A Few Organic Chem Questions (Stereochemistry)

In summary: I'm not too sure if you can "force" a meso to exist, but I think that's kind of what they mean when they say you have to find a chiral diastereomer. In summary, stereochemistry is the study of the orientations of substituents around stereogenic centers on carbon-based molecules. Meso-compounds are a type of molecule where a plane of symmetry can exist and, as long as two substituents are identical on symmetrically located stereogenic centers, a meso-compound can be created. Chiral diasteromers are molecules that are not superimposable with other stereoisomers, and can only be found by rotating single bonds around stereogenic
  • #1
royblaze
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I am currently learning about stereochemistry in my O-chem class. I just have a few questions that I were running through my head. I know there are a lot of questions here, but they're not HW-related at all; my prof. just taught the lecture and I have had these questions on my mind.

1. How are stereogenic centers determined? Are they just locations where enantiomers can exist via "group swapping?"

2. How can one determine a "chiral diastereomer" of a organic molecule? More specifically, what if the molecule is a meso-compound (where a plane of symmetry can exist); how can you find a "chiral diastereomer" if chirality means that it can't super-impose, while the diastereomer means that they are not enantiomers? Is the diastereomer in reference to the original molecule (i.e. diastereomers are just stereoisomers that are not enantiomers with each other)?

3. Is a meso compound really just as simple as locating a plane of symmetry? Can you rotate about single bonds to "force" a meso compounds exist?

Thank you.
 
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  • #2
After much reading, consultation, and model building, I have answered these questions in a way that, for the most part, makes sense for myself.
 
  • #3
Can you try to summarize you PoV?
 
  • #4
Okay, here goes, from what I understand:

1) How are stereogenic centers determined? Are they just locations where enantiomers can exist via "group swapping?"

Stereogenic centers are (for the context of o-chem I) carbons where there are four different substituent groups. Stereogenic centers are also "centers" where the substituents could potentially attach in a different orientation (i.e. enantiomers, where the mirror image has different "viewed" orientation of substituent groups). "Group swapping" isn't really a thing; rather, it's just that stereochemistry is observable if two groups could potentially attach in a different orientation (i.e. methyl and ethyl on a single carbon bonded to R and R').

Stereogenic centers cannot exist when two substituents are the same, since the --Prelog thing has ties in priority at those locations.



2) How can one determine a "chiral diastereomer" of a organic molecule? More specifically, what if the molecule is a meso-compound (where a plane of symmetry can exist); how can you find a "chiral diastereomer" if chirality means that it can't super-impose, while the diastereomer means that they are not enantiomers? Is the diastereomer in reference to the original molecule (i.e. diastereomers are just stereoisomers that are not enantiomers with each other)?

A chiral diastereomer is merely just a chiral molecule that is NOT superimposable with OTHER stereoisomers. In accordance to meso-compounds, a chiral diasteromer could just be an enantiomer with a different stereochemistry about a single carbon having different "into the plane, out of the plane" substituents. One thing I am not sure of, though, is that a chiral diastereomer is no longer meso once it becomes chiral (?).



3) Is a meso compound really just as simple as locating a plane of symmetry? Can you rotate about single bonds to "force" a meso compounds exist?

A meso compound requires at least 2 identical substituents on symmetrically located stereogenic centers, as far as I can tell. You can rotate about single bonds to "see" if a meso exists or not.
 
  • #5


1. Stereogenic centers are determined by identifying a carbon atom that is connected to four different substituents. These substituents can be different atoms or groups of atoms, but they must be distinct from each other. This creates a chiral center, which can exist in two different enantiomeric forms.

2. To determine a chiral diastereomer of an organic molecule, you can start by identifying all of the stereogenic centers in the molecule. Then, you can swap the groups on one or more of these centers to create a new molecule that is not an enantiomer, but also not superimposable on the original molecule. This new molecule would be a diastereomer of the original. In the case of a meso-compound, you can still identify the stereogenic centers and swap groups to create diastereomers, but the plane of symmetry will remain the same in all of the diastereomers. The diastereomer is in reference to the original molecule, as it is a stereoisomer that is not an enantiomer with the original molecule.

3. A meso compound can be identified by locating a plane of symmetry, but it is not always as simple as that. In some cases, the molecule may have multiple planes of symmetry or no planes of symmetry at all. In order to "force" a meso compound to exist, you would need to rotate about single bonds in a way that maintains the plane of symmetry. This can be done by swapping groups on the stereogenic centers, as mentioned in question 2. Additionally, the presence of a plane of symmetry does not necessarily mean that the molecule is a meso compound. It is important to consider the overall structure and connectivity of the molecule to accurately determine if it is a meso compound.
 

What is Stereochemistry?

Stereochemistry is the study of the three-dimensional arrangement of atoms in molecules and how this affects their chemical and physical properties.

What is a chiral molecule?

A chiral molecule is a molecule that has a non-superimposable mirror image, meaning that the molecule and its mirror image are not identical and cannot be overlapped perfectly. This is also known as having a "handedness".

What is the difference between enantiomers and diastereomers?

Enantiomers are a type of stereoisomer that are mirror images of each other and cannot be superimposed. Diastereomers, on the other hand, are stereoisomers that are not mirror images of each other and can have different physical and chemical properties.

Can a molecule have both chiral and achiral centers?

Yes, a molecule can have both chiral centers (atoms with four different groups attached) and achiral centers (atoms with two or three identical groups attached). This would make the molecule a meso compound, meaning it has internal planes of symmetry and is not chiral overall.

How do you determine the stereochemistry of a molecule?

The stereochemistry of a molecule can be determined by looking at the arrangement of atoms and groups around a chiral center. The R/S notation is commonly used to indicate the configuration of a chiral center, with R meaning clockwise and S meaning counterclockwise. Other methods, such as Fischer projections, can also be used to determine stereochemistry.

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