Question

Indicate the chiral carbon atoms found in the monosaccharides D-ribose and D-mannose.

Short answer

The chiral carbon atoms in D-ribose are at positions 2, 3, and 4, while in D-mannose they are at positions 2, 3, 4, and 5.

Step-by-step solution

Molecular structure of D-ribose and D-mannose

D-ribose is an aldopentose having the following structure: $C{H}_{2}OH(1)-CHOH(2)-CHOH(3)-CHOH(4)-CHO(5)$ D-mannose is an aldohexose with the following structure: $C{H}_{2}OH(1)-CHOH(2)-CHOH(3)-CHOH(4)-CHOH(5)-CHO(6)$

Identifying Chiral Carbon Atoms in D-ribose

To identify the chiral carbon atoms, we need to find carbon atoms that have four distinct groups attached to them: 1. Carbon 1: $C{H}_{2}OH$ - not chiral, as it has two hydrogen atoms attached to the carbon. 2. Carbon 2: $CHOH(C{H}_{2}OH)$ - chiral, as it has four different groups attached: H, OH, $C{H}_{2}OH$, and $CHOH(3)$. 3. Carbon 3: $CHOH$ - chiral, as it has four different groups attached: H, OH, $CHOH(2)$, and $CHOH(4)$. 4. Carbon 4: $CHOH$ - chiral, as it has four different groups attached: H, OH, $CHOH(3)$, and CHO. 5. Carbon 5: $CHO$ - not chiral, as it has two bonds to the same oxygen atom. So, in D-ribose, the chiral carbon atoms are located at positions 2, 3, and 4.

Identifying Chiral Carbon Atoms in D-mannose

To identify the chiral carbon atoms in D-mannose, we follow the same process: 1. Carbon 1: $C{H}_{2}OH$ - not chiral, as it has two hydrogen atoms attached to the carbon. 2. Carbon 2: $CHOH(C{H}_{2}OH)$ - chiral, as it has four different groups attached: H, OH, $C{H}_{2}OH$, and $CHOH(3)$. 3. Carbon 3: $CHOH$ - chiral, as it has four different groups attached: H, OH, $CHOH(2)$, and $CHOH(4)$. 4. Carbon 4: $CHOH$ - chiral, as it has four different groups attached: H, OH, $CHOH(3)$, and $CHOH(5)$. 5. Carbon 5: $CHOH$ - chiral, as it has four different groups attached: H, OH, $CHOH(4)$, and CHO. 6. Carbon 6: $CHO$ - not chiral, as it has two bonds to the same oxygen atom. So, in D-mannose, the chiral carbon atoms are located at positions 2, 3, 4, and 5. In summary, the chiral carbon atoms in D-ribose are found at positions 2, 3, and 4, while in D-mannose, they are found at positions 2, 3, 4, and 5.