Question

Draw stereorepresentations for all stereoisomers of this compound. Label those that are meso compounds and thooe that are pairs of enantiomers. CC1C(C(=O)O)CC(C(=O)O)C1(C)C

Short answer

Answer: There are four possible stereoisomers for a compound with two chiral centers, and they can be organized into two pairs of enantiomers (non-superimposable mirror images). There are no meso compounds in this case, as none of the stereoisomers have an internal plane of symmetry.

Step-by-step solution

1. Identify the stereocenters

First, let's look at the structure of the given compound and identify the chiral centers. Chiral centers have four different groups attached to them. The given compound has two stereocenters (chiral centers).

2. Calculate the number of stereoisomers

Next, we will calculate the number of stereoisomers possible for the compound with two chiral centers. This can be calculated using the formula 2^n, where n is the number of chiral centers. In this case, it's 2^2 = 4.

3. Draw the stereorepresentations

Let's draw the four possible stereoisomers for the given compound: 1. Both chiral centers in R configuration 2. Both chiral centers in S configuration 3. One chiral center in R configuration and the other in S configuration 4. One chiral center in S configuration and the other in R configuration

4. Identify enantiomers and meso compounds

Now, we will compare each pair of stereoisomers (1 and 2, 3 and 4): 1. Stereocenters 1 and 2 - These two are non-superimposable mirror images of each other and therefore, they are enantiomers. 2. Stereocenters 3 and 4 - They are also non-superimposable mirror images of each other and form another pair of enantiomers. There are no meso compounds in this case as no stereoisomer found to have an internal plane of symmetry.

Key concepts

Stereochemistry

Stereochemistry is a subfield of chemistry that focuses on the spatial arrangement of atoms within molecules and how this arrangement affects the properties and reactions of those molecules. Imagine you're putting together a model; each piece must go in a specific place. Similarly, in stereochemistry, the layout of atoms can create different 'models' or isomers—molecules with the same molecular formula but with different structures.

Stereoisomers are unique categories of isomers that differ only in the three-dimensional orientations of their atoms in space. A famous analogy used to describe these spatial differences is that of your left and right hands—they are mirror images of each other but cannot be aligned perfectly when superimposed. This property is known as chirality, which is a central concept in stereochemistry and is critically important in fields like pharmaceuticals where the 3D structure of a compound can determine its therapeutic effect.

Chiral Centers

A chiral center, often referred to as a stereocenter, is a specific atom within a molecule that has four different groups attached to it. This uniqueness causes non-superimposable mirror images, or enantiomers, to exist.

Imagine standing in the middle of a room, with each hand touching something different—let's say a book, a cup, a ball, and a pen. If someone else stood in your place, they would need to have the exact items in their hands to be considered the same 'configuration'. If any item, say the cup, switched hands, this would create a different configuration. In chemistry, when a molecule has at least one chiral center, think of it like a junction where different paths (configurations) can be taken, leading to different three-dimensional structures for the molecule.

Meso Compounds

Meso compounds are a type of stereoisomer that, despite having multiple chiral centers, are achiral overall—meaning they do not exhibit optical activity. This occurs because meso compounds have an internal plane of symmetry that allows different parts of the molecule to cancel out each other's optical activity.

To better understand this, consider a paper cutout of a butterfly. If the butterfly is perfectly symmetrical and you fold it down the middle, both halves match exactly. A meso compound is like this butterfly; though it may appear to have chiral centers, the symmetry makes it possible to superimpose one half of the molecule onto the other, indicating that the molecule cannot have enantiomers. Meso compounds are quite interesting in stereochemistry because they contradict the expectation that a molecule with chiral centers must be chiral.

Enantiomers

Enantiomers are pairs of stereoisomers that are non-superimposable mirror images of each other, much like human hands. Enantiomers have identical physical properties in a non-chiral environment, such as melting point and boiling point. However, they rotate plane-polarized light in opposite directions—one clockwise and the other counterclockwise—a phenomenon known as optical activity.

It is important to visualize enantiomers as mirror images that cannot be aligned when superimposed. In the exercise provided, compounds with both chiral centers in R configuration and both in S configuration are enantiomers, as are the compounds with one center in R and the other in S. These pairs are chemically similar but can have dramatically different biological effects. The study of enantiomers is not just an academic exercise but a crucial aspect of drug design and synthesis in medicinal chemistry, where the 'right' or 'left' hand of a molecule can make a world of difference.