CH 220C E-Stilbene and Stereochemistry

Bromine MSDS

NFH NC NM

Dichloromethane MSDS

Slight FH KC PM

d,l-stilbene dibromide MSDS

toxic fumes NC NM

E-stilbene MSDS

Slight FH NC PM

meso-stilbene dibromide MSDS

toxic fumes NC NM

Cyclohexene MSDS

severe FH NC NM

Dimethyl fumarate MSDS

slight FH NC NM

Dimethyl maleate MSDS

Moderate FH NC NM

Ethanol MSDS

severe FH NC PM

Dimethyl fumarate melting point

104-107

meso-stilbene dibromide melting point

241

d,l-stilbene dibromide melting point

113-115

How is the meso product formed?

Cyclic bromonium cation intermediate

How are the d,l products formed?

Acyclic carbocation intermediate

Enantiomers

mirror image isomers that are non superimposable, usually have similar characteristics

Diastereomers

Non mirror image isomers that are non superimposable, usually have different characteristics

Geometric isomers

Isomers with same connectivity but different spatial arrangement due to a double bond or ring

Energy required to break carbon-carbon double bond:

146 kcal or 610 kJ per mol

Energy required to break carbon-carbon single bond:

83 kcal or 347 kJ per mol

Energy required to break bromine-bromine single bond:

46 kcal/mol or 600 nm

Why does the bromine radical attack the pi bond?

The pi bond is electron dense

Rules for mechanism creation

1. Arrow convention

2. No more than ±1 carbon charges

3. No chemical X

4. No google

Limiting reagent in E-stilbene reaction

e-stilbene

d- and l-stilbene bromide are ___?

enantiomers

meso-stilbene bromide is a ___ to the d,l products?

diastereomer

Which cations do NOT rearrange?

Cyclic

Bromination of an alkene is an ___ reaction

oxidation

Eutectic point

equilibrium point at which substance A and B melt in constant ratio.

Eutectic ratio

impure solid at its eutectic point

What kind of reaction is the bromination of an alkene?

Addition

Real product ratio of meso:d:l-stilbene bromide

90:5:5

Energy and wavelength required to break ONE of the two bonds in DMM

70-80 kcal/mol and 300-400 nm

Conformational isomers

stereoisomers interconverted by rotation about single bonds, isolation is rarely possible

Configurational isomers

stereoisomers interconverted by breaking and reforming bonds, high energy process

racemate

50/50 mixture of enantiomers

Resolution of enantiomers

Generally more difficult due to identity of chemical properties, differing effects on plane polarized light not helpful for separation

Dimethyl maleate freezing point

-19

Three ways to promote bond cleavage

thermally, photochemically, chemically

Functional group of alkene

Polarizable carbon-carbon double bond

Functional groups in elimination:

Alkyl halide and alcohol

Principles of alkene addition

1. Pi bonds are weaker than sigma bonds

2. Pi electrons of double bond are more polarizable than sigma electrons

Markovnikov’s rule

Electrophilic addition favors the formation of the more stable carbocation

Why must the e-stilbene reaction be done in an inert solvent?

A polar protic solvent will interfere with the process

Why should the mel-temp apparatus only increase at 1-2 C per minute?

To ensure that the rate of heat transfer to the sample is the reflected in the thermometer, and that the mercury in the thermometer is in thermal equilibrium with the sample

Why can’t you pack the capillary tube on filter paper?

Fibers of the paper may be forced into the tube

What are the most commonly measured physical properties of organic compounds?

Melting point, boiling point, index of refraction, density, specific rotation, solubility

Addition of heat to a mixture of liquid and solid phases of a pure substance at the melting point will cause ___?

No rise in temperature until all of the solid phase has melted

The melting and freezing points of a pure substance are ___

identical

Decomposition products of a sample in the mel-temp constitute:

impurities in the sample, true melting point is lowered