Question

(+)-Glyceraldehyde and (-)-glyceraldehyde refer to the (R) and (S) forms of 2,3 -dihydroxypropanal, respectively. These molecules are considered: (A) enantiomers. (B) diastereomers. (C) meso compounds. (D) structural isomers.

Short answer

(A) enantiomers

Step-by-step solution

Understand the Definitions

Enantiomers are molecules that are mirror images of each other but are not superimposable. Diastereomers are stereoisomers that are not mirror images. Meso compounds are molecules with multiple stereocenters that are superimposable on their mirror images. Structural isomers have the same molecular formula but different connectivity of atoms.

Identify the Stereoisomers

Given that (+)-glyceraldehyde and (-)-glyceraldehyde are (R) and (S) forms of 2,3-dihydroxypropanal, respectively. This indicates that they have opposite configurations at a chiral center.

Assess the Relationship

Since (+)-glyceraldehyde and (-)-glyceraldehyde have opposite configurations at a single chiral center, they are non-superimposable mirror images of each other.

Determine the Type of Isomer

Given the definitions and the relationship observed in Step 3, (+)-glyceraldehyde and (-)-glyceraldehyde are enantiomers.

Key concepts

Chirality

Chirality is a concept in chemistry where a molecule cannot be superimposed on its mirror image, much like how your left and right hands are different. A molecule is termed 'chiral' if it has this property. To identify chiral molecules, look for a carbon atom bonded to four different groups. These unique structures lead to molecules having non-superimposable mirror images, called enantiomers. Chirality plays a crucial role in fields like pharmacology, as different enantiomers of a compound can have vastly different effects in biological systems.

Stereoisomers

Stereoisomers are a type of isomer where the atoms in the molecules are connected in the same order, but differ in their spatial arrangement. There are two main types of stereoisomers: enantiomers and diastereomers. Enantiomers are mirror images of each other but are not superimposable. This was seen in the case of (+)-glyceraldehyde and (-)-glyceraldehyde. Diastereomers, on the other hand, are not mirror images and are not superimposable. It's important to distinguish stereoisomers from structural isomers, which differ in their connectivity rather than spatial arrangement.

Molecular configurations

Molecular configuration refers to the fixed three-dimensional arrangement of atoms within a molecule. This arrangement can give rise to different types of isomers. Configurations are determined by the spatial orientation of atoms around chiral centers, like the carbon atom in 2,3-dihydroxypropanal from the exercise. Configurations are often denoted as (R) or (S) based on the Cahn-Ingold-Prelog priority rules. These configurations are critical in understanding the properties and reactivity of enantiomers and play a vital role in biological systems and chemical reactions.

Chiral centers

Chiral centers, also known as stereocenters, are atoms in a molecule that have four different groups attached to them, leading to non-superimposable mirror images. These centers are the source of chirality in molecules. For instance, the carbon atom in 2,3-dihydroxypropanal is a chiral center, giving rise to the (R) and (S) configurations of glyceraldehyde. Identifying chiral centers is a fundamental skill in stereochemistry as it helps predict the behavior of molecules in different environments, including biological systems where chirality can have significant effects.