Chirality: Refers to the geometric property where an object is not superimposable on its mirror image.
Chirality Center: Also known as a chiral center, stereocenter, stereogenic center, or asymmetric center. It's a tetrahedral carbon atom (sp3 hybridized) with four different groups attached.
Identifying Chirality Centers
Criteria:
Tetrahedral carbon
Must have four different groups attached
Typically sp3 hybridized carbon
Non-Chirality Center Criteria:
Carbon with two or more of the same groups
Carbon not sp3 hybridized (e.g., sp2)
Examples
1. Alcohol Molecule
Structure: Four carbons in a chain.
Findings:
Leftmost carbon: 3 hydrogens attached → not a chirality center.
Second carbon: OH, H, methyl, ethyl groups → chirality center.
Remaining carbons: Not chirality centers (due to repeating groups).
Conclusion: One chirality center in this alcohol molecule.
2. Acetone
Structure: Three carbons.
Findings:
Both ends: 3 hydrogens → not chirality centers.
Middle carbon: sp2 hybridized, trigonal planar geometry → not a chirality center.
Conclusion: Zero chirality centers.
3. Ring Example
Initial Structure: Hydrogen & Chlorine on opposite sides of a ring.
Findings:
All carbons with two hydrogens → not chirality centers.
Apparent chirality center due to chlorine and hydrogen, but identical paths around the ring → not a chirality center.
Modified Structure: Different paths around the ring.
Chlorine, Hydrogen, distinct groups → chirality center.
Conclusion: One chirality center with a modified path.
4. Ibuprofen Molecule
Structure: Complex with benzene ring and various groups.
Findings:
Benzene ring: sp2 hybridized carbons → no chirality centers.
Carbons with repeating groups or sp2 hybridization → not chirality centers.
Specific carbon with methyl, hydrogen, carboxylic acid, and benzene ring → chirality center.
Conclusion: One chirality center in the ibuprofen molecule.
Importance
Skill Development: Essential to practice identifying chirality centers, focusing on attached groups and hybridization.
Terminology: Understand different terms for chirality centers as used in academic contexts.