Orgo 2 Lab Knowledge Checks

You were asked to dissolve 9.36 g of compound A in 60 ml of water. After single extraction with 60 ml ether, you recovered 2.48 g of compound A from the ether layer. Calculate the Kd value for the compound A in ether/water system. Report your answer to 2 decimal places (i.e., 0.01). Recall that Kd = concentration in organic phase/concentration in aqueous phase

0.36

You conducted a TLC experiment and found that your compound traveled 4.96 cm and the eluting solvent traveled 9.71 cm. What is the Rf value for your compound? Report your answer to two decimal places (i.e., 0.01).

0.51 margin of error +/- 0.02

Assume that you are conducting a chain-addition polymerization using 3.68 grams of monomer (MW= 68.7g/mol) and 101 mg of initiator (MW= 190.5 g/mol). What is the expected number of repeat units (n) per chain? Report your answer to the nearest whole number (i.e., an answer of 112.3 should be reported as 112).

101

In an EAS iodination reaction, 1.50 grams of phenol (MW: 94.11 g/mol) was reacted with 2.68 grams of sodium iodide (MW: 149.89 g/mol) . If 0.73 grams of product (MW: 220.01 g/mol) was collected, what was the percent yield (%) of the reaction? Report your answer to one decimal place (i.e., 23.1% should be entered as 23.1).

20.8 margin of error +/- 0.5

How many distinct peaks would you expect to see in the 1H NMR of the following compound?

3

Consider the dehydration reaction shown below. If you started this reaction with 43.53 mL of cyclohexanol (MW 100.16 g/mol, density 0.96 g/mL), what is the theoretical yield of cyclohexene in grams (MW 82.14 g/mol, density 0.81 g/mL)? Report your answer to two decimal places.

34.27

You are asked to synthesize 11.66 grams of coumarin via Pechmann reaction. Assuming that your reaction will proceed with 100%, what volume (mL) of resorcinol is required? Report your answer to two decimal places.

5.69 mL

Assume that you carried out a recrystallization of ibuprofen using ethanol. If you started with 5.37 grams of crude ibuprofen and isolated 3.64 grams of pure ibuprofen, what is your percent recovery? Report your answer to the nearest 0.01%.

67.78

Condensation polymerization results in the formation of a small molecule as a byproduct, while addition polymerization does not. True False

True

In TLC, polar compounds interact more strongly with the silica, so they travel a shorter distance up the plate. True False

True

The density of a solvent will determine its position relative to another solvent in the separatory funnel. True False

True

You need to use your separatory funnel for an extraction, but you notice that there is some residual water in it from when it was washed during the previous lab period. What should you do? a) Take the funnel to the stockroom and ask to exchange it b) Use a paper towel to dry the inside of the funnel prior to using it again c) Borrow a lab mate's funnel and wait for yours to dry d) Go ahead and use the funnel - you will be adding aqueous solutions anyway

d) Go ahead and use the funnel - you will be adding aqueous solutions anyway

What effect do soluble impurities have on the melting point range of an organic compound? a) It decreases and sharpens the range b) It increases and broadens the range c) It has no effect on the range d) It decreases and broadens the range e) It increases and sharpens the range

d) It decreases and broadens the range

A student set up an extraction to separate benzoic acid and phenol using diethyl ether, deionized water and sodium hydroxide. The student completed the extraction but did not get the desired results. What went wrong? a) It is not possible to separate the two compounds using extraction b) Sodium hydroxide is too weak of a base and will not deprotonate either of the compounds c) Deionized water and diethyl ether are miscible d) Sodium hydroxide is too strong of a base and will deprotonate both compounds

d) Sodium hydroxide is too strong of a base and will deprotonate both compounds

Assume that an extraction has been carried out using water and diethyl ether, similar to the Kd experiment in the lab, as illustrated with the separatory funnel drawn below. Chose the correct answers from the drop-down menus: The solvent in the top layer will be diethyl ether and the solvent in the bottom layer will be water .

Answer 1: diethyl ether Answer 2: water

Consider the molecule shown below, and use the dropdown menus to indicate the expected splitting patterns for the indicated protons.

Protons labeled (a): doublet Protons labeled (b): quartet Protons labeled (c): triplet Protons labeled (d): singlet

Rf = distance travelled by substance / distance travelled by solvent

The higher the Rf, the more non polar it is

When choosing a recrystallization solvent, you want to use a solvent in which both the product and impurities are highly soluble at all temperatures. True False

False

Match the items in the filtration apparatus below with their name/function.

Buchner funnel, filtration flask, pinch clamp to control the vacuum, hose connector to lab vacuum

Coumarins are a group of widely used laser dyes that emit blue-green light. Below are the different coumarin derivatives. What specific characteristic in these molecules is responsible for the observed fluorescence of coumarin derivatives? a) Extended conjugation of the molecule b) Presence of ester group c) Solubility of coumarins in polar protic solvents like ethanol d) Nucleophilicity of amine group

a) Extended conjugation of the molecule

If you measure the melting point of a sample, allowed the capillary to cool, and then measure the melting point of the sample a second time, will the second melting point reading be identical to the first? a) No - the crystal structure of the sample may change during the heating and cooling, and this will impact the melting point range. b) It is not possible to take a second melting point on the sample because it will remain in liquid form after the first melting point measurement. c) Yes - the melting point of a compound is a fixed value and would not be impacted by heating and cooling.

a) No - the crystal structure of the sample may change during the heating and cooling, and this will impact the melting point range.

Chloe tried to purify the crude product obtained from the synthesis of iodosalicylamide through recrystallization by using 95% ethanol as a solvent. After cooling the solution at room temperature, Chloe notices there is still no crystal formation. What could Chloe do? Choose all that apply. a) Scratch the bottom of the beaker b) Evaporate solvent to concentrate solution c) Add more ethanol to the solution d) Cool the solution in an ice bath e) Add seed crystals of salicylamide

a) Scratch the bottom of the beaker b) Evaporate solvent to concentrate solution d) Cool the solution in an ice bath

Channel wanted to apply her newly acquired laboratory skills to investigate why leaves change color in the fall by studying their pigmentation. Channel crushed some yellow leaves with a drying agent and sand and extracted the pigments using hexanes. She then spotted the extract on a TLC plate. Following development of the plate in 70:30 ethyl acetate:hexanes, Channel was not able to observe any spots. As Channel's friend, how would you help her to improve the experiment? Select all that apply. a) Use a more polar solvent such as acetone to extract the pigments. b) Replace ethyl acetate in the TLC chamber with ligroin which is a more polar solvent. c) View the plate under UV light since some pigments may be difficult to see with the naked eye. d) It is not possible to improve the experiment as this method can only be applied to spinach leaves. e) Pick some green leaves for Channel because yellow leaves contain no pigmentation.

a) Use a more polar solvent such as acetone to extract the pigments. c) View the plate under UV light since some pigments may be difficult to see with the naked eye.

Which of following reagent(s) in the renewable block copolymer experiment must be weighed very accurately to obtain the molecular weight closer to the theoretical value? Select all that apply. a) benzene dimethanol b) δ-decalactone diphenyl phosphate

a) benzene dimethanol b) δ-decalactone

Which of the sequences below represents a block copolymer? (Assume "A" and "B" as two different repeating units.) a) ·····AAAAAAABBBBBBBBB····· b) ·····AABABBBABABBABAA····· c) ·····ABABABABABABABAB····· d) none of these is a block copolymer

a) ·····AAAAAAABBBBBBBBB·····

When conducting a recrystallization, ideally (check all that apply): a) The product is soluble at elevated (boiling point) temperatures b) The solution is allowed to cool slowly to room temperature, followed by cooling in an ice bath c) The product is insoluble at cool temperatures d) The impurities remain insoluble, even when cooled

a, b, c

Which of the following errors will decrease the yield during the synthesis of acetophenetidin? Select all that apply. a) Forgetting to add the sodium acetate solution to the reaction mixture. b) Using a slightly smaller amount of dilute HCl solution than indicated in the procedure. c) Allowing the temperature of the reaction mixture to cool down during the hot gravity filtration. d) Adding too much activated carbon to decolorize the starting material. e) Adding extra acetic anhydride to the reaction mixture. f) Using warm water to rinse the recrystallization product inside Büchner funnel.

a, c, d, f

Vegetable oil cannot be used directly in a diesel engine because it is too viscous. The oil must be chemically changed into biodiesel through a lab process called transesterifcation as shown below. During this reaction, potassium methoxide is freshly prepared by mixing potassium hydroxide and _________ methanol. Care must be taken to replace the lid on the potassium hydroxide bottle quickly since potassium hydroxide is _________.

anhydrous; hygroscopic

An advantage of synthesizing block copolymers is the ability to tune the properties of the material by varying the length of each block. Of the following block copolymers, which composition would have the highest degree of crystallinity? a) 25% PLA, 75% poly(-decalactone) b) 75% PLA, 25% poly(-decalactone) c) 50% PLA, 50% poly(-decalactone) d) 45% PLA, 55% poly(-decalactone) e) 10% PLA, 90% poly(-decalactone)

b) 75% PLA, 25% poly(-decalactone)

What is the purpose of MgSO4 that is used in an acid/base extraction experiment? a) To lower the vapor pressure of the organic solvent b) To remove residual water from organic solvent c) More than one of these d) To remove remaining organic solvent from aqueous layer e) None of these

b) To remove residual water from organic solvent

Melissa was trying to synthesize a homopolymer of poly(δ-decalactone), however she didn't have any 1,4-benzenedimethanol so she decided to use benzyl alcohol as her initiator instead. How is this going to affect her final polymer? Will she still be able to form a triblock copolymer? a) Her final polymer will have a significantly lower molecular weight than expected because the benzyl alcohol has a lower molecular weight than the 1,4-bezenedimethanol. She will still form a triblock copolymer. b) The initiator is not important, it is only there to get the reaction started. Thus, her final polymer will be unaffected. She will be able to form a triblock copolymer. c) It will not affect her final polymer if she uses half of the amount of the monomer since there is only one alcohol group for it to interact with. She will be able to form a triblock copolymer. d) The polymer will only grow from one side of the initiator. She will not be able to form a triblock copolymer, she will form a diblock instead.

d) The polymer will only grow from one side of the initiator. She will not be able to form a triblock copolymer, she will form a diblock instead.