-2-ketopentose, we'll look at the orientation of the OH group on the carbon atom number 3 (penultimate carbon) in the structure. - D-2-ketopentoses: 1. D-erythro-2-ketopentose 2. D-threo-2-ketopentose - L-2-ketopentoses: 1. L-erythro-2-ketopentose 2. L-threo-2-ketopentose

Determine the enantiomers for each 2-ketopentose

Enantiomers are pairs of molecules that are non-superimposable mirror images of each other. In this case: - D-erythro-2-ketopentose and L-erythro-2-ketopentose are enantiomers  - D-threo-2-ketopentose and L-threo-2-ketopentose are enantiomers  In summary, we've drawn the Fischer projections for all 2-ketopentoses, identified D-2-ketopentoses and L-2-ketopentoses, and determined the enantiomers for each 2-ketopentose.