Organic Chem Lab Exam 2-- Electrophilic Aromatic
Substitution (EAS) Questions With Complete Solutions
8 steps of running a column Correct Answers 1) add small amt
cotton to pasteur pipette
2) add small layer of sand above cotton (1-2 mm)
3) add 4-6 mm silica gel to pasteur pipette
4) wet with hexanes just before you run column
5) add small layer of sand above silica gel (1-2 mm)
6) add sample when eluent is at level of sand
7) after sample loading, add 100% hexanes to column until first
band has eluted off column
8) use 10% ethyl acetate in hexanes to elute second band
a silica gel column behaves exactly like... Correct Answers a
TLC plate run upside down
after observing an adequate amt of rxn between the 2 starting
materials, what did we do? Correct Answers remove via plastic
pipet the aqueous layer and apply 2 spots of organic layer to the
TLC plate at the co-spot and rxn positions
azulene is not as aromatic as...
what is the result of this? Correct Answers the corresponding
benzenoid system napthalene
azulene is much more reactive toward electrophiles in an EAS
type reaction
,azulene reacts directly with trifluoroacetic anhydride. what does
this indicate? Correct Answers indication of azulene's much
greater nucleophilicity than other benzenoid systems
azulenes are a class of... Correct Answers aromatic
hydrocarbons
azulenes do not react directly with acetic anhydride, but they do
react directly with trifluoroacetic anhydride. what does this
indicate? Correct Answers indicates the importance of
electron-withdrawing trifluoromethyl substituents in increasing
the electrophilicity of carbonyl carbons on trifluoroacetic
anhydride
briefly describe how we conducted NMR analysis Correct
Answers combine blue/purple samples in small beaker and
evaporate solvent under flowing lab air; samples must be dry
before reconstituting with deuterate solvent; once dry
reconstitute with chloroform-d; when all solid has been
dissolved in solvent transfer solution to clean/dry NMR sample
tube using pipette; entire volume with sample + chloroform-d
should be 3 fingers width level
CC separates compounds in the same manner as... Correct
Answers TLC; a TLC run upside down
completing the rxn portion of the experiment between TFAA
and TMA what did we do? Correct Answers prepare a
disposable pipette column by packing a small plug of cotton into
a short pipette and adding 3 mm sand on top of it; on top of sand
layer add 7 cm mesh silica gel
, elute the compounds in the sample by using... Correct Answers
a series of increasingly polar elution solvents
elution solvents are used to... Correct Answers dislodge
compounds adsorbed on a column
flash chromatography Correct Answers uses pressure to help
drive eluent down column or involves chromatography of small
samples on small columns
general overview of EAS experiment Correct Answers to
attempt an EAS reaction using 4,6,8-trimethylazulene with
trifluoroacetic anhydride followed by a water workup and
purification using column chromatography; then conduct NMR
analysis on starting material and product to determine identity of
each
how are mono-alkylated species (mono-alkylated benzene rings)
most easily generated? Correct Answers using an acylation
pathway followed by a Clemmensen reduction (Zn(Hg), aqueous
HCl)
how can you determine the purity of each fraction of sample you
eluted? Correct Answers TLC or GC
how can you speed up the rate that the eluent moves through the
silica gel?
what is this called? what type of results does it give? Correct
Answers apply pressure to the column
flash chromatography; better results than a gravity column
Substitution (EAS) Questions With Complete Solutions
8 steps of running a column Correct Answers 1) add small amt
cotton to pasteur pipette
2) add small layer of sand above cotton (1-2 mm)
3) add 4-6 mm silica gel to pasteur pipette
4) wet with hexanes just before you run column
5) add small layer of sand above silica gel (1-2 mm)
6) add sample when eluent is at level of sand
7) after sample loading, add 100% hexanes to column until first
band has eluted off column
8) use 10% ethyl acetate in hexanes to elute second band
a silica gel column behaves exactly like... Correct Answers a
TLC plate run upside down
after observing an adequate amt of rxn between the 2 starting
materials, what did we do? Correct Answers remove via plastic
pipet the aqueous layer and apply 2 spots of organic layer to the
TLC plate at the co-spot and rxn positions
azulene is not as aromatic as...
what is the result of this? Correct Answers the corresponding
benzenoid system napthalene
azulene is much more reactive toward electrophiles in an EAS
type reaction
,azulene reacts directly with trifluoroacetic anhydride. what does
this indicate? Correct Answers indication of azulene's much
greater nucleophilicity than other benzenoid systems
azulenes are a class of... Correct Answers aromatic
hydrocarbons
azulenes do not react directly with acetic anhydride, but they do
react directly with trifluoroacetic anhydride. what does this
indicate? Correct Answers indicates the importance of
electron-withdrawing trifluoromethyl substituents in increasing
the electrophilicity of carbonyl carbons on trifluoroacetic
anhydride
briefly describe how we conducted NMR analysis Correct
Answers combine blue/purple samples in small beaker and
evaporate solvent under flowing lab air; samples must be dry
before reconstituting with deuterate solvent; once dry
reconstitute with chloroform-d; when all solid has been
dissolved in solvent transfer solution to clean/dry NMR sample
tube using pipette; entire volume with sample + chloroform-d
should be 3 fingers width level
CC separates compounds in the same manner as... Correct
Answers TLC; a TLC run upside down
completing the rxn portion of the experiment between TFAA
and TMA what did we do? Correct Answers prepare a
disposable pipette column by packing a small plug of cotton into
a short pipette and adding 3 mm sand on top of it; on top of sand
layer add 7 cm mesh silica gel
, elute the compounds in the sample by using... Correct Answers
a series of increasingly polar elution solvents
elution solvents are used to... Correct Answers dislodge
compounds adsorbed on a column
flash chromatography Correct Answers uses pressure to help
drive eluent down column or involves chromatography of small
samples on small columns
general overview of EAS experiment Correct Answers to
attempt an EAS reaction using 4,6,8-trimethylazulene with
trifluoroacetic anhydride followed by a water workup and
purification using column chromatography; then conduct NMR
analysis on starting material and product to determine identity of
each
how are mono-alkylated species (mono-alkylated benzene rings)
most easily generated? Correct Answers using an acylation
pathway followed by a Clemmensen reduction (Zn(Hg), aqueous
HCl)
how can you determine the purity of each fraction of sample you
eluted? Correct Answers TLC or GC
how can you speed up the rate that the eluent moves through the
silica gel?
what is this called? what type of results does it give? Correct
Answers apply pressure to the column
flash chromatography; better results than a gravity column
