ChE 402 - Organic Chemistry (Stereoisomerism)

Organic Chemistry for Chemical Engineers

Stereoisomers

Stereoisomers

Have the same connectivity and are not identical.

Chirality center

When an atom (like carbon) forms a tetrahedral center with 4 different groups attached to it.

Enantiomers

Two molecules that are mirror images but are not superimposable.

Cahn-Ingold-Prelog system

Used to designate each chirality center as having either the “R” or “S” configuration.

R

Clockwise

S

Counterclockwise

Enantiomers

Stereoisomers that are mirror images.

Diastereomers

Stereoisomers that are not mirror images.

Chiral compound

Any compound with only one chirality center.

Meso compounds

Molecules with an even number of chirality centers that have a plane of symmetry.

Achiral

A compound that has a plane of symmetry.

Fischer projection

Can also be used to represent molecules with chirality centers through lines. Most useful when drawing molecules having multiple chirality centers.

Horizontal lines

In a Fischer projection, it is used to represent attachments coming out of the page.

Vertical lines

In a Fischer projection, it is used to represent attachments going back into the page.

Atropisomers

Stereoisomers would be interchangeable through the rotation of a sigma bond, but because the bond is unable to rotate.

Allenes

Compounds that possess two adjacent C=C double bonds.

Distillation

Separates compounds with different boiling points.

Recrystallization

Separates compounds with different solubilities.

Enthalpy

Used to measure the exchange of energy.

Bond cleavage

For a bond breaking reaction, ΔH is primarily determined by the amount of energy necessary to break the bond homolytically.

Homolytic bond cleavage

Generates two uncharged species, called radicals, each of which bears an unpaired electron.

Heterolytic bond cleavage

Illustrated with a two- headed curved arrow, generating charged species, called ions.

Bond dissociation energy

The energy required to break a covalent bond via hemolytic bond cleavage.

Exothermic

The system gives energy to the surroundings (ΔH° is negative).

Endothermic

The system receives energy from the surroundings (ΔH° is positive).

Entropy

Defined as the measure of disorder associated with a system.

Equilibrium

The state with the lowest free energy overall.

Order

The degree to which a change of reactant will affect the rate is knows as?

Nucleophile

It is when an atom carries a formal or partial negative charge and an available pair of electron.

Electrophile

It is when an atom carries a formal or partial positive charge, and can accept a pair of elections.

Arrow

It is used to show how electrons moves when bond break and form.

Hydrohalogenation

Addition of H-X to an alkene.

Hydrogenation

The addition of H2 across a C=C double bond.

Stereospecific

Only syn addition is observed with hydrogenation.

Halogenation

Addition of two halogen atoms across a C=C double bond.

Radioselectivity

Halogenation occurs with anti addition.

Halohydrins

Formed when halogenation is conducted in water.

Dihydroxylation

Addition of OH and OH across the pi bond.