Question

Hitich of the following are isomers? (a) 3PGA and 2PGA (b) PGAL and DHAP id Glucose and Fructose (d) All of these

Short answer

All of the given pairs (a) 3PGA and 2PGA, (b) PGAL and DHAP, and (c) Glucose and Fructose are isomers as they have the same molecular formula but different structures or functional groups.

Step-by-step solution

Define Isomers

Isomers are molecules with the same molecular formula but different structures. They can be structural isomers with a different arrangement of atoms or stereoisomers with the same arrangement of atoms but different spatial orientations.

Examine 3PGA and 2PGA

3-phosphoglycerate (3PGA) and 2-phosphoglycerate (2PGA) have the same molecular formula, C3H7O7P, but the phosphate group is attached to a different carbon atom. This makes them structural isomers.

Examine PGAL and DHAP

Glyceraldehyde 3-phosphate (PGAL) and dihydroxyacetone phosphate (DHAP) have the same molecular formula, C3H7O6P. PGAL is an aldehyde and DHAP is a ketone, making them structural isomers as well.

Examine Glucose and Fructose

Glucose and fructose have the same molecular formula, C6H12O6. However, glucose is an aldose with an aldehyde group, while fructose is a ketose with a ketone group. This places them in different functional groups of sugars, which means they are indeed structural isomers.

Conclude Isomerism

Since all the given compounds exhibit different structural organizations but the same molecular formulas, they are all considered isomers.

Key concepts

Structural Isomers

When exploring the fascinating world of chemistry, one might come across the concept of isomers. Structural isomers, to be specific, are molecules that share the same molecular formula, yet they differ in the way their atoms are connected or arranged within the molecule. This distinct arrangement can lead to remarkable differences in chemical properties and reactions. Let's take for example, 3-phosphoglycerate (3PGA) and 2-phosphoglycerate (2PGA). Despite having identical molecular formulas of C3H7O7P, the placement of the phosphate group on different carbon atoms in each molecule makes them structural isomers of each other.

Another pair likely to be encountered are glyceraldehyde 3-phosphate (PGAL) and dihydroxyacetone phosphate (DHAP), both composed of C3H7O6P. The structural difference here lies in the functional groups; PGAL contains an aldehyde, while DHAP features a ketone. This difference in the arrangement of functional groups is quintessential to structural isomerism and has profound implications on their biological roles and functions. Understanding this can aid students in grasping why isomers, although seeming similar at a glance, are truly distinct entities with unique properties.

Stereoisomers

Now, let's shift our focus to another dimension of isomerism, one that deals not with the connection of atoms, but rather with their spatial arrangement. Stereoisomers have the same molecular formula and sequence of bonded atoms as another molecule, but they differ in the three-dimensional orientation of these atoms in space.

Picture your hands, they are mirror images but not superimposable, much like stereoisomers. They are further classified into two subtypes: enantiomers, which are mirror images of each other, and diastereomers, which are not. The subtleties of stereoisomerism can have major consequences in biological systems, like how our bodies distinguish between different amino acids based purely on their spatial configuration. Although stereoisomers are not exemplified in the exercise, understanding their significance helps illuminate the diverse complexity we encounter in chemical substances.

Molecular Formula

Circling back to the foundation of isomer discussions, we encounter the concept of a molecular formula. This notation essentially provides a count of each type of atom in a molecule but does not divulge the information about how these atoms are arranged or connected. For students encountering molecules such as glucose and fructose, both of which have the same molecular formula, C6H12O6, the molecular formula alone may suggest similarity.

However, only by analyzing the structure of these sugars does it become clear how functionally different they are. This distinction is crucial in many fields, especially in biochemistry, where enzymes will interface with substrates based on their structure, not just their molecular formula. Here's a practical application: consider a scenario in which you're identifying a mystery compound. If you're only given the molecular formula, you might predict certain properties, but without structure information, you might not predict its true nature or reactivity. That's why a molecular formula, while an essential piece of the puzzle, is only the first step in understanding the complete picture of a chemical species.