Question

Which carbon of an aldopentose determines whether the pentose has a D or L configuration?

Short answer

Answer: The chiral center C5, which is the carbon atom farthest from the carbonyl group (aldehyde), is responsible for determining whether an aldopentose has a D or L configuration.

Step-by-step solution

1. Identify the chiral centers of an aldopentose

An aldopentose has four chiral centers, as there are four carbon atoms (C2, C3, C4, and C5) in the molecule, each bonded to four distinct groups/atoms.

2. Determine the carbon farthest from the carbonyl group

Since the carbonyl group (aldehyde) is attached to the C1 carbon, the carbon atom farthest from it in the chain is C5.

3. Distinguish between D and L configurations of an aldopentose

To determine the configuration, look at the orientation of the hydroxyl group (-OH) attached to the chiral center C5. If the hydroxyl group is on the right side of the molecule, the aldopentose has a D configuration (D-aldopentose). If the hydroxyl group is on the left side of the molecule, it has an L configuration (L-aldopentose).

Answer

The carbon of an aldopentose that determines whether the pentose has a D or L configuration is the chiral center C5, which is the carbon atom farthest from the carbonyl group (aldehyde).