bromination of e-stilbene

when bromine is added to an alkene, what is the result

addition reaction with one or more brominated products

the number of brominated products depends on what

structure of starting alkene

3 isomers formed

meso, D,L

meso stilbene and D/L

diastereomers

D/L

enantiomers

distribution of isomers in reaction depends on what

cation intermediate

two possible cations

cyclic bromonium

acyclic carbocation

acyclic carbocation

50% meso

50% D/L

cyclic bromonium cation forms_

meso product

why do we not get expected extremes of products

both cations are formed and exist in equilibrium w one another

E- stilbene

E-1,2-diphenylethene

meso-stilbene dibromide

(1R,2S)-1,2-dibromo-1,2-diphenylethane

D stilbene dibromide

(1S,2S)-1,2-dibromo-1,2-diphenylethane

L-stilbene dibromide

(1R,2R)-1,2-dibromo-1,20diphenylethane

what are we doing with e-stilbene

brominating e-stilbene

isolating meso product

capping reaction

with glass stopper using keck clip

make sure it isn’t sealed

what is in the flask

silbene, DCM, stir bar, (bromine 1M added later)

how long does reaction stir

10-15 mins

until orange color has disappeared and white solid has formed

what do we do after reaction precipitate is formed

buchner funnel washed with cold DCM

bromine spill

sodium thiosulfate then pick up

bromine safety points

mucous, irritation, burns, vision loss, discoloration of mouth

DCM safety

slight fire hazard, irritation, burns, GI ulceration

D,L- stilbene dibromide safety

toxic fumes under flames

eye irritant

E-stilbene safety

slight fire hazard

skin and eye irritation

harmful if swallowed

meso-stilbene dibromide safety

toxic fumes under fire

may be harmful if inhaled or swallowed

eye and skin irritation

carcinogens and mutagens

C: DCM

M: DCM, e-stilbene

alkene halogenation results in

vicinal dihalide

what makes the halogen ion

pi bond attacks halogen

why is additiona nti

halogen must attack opposite of bridge so it can reach carbon

functional group

atom(s) that govern chemical and physical properties of family of compounds

what is the most common way to make CC pi bond

elimination reaction

why does addition occur across the pi bond

1. exothermic process (strength of CC pi bond is lower than sigma bonds that will be formed)

2. pi electrons are more loosely held (more polarizable)

qualitative analysis of alkyl halids

alcoholic silver nitrate solution

sodium iodide in acetone

stereospecificity of rxn

anti addition

diastereomers and properties

diff physical and chemical properties

for cyclic cation, what happens when you attack either carbon

forms meso

why can acyclic attack from above or below

no restriction

how much meso is expected?

90% but can change based on temperature and solvent

what do we do with meso product

isolate solid

rinse

get MP and percent yield

what is good percent yield for this reaction

70% but most students get 50-60

E-stilbene

meso-stilbene dibromide

d-stilbene dibromide

L-stilbene dibromide

meso numbering chiral centers

1R,2S

D

1S,2S

L

1R,2R

diastereomers

stereoisomers that aren’t nonsuperimposable mirror images

enantiomers

stereoisomers that are non-superimposable mirror images

meso compound

multiple stereocenters but optically inactive

has internal plane of symmetry

what are we doing w product at end of the lab

save product for dehydrobromination