Definitions Flashcards
What is the difference between stereogenicity and chirality?
Chirality is a property of an entire molecule, whereas stereogenicity is a local property, i.e. exchange of two groups generates steroisomers. Have chiral compounds and stereogenic elements.
What are meso compounds?
Achiral stereoisomer in a set of chiral stereoisomers. Superimposable on its mirror image
What are epimers?
One of a pair of diastereoisomers, where the configuration of only 1 of 2 or more stereocentres has been inverted.
What is the exact definition of chirality, i.e. what is the necessary and sufficient condition?
A compound is chiral if it exists in two non-superimposable mirror images. NB. chiral compounds will not contain any improper axes of rotation.
How do we assign priority to groups in order to assign absolute stereochemistry?
Using Cahn-Ingold Prelog rules
How does the assignment change for stereogenic axes or planes compared to atomical centres?
Two rules: Cahn-Ingold Prelog + proximity rule. Closer atoms take priority over further away, even if further away higher priority by CIP.
For a stereogenic axis, look down the axis and make a Newmann projection to do assignment.
For a stereogenic plane, pick a pilot atom that is close to the highest priority substituents but not in the plane and undergo assignment from here.
What is an enantioenriched compound?
A compound that is made up of more of one enantiomer than the other
What is a scalemic mixture?
A mixture of 2 enantiomers in any ratio other than 50:50
What is enantiomeric excess?
(R - S) / (R+S) * 100
