CHEM 233
You create a mixture of water and acetic acid that possesses a mole fraction of acetic acid of 0.2 to perform the recrystallization, but are worried that you may cause the mixture to freeze in the process. At what approximate temperature does this liquid mixture begin to freeze? Look carefully at the X-axis!
-16 °C
Select all of the following molecules that contain stereocenters.
-alkene with H wedges and CH3 dash -both 1,2-dimethylcyclohexane
Select all of the following molecules that are chiral
-alkene with H wedges and CH3 dash -cyclohexane with wedge and dash methyl
Select all of the following compounds that would be unable to pi-stack with the HBTM catalyst. (2 pts)
-all alkanes
Select all spectroscopic information that would be consistent with the below structure. Assume any labile protons do not show up in the 1H NMR spectrum.
-signals in the 13C NMR spectrum around 40 ppm -signals in the 13C NMR spectrum around 120 ppm -signals in the 1H NMR spectrum around 1.5 ppm -signals in the 1H NMR spectrum around 3.5 ppm -signals in the 1H NMR spectrum around 6.0 ppm -stretches in the IR spectrum immediately above 3000 cm-1 -stretches in the IR spectrum immediately below 3000 cm-1 -stretch in the IR spectrum at approximately 1650 cm-1
Select all spectroscopic information that would be consistent with the below structure. Assume any labile protons do not show up in the 1H NMR spectrum.
-signals in the 1H NMR spectrum around 1.5 ppm -signals in the 13C NMR spectrum around 40 ppm -signals in the 13C NMR spectrum around 200 ppm -a broad stretch in the IR spectrum at approximately 3500 cm-1 -stretches in the IR spectrum immediately below 3000 cm-1 -stretch in the IR spectrum at approximately 1700 cm-1
If a liquid mixture containing 80 mole percent B were distilled using an efficient fractional distillation column, what would be the composition of the distillate collected? (2 pts)
0 mole percent A 100 mole percent A
The partition coefficient of a neutral nonpolar organic Compound X is 17. How much of a 25 gram sample of Compound X will be left behind in the 200 mL water layer following three extractions with 75 mL aliquots of an organic solvent? (2 pt)
0.062
You are attempting to brominate Compound A, which contains 2 alkenes, using molecular bromine to make Product B according to the following chemical equation. A + 2Br2 -> B Compound A has a molecular weight of 92.0 g/mol and molecular bromine has a molecular weight of 159.8 g/mol. What is your theoretical yield in moles of B if you use 10.0 g of A and 24.0 g of Br2? Round to the thousandths place. (2 pts)
0.075
You wish to try and perform a recrystallization using a mixture of water and acetic acid as the solvent. The two-component phase diagram for this mixture is shown below. If you wanted a mixture that began freezing at approximately 5 °C, what mole fraction of water would you use?
0.20
A mixture of 0.9 mole fraction B is distilled by fractional distillation using a Vigreux column having two theoretical plates. (Keep in mind that the initial boiling of mixture in the distillation flask before the column adds an additional"plate".) According to the phase diagram below, what is the composition of the distillate (liquid from condensed vapor) you collect? Select the answer closest to the expected value. (2 pts)
0.30 mole fraction B
You possess a solid mixture that is 0.7 mole fraction of water. What is the composition of the liquid that forms upon melting it?
0.7 mole fraction water
You obtain 1.8 g of an impure solid. You know that the sample contains 1.6 g of your desired compound. What is the maximum mass of your desired compound that you could recover from a recrystallization using 100 mL of Solvent A according to the below solubility table?
1.1
If a liquid mixture containing 80 mole percent B were distilled using an efficient fractional distillation column, what would be the composition of the liquid remaining in the distillation pot? (2 pts)
100 mole percent B 0 mole percent B
Trans-cinnamic acid has a molecular weight of 148 g/mol. What mass would you expect to see in an electrospray ionization mass spectrum if a sodium ion attaches itself to the molecule?
171
How many degrees of unsaturation are present in a molecule with the molecular formula C5H8BrNO
2
What integration value would you expect in a 1H NMR spectrum for the indicated proton(s)?
2
A carbon carbon triple bond would contribute how many degrees of unsaturation to a molecule?
2 (2(2)+2-(2))/2=
Which solvent would be the BEST for recrystallization of this product if it is contaminated with a soluble impurity?
2-butane
Which of the listed values is the best chemical shift estimate for the indicated proton(s) in a 1H NMR spectrum?
2.5
How many reaction schemes involving the alkene should you have in the "Reactions" section of your Pre-lab notebook? (1 pt)
3
The partition coefficient of a neutral nonpolar organic Compound X is 22. What volume of organic solvent (in mL) is required to extract 99% of a 15 gram sample of Compound X from 75 mL of water in a SINGLE extraction? (1 pt) Hint: Based on the information in the question, what mass of Compound X should be in the organic layer?
338 ml of organic solvent
How many proton signals are observed in the 1H NMR spectrum for the below molecule?
4
How many signals would you see in the alkene/aromatic region of a 13C NMR spectrum of the following molecule?
4
Select the 1H NMR spectra that corresponds to the below compound by using the 1H signal splitting in the aromatic region. Assume labile protons to will not appear in the spectrum.
4 peaks: 1n, 1n, 1n, 1n
Which of the listed values is the best chemical shift estimate for the indicated proton(s) in a 1H NMR spectrum? (1 pts)
4.0
How many 20 mL extractions of organic solvent are needed to extract at least 99.5% of 50.0 g Compound A from 100 mL of water if K=10? Remember, extractions can only occur in whole numbers! (2 pt) Hint: Based on the information in the question, what mass of Compound X should be in the aqueous layer? Also, you did review your basic logarithmic rules, yes?
5
If a liquid mixture containing 60 Mole Percent B was distilled using an efficient fractional distillation column, according to the below phase diagram, what temperature would be read on the thermometer at the top of the fractionating column? Think back to what you observed in the Elimination experiment! (1 pts) An "efficient" fractional distillation column is efficient when it has at least the required number of theoretical plates to distill a mixture to a desired purity. Assume that the fractional distillation column can do as many distillations as you could need or has an infinite number of theoretical plates.
50 degrees C 74 degrees C
How many signals in the alkene/aromatic region would be present in the 13C NMR spectrum of the below compound? (1 pts)
6
How many signals would you see in the alkene/aromatic region of a 13C NMR spectrum of the following molecule?
6
What integration value would you expect for the signal that includes the designated set of equivalent protons in the 1H NMR spectrum for the below compound? (2 pts)
6
Select the 1H NMR spectra that corresponds to the below compound by using the 1H signal splitting in the aromatic region. Assume labile protons will not appear in the spectrum. (2 pts)
6 peaks: 2n, 1n, 1n, on, 2n, 0n
Calculate the percent recovery of a recrystallization of a 1.3 g sample of solid to the tenths place if you recover 0.88 g after the recrystallization. Round to the nearest tenths. (2 pts)
67.7
If a liquid mixture containing 60 Mole Percent B was distilled using a simple distillation, according to the below phase diagram, what temperature would the liquid mixture boil at? (2 pts)
68 degrees C
Given the partition coefficient between ethyl acetate and water for Compound A is 7.0, what mass of A, to the tenths place, would be extracted from a 50 mL solution of water containing 9.0 g of A using 25 mL ethyl acetate? (2 pt)
7.0
The alkyl halide shown below undergoes an elimination reaction. Select all possible elimation products from the given structures provided below. (1 pts)
A, D
You are performing an elimination reaction using an alkyl halide and a non-bulky base. The three products shown below are produced in the reaction. What product would be created in the smallest amount? (2 pts)
A.
Select ALL that would be true for the proton NMR spectrum of the compound shown below.
A. one signal total in the 1H NMR spectrum
Select ALL answers which are viable methods of distinguishing these two compounds apart by using 1H NMR spectroscopy
A. only one compound has 3 1H NMR signals C. only one compound has 2 1H NMR signals E. only one compound has 1H NMR signals upfield of 2.0 ppm
Select ALL that would be true for the proton NMR spectrum of the compound shown below.
A. three signals total in the 1H NMR spectrum C. only one signal downfield of 3.0 ppm
Match each of the following structures with the 13C NMR spectrum that corresponds to it. Pay attention to the numbers on the X-axis! (4 pts)
A: symmetrical OH in middle B: Symmetrical O in middle C: C attached to OH and C D: C=O bond
Let's push a little further. We did not discuss this in the webcast, but imagine you have a multi-step reaction, whose reaction coordinate diagram is shown below. Using what you know about transition state energies, which step is the rate-determining step? (1 pt)
B to C, highest TS
You are separating anthracene from benzoic acid via an extraction between methylene chloride and a basic aqueous solution in a separatory funnel. How would you recover the benzoic acid? (2 pt)
Collect the top layer and add HCl to precitipate the compound.
You are separating anthracene from benzoic acid via an extraction between ethyl acetate and a basic aqueous solution in a separatory funnel. How would you recover the anthracene? (2 pt)
Collect the top layer, dry with Na 2SO 4, and evaporate the solvent.
The nitrogen in the compound below has what kind of effect on nearby hydrogens?
Dishielding
You are given a mixture of two acids, Acid A and Acid B. Acid A is a carboyxlic acid, and Acid B is a phenol. Which of the following aqueous solutions would you use to separate the two acids via a liquid/liquid extraction? (1 pt)
Na2CO3
You are given a 50:50 mixture of Compound A and Compound B. Both compounds have a K value of 1.5. Can you separate the compounds via an extraction? (1 pt)
No, because Compound A and Compound B have the same solubility in both layers.
The final product of the Elimination experiment was a liquid. Let us say that you wanted to purify that product via a recrystallization of the type you have performed in this course. Would that be feasible? (1 pts)
No, because a recrystallization requires that a compound forms solid crystals and the product is a liquid
Would it be possible to differentiate the two below structures using IR spectroscopy?
No, because both structures would give the same stretches in an IR spectrum.
You attempt to perform the bromination of trans-cinnamic acid shown below. You decide to take an IR spectrum of your product and see a strong, broad signal at 3500 cm-1. Is this signal definitive proof of a successful reaction? (2 pts)
No, because the IR spectra for both the starting material and product would have that stretch
Assuming all solvents are suitable to recrystallize the desired product, which solvent is best for removing the impurity through a hot filtration? (1 pt)
Petroleum Ether
You consider starting material A. You know that A can undergo two reactions as shown in the below reaction coordinate diagram with one reaction pathway labeled in red and one reaction pathway labeled in blue. The red path leads to Product B, while the blue path leads to Product C. Assuming both reaction pathways occur simultaneously in competition with each other, what is the major product, and why? (2 pts)
Product B, because the transition state leading to Product B is lower in energy than the transition state leading to Product C.
n an effort to optimize the bromination reaction, you repeat the reaction three times with each attempt using a slightly different set of reaction conditions. The melting points of the crude products of each reaction are shown below. Which reaction produced the most pure crude product ? (2 pts) Reaction 1: 110 - 114 °C Reaction 2: 108 - 114 °C Reaction 3: 113 - 116 °C
Reaction 3
You replicate the CEC analysis of a secondary alcohol you performed in the lab, except this time using a reverse phase TLC plate producing the plate below. Based on this TLC plate, what can you conclude about the rates of the reactions? (2 pts)
Reaction B was faster
The structure for pseudoephedrine is shown below. Assign the absolute configuration of stereocenter 1
S
You need to extract a nonpolar organic compound from 150 mL of aqueous solution. Which of the following changes will allow you to increase the recovery of your compound? Select all that apply.
Switch to an organic solvent in which your compound has a higher partition coefficient. Perform two extractions using two 75 mL portions of organic solvent instead of one big extraction using 150 mL of organic solvent.
You perform a CEC analysis on a secondary alcohol according to the same procedure you used in the lab using a normal phase TLC plate producing the TLC plate you see below. Based on this TLC plate and the mnemonic in your notes, what can you conclude about the stereochemistry of the alcohol? (1 pts)
The alcohol is a racemic mixture of enantiomers
You replicate the CEC analysis of a secondary alcohol you performed in the lab using a reverse phase TLC plate producing the TLC plate below. Based on this TLC plate and the mnemonic in your notes, what can you conclude about the stereochemistry of the alcohol? (1 pts)
The alcohol was the S-enantiomer
After performing a recrystallization, you calculate a percent recovery of 110%. Select all possible reasons for this result. (1 pt)
The crystals were not dried properly after the recrystallization
When placed inside of a magnetic field, the magnetic field that electrons generate aligns in the opposite direction of the applied magnetic field. This has what effect on the nucleus the electrons are around?
The electrons shield the nucleus from the magnetic field
You attempt to purify a compound in a solvent that you know the compound is completely soluble in at high temperatures in the volume of solvent you are using. You observe the dissolution of most, but not all, of the sample. You cool the liquid slowly to induce slow recrystallization, and then properly filter and collect the recrystallized product. However, you discover the desired product is still impure. Provide a rationaliziation of this result.
The impurity is insoluble in cold solvent and hot solvent, thus it was not removed via the final filtration.
After brominating an alkene, you isolate a solid that is orange in color. The product is known to be a white solid when pure. What do you expect the result of performing a melting point analysis on the product to be? (1 pts)
The melting point will be lower than the melting point of the pure compound
You cool a liquid mixture of acetic acid and water that has a mole fraction of water of 0.9. As you begin to freeze the acetic acid/water mixture, what happens to the mole fraction of water in the liquid phase?
The mole fraction of water decreases because, at this starting mole fraction, solid water forms before solid acetic acid.
The below compound has a retention factor of 0.35 using a silica gel TLC plate and a particular solvent system. What would happen if you repeated the TLC analysis, but used a less polar solvent system? (2 pts)
The retention factor would increase
A compound possessing a carboxylic acid produces a yellow solution when dissolved in diethyl ether. This yellow solution is transferred to a separatory funnel and an aqueous solution of sodium chloride is added as well. After mixing the two solutions and allowing them to settle, two layers form. Which of the following statements is true about the resulting layers? (1 pt)
The top layer will be diethyl ether, and the bottom layer will be yellow.
When placed inside of a magnetic field, NMR active nuclei act in what way?
They align mostly in the same direction as the applied magnetic field
What is the purpose of adding the aqueous sodium bicarbonate to your reaction mixture?
To quench any remaining trace amounts of acid
You know the Bayer test is used to identify the presence of alkenes. You attempt to perform an elimination reaction and test what you hope is the product using the Bayer test. Adding KMnO4 to a solution of the starting material requires 2 drops to remain purple, with no precipitate observed. A solution of your potential product requires 15 drops to remain purple, with no precitipate observed. Did you successfully perform an elimination reaction? (1 pts)
Yes, because the solution of potential product took more drops of KMnO 4 to remain purple.
Your used glass pipettes are disposed in what waste container? (1 pt)
Your used glass pipettes are disposed in what waste container? (1 pt)
You are given a solution of benzoic acid, anthracene, and ethyl 4-aminobenzoate in methylene chloride. If you perform an extraction with acidic aqueous solution, the majority of what compounds will remain in the organic layer? Select all that apply.
anthracene benzoic acid
You are given a solution of benzoic acid, anthracene, and ethyl 4-aminobenzoate in methylene chloride. If you perform an extraction with basic aqueous solution, the majority of what compounds will remain in the organic layer? (1 pt)
anthracene ethyl 4-aminobenzoate
You perform a CEC analysis on a secondary alcohol using a normal phase TLC plate as seen below. Based on this TLC plate, what can you conclude about the rates of the reactions? (1 pts)
both rxs proceeded at the same rate
Which of the following nucleophiles would perform well as a nucleophile, but poorly as a base? (1 pts)
chloride ion
A binary liquid mixture where the two components have a difference in boiling points of 20 °C can be effectively separated using a simple distillation.
false
Percent yield is the same as percent recovery. (1 pt)
false
You want to assess the purity of the product of this bromination experiment via 1H NMR spectroscopy. You would be able to see leftover Br2 in a 1H NMR spectrum. (1 pts)
false
You will weigh and then add pure molecular bromine to your reaction vessel when performing the experiment.
false
The mechanism of the reaction you are performing is a concerted mechanism.
false, it's sn1
You recrystallize the product of a bromination reaction by dissolving the entire product in hot solvent, cooling to room temperature, and then collecting the solid that crystallized. However, you are disappointed with your yield. Select all of the following actions that would increase the amount of solid recovered from the recrystallization. (2 pts)
lower the amount of solvent used in the recrystallization while keeping all impurities dissolved cool the recrystallization solution in an ice bath before collecting the crystals while keeping all impurities dissolved
In the experiment, you added water to the reaction vessel after the reaction was complete, but we did not discuss why. Based on what happened after adding the water, which of the following is the reason for the addition of water? (1 pts)
lower the solubility of the product in solution so it precipitated out
What technique will you use to identify your product? (1 pt)
melting point
A separatory funnel contains methylene chloride and an aqueous solution of some kind. What comprises the bottom layer? (1 pt)
methylene chloride
The below phase diagram corresponds to what type of mixture? (1 pts)
non-ideal solution with a negative deviation
A particular compound has a K value of 1.4 when using an organic solvent and an aqueous solvent. Which phase does the compound prefer? (1 pt)
organic solvent
In this experiment, you are... (1 pt)
producing 2-chloro-2-methylbutane from 2-methyl-2-butanol via a carbocation intermediate.
What technique will you use to purify your product? (1 pt)
recrystallization
The below 1H NMR spectrum corresponds to which structure?
single methyl coming off C=O (pointing up), no double bonds
Consider a situation where you were able to develop TLC conditions to analyze and visualize a mixture of the starting alcohol and the alkene product in the Elimination experiment using a reverse phase TLC plate. Which compound would have the higher retention factor? (1 pts)
the alcohol
The rate law for the esterification reaction used in the CEC experiment is shown below. What would you expect to happen if the concentration of base was changed? (1 pts) rate = k [alcohol] [catalyst] [anhydride
the reaction rate will stay the same
What multiplicity would you expect in a 1H NMR spectrum for the indicated proton(s)?
triplet
The below compound would have strong interactions with the stationary phase of a Normal Phase TLC plate. (1 pts
true
Two of the following proton signals are coupling with each other in a 1H NMR spectrum that was made using a 400 MHz spectrometer. Identify them by selecting both of them.
two are 4.5 Hz
What will the location of the protons on carbon a be relative to the protons on carbon b in a 1H NMR spectrum of following compound?
upfield
You attempt to perform a bromination of trans-cinnamic acid in the hopes of producing the product shown below. You decide to take a 1H NMR spectrum of what you hope is the product. Signals with which of the following approximate chemical shifts would indicate that the product did not form? (2 pts)
~ 5.5 ppm
