Chapter 4: Chirality, R&S, and Enantiomers/Diastereomers/Meso

stereomers

same connectivity different arrangement in space

enantiomers

nonsuperimposable mirror images

chiral centers

sp3 carbon attached to 4 different groups

has a pair of enantiomers

R

clockwise

S

counterclockwise

R,S Rules

higher atomic # = higher priority

most important is 1 —> 2

discount 4 (H/lowest group) is dashed/away

R,S : if lowest group is not away/dashed

rank, assign R,S, reassign the opposite

or

rotate around one group so the lowest ranked group is away/dashed

More than 1 Stereoisomer

max # = 2ⁿ

n = # stereocenters

ex.

1 center = 2¹ = 2 stereoisomers

2 centers = 2² = 4 stereoisomers

diastereomers

stereomers that are not enantiomers

½ enantiomers ½ same

meso

when 2 stereomers are the same/the same compound

there is a plane of symmetry

fisher projections

1) assign priority

2) if H is vertical, assign R,S,

—> if H is horizontal, assign R,S & take the opposite