Question

The number of asymmetric carbon atoms in a molecule of glucose is (1) 6 (2) 4 (3) 5 (4) 3

Short answer

The number of asymmetric carbon atoms in a glucose molecule is 4.

Step-by-step solution

Understanding Asymmetric Carbons

An asymmetric carbon (also known as a chiral carbon) is a carbon atom that is attached to four different atoms or groups of atoms.

Structure of Glucose

Glucose has a chemical formula of C_6H_{12}O_6. The structure of a glucose molecule consists of a chain of six carbon atoms.

Identifying Carbons in Glucose

Label the carbon atoms in the glucose molecule from C1 to C6. Examine each carbon to see which ones are attached to four different groups.

Check Each Carbon

C1 is attached to an H, OH, a C2, and an O. C2 through C5 are each attached to an H, OH, and two C atoms that form either an aldehyde group (C1) or part of a chain. C6 has two H and is not asymmetric.

Count Asymmetric Carbons

Carbons C2 through C5 in glucose are all connected to four different groups. Thus, there are 4 asymmetric carbons in the glucose molecule.

Key concepts

chiral carbon

In organic chemistry, a chiral carbon—also known as an asymmetric carbon—is a carbon atom that is bonded to four different atoms or groups of atoms. This unique bonding creates a non-superimposable mirror image, similar to your left and right hands. When we say a carbon is chiral, it means that the molecule can exist in two forms (enantiomers) that are mirror images of each other. Understanding chiral carbons is important in fields like pharmacology because different enantiomers of a drug can have very different effects in the body.

glucose structure

Glucose is a simple sugar with the chemical formula \text{C}_6\text{H}_{12}\text{O}_6. This molecule consists of a chain of six carbon atoms, each connected to different groups. The specific arrangement of these atoms is what gives glucose its unique properties. In a solution, glucose can exist in an open-chain form or in a cyclic form commonly found in two forms: \(\text{alpha-glucose}\) and \(\text{beta-glucose}\).

identifying asymmetric carbons

To identify asymmetric carbons in glucose, we need to look closely at each carbon atom in the backbone of the molecule and check their attachments. We label the carbons from \(\text{C}_1\) to \(\text{C}_6\). Only the carbons \(\text{C}_2\) to \(\text{C}_5\) each have four different substituents:

• C1 is attached to a hydrogen (H), a hydroxyl group (OH), a carbon (C2), and an oxygen (O).
• C2 through C5 each have an H, an OH, and two different carbon groups.
• C6 has two hydrogens and is thus not chiral.

By counting these, we find that glucose has 4 asymmetric carbons.