CHEM 3105 Lab Final A1 OG 2.0
Determine the mass in grams of a compound with a molecular weight of 105.38 g/mol that you would need to weigh out in order to get 2.5 mmol of the compound.
0.26
Predict the more stable alkene of each of the following pairs: 2-Methyl-2-hexene or 2, 3-dimethyl-2-pentene
2, 3-dimethyl-2-pentene
The reaction scheme below is also shown on p 173 of your lab manual. Which alkene is the principal product?
2,3-Dimethyl-2-butene
How many points are deducted per business day for late lab reports?
3 points
Determine the volume in milliliters (mL) that would be measured to get 2.5 mmol of a compound with a density of 0.88 g/mL and a molecular weight of 121.9 g/mol.
3.46
GC separations and distillations (which are separations as well) are similar in that the increase of theoretical plates increases resolution (separation). A theoretical plate is _______________________.
An evaporation-condensation cycle
The gas chromatography instrument used in the organic chemistry instructional laboratories injects a very small sample (0.05 - 0.10 μL) of a dilute solution into the instrument. What type of separation is this?
Analytical GC Separation
Wall coated (WCOT) columns are not packed; the liquid phase is applied directly on the walls of the columns. This is the type of column used in the GC for our organic chemistry labs. This type of column can only be used in what type of separation?
Analytical GC Separation
What conformation is preferred for E2 elimination to occur?
Anti-periplanar
Which of the arrows shows where the clamp should be affixed to the distilling flask on the simple distillation apparatus depicted?
Arrow A
Which of the arrows shows where the water inlet is on the simple distillation apparatus depicted?
Arrow B
After notifying your TA, how long should you wash the affected area if you spill NaOH on your skin? Note - you should always wear gloves when handling caustic/potentially hazardous chemicals
At least 15 minutes
Bromophenol blue changes from ______________ to ______________ when the HCl produced in the reaction below neutralizes the known amount of NaOH that was added to the reaction mixture
Blue to yellow
Why is a boiling stone typically added anytime liquids are going to be heated to boiling?
Boiling chips are added to liquids that are being boiling to prevent it from superheating and cause a more controlled boil.
What is the "rate of reaction"? A. The rate at which a catalyst is turned over as a function of time B. The rate at which the solvent is solvated as a function of time C. The rate at which a reactant is consumed as a function of time D. The rate at which a product is formed as a function of time
Both C and D
Which type of intermediate is formed in E1 reactions?
Carbocation
After a sample is analyzed, the GC software will produce a plot/graph that you can analyze. You can see the sample component peaks as well as a peak for the solvent used to dilute your sample. This plot/graph is called a _______________________.
Chromatogram
What are some clues that tell you that you have made a different isomer product in this reaction?
Color changes from bright yellow to colorless af.
Determine which compound is the limiting reagent in the following generic reaction: Compound A + Compound B --> Compound C if you start with 0.15 g of Compound A and 0.30 g of Compound B. MW of Compound A - 100 g/mol MW of Compound B - 300 g/mol
Compound B
Which of the following compounds contains the more stable carbocation?
Compound B
Which of the following compounds is the most stable alkene?
Compound B
The following figure shows an example of a TLC plate spotted with 3 standard samples (Lanes 1-3) and one unknown sample (Lane 4). What compound(s) are present in the unknown sample?
Compound B and C
What would happen if you used HCl in the extraction?
If we had used HCl in the extraction, we wouldn't get two different layers and oxidation would not be possible
An extraction solvent should be __________________ the solution solvent.
Immiscible with
Why does TLC not scale-up very well when using it to separate compounds?
TLC can only be used with very small quantitates of material, usually 2-20 micrograms
Why does the endothermic photoisomerization of trans-1,2-Dibenzoylethylene to the cis isomer only proceed in the forward direction?
The reaction conditions are under visible radiation and the cis isomer product only absorbs ultraviolet radiation
Based on the data presented in the Data set A chromatographic separation, can you explain why there is such a steep decline in column efficiency with temperature change?
The resolution of GC peaks may be very sensitive to changes in retention time, which is caused by unstable temperatures. So then it can be inferred that resolution of GC peaks are dependent on stable temperatures. These temperature fluctuations can cause significant degradation in column plate values since the number of theoretical plates is related to resolution values. This indicates a decline in column efficiency when there is temperature change, because of the significant degradation in column plate values are caused by temperature change. The increase in temperature during the run showed a sharp decrease in the number of theoretical plates in the column. Therefore, equilibrium distribution of the sample between the solid and mobile phase was not sufficiently established to allow for good resolution of the mixture.
Why is the organic acid/hydrocarbon mixture dissolved in diethyl ether reacted with aqueous sodium hydroxide?
The sodium hydroxide deprotonates the organic acid and its ionic conjugate base is more soluble in water thus removing it from the diethyl ether solution
Why is the SN1 reaction referred to as solvolysis?
The solvent is one of the reactants
What feature of TLC makes it useful for monitoring reactions?
The speed of the technique
The solubility of a sample in a carrier gas depends mostly on what?
The vapor pressure of the substance(s) in the sample
Students and TAs must wear safety goggles in the laboratory. Even if you are finished with your experiment, if there are chemicals in use and/or glassware is out, goggles must be worn by everyone in the lab.
True
Concentration of the TLC sample is very important. For liquid compounds (like benzyl alcohol), just __________________ the compound then a few drops of solvent. For solid compounds (like benzoic acid), just __________________ the compound and dissolve it in the solvent
Use 1 drop of; cover the tip of your spatula with
When the provitamin, 7-dehydrochloesterol, is exposed to sunlight, it photoisomerizes to what compound?
Vitamin D3
Why is brine (saturated aqueous NaCl solution) added to the diethyl ether solution after extracting the organic acid from the mixture?
Water is partially soluble in diethyl ether because of intermolecular forces involved between the two molecules. When the mixture is washed with brine, the water molecules are much more attracted to the polar ions of the brine solution than the relatively non-polar diethyl molecules.
Suggest a way to separate a mixture of these two compounds.
We can use ammonia as the base and using a strong acid will result in a salt. We could use hydrochloric acid as the strong acid, we can also wash this with ether to get the salt. Then we could separate it and get NaOH as the bottom extract
What piece of lab equipment should you use to collect your crystals?
hirsch funnel
In liquid-liquid extractions, the extraction solvent should be __________________ the solution solvent.
immiscible with
Why are steel turnings added to the condensor column used in half of the distillation setups for the class?
increases surface area creating more theoretical plates and a purer distillate
Biphenyl has a known melting point of 68-70 °C. You measure the melting point of Unknown X to be 68-70 °C. The Biphenyl-Unknown X mixture melts at 60-66 °C. Unknown X _________________ Biphenyl.
is not
Which of the following best describes the hazards of acute methanol exposure through skin contact?
small amounts are corrosive
The process of evaporation and condensation is achieved by the theoretical construct known as a __________________.
theoretical plate
How can you tell when an aqueous solution is basic?
when the pH is greater than 7 or when the LITmus paper turns blue
The natural product being isolated in this experiment is a white crystalline ______________________.
alkaloid
What are the cis and trans isomers of an alkene system called?
diastereomers
Which of the following is not one of the essential steps of crystallization?
dissolve the material in a maximum of warm solvent
Which solvent is the best choice to dissolve your hydrocarbon for recrystallization?
ethanol
Documentation for an absence can be submitted 8 days after the missed lab.
false
Which of the following is pourous thus allowing powders to stick more easily and therefor is not a good choice for use when weighing solids?
filter paper
Simple distillation is best used to separate two liquids that have boiling points that differ by ____________ 30-40 °C.
more than
In today's reaction, TEMPO is used as a stoichiometric oxidant
False
The injection temperature causes vaporization. True or false: 400 °C is a good injection temperature for a sample that decomposes at 350 °C.
False
The trans isomer of 1,2-dibenzoylethylene is less stable than the cis isomer.
False
You should always heat a distillation flask to dryness.
False
A _______________________ is very sensitive; it can detect material of amounts less than a microgram.
Flame-ionization detector
In today's reaction, you will be distilling your product away from the reaction mixture. You must ensure that the distilling vapor does not go above 102 °C. The boiling point of cyclohexanol (the starting material) is:
Greater than 102 °C
Percent Yield
((actual yield)/(theoretical yield))*100%
Predict the predominant alkene product that would form when 2-bromo-2-methylpentane is treated with sodium methoxide in methanol. If the base were changed to KOC(CH2CH3)3 would the same alkene predominate? If not, why? What would be the structure of this alternate product, if it formed?
- If treated with sodium methoxide in methanol the predominant product would be the more stable product. That product being 2-methyl-2-pentene because as a result it's the more substituted alkene. The use of of KOC(CH2CH3)3 would form a different product because it is bulky compared to the other base. That product would be methyl-1-pentene.
How much of the unknown sample will you use in this experiment?
.50g
What is the number of moles in 5.00 mL of a 0.10 M solution?
0.00050 mol
The photoisomerization of cis-Rhodopsin in the retina is extremely sensitive, how many photons are required for the photoisomerization reaction?
1
The equation to calculate relative retention time is given below. Calculate the relative retention time (r) of the analyte with respect to air/solvent(s) if the air or solvent peak(s) (ts) appear at 15 s retention time, and the analyte peak (ta) appears at 4.50 min.
18
One mole of t-butyl chloride will produce one mole of HCl. One mole of HCl can neutralize one mole of NaOH. Fill in the blank below with the amount (mL) of 0.10 M NaOH needed to be added to the reaction mixture to observe 20% completion when using 5.00 mL of of 0.10 M t-BuCl. (Remember significant digits) [x1] mL of 0.10 M NaOH needs to be added to the reaction mixture to observe 20% completion when using 5.00 mL of 0.10 M t-BuCl Hint: 20% x the amount of 0.10 M t-BuCl
1.0
The equation to calculate the number of theoretical plates in a column is given in your prior reading section and below. Calculate the number of theoretical plates (n) for an analyte in a column that appears at 3.5 minutes (retention time) and has a baseline width of 20 s.
1764 theoretical plates
You start with 1.00 g of crude product and isolate 0.55 g of pure product after recrystallization. What is the percent recovery?
55%
Determine the percent yield for the following generic reaction using the information given below: Compound A → Product P You start with 11.0 mL of Compound A and obtain 11.0 mL of Product P. MW of Compound A: 220 g/mol; Density of Compound A: 2.20 g/mL MW of Product P: 110 g/mol; Density of Product P: 0.75 g/mL [x1] % yield
68
You will start this experiment with 25 mg of the trans isomer. What is the percent yield if you obtain 20 mg of the cis isomer? [x1] % yield HINT: Do isomers have the same molecular weight?
80
Match the letter with the correct column component (one option will be used twice).
A - Elution Solvent B - Sand C - Stationary Phase (SiO2 or Al2O3) D - Sand E - Cotton (or glass wool) plug
The role of the phase transfer catalyst, (C4H9)4N+,Br-, is depicted below where X = halogen (Br or I, in this case). Match the indicated structures/compounds with their descriptions
A - Sodium phenoxide ion pair (generated from p-cresol reacting with NaOH) B - Phenoxide/phase transfer catalyst ion pair C - Ether product
Should you expect to see any difference in the measured boiling point of a pure liquid when determined in Houston (elevation 30 ft) compared to Lubbock (elevation 3221 ft)? If the boiling points differ between these two locations, how would you expect them to differ relative to each other and why?
A difference in the measured boiling point of a pure liquid when determined should be expected because a substance boils when it is heated and the vapor pressure matches the local pressure which is affected by altitude. Since Lubbock, is at a higher altitude, the pressure increases and so the liquid would boil faster in Lubbock.
What are the two most common adsorbents used in column chromatography?
Alumina Silica Gel
A compound's IR spectrum shows a very intense peak between 3500-3200 cm-1 (see the red peak in the IR spectrum below). What functional group would you expect is present in the compound?
Alcohol
Which of the following alcohols will undergo acid-catalyzed elimination the fastest?
Alcohol C
The Zaitsev rule says that a reaction will proceed in the direction that yields the most highly substituted alkene. Which of the following compounds is an example of a Zaitsev product?
Compound C
When tert-pentyl bromide is treated with 80% ethanol, the following amounts of alkene products are detected on analysis: Offer an explanation of why compound I is formed in far greater amount than the terminal alkene.
Compound I is in formed in greater amount because of its stereochemistry that being it is in a more stable conformation that compound II.
You have performed TLC analyses in previous lab experiments and will perform column chromatography in this experiment. In column chromatography, the mobile phase __________________ the column; in TLC, the mobile phase __________________ the plate.
Descends, ascends
Which is the only solvent that should ever come in contact with an IR salt plate in the organic chemistry teaching labs?
Dichloromethane
This experiment requires use of bromine, sulfuric acid, and phosphoric acid. Your TA will dispense the concentrated acids, but precautions still need to be taken when working in the presence of these chemicals. Select all precautionary measures that must be taken when using these chemicals. (Select all that apply)
Don't use more of the reagent than recommended Don't add water to hot acid (make sure to properly separate an aqueous layer from an organic layer) Notify your TA immediately in the case of a spill or incident Wear goggles Take care not to spill any chemicals Ask the TA if you have any questions Wear gloves
Which of the following is a/are major difference(s) between E1 and E2 reactions in terms of the reaction mechanism? (Select all that apply)
E1 reactions frequently undergo rearrangements E1 reactions form a carbocation intermediate and are not concerted E2 reactions are concerted reactions with no intermediate
Reactions like those described in Experiment 11 are called elimination reactions because a small molecule is _______________________ from the organic molecule. When that small molecule is water, the reaction can also be called _______________________.
Eliminated, dehydration
Ether (MW=46) evaporates much faster than water (MW=18), yet ether's molecular weight is about 2.5 times than that of water. Explain.
Ether evaporates much faster than water because it has a lower boiling point. This is due to the fact that the intermolecular forces in ether are not as strong as the hydrogen bonds in water. The stronger the intermolecular forces, the more energy that is required to break bonds.
You will run a dilute sample of cyclohexanol and heptanal in dichloromethane through GC. The following IR spectrum is for which compound?
Heptanal
In the presence of water, aldehydes exist in equilibrium with their ________________________.
Hydroxates
What two effects can impurities have on a melting point range? Did you see these consequences in your results?
Impurities can effect melting point range by causing a melting point depression, which means the melting point observed will be lower. They can also effect the melting point range if you mix the unknown with something that is inaccurate because you got an inaccurate reading due to the impurity. This then makes it impossible to identify an unknown based on the melting point alone. The melting point of the hydrocarbon and the carboxylic acid were almost identical to the melting points of the their correlating base and acid - biphenyl and benzoic acid. This leads to the conclusion that those samples had few, if any, impurities. The initial melting point of the unknown that was found may have contained impurities due to its large range of temperatures for it melting point. Having been stored on an open filter paper in the equipment drawer, left it susceptible to many impurities.
Compare and contrast the OH peaks that are present in the benzyl alcohol and benzoic acid IR spectra; compare and contrast the C=O peak that are present in the benzaldehyde and benzoic acid IR spectra. How does the spectrum you obtained in lab compare to the standard spectra for your assigned compound?
In benzyl alcohol and benzoic acid, the OH/alcohol peak is approximately the same frequency in both IR spectra, but the benzyl alcohol covers a larger wavelength range (3200-3400 cm-1). The OH group appears at a transmittance percent of 55% in benzoic acid, whereas in benzyl alcohol it is present at 15-20%. Both compounds show an OH stretch, but it is a lot larger in benzyl alcohol. C=O/carbonyl peaks for benzaldehyde and benzoic acid are very similar and occur at approximately 1700 cm-1; in benzoic acid, it is at 26% transmittance, and in benzaldehyde, it is close but not quite at 0%.
Experiment 4 Procedure
Isolation and Characterization of a Natural product: Extraction of Caffeine from Tea Purpose- to extract the alkaloid caffeine from tea leaves using different types of extraction, as well as sublimation. Results-The solid-liquid extraction of the caffeine and tannic acid from the leaves was carried out through the use of water and sodium carbonate. The sodium carbonate serves to make the tannic acids more soluble in water, while the water makes transport through the solid-liquid interface of the leaves easier. The liquid-liquid extraction was seen when separating the clear (organic) caffeine layer from the bottom of the centrifuge tube to its own centrifuge tube to be dried with magnesium sulfate. Because the tannic acids are now more soluble in water, the addition of methylene chloride allows the caffeine to transfer to the organic layer, while the ionic salts of the tannic acids are left in the aqueous phase on the top. After going through three extractions, the end result should be a centrifuge tube with only the methylene chloride solution containing the caffeine. The methylene chloride was then evaporated out.
What is the reason behind filtering your reaction mixture through celite on a Buckner funnel fitted with a piece of filter paper?
It helps to filter finely divided undissolved TCCA better than just filter paper
Based on table 8.7 Carbonyl Group Vibrational Frequencies (page 296), which peak in the following IR spectrum of acetone is the carbonyl peak?
Peak B
Experiment 12 Procedure
Photochemical Isomerization of an Alkene: cis-1, 2-Dibenzoylethylene Purpose- to illustrate the isomerization of a trans alkene to the corresponding cis isomer through the process of photochemical excitation.
What conclusion can you make if it takes 20 s for bromophenol blue to change colors in the following scenario? You have a mixture that contains 0.50 mL of 0.10 M NaOH, 4.50 mL of water, and 5.00 mL of 0.10 M t-butyl chloride.
It took 20 s for 10% of the t-butyl chloride to react
Experiment 9 Procedure
Kinetics of an SN1 Reaction: Solvolysis of t-Butyl Chloride Purpose- to obtain the measure of the rate of the SN1 reaction of t-butyl chloride with water as the nucleophile and solvent. Results- This was done by conducting 4 different experiments each with less NaOH solution added and more water added. As the experiments progress, so does the percent amount of remaining t-butyl chloride. The experiments progress from only 80% of t-BuCl remaining to 95% of t-BuCl remaining. As the percent amount of remaining t-BuCl increased, the time for reaction to complete decreased. This can be seen in the graph that has a negative slope. The negative slope can be attribute to the fact this is a first order reaction. Also based on this negative slope, it can be stated that the proposed equation for a first order reaction is correct.
What is the best way to know the contents in any given flask?
Label it
The automatic pipets should never be ______________ and always returned ______________.
Laid flat or inverted, to the pipet stand in an upright position
Why are methyl and primary ethers preferable products for Williamson synthesis of ethers? (Select all that apply)
Methyl and primary halides are more amenable to the SN2 reaction Secondary and tertiary halides could undergo an elimination reaction
You have now performed a solvent extraction and a recrystallization in the labs. The solvents used in recrystallizations should be ______________ and solvents used in extractions should be ______________.
Miscible, immiscible
What is the term used to describe the solution that is separated from crystals in a crystallization or recrystallization?
Mother liquor
Extra Credit (1 point). There are four nitrogen atoms in caffeine. Only one acts as a base. Which one?
N9 acts as the base.
Explain the role of each of the three aqueous washes in the workup procedure.
Na2CO3 is the basic wash, and it neutralizes and removes any remaining acids in the reaction mixture (TCCA). The HCl wash is the acidic wash, and it neutralizes the reaction mixture solution after the basic wash. The brine was added to remove any residual water from the organic layer.
If a sample does not have sufficient vapor pressure to be soluble in a carrier gas will you be able to use GC as an analytical technique?
No
Where should the liquid waste from this experiment go?
Non-halogenated waste jar
The experimental procedure instructs you to keep about 40 mL of 2 M sodium hydroxide solution in a flask and cool it over ice. How much of this are you supposed to use in the procedure?
One or more 5-10 mL portions determined depending on how many it takes to make the resulting aqueus layer basic
Bonus question (1 point): The qualitative bromination test for the presence of unsaturation is actually a stereospecific reaction. Which of the following is/are the stereospecific
Option D
The process of converting an alcohol to an aldehyde or ketone is called ________________________.
Oxidation
Experiment 6 Procedure
Oxidation of Alcohols: Trends in Infrared Spectroscopy Purpose- to prepare a library of aldehydes and ketones by oxidation of alcohols and to compare the IR spectra of each of the compounds and their trends in the carbonyl absorption. Results- Ketones have a distinct peak around 1700-1750cm-1, while aldehydes have a double peak around 2700-2900cm-1. The alcohol Geraniol was oxidized and produced the aldehyde Citral. 9 alcohols total were oxidized to produce their aldehyde or ketone.
Different stationary phase materials have different binding properties, which stationary phase material would be useful to help elute two unknowns based on their polarity?
Polyethylene glycol (carbowax)
In today's experiment, to achieve an aldehyde product, you will use a(n) ________________________ alcohol.
Primary
Match the chemical with its safety hazard. Note - you should always wear gloves when handling caustic/potentially hazardous chemicals
Propyl iodide - Cancer suspect Agent Sodium hydroxide - Strong base, can burn skin and eyes Concentrated Acids - Strong acids, can burn skin and eyes (TA will dispense)
Experiment 3 Procedure
Recrystallization: Separation of an Acid and a Hydrocarbon Purpose- be able to identify the unknown compounds that we isolated and kept from the last experiment, through the use of melting points and recrystallized material. Results- The melting points of the crystallized hydrocarbon and carboxylic acid from last experiment were determined. The compounds were then recrystallized. The melting point were found and then paired to a known substances melting point. The recrystallized substance were then put into a solution of the compound with a common melting point and the melting point of the two were calculated once again. Unknown #6 contained Biphenyl as the hydrocarbon and Benzoic acid as the carboxylic acid.
You measured the Rf of various compounds on the TLC plates in Experiment 5. What does Rf stand for?
Retention Factor
Experiment 1 Procedure
Simple and Fractional Distillation: Separation of Methanol and Water Purpose- Separate a mixture of methanol and water using two different distillation methods—simple and fractional distillation. Results- Simple distillation occurred faster with a more sporadic rise in temperature, but the product was less pure. Fractional took longer with a more gradual rise in temperature, and produced a much purer product. Methanol has a lower boiling point, and is therefore separated from the mixture first.
A molecule that is strongly adsorbed on the stationary phase of a column will move __________________ down the column.
Slowly
Why was it helpful to use Na2CO3 in the extraction?
Sodium carbonate was helpful because it helped to increase the solubility of the tannic acids in the water by forming ionic salts. This caused them to stay trapped in the aqueous layer while the caffeine was made less water soluble allowing it to be moved into the methylene chloride layer.
Experiment 2 Procedure
Solvent extraction: Separation of an acid and a hydrocarbon Purpose- separate a hydrocarbon from an acid using the difference in water solubility of the neutral carboxylic acid and its anionic conjugate base. Results- (organic layer on top, hydrous layer on bottom) Hydrocarbon is isolated by concentration, while the carboxylic acid is isolated through filtration. Hydrocarbon is contained in the ether solution (top layer) and the carboxylic acid is contained in the water layer (on the bottom). Ether was evaporated from the beaker to obtain the hydrocarbon. Both the hydrocarbon and carboxylic acid were kept to be analyzed for the next experiment.
Why are sulfuric or phosphoric acids, rather than hydrochloric acid, used to catalyze the dehydration of alcohols?
Sulfuric and phosphoric acid are used to minimize the presence of water, promote protonation, and eliminate the risk of evolution of sulfur dioxide. Hydrochloric acid wasn't used because as a result a Sn1 reaction would compete with the E1 reactio
Experiment 11 Procedure
The E1 Elimination Reaction: Dehydration of Cyclohexanol to Yield Cyclohexene Purpose- to isolate and characterize the product of an E1 reaction with Cyclohexene. Results- The IR spectrum showed peaks at 3430, 3025, 2927, 2825, and 1675. The peak at 3430 is indicative of an OH peak, while the one at 3025 Csp2-H bond. The peaks at 2927 and 2825 are indicative of Csp3-H bonds. There is a smaller peak around 1675. This correlated to a C=C bond. The Br2 test was one to test for unsaturation to see if the alkene had formed. Because the color disappeared when it was dropped into the product, it can be said that the alkene has formed.
Experiment 10 Procedure
The E2 Elimination Reaction: Dehydrohalogenation of 2-Bromoheptane to Yield 1-Heptene, trans-2-Heptene, and cis-2-Heptene Purpose- to illustrate the base-induced dehydrohalogenation of alkyl halides with a strong base and is used for the preparation of alkenes. Results- The two bases analyzed are NaOCH3 and KOC(CH3)3. NaOCH3 is a very strong base, while KOC(CH3)3 is a very bulky base. This difference is what accounts for the different abundance of each isotope in each reaction. When using the strong base (NaOCH3), there are two possible routes the reaction can take. Based on Zaitsev's rule, the most stable, major product was formed—trans-2-heptene. Due to how bulky the base KOC(CH3)3 is, it cannot effectively abstract an internal β-hydrogen atom and chooses instead to abstract a more accessible β-hydrogen atom. This causes the Zaitsev rule to be violated and the less stable cis-2-heptene isomer is formed. Because the alkyl halide is a secondary halide, a peak for side products can be seen, but is not the focus in this particular experiment.
What major IR absorption would disappear in going from reactant to product in this reaction?
The IR absorption of an OH would disappear from the graph when going from reactants to products
Experiment 7 Procedure
The Seperation of a 25-µL Mixture of Heptanal (bp 153°C) and Cyclohexanol (bp 160°C) by Gas Chromatography Purpose- to use gas chromatography to separate heptanal and cyclohexanol which boil within in 7°C of each other. Results- Gas chromatography separates very small amounts of compounds with very close boiling points. Cyclohexanol separated first and then heptanol separated. While cyclohexanol has a high boiling point, heptanal has stronger polar forces making it interact with the stationary phase longer.
You will use either sodium methoxide or potassium tert-butoxide as base in this experiment. Potassium tert-butoxide is a "bulky" base. What does it mean to be a "bulky" base?
The base is relatively large, or bulky. It is actually so big that it can only abstract an unhindered β-hydrogen and will usually produce an anti-Zaitsev product.
What are some differences expected to be seen when comparing the IR spectra of the trans starting material to the cis photoproduct? (Select all that apply)
The cis isomer will display a cis, in-phase out-of-plane bend at 820 cm-1 The trans double bond will appear as a single medium intensity band at 970 cm-1
Why are phenols typically stronger acids than simple alcohols?
The conjugate base of a phenol is stabilized by resonance delocalization
In addition to obtaining an IR spectrum, you will use bromination as a qualitative test for the presence of unsaturation (a double bond, in this case), see the reaction below. What is the change you will observe in the reaction solution?
The deep orange color of bromine will disappear
The density of dichloromethane (CH2Cl2) is 1.33 g/mL. Which layer should your organic product be found in during workup with aqueous solutions and dichlormethane solvent?
The desired product is in the methylene chloride layer which is the bottom layer when combined with aqueous solutions.
How do you calculate the Rf value?
The distance traveled by the substance divided by the distance traveled by the substance
List the names if the functional groups that are present in each of the 3 chemicals above.
The functional groups present in benzyl alcohol are an aromatic compound and an OH (hydroxyl) group. The functional groups present in benzaldehyde are an aromatic compound and an aldehyde. The functional groups present in benzoic acid are an aromatic compound and a carboxylic acid.
What is one of the factors for group frequency molecular vibration in infrared spectroscopy? Hint: Page 291
The group must have a dipole moment change
For either fractional or simple distillation experiments, what compound will be present in the highest amount in the initial few mL of distilled liquid? At the conclusions of the experiment what compound remains in the distilling flask?
The initial millimeters of collected distillate in both distillation methods should contain the highest composition of methanol. By the end of the distillation process, water should be the only substance remaining in the distilling flask
Why is the phase transfer catalyst soluble in the organic layer?
The large organic groups attached to the catalyst
Methanol is flammable.
True
What new IR absorptions would you see?
The new IR absorption on the graph would be an alkane ranging from 2800-3000.
The --+SR2 group is easily removed in elimination reactions, but the -SR group is not. Explain.
The overall positive charge for SR2 makes it easier to be removed by attacking other electrons whereas the SR groups is satisfied with its electrons and doesn't want to be removed so it doesn't lose its electrons.
Electrons in which type of bond are excited by radiation during this experiment?
The pi bond
How would the rate change with 2-chloropropane instead of t-butyl chloride?
The rate of formation would be would be much slower since Sn1 reactions favor tertiary structures and the 2-chloropropane is secondary structure.
Experiment 5 Procedure
Thin-Layer Chromatography Analysis and Analgesics Purpose- identify several analgesics, using thin layer chromatography Results- Known chemicals will be dissolved in methylene chloride then spotted on a TLC plate. An unknown chemical was dissolved in methylene chloride and spotted on a TLC plate. The Rf values for each are specific to that certain chemical so the values can be used to identify the chemicals and their composition in the unknown. An IR spec was done on Benzoic acid, Benzaldehyde, and benzyl alcohol.
What is the purpose of NaOH in this experiment?
To help measure the rate of reaction
Phosphoric acid is used as a protonating acid in the reaction below. Why is it important to protonate the starting alcohol? (Select all that apply)
To produce a good leaving group, water Without the protonation step, the hydroxide ion, a poor leaving group, is the only available leaving group
According to the lab manual, the first step in any filtration is:
Wet the filter paper with the solvent being used
Experiment 8 Procedure
Williamson Synthesis of Ethers Purpose- to prepare alkyl aryl ethers by Sn2 reactions of alkyl halides with substituted phenoxide anions. Phase-transfer catalysis will also be demonstrated. Results- Success of SN2 reaction was seen through peaks found on the IR spec. Upon analysis of the IR spec, alkyl sp3 C-H bond, benzene C=C bond, and C-O ether bond peaks were present.
How much sample should be added to the melting point capillary?
approximately 1mg, about to 2mm once added to the capillary
When should you remove the rubber tubing from the filter flask?
before turning the water off
If the following three chemicals (benzyl alcohol, benzaldehyde and benzoic acid) were chromatographed using silica gel TLC plates, which should have the highest Rf value? Hint: What intramolecular forces are involved between each of these chemicals and the SiO2 of the silica gel?
benzyl alcohol < benzoic acid < benzaldehyde Benzaldehyde should have the highest Rf value since it has the lowest polarity among the three chemicals.
Which of the following is considered a corrosive hazard for acute skin contact?
both the hydrochloric acid and sodium hydroxide
What piece of equipment is in the laboratory that can help get rid of emulsions?
centrifuge
Which component in the mixture used in this experimental procedure has the highest vapor pressure?
methanol
Why is it important to be careful when evaporating the organic solvent during the final isolation step of the experiment?
once all of the solvent has evaporated, the caffeine may sublime or oxidize if heated too much
What should you use to mark your TLC plate?
pencil
Brewing tea in an aqueous sodium carbonate solution and then separating the water away from the tea leaves is an example of what kind of extraction?
solid-liquid
If there is no suitable single solvent available for recrystallization, you can use a(n):
solvent pair
Which of the following is the structure of caffeine?
structure B
You should start timing the reaction after adding what compound to the solvent?
t-Butyl chloride
How can you tell when you have added enough anhydrous magnesium sulfte to an organic solvent to dry it?
the added magnesium sulfate appears mobile (free flowing powder)
Which of your isolated compounds is more soluble in pure water?
the carboxylic acid
Which of the following statements about a water/ether mixture is most accurate?
the diethyl ether forms the organic top layer because it is less dense
In chemistry, the term "wet" means:
the material in question contains water
Which layer will be the bottom layer in the liquid-liquid extraction performed in this experiment?
the organic layer (methylene chloride)
What is distillation?
the process of heating a liquid to the boiling point, condensing the heated vapor by cooling, and returning either a portion of or none of the condensed vapors to the distillation vessels
What combination of compounds do you expect to be present in the aqueous solution after brewing the tea leaves?
tonic acids, caffeine, and sodium carbonate
You will perform the reaction shown below in this experiment and you should obtain a mixture of the products shown. You will submit samples of your product mixture to be analyzed by gas chromatography. From what you know about Zaitsev elimination products and alkene stability, identify which of the products is the most stable. Would the most stable product be the major product or the minor product?
trans-2-Heptene is the most stable product; it would be the major product if M+ -OR is a small base
Predict the more stable alkene of each of the following pairs: 1-Hexene or trans-3-hexene
trans-3-hexene
Predict the more stable alkene of each of the following pairs: trans-3-hexene or cis-3-hexene
trans-3-hexene
