Stereochemistry

chiral center

tetrahedral atom with four different substituents

lacks a plane of symmetry

achiral molecule

rotated molecule can be superimposed on its mirror image

has a plane of symmetry

chiral molecule

a molecule that has a chiral center and lacks a plane of symmetry

rotates polarized light

geometric isomers

Compounds that have the same molecular formula but differ in the spatial arrangements of their atoms.

Enantiomers

isomers that are mirror images of each other but are not superimposable

Diastereomers

stereoisomers that are not mirror images of each other

must have at least 2 stereo centers

Priority ranking in determining chirality

Based on atomic number

Ex: F > nitro > carboxyl > propyl

R and S

Draw (R) 2-butanol, CH3CHOHCH2CH3

meso

an achiral compound that contains chiral centers

RS and SR

have a plane of symmetry between the chiral centers

optical activity

rotation of the plane of polarized light

optical activity of enantiomers

enantiomers have equal and opposite specific rotations

racemic mixture

A mixture that contains equal amounts of the (+) and (-) enantiomers.

Racemic mixtures are not optically active.

optical activity of diastereomers

diastereomers have different specific rotations

optical activity of meso compounds

meso are not optically active

enzymes bind to [ either, both, or just one] chiral molecule

one of the stereoisomers fits the active site of the enzyme

physical properties of enantiomers

identical

physical properties of diastereomers

different

If you are trying to determine R or S, and the H happens to be pointing toward you, then....

You need to either

1. Turn the molecule over and then look at the priorities

OR

2. Assign the priorities and know that your answer is the opposite