LAB FINAL!! IR, TLC, Simple Distillation, Gas Chromatography, Dehydration of cyclohexanol, WHMC, Natural Products and Alkenes, Kinetics, Oxidation, Phase Transfer Catalysis
positive ferric chloride
red, blue, purple, or green color
what does the solvent do
aid in the dissociation of the alkyl halide
how to detect alkene vs aldehydes, ketones (especially acetone), amines, and phenols
aldehydes, ketones, amines, and phenols add bromine by substation (not addition) and produce HBr
just above 3000 (3000 - 3100)
alkenes and aromatics
bromine test dectects
alkenes/alkynes
dehydration is often used to prepare _____ from ____
alkenes; alcohols
effect of diluting a reactant before mixing
allows heat to dissipate
doublet above 3000
amines
what is the greatest limit of tlc
amount of sample size that can be used is very small
what is IR not great at doing
analyzing complex samples
How do the bromines add in this rxn
anti
the lower layer in this lab will be the
aqueous layer
How does the FTIR handle air interference
at the beginning of the day the IR takes a background reading which it subtracts (imagine zeroing out a scale)
fractional distillation can be used on compounds with ______ bps but requires a ______ sample
closer;larger
what do organic reactions usually have
competing pathways; yield more than one product
requirements for steam distillation
compound can't be water soluble must be thermally stable
sublimation
compound goes from solid to gas skipping liquid phase
requirements for using gc or distillation
compound must be volatile compound must be thermally stable
volatile compound
compound that can be converted to gas phase at a reasonable temp without decomposition
polymorphic compound
compound with more than one pure crystalline form; each form has different mp
what does it mean when it says that a gas chromatography sample must be dry
contain no water
flow controller
controls the rate of flow of helium
ferric chloride dangers
corrosive, staining, not toxic though
crystal dissolves in solvent at room temp
crap
crystal doesn't dissolve in hot solvent
crap
in this lab cyclohexanol will be dehydrated into
cyclohexene
positive bromine test
dark orange -----> clear
what will the spot look like if you have plenty of sample
dark purple
because the coatings are made of organic materials they will _____ at high temps. For this each column as a maximum _____ _____
decompose; operating temp
what is a risk of distilling a super high boiling compound
decomposition
solubility of a dissolved gas _____ with temperature
decreases
when cleaning what should be done
dehydrating acid container should not be cleaned with acetone bc they react violently with each other
purpose of gas chromatography in the simple distillation lab
determine the percentage of component in each fraction
best ATR crystal
diamond
a mixture melting point of two different compounds will have a melting point that is _____ than either of the two pure compounds
different
why do spots differ in how far they go
differential adsorption and dissolution in the solvent
rf equation
distance spot moved/distance solvent traveled
theoretical plate
each condensation and vaporization step
what if not all of the compound melts
salt (inorganic/organic) or impurity
weaknesses of Baeyers test
gives false positive with easily oxidizable functional groups like aldehydes, ketones, and 1'/2' alcohols
joint freezing
glass expanding locking glass pieces together
advantage of tlc
great separation and excellent sensitivity
neutral bromothyol
green
more theoretical plates = more _____
separation
tlc is a _______ technique
separation
distillation
separation based on difference in boiling points of constituents in a mixture of miscible materials
breathing in bromine/getting it on skin
serious chemical burns
what should and shouldn't a good solvent do
should dissolve the reactant; shouldn't undergo competing rxn
why should acid be added slowly
heat is evolved
source of most natural products
plants
advantage of dual beam IR
prevents detection of functional groups in the air
Recyrstallization
process of dissolving solid material into a solvent and allowing it to recrystallize
why will the chromium reagents not be used in this lab? What will be used?
produce toxic non volatile salts; bleach
bleach + acid
produces hypochlorous acid (the actual oxidizing agent)
what effect does thicker plates have on chromatography
provide excellent separation, but don't have as good sensitivity
what do spectroscopic techniques such as FTR and NMR do
provide many data points for comparison with known materials
reverse phase tlc
silica gel has been derivatized and aliphatic hydrocarbons have been chemically bonded to SiOH groups present on the surface of the adsorbent.
adsorbent usually used in tlc
silica or alumina
which type of distillation will be be using in this lab
simple
what two things does flow rate depend on
size of column conditions necessary for separation
why should the solution be added slowly during filtration
so you do not float the filter paper and allow impurities to get into the purified sample
what reagent will be used to test solubility
sodium bicarbonate
how will excess oxidant be destroyed
sodium bisulfate
bleach
sodium hypochlorite
why should the sample not contain water
- water tends to contain dissolved solids in it such as sals that will clog the injector -water will degrade the column; columns are expensive -water signals are broad on the GC and make it hard to interpret ate
simple distillation provides good separation for liquids with boiling points that are at least ______ degrees apart
25
temperature difference between distillate and condenser require to cause condensation
25 degrees
sn1 is how many steps? which one is slow?
2; first one
which dehydrates faster, a 3' or 1' alcohol
3'
wich carbocation is most stable
3'
sharp doublet at 2500
CO2 (not part of sample)
What might air generate in an FTIR spectrum
CO2 in air may cause doublet peak between 2000 and 2500
solvolysis
SN1 reaction in which the solvent is the nucleophile
retention time
The time for a component to pass through a chromatographic column up to the detector.
after identifying the first major peak, what should you look for?
a confirming peak
what happens during the Baeyer test
a cyclic manganate ester is formed and then hydrolyzed into cis-1,2-cyclohexanediol
How is IR done on solid samples
a device that creates force/pressure is applied to the sample to ensure close contact
what will happen if the temp difference between the condenser and the distillate is less than 25 degrees
a lot of the vapor will escape
what type of solution are most rxns carried out in?
homogenous
what would happen if the column were allowed to rest on the sides of the oven
hot spots might develop messing up separation
safety precautions mp capillaries
hot/break easily
factors that affect how strongly the coating interacts with vapor
how much coating was used character of support
what is a fourth factor to keep in mind when choosing the type of chromatography; when must you keep this in mind
how much sample an be used (capacity); when using chromatography to separate
what cause the carboxylic acid group to range so far
hydrogen bonding
which drug is a racemic mixture
ibuprofen (only S isomer has analgesic activity)
presumptive identification
idea that you can rule out all ridiculous things, but never 100% confirm close thing
parts of a buchner funnel vacuum filtration
flat filter paper buchner funnel filter adapter/filter vac (seals buchner to erlenmeyer/suppport) clamp hose to connect flask to aspirator filter flask
what field uses ATR/FTIR frequently
forensic science
what does the co2 produced by carbonic acid do
forms bubbles in the solution
how are functional groups detected
functional groups absorb IR energy at very specific wavelengths
in gc what is the fluid
gas
how to detect HBr
gently blowing across the top of the test tube. The moisture in your breath will condense with it and produce a fog if HBr is present
why are things like melting point, boiling point, smell, and density not always useful
give no structural information
why are plastic pipettes used instead of glass pipettes
glass pipettes may scratch the ATR crystal
crystal doesn't dissolve at room temp, but will dissolve when solvent heated
good; move onto cooling the solution to create recrystallization
how to increase sped of rxn if it is slow
heat it
how is distillation carried out
heating a liquid to boiling and then collecting the condensed vapors
gas usually used in gc
helium; although sometimes n2 or other gases used
when should the tube be removed
hen the signal for the peak returns near baseline (or near the start of the signal for another component),
compounds held together by ionic bonds tend to have ____ melting points
high
do samples with close booing points have high or low reflux ratios
high
what makes steam distillation special
high boiling materials that are present in tars, oils, plant matter, or other hard-to-manage materials are distilled at temperatures well below their true boiling points in the presence of steam (water vapor).
why does vapor pressure increase with temp
higher temp = more mlcs going into gas phase = higher vapor pressure
when will a mixture of alkenes result
if the carbocation can lose chemically different alpha hydrogens
what does fractional distillation do
improves separation (fractioning)
melting point range broader than two degrees
impure
resolution ____ with theoretical plates
increases
vapor pressure ____ with ______ temp
increases; increases
way to increase number of theoretical plates
increasing length of column
column packing is usually ____ and ____
inert; organic
what else may analgesics contain
ingredients not directly related to pain relief such as caffeine
which fractions have the highest purity
initial and final
more coating = more _______
interaction
what can amino acids do to ibuprofen? What is this process called
interconvert S and R configurations; glucuronidation
where does the ir beam go once it has traveled the length of the crystal
into the detector
why do impurities lower melting point
introduce entropy into the lattice, lowering the amount of nrn needed to break it
phase transfer catalysis is often used when one of the reactants is an _____ ______
ionic nucleophile
which test is superior?
potassium permanganate; reacts with aliens that are not reactive enough to decolorize br
how should you not pack a capillary tube? Why?
pounding it on the bench between your fingers, the tube could shatter and cut, if not go through, your fingers.
preparative chromatography differs from tlc in what way
preparative chromate uses thicker plates
what is one of the uses of gc
separate a mixture of components
what happens if the solution is not slowly cooled
small impure crystals form
how steam distillation lowers boiling point
their combined vapour pressures are bound to reach the external pressure before the vapour pressure of either of the individual components get there.
type of detector used in this gc lab
thermal conductivity detector
when do organic chemists usually choose to use recrystallization
thermally unstable compounds (decompose when you try to take melting point) high melting solids
why are injector points dangerous
they are hot
Do rxns in ocher go perfectly? What usually happens?
they don't go to completion or form a mixture of products
which functional groups are easiest to detect
those that contain oxygen
what type of materials is steam distillation useful for
those that may decompose at high temps
disadvantage of using more theoretical plates
time and money
most common form of chromatography
tlc and gc
Purpose of using tlc analgesic lab
to identify the major active ingredients in an unknown analgesic
why is the buchner funner heated in water
to prevent crystallization on the walls of the buchner funnel
why should you grease
to prevent joint freezing
what is the solvent used in this lab
water
what should not be used as a solvent in this lab
water
what solvents are usually used in reverse phase tlc
water and alcohol
what does carbonic acid rapidly decompose into
water and co2
best known azeotrope
water and ethanol
spill acid on skin
water followed by sodium bicarbonate
what products are usually distilled by steam distillation
water insoluble oils; h/e can be done on some solid organic materials
cyclohexene will be washed with ____ followed by _____
water, NaCl
spill potassium permanganate on skin
water,soap
____ is eliminated to form a _______ ______ ______bond
water; carbon-carbon pi
what is not required for the condensation of liquids with boiling points above 150? why
water; the difference between the boiling point of the liquid and the condenser is so great that it doesn't require water to condense
intensity of peaks in the 3000-3100
weak to medium
what should be done to the filter paper
wet it with hot solvent so it sticks to the funnel
when should dehydration not be used
when alcohol contains other functional groups
when is fractional distillate preferred
when bp difference between the liquids is less than 20 degrees
when should you record the temperature
when the first drop lands in the receiving flask
when do the best crystals form
when the solution is cooled slowly
isocratic
when the temp during gc remains constant
ramped up
when the temp is fluctuated during gc
more surface area = ____________ theoretical plates
more
what does elute mean
move up
regional most useful for comparing isomers with same functional group
1400-400
what boiling point can simple distillation can safely done up to
150 degrees
most commonly used ATR crystal
ZnSe
we want the compound to crystallize _____ impurities have been removed
after
large peak at 3200
alcohol or phenol
primary alcohol
aldehyde
2200 peak
alkyne or nitrile (both types of triple bonds)
why is the yield of cyclohexene usually high with cylohexanol
all the alpha hydrogens are chemically the same, meaning deprotonation results in only one type of alkene
what happens if the sample is a solid
dissolved in a solvent other than water
what does water do to normal tlc
dissolves adsorbent and hydrated calcium carbonate
____ most useful technique for separating and identifying compounds
chromatography
stereochemistry of Baeyer's test? Why?
cis; cyclic intermediate
signs of sublimation
crystals may form at top of capillary tube (do to gas condensing)
weird way to calculate peak composition
cut out and weigh them
heating mantles should never be
directly connected to an outlet
what does the water produced by carbonic acid do
dissolve the ionic salt formed by sodium bicarbonate
retention time formula
distance from start to center of peak (max height) / rate
how to lessen polymerization and substitution
distill cyclohexene as it is formed
why do tertiary alcohols not undergo oxidation
do not have a hydrogen on the a-c
how do you decide which purification method to use?
easiest procedure fastest procedure which will give best results
resolution
efficiency of separating components in the distillation mixture
what type of reaction is this
elimination
why is the heated block kept 10 degrees above the column
ensures that volatile compound will not condense in the detector
vapor pressure of immiscible liquids
equal to the sum of the vapor pressures of the individual parts
what does the ability of tlc to separate depend on
equilibrium between solvent, non mobile adsorbent, and the sample
what type of container should be used for recrystallization? Why
erlenmeyer flask, crystals can escape from beakers
which two compounds will not decompose at high temps
ester or aromatic
why is ethanol a good solvent for dehydrohalogentation of alkyl halides by potassium hydroxide
ethanol polar enough to dissolve ionic potassium hydroxide, and organic enough to dissolve alkyl halide
liquids with high vapor pressure will _____ quickly
evaporate
how are adsorbents dangerous
fine powder, may get into eyes and hurt and cause corneal abrasions
what reagin of the ir will be examined for this lab
fingerprint
what should you not use to put out a recrystallization fire, why?
fire extinguisher; too powerful/ creates a mess
what is the packing material made out of
firebrick (inert clay that can withstand high temps)
distillation
method for purifying volatile compounds
gas chromatography
method for quantitatively determining the relative proportions of compound in each sample
the two liquids in simple distillation must be
miscible
azeotrope
mixture of two or more liquids with a single sharp boiling point
the smaller the difference in boiling point, the _____ theoretical plates you need for separation
more
the thermal conductivity sector is the ______ common and the _____ sensitive
most; least
disadvantage of fractional distillation
much slower
most recent otc analgesic
naproxen
will pure compounds have a broad or narrow range
narrow (1-2 degrees)
can azeotropes be separated by distillation
no
will the solvent used to dissolve the sample have an affect on retention time
no
why is a thermocouple not used in stem distillation
no fractions are taken and the distilling temperature will vary little from the boiling point of water
the carbocation can react with nucelophiles to form substitution products, why did this not happen in this lab
no good nucleophile present in the dehydrating acid
tertiary alcohol
no rxn
will water damage the ATR
no, but it will show up in the spectrum so dry the sample
should you blow on the acetone to make it dry faster
no, metabolites in your breath will show up on the IR
is dehydration by a strong proton acid gentle
no, subjects alcohol to harsh conditions
in normal phase chromatograpy _____ compounds will move the farthest
nonpolar
which type of tlc was used in the analgesic experiment
normal phase
why can cotton not be used as a plug
not stable at high temps
what happens to the intermediate carbocation
not stable in the aqueous environment and is rapidly hydrated (water adds to the carbocation) to yield a protonated alcohol
advantages of FTIR
samples that were once too small can now be run
FTIR stands for
Fourier transform infrared
boil up rate
volume of liquid that enters the column as vapor per minute
when to use gc instead of distillation
- very little sample (main) -samples have identical bps but different functional groups -can be used on compounds not thermally stable enough to survive distillation
below 925
-aromatic hydrocarbon (one or more strong peaks) -aliphatic roll (caused by hydrocarbon chain rotating) -broad triangular absorption indicates carboxylic acid -halogenated hydrocarbon (can be caused by not removing all of dichloromethane)
three factors to keep in mind when choosing which type of chromatography to use
-best separation (resolution) -highest sensitivity -speed of separation
map signs that the compounds are different
-broad mp range -mp way different than pure mp
what are the four factors of the chromatography tetrahedron
-capacity -resolution/separation -purity/sensitivity -speed
two requirements for gc
-compound must be volatile -compound must be thermally stable
features of most organic reactions
-each reactant dissolved in a solvent -one solution is added slowly to another -extothermic
components of a good qualitative test
-fast -easy -gives easily detectable change (i.e. color or gas evolution) -specific for a particular functional group
three advantages of Spectroscopy
-fast -nondestructive -only small amount of material required
what are adsorbents mixed with, why?
-inorganic material such as gypsum or hydrated calcium carbonate (allows it to stick to plate) -inorganic fluorescent material
why should you not use too much grease
-it will get into sample -less grease = surface tension=slows down erosion of grease
signs of decomposition
-material darkens (obvious color change) -effervescing -evolution of liquid (droplets condense at top of capillary tube)
two purposes for determining mp
-measure of purity -identifying unknown
what are the 5 major types of chromatography
-paper -gas -flash -thin layer -column
advantages of FTIR over dispersive IR
-signal is much stronger -can do multiple scans and combine them to generate highly accurate IR -spectrum automatically calibrated with He-Ne laser
giant blob at the top of the plate means
-solvent is contaminated -plate was overloaded with too much sample which destroyed resolution (separation) -spot was too large (equilibrium not established)
what could yield a negative bromine test
-unreactive alkene -electron groups on c=c bond slowing rxn
what is one way to proven the solvent front from moving too far, problems with this?
-use you pencil to scratch a line; no adsorbent = no movement -tend to stop watching it and leave it in too long...solvent will spread out and mix dots
Rf values can range from
0 to 1
how big should spots be ideally
1-2 mm
what are the the two regions the 2000-1600 is dived up into
1. 2000-1667 2. 1650 -1600
what are the first three areas you should you focus on for IR
1. 3600-3000 2.1800-1600 3.1200-1000
which set of crystals produced by the mother liquid is most pure
1st set
spill bromine on skin
warm water, soap, followed by sodium thiosulfate
procedure for experimentally finding a good solvent
1. attempt to dissolve some crystal into the solvent; if it dissolves at room temp, the solvent is crap 2. if crystal doesn't dissolve, attempt to heat the solvent 3. if the crystal still doesn't dissolve in the hot solvent, then the solvent is crap 4. if the solvent does dissolve, when the solvent is hot allow the solution to cool and recrystallize 5. if crystal form it is great!!!
recrystallization procedure
1. dissolve impure compound in hot solvent 2. continue adding solvent until no more compound dissolves (i.e. only impurities remaining) (always add less solvent than you did previously) 3. remove any impurities using a hot vacuum filtration 4. after removing impurities allow the solution to cool 5. once the solution has cooled to room temp you can place it in ice water bath 6. once solution is ice cold , vacuum filter it again 7. dry/weigh sample and obtain melting point
what are the two major goals of successful recrystallization
1. get the maximum amount of purified compound back as a solid 2. purify the sample
what are the second three areas you should focus on for IR
1. just above 3000 2. 2000-1600 3. below 925
tips for picking a good solvent
1. solvent should not chemically react with compound 2.solvent should dissolve compound while hot 3.the same solvent should not dissolve the compound while cold 4.solvent should dissolve the impurities at all temps or not at all
three factors resolution depends on
1.theoertical plates 2. boiling up rate 3.reflux ration
where is the fingerprint region
1500-400
anything above _____ intensity is too strong to be an aromatic substitution
30%
how many major techniques are there to purify/separate samples
4
what is the FTIR range
4,000 to 4000
where are the majority of functional groups found
4000-1500
mid peak absorbance
50%
Which part of the FTIR range doesn't provide much structural information
600 to 400
what temp must the experiment be kept under to avoid distilling cyclohexanol as an azeotrope
90
Asprin
ASA (acetylsalicylic acid)
Naproxen Sodium
Aleve and Naprosyen
oxidizing agents usually contain
Cr
How does ATR work
IR beam passed through beveled crystal(internal reflectance element) at 35-45 degree angle (45 for liquids).....causes beam to reflect down crystal.....as the beam reflects down the crystal it penetrates about one micrometer into the sample
fase negative bromine test
If an electron withdrawing group is neighboring the double bond or if you have unusual steric hindrance
what should you not do before Bromine test
wash test tube with acetone
the IR used to not be very popular, what changed?
It's identification abilities are unmatched;amazing at identifying and detecting functional groups
cause of ferric chloride color complex
Most phenols form colored complexes upon reaction with ferric ion, Fe3+
why is proton acid catalysis required
OH is a poor leaving group
how does recyrystalliation purify a compound
Recrystallization takes advantage of the fact that most crystal growth prefers incorporation of molecules of the same structure - leaving other structures (impurities) out of the crystals.
false positive ferric chloride
Some carbonyl compounds with a high equilibrium concentration of enol can give a false positive response to this test.
advantage of steam distillation
able to vaporize and distill a material at a temperature well below its boiling point.
how far does the ir penetrate into the sample
about 1 micrometer
where should your origin and spots be relative to the solvent
above
strong peak absorbance
above 70%
three most common orc pain killers
acetaminophen aspirin ibuprofen
what compound will be dissolve in this lab
acetanilize
____is used to clean the ATR
acetone
why should you allow acetone to completely dry before loading your sample
acetone will show up in the IR
which type of dehydration will be used in this lab
acid catalyzed
what technique can be used if the solution is dark in color(i.e) not the right color
activated carbon
what should you do if an oil forms
add more hot water
what is the difference between fractional distillation and simple distillation
addition of a fractioning column
why might these non-analgesics be added?
advertising purposes
ibuprofen
advil/motrin
should you turn of the water before or after disconnecting the tubing
after
mechanism of permanganate test
attack of two oxygen atoms of the permanganate ion, MnO4- on the pi bond of an alkene or alkyne resulting in a change in oxidation state of the manganese ion, resulting in the disappearance of the very deep purple color of permanganate and the simultaneous formation of a brown precipitate of manganese dioxide (MnO2)
ATR stands for
attenuated total reflectance
in azeotropes, the vapor and the liquid have the composition of the ______
azeotrope
minimum boiling azeotrope
azeotrope that boils at temp below the boiling point of the liquids in the mixture
is sodium bicarbonate a weak acid or base
base
how will eugenol be obtained
base extraction
where is the thermocouple placed in micro-distillation
base of the distillation head
how does non polar coating separate
based on differences in boiling point rather than polarity
how are the vapor components separated
based on their interaction with the packing material coating
why is it better to decant the cyclohexene away from the calcium chloride rather than filter it out
because cyclohexene is volatile
slower boil up rate = ____ resolution
better
larger reflux ratios = _____ resolution
better (more liquid coming back than being distilled)
DMF danger
birth defects
how to put out a fire
blow it out, or smother it using damp towel, watch glass, beaker, etc
basic bromothyol
blue
what color will the test turn
blue black
how is hcl colorized
bromothyol blue
potassium permanganate on skin
burns and stains
DMSO danger
burns through skin
how is the rxn monitored
by following the rate of acid formation
peak from 1200 to 1000
c-o group
1650 to 1600
c=c (indicated by medium intensity sharp peaks)
what is now possible with the use of a catalyst
can transfer reactant between aqueous and organic phase
what principle allows the solvent to move up the plate
capillary action
when will polymerization occur
carbocation adds to the alkene
what happens in the last step
carbocation rapidly loses proton from the adjacent alpha carbon forming double bond
peak from 1800-1640
carbonyl group
alcohols are oxidized to form
carbonyls
inverted mountain peak from 3200-2500
carboxylic acid
the _____ _____ is essential to gc
carrier gas
septum purge
carrier gas flowing just below septum prevents vapor from sticking to septum and contaminating future gas
why are chemwipes not used to clean the ATR
chemwipes have an abrasive in them that may scratch the ATR crystal
how can cyclohexene be removed
it forms an azeotropic mixture with water which is distilled out
how does gc differ from other separation methods in terms of theoretical plates
it has tons (2500)
why can't an unknown liquid with a constant boiling point be called pure
it may be an azeotrope
what happens when the upward flow of the solvent reaches equilibrium
it will stop moving up and the solvent will begin to spread out (i.e. mixing spots together)
where should the thermocouple be placed
just below the lip of the condensation assembly
secondary alcohol
ketone
why is phenacetin no longer used
kidney damage/possible carcinogen
acetone + bromine
lachymator
simple distillation requires the ____ amount of theoretical plates compared to other methods
least
what does the number in reverse tlc represent
length of aliphatic chains
higher the rate of temp, the _____ theoretical plates
less
less theoretical plates = ____ separation
less
weak beak absorbance
less than 30%
rule for insolubility in water
less than one OH per 5-6 carbons
why can some compounds be purified by gc and not by distillation
less time at higher temp
why does melting point depression occur
liquid formed from melting must dissolve some of the other material
mother liquor
liquid in the filter flask containing soluble impurities and pure sample
why does gas chromatography not always work on organic compounds
not sufficiently volatile at temperatures below their decomposition temperatures
why is below 925 significant
nothing really shows up here
larger reflux ratios = ____ distillation time
longer
relationship between aliphatic chain and organic compound affinity
longer chain = more affinity
length of column
longer column = longer retention time
Why are qualitative test not the bests
lose material, ambiguous, can't 100% identify, etc....
what does the rate of reaction depend on in this lab
loss of the leaving group to form a carbocation
which step is slow in E1
loss of the leaving group to form a carbocation
liquids with high vapor pressure will have ____ boiling points
low
sample spends more time in gas phase than in liquid phase
low retention time
do mixtures of different compounds usually have higher or lower mp?
lower (melting point range starting below the melting point range of the lowest melting point of the two organic materials.)
high temp
lower retention time
fast flow rate of carrier gas
lowers retention time
2000-1667; when do we care about these
lumps and bumps corresponding to aromatic substitutions (only if they are weak and broad)
what are the two types of apparatuses used in simple distillation
macro and micro scale
purpose of starch test
make sure there is enough bleach
why is reverse phase tlc called reverse phase
many of the solvents and properties are reversed
solvent doesn't rise above origin
marked too hard with pencil removing adsorbent
nonvolatile material
material with a very low vapor pressure
why does a sharp melting point not guarantee a pure compound
may be a eutectic mixture
how to determine rate of chemical rxn
measure the concentration of either reactants or products as they change over time
melting point can be more accurately described as a
melting range
although recyrstallization is usually performed using a solid sample, recyrystallization is occasionally performed on ______ a _____
oil; liquid
when is vacuum filtration used in this lab
once to remove insoluable impurities form the hot filtrate once isolate purified crystals from remaining isolate
what is the main difference in the two types of filtration
one is cold and one is hot
easiest type of product to purify
one that is relatively pure already
should the apparatus be open or closed?
open, a closed system will explode
point of the tetrahedron
optimizing one point means sacrificing one of the other three
what part of recrystallization is very flammable
organic vapors
how should you measure spot distance
origin to middle of spot
spot looks like one big trail
overloaded plate or solvent not sufficiently polar
what happens in oxidation
oxidizing agent removes two hydrogens (one from the a-c) and one from the alcohol
____ used to be used in lieu of _____ (pain killers)
phenacetin; aspirin
ferric chloride test
phenols
compounds that can cause a false positive bromine test
phenols, enols, amines, aldehydes, ketones (substitution rather than addition)
melting point physics definition
physical measure of the forces holding molecules of a compound into a crystal lattice
natural products isolated from plants
phytochemicals
slick trick for saving tlc plate
place tape over it
over-spotting or co-spotting
placing one spot on top of another in order to confirm that it is the same compound
in reverse phase chormatography _____ compounds will move the farthest
polar
what type of solvent is used
polar
method for solving solubility issues in past
polar aprotic solvents such as DMSO and DMF can dissolve polar salts as well as organic materials
effect of polarity on retention time
polar coating + polar sample = longer retention time nonpolar coating = retention time based on bp
deciding factor in reaction pathway
polarity of solvent
what does an extreme rf value indicate
poor choice of solvent
three general steps of acid-catalyzed dehydration
protonation dehydration deprotonation
what does a fractioning column do
provides more surface area for the vapor to contact increasing the number of theoretical plates
why is it important to replace the septum
puncture holes in it will allow carrier gas and vaporized sample to escape
What does recrystallization do?
purify impure samples
number one major concern of organic chemists
purity of product
positive Baeyer's test
purple ----> dark brown manganese dioxide precipitate
was qualitative or quantitative data collected in analgesic TLC lab?
qualitative (want to see what is present, not how much)
besides being good for isolation/purification, what else can tlc do
quantitative tool for telling you how much of each component present
purpose of vacuum filtration
rapidly separating solids from liquids
why are rf values useful
rate at which organic compound elutes is highly characteristic and can be used to id it
what does Rf stand for
ratio of fronts retention factor
solubility issues in rxns
reactants tend to have diff solubilities
sodium bicarbonate mechanism
reacts with ptotic acid to form sodium salt and carbonic acid
flourescant finger print
really just a spot that wandered off
which experiment is most likely to cause a fire
recrystallization
what are the four major methods of purification
recrystallization extraction distillation chromatography
after hot filtration, what should be done if crystals form
reheat and stir
purpose of drying tube
removes moisture from gas extending the life of the column and detector
what to do if product is still remaining in funnel
rinse sample flask with hot solvent and pour that into funnel, then wash the funnel/filter paper with more hot solvent
calculating percent composition
same as area of triangle A=height of peak * width at half height
what is something that makes recrystalliztion unique compared to the other four major purification techniques
sample most be solid
What is the issue with sample preparation
sample must be in the path of the beam, means it can't absorb nrg between 40000-400 ( all organic/most inorganic do) (esp ones containing oxygen)
in order to perform recrystallization, the material to be purified most be __________
solid
If the compound you are purifying is known, what type of information can you get from the handbook
solvent mp bp color of purified compound (assume white or colorless if unspecified) crystalline form (ex. flakes, needles, etc)
compound doesn't reappear after cooling
solvent crappy
what will a liquid at any temp have?
some molecules escaping into the gas phase
how does tlc work
spots are placed on plate (glass, plastic, or aluminum) containing adsorbent....plate is placed in solvent......solvent travels up plate....as solvent passes spot, the spot partially dissolves into it
one big blob forms in middle
spots spotted too close together
what does the rate of an E1 rxn depend on
stability of carbocation
How is I2 colorized
starch
potassium iodide
startch test
how will limonene be obtained
steam distillation of orange peel
false negative ferric chloride
sterically hindered phenols do not give a colored complex
reflux ratio
volume of liquid returned to the distilling flask/volume of liquid removed as distillate
How do you get an IR spectrum for a seemingly empty vial
swab the vial and rub the swab on the ATR crystal
how/what did distillation used to be used for
taking dilute alcohol solutions and distilling them to give alcohol solutions with high concentrations
boiling point
temp at which vapor pressure = atmospheric pressure (bubbles able to form and rise bc the vapor pressure can overcome the atmospheric pressure)
melting point
temp range from when you see first crystal melting (or crumbling/collapsing) to when last one melts
peak at exactly 925
terminal =CH2
peak at 3300
terminal alkyne
what are the two natural products in this lab
terpene and acetogenins
what will happen if the column is subjected to a temp higher than the operating temp
the coating will vaporize and be carried out or decomposed effectively destroying the effectiveness of the column
the vapor condenses from simple distillation should contain more of what component
the component with a lower boiling point
what is done after performing the hot vacuum filtration
the filtrate is reheated to dissolve any crystals, the solution is then allowed to slowly cool
why are flow controllers important
the flow rates of the two streams must be balanced or the thermal conductivity detector will not work
what happens to gas when the gc use a thermal conductivity detector
the gas is split into two streams....one stream directed by injection port....other stream directed through another column to the detector
what will happen if a polar packing material like carbowax is used
the polar components of the sample will interact with it much more, taking a longer time to pass through the column resulting in a greater retention time
vapor pressure
the pressure exerted by a vapor over a liquid
ideally all of the sample will be flash vaporized, unfortunately this doesn't happen. What happens
the sample that is not flash vaporized remains as an aerosol that will travel with the carrier gas, not interacting with the column packing. This aerosol is detected as an air peak and will have the exact same composition as the sample
chromatography
the separation of a mixture into its components by passing the fluid over a non-mobile adsorbent and separating the components by differential absorption and elution
what will happen if you let tlc sit in solvent for too long
the solvent will run up and off the plate
Bromin Test forms what compound
trans-1,2-dibromocyclohexane
crystals don't form during recrystallization
try agitating the sample by shaking or rubbing the inside of tube with stirring rod; if all else fails try adding a little bit of impure sample
compound completely dissolves in solvent, solvent doesn't dissolve compound at all
try mixing these solvents
what is ATR penetration called
tunneling
what happens to iodide when it is oxidized
turns into I2 (little color)
how many times is vacuum filtration used in this lab
twice
how many hands should be used to handle a gc syringe
two
eutectic point
unique mixture of A and B that has a sharp melting point; also point where the mixture melts at the lowest temperature observed for any mixture of the two compounds
cause of azeotrope
unknown; no relationship
Baeyer test (potassium permanganate) tests for
unsaturation
how long will the azeotrope distill for
until one of the components is exhausted
often textbooks and google will give one number for the mp, what is this
upper limit of the range
calcium chloride
used to dry cyclohexene
why are two hands used to handle the gc syringe
using one hand my bend the wire
in gc the sample is
vapor
Raoults Law
vapor pressure always proportional to the mole fraction of each component
benefits of caffeine
vasodialator; cuts relief time in half
sport ran off the side of the plate
very wet sample or defective plate
advantage of tcd over other detectors
volatile components can be collected unchanged as they leave the detector. This allows a GC equipped with a TCD to be used for the purification of relatively small quantities of volatile material While this collection may be slow and tedious, it is one of the most rapid methods for the purification of small quantities (less than 1 mL) of volatile compounds.
simple distillation is used to separate a ____ liquid from another soluble ________ or ______ impurity
volatile; nonvolatile; less volatile
acidic bromothyol
yellow
can a combination of solvents be used to reach the ideal solvent?
yes
is it okay to use more than one technique in conjunction
yes!
what will happen if purification has taken place
your starting sample will weight less than your beginning sample
