Stereoisomerism & Chirality Flashcards
(20 cards)
What is a stereoisomer?
Molecules with the same molecular formula and connectivity but differ in the spatial arrangement of atoms.
What is chirality?
A property of a molecule being non-superimposable on its mirror image.
What defines an asymmetric (chiral) carbon?
A tetrahedral (sp³) carbon atom bonded to four different substituents.
What are enantiomers?
Non-superimposable mirror image molecules that have identical physical and chemical properties except for optical rotation and behavior in chiral environments.
What is a racemate?
A 1:1 mixture of enantiomers that is optically inactive.
What is optical activity?
The ability of a chiral compound to rotate plane-polarised light.
What device measures optical rotation?
A polarimeter.
How is specific rotation calculated?
, where α = observed rotation angle, l = path length (dm), c = concentration (g/mL).
Why is chirality important in biological systems?
Because many biological interactions are stereospecific—only one enantiomer may be active or safe.
Give an example where chirality affects biological activity.
Thalidomide: R-enantiomer is safe; S-enantiomer is teratogenic.
What are the CIP priority rules?
Assign priorities to groups on chiral carbon based on atomic number; higher atomic number = higher priority.
How do you assign R or S configuration?
View from the chiral center toward the lowest priority group; if 1→2→3 is clockwise = R, anticlockwise = S.
How are ties resolved in CIP rules?
Compare atoms further along the chain until a difference is found.
What are phantom atoms in CIP?
Imaginary atoms used to treat double or triple bonds as multiple single bonds for priority assignment.
What are diastereoisomers?
Stereoisomers with more than one chiral center that differ at some but not all chiral centers; not mirror images.
How many stereoisomers are possible for a molecule with n chiral centers?
2^n stereoisomers.
What is a meso compound?
A molecule with two or more chiral centers that is achiral due to an internal plane of symmetry.
Are meso compounds optically active?
No, they are optically inactive despite having chiral centers.
How can you identify meso compounds?
Look for internal symmetry and superimposable mirror images.
What is the significance of the lock & key analogy in chirality?
It explains how only one enantiomer fits and reacts properly in biological systems.
