stereochemistry

STEREOCHEMISTRY

the branch of chemistry concerned with the three-dimensional arrangement of atoms and molecules and the effect of this on chemical reactions

ISOMERS

same molecular formula but different structural or spatial arrangements.

Constitutional Isomers

different connectivity of atoms.

Functional Isomers

different functional groups.

Positional Isomers

different positions of functional group.

Skeletal Isomers

different carbon skeleton.

Stereoisomers

same connectivity but different spatial orientation of atoms.

Configurational Isomers

different

not the result of rotation about single bonds

different compounds.

Geometric Isomers

result from restricted rotation around a double bond or on polysubstituted cyclic alkanes.

Cis-Trans Isomers

a type of geometric isomerism.

E/Z Isomers

a type of geometric isomerism based on priority rules.

Optical Isomers

around a chiral carbon.

Enantiomers

nonsuperimposable mirror images.

Diastereomers

nonmirror images.

Conformational Isomers

different

the result of rotation about single bonds

the same compound.

Aliphatic Alkanes

staggered and eclipsed conformations.

Alicyclic Alkanes

chair and boat conformations.

Chiral Molecule

has a nonsuperimposable mirror image.

Achiral Molecule

has a superimposable mirror image.

Stereocenters/Asymmetric Centers

An atom connects to 4 different groups

stereocenters cause chirality.

Drawing Enantiomers

Perspective Formula: two bonds in the plane of the paper

Fischer Projection

horizontal lines directed toward the viewer

Enantiomers: Absolute Configuration (R/S System)

a.k.a. the Cahn-Ingold-Prelog system

rank the groups bonded to the asymmetric center in order of priority.

Priority Ranking

The higher the atomic number

Tie-breaking in Priority

If there is a tie

Multiple Bonds Treatment

If there are multiple bonds in the substituents

Molecule Orientation

Orient the molecule in space so that the group of lowest priority is directed away from you.

Reading Groups

Read the three groups projecting toward you in order

Clockwise Configuration

If clockwise

Counterclockwise Configuration

If counterclockwise

Enantiomers

Molecules that are non-superimposable mirror images of each other.

Optical Activity

Chiral molecules rotate plane-polarized light and achiral molecules do not.

Dextrorotatory

If a chiral molecule rotates the plane of polarization clockwise/to the right

Levorotatory

If a chiral molecule rotates the plane of polarization counterclockwise/to the left

Enantiomers Properties

Enantiomers have the same properties except for direction of rotation.

Racemic Mixture

An equimolar mixture of 2 enantiomers that does not rotate plane-polarized light because of the presence of both enantiomers.

Diastereomers

Stereoisomers that are not mirror images of each other.

2n Rule

For a molecule with n stereocenters

Maximum Stereoisomers

The maximum number of stereoisomers possible for a molecule with 2 stereocenters is 2^2 = 4.

Meso Compounds

Achiral compounds (optically inactive) but contain chirality centers.

Identical Groups in Meso Compounds

Four atoms or groups bonded to one asymmetric center are identical to the four atoms or groups bonded to the other asymmetric center.

Tartaric Acid Example

A compound with the same four atoms or groups bonded to two different asymmetric centers will have three stereoisomers: one will be a meso compound