CHM2211L Final Exam UF

24 July 2022
4.7 (114 reviews)
135 test answers

Unlock all answers in this set

Unlock answers (131)
question
Melting Point
answer
temperature at which the solid phase is in equilibrium with the liquid phase
question
Pure Compound
answer
sharp melting point, range is narrow (1-2 degrees)
question
Why does the presence of a soluble impurity in a sample has the effect of lowering and broadening the melting point range?
answer
because the impurity disrupts the crystalline lattice of the sample so less energy is required to convert the solid phase into a liquid phase
question
What effects does insoluble impurity like sand and glass has on MP?
answer
no effect
question
Errors of taking melting points:
answer
1. improper amount of sample in capillary tube 2) mistaking sagging or shrinking sample as melting 3) presence of solvent cause crystals to "sweat"
question
Benzoic acid
answer
122-123°C
question
Mandelic acid
answer
120-122°C
question
An unknown compound was determined to be 74.97% C, 8.39% H, and no nitrogen. What is the empirical formula
answer
100-74.97-8.39 = 16.64% O # of C: 74.97/12 = 6.25/1.04 = 6 # of H: 8.39/1=8.39/1.04= 8 # of O: 16.64/16 = 1.04/1.04 = 1 EmF: C6H8O
question
Can IR spectroscopy be used to distinguish 2-pentanone from 2-hexanone? why or why not?
answer
No because IR spectroscopy is used to distinguish functional groups presents on molecules. Both 2-p and 2-h contains the same functional group.
question
Acetophenetidin
answer
analgesic and antipyretic (pain and fever relief)
question
p-acetamidophenol
answer
Williamson ether synthesis
question
p-phenetidine
answer
Amide synthesis
question
Recrystallization
answer
solvent that will completely dissolve both desired compound and impurities when the solvent is hot; desire compound must be insoluble in the chosen solved at cold temperature and inorganic remains soluble when cooled
question
What do seed crystals do?
answer
They serve as nucleation sites where more molecules of the desired compound deposit themselves in layers.
question
Explain the purpose of the hot gravity filtration. Why is it good to use the stemless funnel for this technique?
answer
- Hot gravity filtration serves to remove any insoluble impurities that do not dissolve when the solution is brought to its boiling point. - it is good to use the stemless funnel for this technique because this would minimize any contact between the hot solution and the funnel. If a funnel with stem is used the droplets of hot solution might get stuck on the stem inner surface and early crystallization of the solution might occur
question
ligroin
answer
solvent derived from petroleum consisting of C7 and C8 hydrocarbon, non polar
question
Amide synthesis of acetophenetidin
answer
p-phenetidine + acetic anhydride (solvent: Sodium acetate and hydrochloric acid)
question
Why is the sample of p-phenetidine reddish brown?
answer
small amount of impurities caused by air oxidation of the amino functional group
question
how to remove reddish brown from p-phenetidine?
answer
decolorizing carbon
question
Why should you not stir the crystals in the buchner funner?
answer
this makes the filtration less efficient and does not adequately remove the solvent from the crystal
question
Williamson Ether Synthesis
answer
1) p-acetamidophenol +sodium methoxide, methanol, and ethanol 2) 1st product (addition of sodium) + Bromoethane
question
Why does the williamson ether synthesis take two steps?
answer
Because the hydrogen on the alcohol group of acetamidophenol would react with the bromoethane to create ethane and there would not be any reaction. The sodium acetate turns that alcohol group into a nucleophile that would attack the C of the bromoethane
question
Reflux condenser
answer
Allows the reaction to be carried out at the boiling point of the solvent and yet it prevents loss of solvent or reagent due to evaporation. The vapors condense as they rise up the condenser and thus prevent them from escaping.
question
What was the best recrystallization solvent for the acetophenetidin?
answer
Water because the solute is completely soluble at boiling point, but the crystals reappear when solution is placed in an ice bath.
question
Wooden applicator
answer
helps with gentle boiling
question
Simple experiment that could be used to determine if the samples made through the two synthetic routes are identical:
answer
If the sample made through two synthetic routes are identical, one can create a mixture from the same amount of two samples and the MP should be sharp and close to the recorded MP. If MP is lower than theoretical MP and has big range: samples are different from one another.
question
Why is HCl used instead of just DIW?
answer
HCl is a much stronger acid which protonates the amine group of the p-phenetidin, which makes it more soluble in the solution
question
What is the purpose of the sodium acetate solution in the amide synthesis?
answer
HCl protonates p-phenetidine and drives the reaction to the right but too much HCl would convert all of the compound to its conjugate acid and no reaction with acetic anhydride would occur. Sodium acetate creates a buffer within the reaction that would control HCl's acidity.
question
NMR of acetylphenetidin
answer
N - 8ppm CH3 (acetyl group) - 2ppm H(2) (closer to N)- 7.4 ppm H(2) (closer to O)- 6.8-7ppm CH2 (closest to O)-4 ppm CH3 (closet to O) - 1.4 ppm
question
Hexane vs water
answer
immiscible (Hexane top)
question
Methylene chloride vs water
answer
immiscible (Water top)
question
Ethanol vs. water
answer
miscible
question
ether and water
answer
immiscible (ether top)
question
Why is phenol much more acidic than cyclohexanol
answer
There more stable or the weaker the conjugate base, the more acidic the compound is. When losing a proton, phenol's conjugate base has resonance stability from its double bond.
question
Could you separate 2,4-dinitrophenol (pH 3.96) from benzoic acid using extraction procedure IN THIS EXPERIMENT?
answer
no since both are very close in acidity; cannot use reagents in this experiment to neutralize one and keep one (stronger acid) as a weak acid; both would be neutralized
question
What is extraction? What types are there?
answer
Extraction is a technique that chemists use to remove selected components from a mixture. The different types are solid-liquid extraction and liquid-liquid extraction.
question
Why is carbon dioxide used as a solvent for solid-liquid extractions?
answer
It offers a greener alternative to other solvents, it is readily available, nonflammable, nontoxic, and safe for the environment. Ease of removal of solvent at the end of procedure, and it is relatively quick.
question
What criteria must be met in order for a liquid-liquid extraction to be successful?
answer
The two solvents that are chosen for the extraction must be immiscible. In addition, the compound to be extracted must have different affinities for the two solvents.
question
Treating NaOH vs NaHCO to the carboxylic-phenol mixture
answer
NaOH is so strong that it would neutralized both strong acid such as carboxylic acid and weaker ones like phenol. On the other had NaHCO3 is weak enough that it can only react with strong carboxylic acid and remains unreacted with phenol
question
Carboxylate ions + HCl solution
answer
this protonates carboxylate ions back into carboxylic acid compounds that forms solids when put in ice bath
question
If carboxylic compounds remain aqueous
answer
use ETHER for back extraction
question
Phenol and Ether + BRINE
answer
wash the organic layer - removing remaining water in solution
question
Anhydrous Magnesium Sulfate
answer
The salt absorbs the water that is dissolved in the organic solvent.
question
What is present in the aqueous layer you drained? How do you neutralize it? How do you isolate it?
answer
The carboxylate ion is present. In order to regenerate the carboxylic acid it must be added to HCl in an ice bath to induce crystallization. To isolate the crystals, vacuum filtration is performed.
question
What is present in the organic layer? What steps do you need to take to isolate the desired product?
answer
The phenol is present. There may be some water present in the solution so it must be dried with brine and anhydrous magnesium sulfate until it no longer clumps together. The drying agent is then separated from the organic solution through gravity filtration. Once this is done, the ether must be evaporated under reduced pressure so that the pure phenol solid is left in the flask.
question
What is the difference between "extracting" and "washing"?
answer
Extraction and washing can share very similar procedure but ultimately have different purposes. Extraction removes desire compounds/solutions from a mixture whereas washing filters out the impurities from the desired solution. Keep extraction and discard washed impurities.
question
Describe the practical reasons behind the direction of the flow of water through condenser:
answer
Since the heated vapor from the distillation flask will travel from high to low, the water flows in the opposite direction in order to effectively cool the vapor which would liquify and flow down into the collection tube
question
Why is it important to soak the clover in water?
answer
Since cloves are dried up, soaking them would allow water to penetrate into the cloves and more eugenol would be isolated.
question
Why is dichloromethane (CH2Cl2) added to the solution in the collection vessel? What process is this called?
answer
To extract the eugenol from the water. This process is liquid-liquid extraction and the lower layer will be the dichloromethane along with the desired essential oil.
question
To dry the CH2Cl2:
answer
brine and anhydrous magnesium sulfate
question
Major functional groups for eugenol
answer
-OH group : 3517.6 (3600-3300)--10ppm -OCH3 group: 2934 (3100-2700)--
question
Advantages and disadvantages of distillation vs. CO2 extraction:
answer
with distillation, cloves are allowed to sit in water for full penetration which would be more advantageous because it would yield higher % of product. Extraction using CO2 reduces the chance of water remnant and impurities. CO2 extraction would produce better quality result; during the heating process of distillation, a lot of quality from the oil is evaporated
question
Is chlorophyll b more or less polar than chlorophyll a?
answer
Chlorophyll b should be more polar than chlorophyll a because the former has a CHO group where the latter only has a CH3 group.
question
Which one is more polar? B-carotene vs. xanthophyll
answer
xanthophyll would be more polar than B-carotene because of the -OH group at the ends of the molecules. B-carotene contains no oxygen and is quite non polar.
question
Ethyl acetate
answer
polar solvent (-CO interaction)
question
Pencil for TLC plates?
answer
the ink in the pen can tamper with the process; the ink would travel up the TLC plate with the solvent
question
Chromatography
answer
techniques for separating, analyzing, and identifying compounds (column, thin layer, gas, high performance liquid)
question
Mobile phase
answer
the eluent, the has or liquid phase in which the sample mixture is placed in
question
Stationary phase
answer
a solid support that contains an adsorbent
question
If a component has a greater affinity for the stationary phase
answer
travels more slowly
question
If a component has a greater affinity for the mobile phase
answer
travels thought the stationary phase more quickly
question
Silica gel
answer
has many sites for hydrogen bonding; polar compounds would interact with the silva and adsorb readily to the stationary phase
question
Rf value
answer
distance from the origin to the center of the spot DIVIDED BY the distance form the origin to the solvent front; Polar compounds interacts more strongly with stationary phase and travel a shorter distance --> the more polar the compound, the smaller the Rf values
question
UV Light for TLC
answer
UV lights activates a fluorescent indicator on the plates
question
Why is acetone used in chlorophyll extraction?
answer
Acetone breaks down chlorophyll's lipid bonds to a plant's thylakoid structure and suspends the pigment in solution.
question
Why do we have to cover the test tube of acetone and spinach mixture with parafilm?
answer
Acetone evaporates extremely quickly when interacting with air and all the solution would evaporate
question
What is the perfect composition of the eluent for the spinach lab?
answer
50:50 hexane/ethyacetate
question
Why is a 50:50 ratio the best for this case?
answer
Ethyl acetate is a polar compound while hexane is non polar; one compound interacts with the polar compounds of spinach while the other with the non polar compounds. The 50:50 ratio was enough to separate the polar and non polar compounds of the spinach, at the same time, the polar compounds also get to move up from the origin due to its interaction with the ethyl acetate. If only hexane was use, the chlorophyll a and b would remains at the origin and would not be separated form one another.
question
Why do we need to take pictures of TLC plates during lab?
answer
because the compounds being separated will oxidize rapidly on exposure to air so it would fade away
question
Which pigment is the least polar which is the most?
answer
B-carotene is the least polar and chlorophyll b is the most polar
question
What is the purpose of salicylamide?
answer
an analgesic and antipyretic drug
question
Considering the directing effects of the substituents on salicylamide and predict the possible structures of the iodination products. Which do you think will be the major product?
answer
-OH is an ELECTRON DONATING GROUP, the substituent would be directed to its para and ortho position. -NH2 is an ELECTRON WITHDRAWING GROUP and would direct the substituent to its meta position. The major projects has iodine at the ortho position to -OH and meta position to -NH2. (compare to the iodine group being para to the -OH)I think this would produce a higher % yield because the iodine group is being paced farther away from both functional groups which reduce the strain.
question
Electrophilic aromatic substitution
answer
common reaction of benzene and its derivatives; two steps: 1) aromatic ring acts as a nucleophile and attack electrophile 2) aromatic ring is regenerated through the loss of proton
question
Charged intermediate species
answer
stabilized by resonance
question
Why is iodine used instead of chlorine and bromine?
answer
EAS with Cl2 and Br2 can occur in the presence of Lewis acid such as AlCl3, BUT iodine is the least reactive of the halogens
question
Green method for EAS:
answer
iodination reactions using sodium iodine as the source of iodine and household bleach as an oxidizer (instead of nitric acid and I2)
question
What does absolute ethanol do to the salicylamide?
answer
Dissolve the solid - use warmth of your hand to speed up dissolution
question
6% sodium hypochlorite solution (household bleach)
answer
is an oxidizing agent that reacts with sodium iodine and turns it from a stable compound to a strong electrophile that would now react with the salicylamide in the electrophilic aromatic substitution
question
sodium thiosulfate
answer
removes any residual iodine from the solution
question
1M hydrochloric acid
answer
acidify the aqueous solution which drives the products to precipitates
question
IR Spectrum of Iodine at the ortho position to -OH
answer
815.3cm-1
question
IR: -CO
answer
1095.3
question
IR: -C=C
answer
1621.6
question
IR: -NH2
answer
3200-3300 (double peaks)
question
IR: -OH
answer
3450.1
question
What is the directing effects of the substituents on salicylamide?
answer
Major product gives the less strained position of Iodine that followings the directing effect of both substituent: meta to NH2 and ortho to OH
question
Interpret NMR:
answer
H between I -NH2: 8.15 ppm (singlet) H closer to I (between I and O): 7.7 ppm (doublet) H closer to O (between I and O): 6.75ppm (doublet)
question
How would the Rf values change if a more polar solvent (like ethyl acetate) were used?
answer
When a more polar solvent is used instead of non polar one like ligroin, it will interact more with the polar molecules and less with the non polar molecules causing a less dramatic separation. Rf values would be higher.
question
Why is it important not to dilute the initial sample before it has been loaded onto the chromatography column?
answer
The more concentrated sample would produce a more significant or finer separation between polar and non polar compounds. Diluting the sample would cause a blurry separation between complex compounds instead of a fine separation
question
Which compound would elute first from the column: unreacted ferrocene, acetylferrocene, or diacetylferrocene? Why?
answer
Non-polar or least polar compound elute first and therefore unreacted ferrocene elute first because it has no polar group. Acetylferrocene elute seconds because it only has 1 polar C=O group compared to diacetylferrocene which would elute last with 2 polar C=O groups.
question
Reaction of acetic an hydride
answer
acetic anhydride reacts with phosphoric acid to form asylum ion which is an electrophile that can be used to add into an aromatic ring
question
Why is ferrocene called the super aromatic molecule?
answer
it is about 10^5 times more reactive than benzene in electrophilic aromatic substitution because it consists of an iron atom sandwiched between two cyclopentadienyl anion
question
3M sodium hydroxide
answer
neutralize the solution
question
TLC of acetylferrocene: eluent
answer
methylene chloride
question
Why can you not introduce water into the chromatography column?
answer
Water is very polar and should not be in the mix of the chromatography column. If water is present, it would interact with the acetylferrocene and diacetylferrocene and the whole solution would travel down together with no separation
question
Why cant you allow the volume of solvent to go below the top of the adsorbent?
answer
because the drop would dry out and channels can form in the packing material which leads to inappropriate, poor separation.
question
What is the goal of pipets full of ligroin after addition of crude sample of acetylferrocene?
answer
To load the sample onto the top of the column
question
How to elute ferrocene?
answer
use ligroin
question
More polar solvent that is used to elute acetylferrocene
answer
70:30 ligroin:ethyl acetate
question
Solvent for diacetyl ferrocene:
answer
pure ethyl acetate
question
Comparing TLC plates: did chromatography serve to purify the sample?
answer
the column chromatography served its purpose of separating and purifying samples. with the crude sample there are ferrocene, acetylferrocene and diacetylferrocene all present in the product. After purifying through the chromatography column, only acetylferrocene was collect.
question
Use knowledge of the mechanism and theory of electrophilic aromatic substitution to explain the formation of the diacetylferrocene isomer:
answer
1,1'-diacetylferrocene would be the isomer present. If 1,2 and 1,3-diacetylferrocene were to be formed, both C2 and C3 would have to be able to accept the acetyl group which means those position has to be nucleophilic. However if looked at the resonance structure of those positions, those carbon has the tendency to be positively charged which means they are electrophilic and would not be able to accept acetyl group. Therefore acetyl group at C1 an C1' is the best option
question
What is the purpose of crushing magnesium turnings?
answer
Helps expose fresh metal surface by removing some magnesium oxide on the exterior.
question
How does iodine help facilitate the reaction of the magnesium turnings?
answer
Cleaning the surface of the magnesium metal.
question
What takes place during a Grignard reaction?
answer
First bromobenzene reacts with magnesium to form phenyl magnesium bromide. Then by adding the electrophile, the PMB would nucleophilically attack the compound.
question
Why must the apparatus be flame dried prior to the beginning the reaction?
answer
Grignard reagents are sensitive to water. If water is introduced into the mix, the benzene will become unreactive because it would take an H from H2O.
question
Why must bromobenzene be mixed with anhydrous diethyl ether during formation of the Grignard reagent?
answer
Grignard reagents are sensitive to water so if diethyl either containing more water is used it will interfere with the formation of the Grignard reagent.
question
Why is the reaction mixture added to hydrosulfuric acid and ice?
answer
- ice prior to hydrosulfuric acid to complete the precipitates before it is dissolved by the acid to. - The double bond with Oxygen (benzophene) reacts with the hydosulfuric acid and it is protonated by an addition of hydrogen creating an alcohol
question
After all of the ether has evaporated, what can we do to purify the organic solid?
answer
Recrystallization using ethanol. The desired compound is soluble in ethanol at boiling point and is insoluble in ethanol when it cools.
question
When the reaction mixture is added to the separatory funnel with diethyl ether what happens? Where is the desired compound?
answer
An aqueous layer forms (bottom) and an organic layer forms (top). The desired compound is dissolved in the organic layer (like dissolves like).
question
Why aldehydes and ketone add only one equivalent of Grignard reagent, but esters added two equivalent
answer
While for aldehydes and ketones, after the first Grignard reaction, there is nothing left to react, for esters, after the first reaction the compound becomes a keno or aldehyde and can drive further Grignard reaction
question
Common bi product o the Grignard Reaction lab is biphenyl which is generated through a coupling reaction of phenyl magnesium bromide with unreacted bromobenzene. Which part of the workup remove this byproduct?
answer
Since the compound is very non polar due to the lack of O group, it can only be remove through a workup step using a non polar substance. By adding the cold ligroin, the biphenyl would be removed which followed the ligroin down the Buchner funnel.
question
OH (IR)
answer
3374
question
Phenyl (IR)
answer
600-800 (ring torsion)
question
C=C (IR)
answer
1500
question
C-H (IR)
answer
3000
question
C-O (IR)
answer
1200
question
presence of benzene rings (IR)
answer
small stretches from 1500-2000
question
why is it important that the glassware and reagent used in a Grignard reaction are completely dry?
answer
Grignard reagent is extremely sensitive and reactive with water. Since it is a strong nucleophile it would react with water first and will not be able to produce the desirable reaction and product
question
What is the reaction what would happen if phenyl magnesium bromide reacts with water
answer
Phenyl magnesium bromide + h2o --> benzene + hydroxyl magnesium bromide
question
Why is isolating neutral p-aminobenzoic acid in step 3 difficult?
answer
PARA is difficult to isolate because it has so many resonance that the compound can have many charges on it at different pH. Isoelectric point is where the compound carries not net charges, containing equal amount of (+) and (-) that neutralize each other. It is where it is easiest to gain precipitates and therefore its is very unstable and sensitive to pH.
question
Reducing the number of steps in synthesis:
answer
increase % yield
question
Ginkgo biloba
answer
most widely used herbal remedies, treating various ailments including asthma, macular degeneration, cardiovascular disease, vertigo, and memory loss and dementia associated with Alzheimer's disease
question
If the p-toluidine in water+HCl is excessively dark,what would you do?
answer
decline with charcoal before proceed
question
What is the reaction of the first step? (Protection)
answer
P-toluidine + acetic anhydride (NaOAc, HCl aq) --> N-acetyl-p-toluidine
question
How do you test for the completion of reaction with magnesium sulfate, n-acetyl-p-toluidine, and potassium permanganate?
answer
via halo test: dip the stirring rod into the mixture then touch the tip to a piece of filter paper --> purple halo = incomplete; light pink/clear halo = complete
question
Oxidation reaction
answer
needs to boil gentle: too little heat will keep the reaction from occurring at a good time, too much heat will cause excessive frothing and possible boo over
question
Why cant you let the Celite dry out?
answer
this will cause cracks in the filter bed and result in insufficient filtration
question
why must the solution of KMnO4 be hot when filtering using the Celite bed?
answer
this would minimize crystallization of product in the filter --> precipitate should form when being acidified
question
For step 3- why do you need to scratch the wall of the flask?
answer
the precipitates needs a nucleation site that can be stimulated by glass particles.
question
mechanism of Step three (Deprotection)
answer
At the isoelectric pt. the desirable precipitate will form, more acidic = salt precipitates (NH3+), more basic = no precipitate 1) add 3M NH4OH solution --> decrease pH to isoelectric pt 2) Adjust pH of the filtrate until it is just basic 3) adjust pH again with glacial acetic acid
question
C=O (IR)
answer
1663
question
NH2 (IR)
answer
double peaks at ~3000+
question
why don't we simply oxidize p-toluidine with KMnO4 to make p-aminobenzoic acid? wouldn't that be faster? what unwanted reactions may occur?
answer
we cant oxidize p-touluidine with KMnO4 because the NH2 must first be protected or else it would be oxidized also. the side product would have been a R-NOO-
question
Why don't we do the esterification step prior to the deprotection step?
answer
if esterification occur prior to deprotection then both functional would would be deprotected and we would have to report esterification.