Question

Write the open-chain structure of the only ketotetrose. Name this compound. Does it have an optical isomer?

Short answer

The only ketotetrose is erythrulose, and it has optical isomers.

Step-by-step solution

Understand the Definition

A ketotetrose is a four-carbon sugar molecule containing a ketone group (instead of an aldehyde group) on the second carbon, with two hydroxyl groups attached to the remaining carbons.

Identify the Structure

Since we are dealing with a tetrose, there should be four carbon atoms. For a ketotetrose, the ketone group (C=O) should be on the second carbon atom in the chain.

Draw the Open-Chain Structure

Start with CH2OH-CO- on the first two carbons, followed by -CHOH-CHO with hydroxy groups on the third and fourth carbons, forming the full open-chain structure: CH2OH-CO-CHOH-CHOH-CH3.

Naming the Ketotetrose

The only ketotetrose is called 'erythrulose'. It is named based on its configuration and the total number of carbon atoms in the structure.

Determine the Existence of Optical Isomers

Optical isomers occur if there is at least one chiral center in the molecule. Erythrulose has one chiral center at the third carbon, hence it has optical isomers.

Key concepts

Erythrulose

Erythrulose is a simple sugar molecule known as a ketotetrose. This name indicates that it has four carbon atoms ('tetrose') and a ketone group ('keto') in its molecular structure. In erythrulose, the ketone group is located on the second carbon atom. This places erythrulose within the family of monosaccharides, which are the simplest form of sugars.
Erythrulose's structure is relatively straightforward. It consists of four carbon atoms arranged in a chain. The chemical formula for erythrulose is C\(_4\)H\(_8\)O\(_4\). Its open-chain configuration can be represented as CH\(_2\)OH-CO-CHOH-CH\(_2\)OH. In this formation, the ketone group (C=O) on the second carbon and the presence of hydroxyl groups (-OH) on the other carbons define its classification. As the only ketotetrose, erythrulose plays a role in biological processes and is sometimes used in cosmetic products for its self-tanning properties due to its ability to react with amino acids in the skin.

Optical Isomers

Optical isomers are fascinating entities in chemistry, having structures that are mirror images of each other but are not superimposable. This characteristic is crucial in compounds like erythrulose. Such isomers exhibit different interactions with polarized light and can have different biological effects. These isomers are a subset of stereoisomers, which are compounds that have the same molecular formula and sequence of bonded atoms but differ in the three-dimensional orientation.
In erythrulose, the optical isomers arise due to the presence of a chiral center. This chiral center is what allows erythrulose to exist in two forms that are mirror images. The way these isomers interact with light is used in numerous applications, such as determining the concentration of certain sugars in solutions through polarimetry, which can discern the specific rotation of each isomer.

Chiral Center

A chiral center is a specific carbon atom that is bonded to four different groups. This unique configuration makes optical isomerism possible. In erythrulose, the presence of a chiral center is crucial for its classification as an optically active compound.
For erythrulose, the third carbon atom serves as the chiral center. This is because it is attached to four distinct groups: a hydrogen atom, a hydroxyl group, a ketone group, and another carbon chain. The differing spatial arrangement of these groups allows for the possible formation of isomers that are non-superimposable mirror images. The presence and arrangement of chiral centers in molecules not only affect optical activity but also have significant implications in chemical reactions and interactions in biological systems.