when vapor pressure = atmospheric pressure, the liquid
boils
2 secrets to the rotary evaporator
(1) increase surface area of solution you are distilling
(2) perform distillation at reduced pressure by evacuating the distillation apparatus with a water aspirator
the rotovap is useful for
removing solvents from nonvolatile solutes
washing
dissolves the impurities and leaves behind material we want to isolate
in extraction/washing, solvents must have two characteristics
(1) capable of extracting desired material from original solution while leaving undesirable material behind or vice versa
(2) two solutions must be insoluble in each other (immiscible); most organic solvents are miscible in each other; methanol, ethanol,
_____ is the most common procedure for purifying solid compounds
recrystallization
recrystallization is most successful when
material to be purified is insoluble in solvent when it's cold, and much more soluble when solvent is hot
bond stretches require ______ infrared energies to occur and appear at ________ frequencies
higher;higher
bond bends require _____ infrared energies to occur and appear at ______ frequencies
lower;lower
IR frequency of OH: alcohols and phenols
3600-3250 cm?�
IR frequency of sp2 C=C: alkenes
1680-1600 cm?�
IR frequency of sp2 C=C: aromatics
1600 and 1475 cm?�
IR frequency of sp2 C-H: aromatics (stretch)
3150-3050
acid-base extraction
aqueous acid used to extract organic bases from organic solutions; aqueous base used to extract organic acids from their solutions; as two solutions shaken together, acid and base react to form a salt; since salt ionic, salt extracted into aqueous phase a
what apparatuses are used for recrystallization procedure?
to dissolve compound: heating mantle and an erlenmeyer flask
to isolate crystals: vacuum flask, rubber vacuum tubing, bruchner funnel, and an adapter.
why do you use an erlenmeyer flask for heating during recrystallization?
it reduces the evaporation of the solvent because the shape of the flask "catches" and condenses evaporating molecules that would otherwise escape the flask.
what two compounds were used in lab #2 - recrystallization, solubility, and melting points?
trans-cinnamic acid
acetanilide
draw the structures of trans-cinnamic acid and acetanilide
check p. 55 lab manual
what solvent system did you use to dissolve the compounds?
acetanilide: water
trans-cinnamic acid: ethanol/water mixture
why do you use recrystallization procedure?
to remove impurities in solid compounds
what is the significance of acetanilide being sparingly soluble in room temp. water and very soluble in boiling water?
acetanilide will dissolve into the heated water due to its high solubility in boiling water but will drop out of solution and crystallize in room temperature water due to its low solubility in cold water.
what is the iupac name for trans-cinnamic acid?
(e)-3-phenyl-2-propenoic acid
what is the iupac name for acetanilide?
n-phenylethanamide
what is the significance of trans-cinnamic acid's solubility in water and versus its solubility in ethanol?
trans-cinnamic acid is insoluble in water but very soluble in ethanol. being insoluble in water allows it to stay out of solution and form crystals in higher yield and more purely than a flask with only/mostly ethanol.
how do you collect crystals in recrystallization?
1. set up vacuum flask with rubber adapter and bruchner funnel on a ringstand clamp to steady it; hook up to vacuum tubing and put a flat filter in funnel
2. turn on the vacuum
3. add a small amount of solvent to ensure a tight seal between the flat filte
what method worked better for each compound in achieving higher yield? (recrystallization)
for acetanilide: 20 mL flask because with less volume there was higher chance for collision of molecules. it works adversely for purity, because there is also a higher chance impurities will collide and be incorporated into the crystal structure.
for tran
which method worked better for each compound in achieving purity?
Acetanilide: the 40 mL flask was more pure as indicated by the m.p. because, although it had lower yield, there was less likelihood of collision with impurities in solution
TCA: the ethanol and water mixture; allowed tca to stay out of solution because in
why must recrystallized samples be completely dry?
water acts as an impurity when determining the melting point and thus will lower m.p. you must completely dry samples to remove all water.
what are 2 reasons you need to know literature values for solubility?
to determine if the compound is soluble or insoluble
to obtain the correct g/mL ratio of solute:solvent.
do literature values of acetanilide in water hold true?
yes. it dissolved readily in hot water but dropped out of solution when the temperature dropped to room temp and formed crystals.
why is acetanilide soluble in warm water but trans-cinnamic acid is not?
TCA has a larger surface area and smaller polar surface area than acetanilide. acetanilide has higher PSA:TSA and can interact/associate with water molecules at warm temperatures whereas TCA would interact with other TCA molecules due to higher non-polar
a completed experimental lab report written by a student consists of three major components, what are they?
observations and safety
data analysis
questions
what are the two tickets you need to be permitted to perform an experiment?
pre-lab
proper attire/goggles
if someone catches on fire, there are three possible courses of action to assist them. what are they?
stop them from moving
apply a fire blanket
safety shower/roll the person on the floor
broken glass can be sharp, so it should be placed in a glass box. how should you dispose of ordinary glass such as used pipettes and melting point tubes?
you should also place them in a glass box.
liquid organic waste should be separated into which two categories before disposal?
halogenated
non-halogenated
T/F: safety goggles need only to be worn when you are boiling solvents to avoid splashing in your eyes
false
T/F: there are 5 categories of chemical waste; simply discard them in the appropriate waste containers
true
what are the 5 categories of chemical waste?
halogenated organic, non-halogenated organic, aqueous acid, aqueous base, and solids
T/F: all chemical burns should be rinsed under cold water for at least 15 minutes
true
T/F: throw sodium bicarbonate on chemical spills and wipe it up with a mop and a bucket of water
false
T/F: lightheadedness, malaise, or dizziness can be the result of breathing chemical vapors and should be reported to your TA
true
T/F: the inward flow of air in a fume hood creates a dynamic barrier that minimizes the movement of vapor/gases out of the hood and into the lab
true
if a classmate cuts themselves on a broken shard of glass, what should you do prior to applying pressure to stop the bleeding?
you should ensure that there is no glass in the cut.
what are five keys to working safely in the fume hoods?
1. place equipment behind the red line
2. keep doors closed when not working in the hood
3. when done working ensure that vacuum, water, and gas are off.
4. clean up all spills; leave the hood area clean when finished
5. keep the sash down
what do you do with broken thermometers?
bring any broken mercury-filled thermometers to Dr. Ma
broken lab equipment:
bring to dr ma
what do you do when an acidic chemical spill occurs?
you should neutralize before trying to clean up. after neutralizing use a wet sponge or paper towel to wipe up the mess and ask ta how to dispose.
what do you do when a solid spill occurs? what do you NOT do?
sweep up with broom. do not use water/wet paper towels. the solid may react with water!
what do you do when you get chemicals in your eye?
flush with water for 15 minutes using eyewash. hold the eye open.
what do you do when you get an acid/base/chemical/thermal burn
flush area with cold water for 15 minutes. large area: safety shower
what do you do to burning reactions/reagents?
do not use water. clear away combustible materials; small fires use a beaker to smother the flames; if in hood close the slider and alert ta; large fires require co2 chemical extinguisher
where should you ALWAYS be working?
the hoods
why do you never return unused chemicals to stock bottles?
to limit contamination.
the solvents ethyl acetate and toluene were used in experiment one; which solvent is polar and which is non-polar?
ethyl acetate: polar
toluene: non-polar
would toluene or ethyl acetate readily dissolve napthalene? benzophenone?
napthalene: toluene
benzophenone: ethyl acetate
draw toluene and draw ethyl acetate
quiz 1
is DCM water soluble?
no, it is more dense than water
is acetone water soluble?
yes
when should you stop heating a solution during recrystallization?
when all of the solid compound is dissolved
draw trans-cinnamic acid and circle the functional group that makes it more soluble in a polar solvent like ethanol. what is the main bonding type responsible for this solvation?
quiz 1 for structure;
carboxylic acid group responsible; hydrogen bonding for solubility
how many HBA and HBD's are in acetanilide?
1 HBD
3 HBA's
chemical informatics =
looking for relationshipo between structure of a molecule, how soluble it is in water, its density, its boiling point, and what molecules it can dissolve (for solvents)
what determines if a compound is miscible with a solvent
whether the molecular forces in the solvent are similar to or different from those in the molecule
most organic solvents have ____ density than water
lower
most organic solvents ____ more easily than water
evaporate
molecules with weak IMFs (i.e. ___ ___ ___, and ___ ____) have high/low density
van der waals, london dispersion
low
molecules with heavier atoms have stronger IMFs (i.e. ____ ___ and ___ ___) have high/low density
h-bonding dipole-dipole
high
what are characteristics of solvents that have high vapor pressures?
evaporate easily and boil at low temperatures
what determines the boiling point of a solvent?
size, shape/symmetry, and strength of IMFs
organic solvents with weak IMfs are said to be
nonpolar
organic solvents with strong IMFs are said to be
polar
why are organic compounds typically soluble in a wide range of solvents?
organic compounds typically have multiple functional groups which allow a variety of IMFs
ionic compounds only dissolve in ___ ____ solvents
highly polar
why do ionic compounds only dissolve in highly polar solvents?
attractive interaction between non-bonding pairs and positive partial charge of hydrogen of water and the positive/negative charges of the ion
what is a dielectric constant?
measure of a solvents insulating ability when interacting with formal charges
the better a molecule insulates or is ____ to solute charges, the ____ its dielectric constant
attracted; higher
what is n-hexane's dielectric constant
2.0
what is CCl?'s dielectric constant
2.2
what is methyl t-butylether's dielectric constant
2.6
what is diethyl ether's dielectric constant
2.8
what is dichloromethane's dielectric constant
9.1
what is CHCl?'s dielectric constant
4.7
what is ethyl acetate's dielectric constant
6.0
what is acetone's dielectric constant
21
what is methanol's dielectric constant
33
what is DMSO's dielectric constant
46.7
what is water's dielectric constant
80
what is the reason for trends in dielectric constants and dipole moments?
electronegativity differences of individual atoms in a molecule
why does methanol have a similar dipole moment to water but different polarity index (lower)?
because methanol has a higher non-polar:polar surface area ratio than water
order aromatic substitution patterns (ortho/meta/para) in order of increasing polarity
para < metha < ortho
is the E or Z alkene substitution pattern more polar?
Z
Draw the structures for the following:
acetone, dichloromethane, ethanol, ethyl acetate, hexane, water, methyl t-butyl ether, toluene, naphthalene, benzophenone, vanillin, benzoic acid
check prelab #1
which solvent from lab #1 - physical properties of organic solvents has a density that is higher than water?
dichloromethane
is acetone soluble in water?
yes
is dichloromethane soluble in water?
no
is ethanol soluble in water?
yes
is ethyl acetate soluble in water?
no
is hexane soluble in water?
no
is methyl tert-butyl ether soluble in water?
no
is toluene soluble in water?
no
what was the only compound in lab #1 that was soluble in water?
citric acid
what is TLC?
thin layer chromatography is a technique in which compounds separate so that different compounds can be "seen" even if part of a mixture-separate based on polarity
why is TLC useful?
it is inexpensive, little sample required, numerous samples can be tested at once, samples can be recovered
TLC can be used to determine when a reaction is complete by
appearance of product and disappearance of the starting material
what is the equation for the Rf value?
distance travelled by compound/distance travelled by developing solvent
why do you spot compounds at a higher level than the solvent?
so the spot doesn't dilute into the solvent and instead will travel up the plate
why are UV lamps used to visualize spots?
the gel has dye that lights up under the light; wherever there is a sample light will not reach the plate/dye and there will be a dark spot indicating the sample.
what is the set up for TLC
silica gel with line drawn across bottom of plate, 5 mm from the bottom.
developing chamber with small amount of developing solvent
watch glass to place over the chamber
why do compounds have different Rf values
the polarity of the molecule
specific Rf values depend on the
developer
the silica gel on the TLC plate is _____ ___ and attracts ____ molecules
extremely polar; polar
polar molecules prefer the ____ and non-polar molecules prefer the ____ in TLC
gel;solvent
non-polar compounds generally have ____ Rf values
higher
why do you use a mixture of developer solvents in TLC
to control polarity differences and to separate compounds efficiently
common developers in TLC
chloroform/methanol; hexane/ethyl acetate
draw the following structures:
acetophenone, anisole, benzoic acid, butyl phenyl ether, phenol, caffeine, acetominophen, and asipirin; water, hexane, ethyl acetate, dichloromethane
check prelab #5
which analgesic was the most polar? which was the least?
caffeine was the most and aspirin was the least
how did we ID analgesics in the compound mixture?
by using TLC and comparing those spot Rf values to those of the pure compounds
what happens if the TLC spot is very large?
it will spread into other lanes
which solvent system for TLC was the best in determining the unknown mixtures of analgesics? why?
the 10:1 ethyl acetate to hexane mixture
the polarity of ethyl acetate was offset by the highly nonpolar portion of hexane. this caused the two more polar compounds to travel less and differentiate more by associating with the polar plate, while aspirin a
what was the point of lab #3-principles of chemical extraction?
to separate a mixture of cellulose, caffeine, and benzoic acid by liquid-liquid and acid-base extraction methods based on their physical properties and properties of solvents.
what are the structures of :
caffeine, a cellulose monomer, benzoic acid, dichloromethane, caffeine salicylate
look at prelab #3
what is the basis for separation?
like dissolves like
why are most organic solvents relatively nonpolar when compared to water and insoluble in water?
they have higher non-polar surface area:polar surface area ratios.
caffeine is a ___ because of the presence of a
base; amine group
are caffeine and benzoic acid more soluble in water or DCM
DCM
how does pH affect solubility and polarity?
the pH can make compounds that are typically more soluble in organic solvents more soluble in aqueous solutions because stronger dipole presence after protonation/deprotonation
how do you remove/dry water from caffeine organic layer?
the solution is dried with chemical drying agents that are anhydrous organic salts. they can accept water into their crystal structure to form hydrates
MgSO?(anhydrous) + H?O->MgSO?*xH?O where x=1-7
what is the reaction that occurs when you add NaOH to the organic caffeine +benzoic acid solution
Benzoic acid is deprotonated at the hydroxyl group; converted to its conjugate base
what is the reaction that returns the conjugate base of benzoic acid back to benzoic acid?
adding HCl or strong acid
why do you make the solution basic and then acidify in extraction?
to ionize the benzoic acid so that it is more soluble in the aqueous layer, leaving the other compound (caffeine) separated into the organic layer. acidifying returns benzoic acid to water insoluble state allowing crystallization
how many hydrogen bond acceptors and hydrogen bond donors does caffeine have
HBA 6
HBD 0
why does the basicity of amines and amides differ?
although both contain nitrogen atoms, they react intramolecularly differently and thus differ in reactivity and solubility. amides have a lone pair on nitrogen that is delocalized by conjugation with the carbonyl group which decreases the basicity of the
what is the apparatus for gravity filtration?
o-ring stand holding a erlenmeyer flask with a narrow stem funnel and fluted filter paper
gravity filtration - when do you use it? what is the downside?
use it to filter granular material - i.e. drying agents
it's slow
vacuum filtration - when do you use it; what is the upside
filtering powders in large or small amounts
faster than gravity filtration
when did you use gravity filtration in #3?
to separate the cellulose from DCM mixture and to remove the drying agent from caffeine
what glassware is used for liquid-liquid (acid-base) extraction?
seperatory funnel with stopcock; stopper; erlenmeyer flask; o-ring stand
when did you use the technique of acid-base extraction?
to separate benzoic acid and caffeine (organic and aqueous layers)
given a mixture of caffeine and benzoic acid what would happen if they were added to a separatory funnel with DCM and 1M HCl? which compound goes into which layer and why?
caffeine goes into the aqueous layer (it is protonated at basic amine site and is now soluble in water) and benzoic acid goes into the organic layer because it is more soluble in it.
will a gas or a liquid have a lower b.p.
gas
will a gas or liquid have a higher vapor pressure?
liquid
will a gas or liquid have a higher melting point?
liquid
will a gas or liquid have higher intermolecular forces?
liquid
when thinking about general trend in TLC, which typically has a higher Rf val? polar vs non polar
non-polar
when using a polar solvent, which has a lower Rf value? polar vs. non polar
non polar
which solvent system is more polar? 80:20 hexane:ethyl acetate or 60:40 hexane:ethyl acetate
60:40 hexane:ethyl acetate
what type of IMF is dominant force in the solvent that has a higher boiling point?
dipole dipole interactions are the dominant force in ethyl acetate having a higher boiling point than hexane
which solvent has stronger IMFs? hexane vs. ethyl acetate
ethyl acetate
what is the mechanism of the reaction that was performed in lab #4?
Sn1 hydrolysis of tertiary alkyl halide
write the mechanism (general) for Sn1 hydrolysis of tertiary alkyl halides
check post lab
how do you calculate k? what does k represent?
slope=k/2.303
k is the rate constant
what is the rate determining step of Sn1 hydrolysis
the dissociation of the leaving group / formation of carbocation
draw the structure of the intermediate in the rate determining step
p. 63
what stabilizes the charge-separated nature of the transition state (rate determining step)
polar solvents; have larger dipole separation and therefore interact with polar solvents more efficiently
what solvent system was used in lab #4 Sn1 hydrolysis of RX? which was the best?
water:acetone in varying proportions
for both chloride and bromide, the mixtures with higher % water increased reaction rate and k. (higher polarity)
increasing/decreasing the polarity of solvent makes it better at solvating the polarized transition state and therefore 1. and 2.
increasing
1. lowers the activation barrier
2. increases rate of hydrolysis reaction
a better hydrogen bond donating solvent allows _____ though H bonding with the halogen bearing partial negative charge. this ____ the rate of reaction
stabilization; increases
what variables influence the rate of the Sn1 reaction?
alkyl halide structure, leaving group ability (changing solvent and leaving group)
which, out of chloride and bromide, is a better leaving group? why?
bromide - larger molecule so greater electron delocalization - stabilizes the transition state; it is also more polarizable because of its larger diameter - makes breaking the bond easier.
how did you monitor the reaction at t1,2,3? (Lab #4)
we determined the amount of HX present by adding known amount of NaOH to determine the 1:1 ratio of how much acid is consumed - use bromothymol blue to monitor pH and rxn
what color does pH change to for acidic soln and basic soln?
acidic - blue
basic - yellow
for every mole RX consumed ___ mole(s) of HX is produced in sN1 hydrolysis
one
in Sn1 hydrolysis : total amount NaOH added at time infinity = amount of __ produced = amount of __ initially pressent
HX; RX
what are the units of k?
s?�
what competing reaction occurs during Sn1 hydrolysis of RX; show mechanism
E2 elimination, mechanism on p. 46 of notebook
draw the structures of tert-butyl chloride, tert-butyl bromide, acetone, bromothymol blue, and bromophenol blue
check prelab and p 46
ClCH?OCH?CH? + CH?CH?OH -> what diether? two mechanisms?
CH?CH?OCH?OCH?CH?; mechanism p. 47
aromatic rings are generally reactive/unreactive?
unreactive
what do aromatic rings react with readily?
strong electrophiles to give substitution products
what is the general mechanism? include possible intermediates.
check lab #6 chem lab manual
what is the driving force of the nitration of methyl benzoate?
resonance stabilization of the carbocation where in the end aromaticity is restored to the molecule
when there is substitution of a monosubstituted benzene ring there are _ possible monosub products
3, ortho/meta/para
what determines what the major product of aromatic substitution is?
whether the substituent on the ring is electron donating or withdrawing
if a substituent is e? withdrawing, it ____ the reaction and produces ______ as the major product(s)
accelerates; ortho/para
if a substituent is e? donating, it ____ the reaction and produces ____ as the major product(s)
slows down; meta
what is the reaction of sulfuric acid with nitric acid?
look at postlab #6
how does the ester substituent effect aromatic substitution major products?
it is electron donating ; ortho
what is the mechanism of the reaction performed in lab #6
post lab #6
what is rotary evaporation for?
to evaporate large volumes of solvents in a fast and convenient manner
when did we use the rotovap?
to separate the caffeine from the organic solution
why does rotovap rotate?
increases the surface area of the solution and reduces the possibility of bumping
what is the diels alder reaction?
a concerted reaction where a diene and a dienophile undergo favorable alignment of molecular orbitals
what can catalyze a diels alder reaction?
lewis acids
what are three notable things about the diels alder reaction?
predictable stereochemistry, regiochemistry, and reversibility
what is formed during the diels alder reaction?
2 C-C bonds and a final cycloalkene product
diene =
strong electron donating substituent (nucleophile)
dienophile =
strong electron withdrawing substituent (electrophile)
why is benzyne unstable?
it has a triple bond in a 6-membered ring
what is the order kinetics of diels alder?
2nd order overall
what is the second consideration for stereoselectivity in the diels alder reaction?
endo and exo adduct
what promotes the formation of the exo adduct?
thermodynamic control
what promotes the formation of the endo adduct?
kinetic control
thermodynamic control=
permitting the reaction to proceed to equilibrium over an extended period of time; forms the more stable product (exo)
kinetic control=
At low temperature, the reaction is under kinetic control (rate, irreversible conditions) and the major product is that from fastest reaction; forms the endo adduct, less stable;
why does endo adduct form faster?
transition state leading to it is stabilized by more extensive pi-electron overlap; has a lower activation energy
is endo/exo adduct more stable? which forms faster?
exo is more stable
endo forms faster
how do you test stereoselectivity?
the melting points of endo and exo adducts are different
what two molecules were reacted in lab #6? what was the solvent?
maleic anhydride and furan
ethyl ether
draw ethyl ether, maleic anhydride, furan, and product of diels alder reaction between them
refer to prelab #8
what factors favor thermodynamic control products? what is the product?
exo;
At high temperature, the reaction is under thermodynamic control (equilibrium, reversible conditions) and the major product is the more stable system
energy can be absorbed by molecules giving rise to excited states which includes (2 types)
vibration/rotation excitations (IR)
nuclear spin excitation (NMR)
__ excites vibrational energy levels in IR
hv
where h = planck's constant
v=frequency
infrared transitions require what to occur?
bond dipoles
the ___ polar the bond the more intense the absorptions
more
what does the intensity of a band in IR depend on? (2 things)
1. polarity of the bond
2. # bonds responsible for absorption
what effect does symmetry have on IR absorptions?
symmetrical bonds will have no dipole moment and therefore no IR absorption - infrared inactive
stronger bonds absorb at ____ wavenumbers
higher
stretches absorb at ___ wavenumbers than bends
higher
bonds to hydrogen absorb at ___ wavenumbers
higher (smaller mass)
polar bonds have more ____ absorptions
intense
on IR spectra O-H is represented by
intense (b/c polarity) very broad peak at 3550-3200 cm?�
on IR spectra N-H is represented by
less intense, less broad peak at 3400-3200 cm?�
NH2 has 2
NH has 1
C(sp)-H on IR spectra is represented by
peak at 3300 cm?�
C(sp�)-H on IR spectra is represented by
peak at 3100-3000 cm?� (can be weak)
3000 cm?� on IR spectra typically divides
divides sp� and sp�
C(sp�)-H on IR spectra is represented by
3000-2850 cm?�
aldehyde C-H bond on IR spectra is represented by
2830-2700 cm?�
on IR spectra CN group represented by
intense polar peak at 2260-2200
on IR spectra C(triple bond)C represented by
2150-2100
a carbonyl group is represented on IR spectra by
very intense and characteristic peak at around 1700
on IR spectra C(double bond)C is represented by
weak, less intense peak at 1660-1640
double bonds on phenyl group on IR spectra represented by
four bands near 1600, 1580, 1500, 1450
C-O single bonds (of esters, ethers, carbonyls) on IR spectra represented by
intense peak at 1300-1000
phenyl group on IR spectra represented by
900-675
one or more bands of variable (moderate-strong) intensity --
Substitution pattern (o-, m-, p-) gives rise to unique
absorption patterns
what are the 5 regions? groups found in them?
1. hydrogen bonding CH, OH, NH
2. triple bonds (CN, CC)
3. double bonds (CC, those of benzene)
4. carbonyl / double bonds
5. fingerprint (single bonds, CO single bond alcohol, ether, ester)
what properties are affected by attractions between molecules? (give 5)
Many properties such as solubility, boiling point, density,
state of matter, melting point, etc. are affected by the
attractions between molecules. (adhesiveness)