Question

Write the open-chain structure of a ketotetrose.

Short answer

A ketotetrose has the open-chain structure CH2OH-C(=O)-CH(OH)-CH2OH.

Step-by-step solution

Understand the Definition of Tetrose

A tetrose is a monosaccharide with four carbon atoms. It has the general molecular formula C4H8O4. Tetroses can be classified as aldoses or ketoses depending on the type of carbonyl group they contain.

Identify the Functional Group for Ketotetrose

Since we are asked to write the open-chain structure of a ketotetrose, we should focus on the ketose configuration. A ketose contains a ketone functional group, typically represented as a carbonyl group (C=O) bonded to two carbon atoms within the carbon chain.

Determine the Basic Structure of a Ketotetrose

Plan the structure by arranging the four carbon atoms in a chain. For a ketotetrose, the ketone group is located on the second carbon atom in the chain. Thus, the structure should be arranged as follows: CH2OH-C(=O)-CH(OH)-CH2OH. This ensures the carbonyl group is in the second position appropriate for ketoses in a four-carbon chain.

Complete the Open-Chain Structure

Recreate the open-chain structure with the identified elements. Properly arrange each carbon atom with the correct number of hydrogens and attach the hydroxyl groups to the appropriate carbons.

Key concepts

Monosaccharide

A monosaccharide is the simplest form of carbohydrates and plays a crucial role in nutrition and biology. These are single sugar molecules, often known as simple sugars. They are the building blocks from which more complex sugars and carbohydrates are made.
Monosaccharides are distinguished by their carbon atom count, with common forms being trioses (3 carbons), tetroses (4 carbons), pentoses (5 carbons), and hexoses (6 carbons).

• Monosaccharides have the general formula \( C_nH_{2n}O_n \), where n is the number of carbon atoms.
• They are important for energy production as they can be easily used by the body.
• The most common monosaccharides include glucose, fructose, and ribose.

In the case of ketotetrose, it is a tetrose (4 carbons) with carbonyl group's specific placement defining it as a ketone structure.

Carbonyl Group

A carbonyl group is a functional group characterized by a carbon atom double-bonded to an oxygen atom, written as \( C=O \). It is a versatile group found in many organic compounds. This fundamental group influences the chemical properties and reactions of molecules it resides in.
Carbonyl groups are seen in two primary forms in carbohydrates:

• Aldehydes, where the carbonyl group is at the end of the carbon chain.
• Ketones, where the carbonyl group appears within the chain.

In ketotetrose, the carbonyl group identifies it as a ketose instead of an aldose. The position of this group within the molecule is key to classifying and distinguishing different sugars.

Ketone Functional Group

The ketone functional group is a specific type of carbonyl group where the carbon atom is bonded to two other carbon atoms. This structure is expressed as \( \text{RC(=O)R'} \). It is an essential characteristic that separates ketoses from aldoses in monosaccharides.
The ketone group adds unique properties to the molecule:

• Contributes to particular chemical reactions, including reduction and nucleophilic addition.
• Influences the molecular structure, making these sugars critical in metabolic pathways.

In a ketotetrose like xylulose, the ketone group is positioned on the second carbon, differentiating it from aldoses, where the carbonyl group is at the end of the chain.

Open-Chain Structure

The open-chain structure of monosaccharides refers to their linear form, where carbon atoms form a straight chain. This structure contrasts with the ring (cyclic) form commonly found in aqueous solutions.
Understanding the open-chain form is important for grasping how sugars interact chemically and biologically.

• This linear structure is pivotal when drawing or predicting reactions.
• In an open-chain ketotetrose, we find specific arrangements: \( \text{CH}_2\text{OH}-\text{C(=O)}-\text{CH(OH)}-\text{CH}_2\text{OH} \).

This setup for ketotetrose signifies the presence of the ketone at the second carbon, impacting its reactivity and biological role. The open-chain form is crucial for distinguishing the molecule’s actual structure and functions before it adopts a cyclic form through intramolecular interactions.