Problem 89 - Chemistry Matter and Change

Question

Infer The sugar glucose is sometimes called dextrose because a solution of glucose is known to be dextrorotatory. Analyze the word dextrorotatory, and suggest what the word means.

Step-by-Step Solution

Answer

A solution of glucose is called dextrorotatory because the term "dextrorotatory" indicates a rotation or movement in a clockwise or rightward direction. This suggests that a solution of glucose rotates plane-polarized light in a clockwise or rightward direction, which is an important characteristic in distinguishing between different isomers and conformations of molecules in stereochemistry.

Step 1: Identify the components of the word "dextrorotatory"

The word "dextrorotatory" can be divided into two parts: "dextro-" and "rotatory". Let's analyze both parts.

Step 2: Analyze the prefix "dextro-"

"Dextro-", originating from Latin dexter, means "right" or "to the right". This prefix is commonly used in scientific terminology to denote right-sidedness or a clockwise direction.

Step 3: Analyze the word "rotatory"

"Rotatory", derived from the Latin word "rotare" (to rotate), is an adjective that means pertaining to, causing, or marked by rotation.

Step 4: Combine the meanings of the word components

By combining the meanings of the prefix "dextro-" and the word "rotatory", we can deduce that "dextrorotatory" refers to a rotation or movement in a clockwise or rightward direction.

Step 5: Suggest what the word "dextrorotatory" means for glucose

Based on the combined meaning of the components, the term "dextrorotatory" suggests that a solution of glucose rotates plane-polarized light in a clockwise or rightward direction. This characteristic of glucose is important in the field of stereochemistry, as it helps to distinguish between different isomers and conformations of molecules.

Key Concepts

Understanding Glucose

Glucose is a simple sugar and is classified as a carbohydrate. Often referred to as "blood sugar," glucose is a primary source of energy for living organisms. It is crucial for metabolic processes and is found in many organisms, from humans to plants.
In its most common form, glucose is a six-carbon sugar, with the chemical formula \( C_6H_{12}O_6 \). It can exist in several forms, including a straight-chain form and two cyclic forms which are the alpha (α) and beta (β) glucose.

• Alpha glucose has its hydroxyl group (-OH) on the first carbon pointed downward.
• Beta glucose has the -OH group on the first carbon pointed upward.

These forms play a significant role in the structuring of polysaccharides like starch and cellulose.

The Meaning of Dextrorotatory

The term dextrorotatory pertains to the way glucose interacts with light. Specifically, it describes glucose's ability to rotate plane-polarized light. When light passes through certain substances, it can be polarized, meaning the light waves vibrate in a single plane.
"Dextrorotatory" indicates that glucose will rotate this polarized light to the right or in a clockwise direction. This characteristic is key in identifying and studying sugars and other compounds in stereochemistry. It helps differentiate between molecules that may have the same structure but rotate light differently.
For glucose, specifically, this behavior contributes to its alternative name, "dextrose".

Exploring Isomers

Glucose is an example of a molecule with several isomers. Isomers are compounds with the same chemical formula but different structural configurations.
There are different types of isomers, such as:

• Structural isomers, where the arrangement of atoms differs.
• Stereoisomers, where the atoms are connected in the same sequence but differ in the three-dimensional orientation.

In the case of glucose, its stereoisomerism is due to the existence of α-glucose and β-glucose. The different arrangements affect their physical and chemical properties, playing crucial roles in how they function biologically.
Recognizing and differentiating isomers is a central focus in fields such as organic chemistry and biochemistry.

Role of Plane-Polarized Light

In the study of stereochemistry, plane-polarized light is a powerful tool. When light is directed through a polarizing filter, the light that emerges vibrates in a single plane. This is called plane-polarized light.
Compounds that can rotate this light are called optically active. Their ability to rotate light either to the left (levorotatory) or right (dextrorotatory) reveals information about the compound's molecular structure.
The rotation of plane-polarized light helps identify the stereochemistry of molecules, determining whether they are right-handed or left-handed. For glucose, this optical activity indicates the specific arrangement of molecules, aiding in the comprehension of its unique properties and behaviors.