Chirality centers are atoms in a molecule that can be asymmetric. These atoms can cause a molecule to be either right-handed or left-handed.
Chiral molecules can be linear, where all of the atoms are arranged in a line, or spherical, where all of the atoms are arranged around a center point.
When solving for chirality centers, only one of these types can be used per solution, as they only have one chiral atom. The rest of the molecules must be rotatable to determine if they are right-handed or left-handed.
There are three main steps to solving for all of the chirality centers in a structure using ChemDraw Ultra and ChemDraw Professional Edition.
Click ‘Turn On’ button
The next step is to select all of the chirality centers in the structure. A ‘chirality center’ is defined as a unique atom in the structure that can be flipped and still maintain the same molecule.
By clicking the ‘Turn On’ button, Chimera allows you to select all of the chiral centers in the structure by looking for green atoms. Green atoms indicate that atom is a chiral center and can be flipped to create a mirror image of the molecule.
Chiral centers can be difficult to find depending on how complex the molecule is. It can take some time to find all of them, so don’t feel like you need to get them all or you are doing it wrong!
Check out some videos on how to find them, or try experimenting with different structures to gain more experience finding them.
Click ‘Show Selection’ button
Now it is time to select the chirality centers in your structure. To do this, you must first select all of the atoms in your molecule.
To do this, click the ‘Select All Atoms’ button and all of the atoms in your structure will be highlighted in blue. Then, click the ‘Show Selection’ button and all of the atoms will turn green, indicating they are part of your selection.
Now you can go back to the ‘Chirality Center Finder’ tab and click the green ‘Select All Chirality Centers’ button. The program will then highlight each of the chirality centers in your molecule with a green circle.
View image of structure
Once the final structure is complete, you can view the molecule in all its glory. You can see how all the atoms fit together perfectly, how all the rings fit together perfectly, and how each atom type is surrounded by other types of atoms.
This view also lets you see any chirality centers that may be in the molecule. A chirality center is a location where the molecule can be rotated 180 degrees and still fit into the structure.
If there are no chirality centers in the molecule, then your molecule is chiral pure. If there are one or more than one chirality center, then your molecule is non-chiral.
Checking for these spots in the structure takes some practice, but looking at other people’s molecules can help you identify these spots.
Select an atom by clicking on it
Once the atom is selected, the software will determine whether the atom is chiral or not. If it is chiral, the software will search for its counterpart and mark it as not selected.
If it is not chiral, the software will select its mirror image instead. Both atoms will turn green, and only one can be green at a time.
The software then searches for neighboring atoms of the same type and selects them. It then repeats this process until all of the atoms in the structure are colored green.
This process can take some time depending on how many atoms are in the structure and how many of them are chiral. The user can set a limit on how many to select to speed up the process.
Click ‘Turn Off’ button
The last step is to click the ‘turn off’ button. This will generate a new molecule that matches all of the chirality centers in the current molecule.
This feature can be used to test if all of the chirality centers are selected or not. If a new molecule is generated, then all of the atoms are selected, thus proving that the original structure has all chirality centers represented.
Using this tool can be time consuming, so make sure to save your work before clicking ‘turn off’!
Chiral molecules have many applications in science and medicine. The ability to identify these molecules is an important skill to have when working with them.
Repeat steps 4-6 for all chirality centers
Once all the chirality centers are selected, the last step is to generate the diastereomeric transition. This can be done by clicking the green “Diastereomeric Transition” button at the top.
Diastereomers are molecules with at least two distinct spatial arrangements of atoms. In benzene compounds, they refer to different configurations of the six carbon rings.
The software will then ask you to confirm whether you want to generate the transition or not. Click “Yes” to proceed with the transition and then wait a few minutes for it to complete. You can check the progress bar to see how much is left.
Once it is completed, you can view your model on screen or as a 3D model depending on your settings.
Green atoms indicate a chirality center
Once all of the chirality centers are selected, the next step is to link all of the chirality centers together. This is called generating a skeleton and requires some careful thinking.
The first rule when generating a skeleton is to only connect atoms that are next to each other. You also cannot have any gaps in the chain, so make sure to pay close attention to that!
Once the atoms are linked, you can confirm that there are an even number of atoms in the chain and that there are no gaps. If there are either of these things, then you have done it correctly!
The last step is to double check that all of the skeletons are facing opposite directions. If they do not all turn out facing opposite directions, then you did something wrong and need to go back and check your work.
Red atoms indicate an incorrect selection
Once the correct atom is selected, the next step is to make sure all of the chirality centers in the structure are selected. If any are left unselected, then they will be displayed as red atoms, indicating an incorrect selection.
At this point, you can either save the file or continue to the next step. If you choose to continue to the next step, make sure all of the chirality centers in the structure are selected!
Checking All Chirality Centers in a Structure Takes Time, But It Is Worth It!
It can take a while to check all of the chirality centers in a structure, but this feature is very useful. It helps ensure that your molecule is displayed correctly and accurately.
