Carbohydrate Sterochemistry (5/13) Flashcards
Stereoisomer
Isomers that differ in the spatial arrangement of their atoms around a stereocenter
Stereocenter/chiral center
a carbon with 4 different substituents attached
A molecule with a single chiral center
asymmetrical and non-superimposable mirror image
EX) hands
Enantiomers
Specific non-superimposable mirror images
Achiral molecules
Are superimposable with their mirror image
They either lack a chiral center or are meso compounds
Meso compounds
Contain multiple chiral centers that create a plane of symmetry within the molecule
Diaseteromers
Differ at one chiral carbon
d/l or +/- system
d/+= rotates light to the right l/-= rotates light to the left
R/S system
One or two stereocenters and is based off of the Cahn-Ingold-Prelog Priority Rules
Rules of R/S system
1) identify stereocenters
2) assign priority to side groups (higher atomic number, then mass, then # of bonds)
3) lowest priority group should point away
4) assign R/S
D/L system
Based on fisher projection of glyceraldehyde
D= when OH on stereocenter points right
L= when OH on stereocarbon points left
What to do when more than one stereocenter in a molecule and using the D/L system
Go off of the furthest from the carbonyl we use
Enantiomers
Stereoisomers that are not superimposable mirror images of each other
Example of enantiomers
L-glucose and D-glucose
Examples of Diastereomers
D-glucose and D-talose because they do not differ at all chiral centers
Epimers
Special typer of diastereomers that only differ at one chiral center
Anomers
carbonyl carbon when open chain is anomeric carbon. When cyclized, the hydroxyl group on the anomeric carbon may either point up or down. down= alpha, up=beta
Difference between configurations and conformations
Different conformations can be achieved without breaking any bonds
