Stereochemistry
Chiral
-non symmetrical molecules
-if it contains a plane of symmetry, it’s not chiral
-a carbon is considered chiral if it has 4 different groups
attached to it
-a chiral carbon does not mean the overall molecule is chiral
Meso Compounds
What if you have more than 1 chiral center?
The whole molecule can be chiral
The whole molecule can be achiral, then it is called a meso
compound
Isomers
Isomers are compounds that have the same chemical formula
but different structures
-two different types: constitutional isomers & stereoisomers
Constitutional Isomers
Compounds with the same number of carbons that are
connected differently
I.e.) methyl propane vs. butane
Stereoisomers
Compounds are connected in the same order but with different
geometry
Can be either enantiomers or diasteromers
Enantiomers
Non super impossible mirror image stereoisomers
Have the same physical properties but differ in the direction in
which their solutions rotate in polarized light
Enantiomers
Do you need to be chiral to have an enantiomer?
Diasteromers
-only occurs when you have molecules with more than one chiral
center
-non-superimposible non-mirror images of each other
Enantiomer vs. Diasteromers
-diasteromers have opposite configurations at some chiral
centers while enantiomers have opposite configurations at all
chiral centers
R vs. S
-a way to differentiate between enantiomers
-assign priority for each for the 4 atoms attached to the chiral
carbon
1) Atom with the highest atomic number is 1st, atom with the
lowest is 4th
2) If substituents are the same, continue branching out until a
difference is found
3) Single bonds and double/triple bonds have the same
priority
R vs. S
-Rotate the molecule so the lowest priority is facing away from
us
-keep one the same and “spin” the other 3
-If 12  3 is clockwise direction, it is R rotation, also -If 12  3 is counterclockwise direction, it is S rotation, also +
Let’s practice!
Racemic mixtures
A 50/50 mixture of R/S enantiomers