ochem lab final

Question 1

Calculate % recovery of the essential oil for the hypothetical experiment, if you started with 9.8660 grams of orange peel and after the experiment were able to recover 0.1843 grams of limonene. Report numerical value only (do not include % sign), and use correct number of significant figures.

Answer 1

1.8680

Question 2

Calculate % recovery of your essential oil you obtained experimentally, show calculations. We recovered 1.7705g of oil from 11.2341g of cinnamon sticks

Answer 2

1.7705g / 11.2341 * 100 = 15.7601

Question 3

Based on your knowledge of liquid-liquid extraction technique answer the following question: In which layer of the separatory funnel do you expect to have the majority of your essential oil present, if you replaced dichloromethane with ethyl acetate in step 5 of the procedure?

Answer 3

oil will dissolve in ethyl acetate and be present in the top layer

Question 4

(exp PL 1) Choose ALL the compounds that are NOT LIMONENE and NOT AN ISOMER of limonene.

Answer 4

D

Question 5

% recovery formula

Answer 5

( actual yield / theoretical ) * 100

Question 6

Based on the structure of piperine, do you expect it to have better solubility in water or in dichloromethane?

Answer 6

In DCM, because polarity of the molecule matches polarity of DCM

Question 7

(exp 2 PL) Given structures of the following molecule, also found in black pepper, what is the relationship between this molecule and piperine?

Answer 7

stereoisomers

Question 8

(exp 2 PL) What is molecular fromula for the another compound that can be isolated from black pepper shown below?

Answer 8

C19H21NO3

Question 9

Molecule of piperine contains amide functional group in its structure (T/F)

Answer 9

True

Question 10

(exp 3 PL)Select ALL the TLC plates that would suggest that your caffeine isolation was NOT successful or that your isolated caffeine contained impurities.

Answer 10

A and D

Question 11

Predict what would happen with the Rf values of your isolated caffeine and pure caffeine samples, if instead of ethyl acetate you used hexanes as eluting solvent.

Answer 11

Both Rf values will decrease, due to hexanes being less polar solvent than ethyl acetate.

Question 12

(exp 3 PL) Given the TLC sketch for the compounds 1 and 2 ran side by side, calculate Rf value for the less polar compound. Provide only numeric value in the answer box with correct significant figures. (Remember: Rf values do not have units).

Answer 12

0.76

Question 13

(exp 4 PL) Out of four compounds that we tested in this experiment, only one is optically active. Determine which one it is and draw both enantiomers of it, label each enantiomer as R or S.

Answer 13

R and S ibuprofen

Question 14

Mixtures can be easily identified by TLC method due to:

Answer 14

mixture will result in multiple spots on TLC plate

Question 15

(exp 4 PL) Which of the following compounds is the most polar based on the TLC plate shown below?

Answer 15

3

Question 16

Does Rf of the compound’s spot depend on the solvent system used as eluent?

Answer 16

yes

Question 17

Calculate ee for the mixture of (S)-2-bromobutane and (R)-2-bromobutanes if specific rotation of the pure enantiomers = +23.1 and -23.1 degrees respectfully. And the mixture showed specific rotation of +10.5 degrees. (show numeric value only, no % sign)
For the same mixture of (S)-2-bromobutane (+23.1 degrees) and (R)-2-bromobutanes (-23.1 degrees) with specific rotation of +10.5 degrees, calculate what is % of R isomer in the mixture. (show numeric value only, no % sign)

Answer 17

answer

Question 18

What do you expect your calculated [α] value be for 50% to 50% mixture of D and L arabinoses?

Answer 18

answer

Question 19

How many asymmetric carbon atoms does the following molecule have?

Answer 19

0

Question 20

(exp 6 PL) Predict which of the following compounds you will NOT be able to prepare from corresponding alcohol through the SN1 reaction with HCl.

Answer 20

C

Question 21

Predict which of the following compound(s) will give positive result in the NaI test for alkyl halides? (choose all that can react)

3-chloro-3-methylhexane

1-bromoheptane

1-chloro-1-methylcyclohexane

(2-bromoethyl)cyclohexane

1-chloro-1-isopropylcyclopentane

Answer 21

1-bromoheptane
(2-bromoethyl)cyclohexane

Question 22

Predict which of the following compound(s) will give positive result in the AgNO3 test for alkyl halides? (choose all that can react)

2-chloro-2-methylhexane

1-chlorooctane

1-bromo-1-methylcyclopentane

3-(3-chloropropyl)heptane

1-chloro-4-isopropyloctane

Answer 22

2-chloro-2-methylhexane

1-bromo-1-methylcyclopentane

Question 23

What will be a major product produced in the reaction of cyclohexanol if instead of heating in H2SO4/H3PO4 mixture you used aqueous HCl at room temperature (recall experiment 5)?

Answer 23

chlorocyclohexane

Question 24

(exp 7 PL) Select all compounds for which you would expect to see a positive result (disappearance of color) in Bromine test?

Answer 24

A, C

Question 25

(exp 7 PL) Choose a major product that will result from the dehydration reaction of the following compound.

Answer 25

C

Question 26

What feature in the structure of carotenoids is responsible for their colorful appearance?

Answer 26

Presence of conjugated double bonds

Question 27

If the “yellow” component of spinach should elute in hexane (mixtures of C6H14), and the “green” component in acetone (CH3COCH3), which of the components is more polar – β-carotene (yellow) or chlorophyll (green)?

Answer 27

chlorophyll is more polar - it interacts with silica gel more than carotene and thus elutes slower from the column

Question 28

Differences in what property will allow components of spinach to be separated in today’s experiment? (extraction of spinach pigments) Smell Specific gravity polarity solubility

Answer 28

polarity

Question 29

How many π-bonds are there in the structure of β-carotene

Answer 29

11

Question 30

Which method will you use to analyze the obtained pigments from today’s experiment? (extraction of spinach lab)

Answer 30

UV-vis spectroscopy

Question 31

Select all the solvents that could be successfully used instead of diethyl ether in the procedure you performed (assume all the compounds from the mixture will have good solubility in the solvents below). (acid base extraction) dichloromethane ethanol acetone ethyl acetate methanol

Answer 31

DCM, ethyl acetate

Question 32

If you added benzoic acid to a separatory funnel containing diethyl ether and water, predict in which layer will benzoic acid be present after shaking the separatory funnel?

Answer 32

top, ether

Question 33

If you were asked to isolate para-toluic acid from the mixture of para-toluic acid and naphthalene, what steps should you perform? List in correct order.

Answer 33

1. Dissolve mixture in organic solvent, such as DCM 2. Conduct liquid-liquid extraction with NaOH solution 3. Acidify aqueous layer with HCl to obtain pure para-toluic acid as precipitate 4. Isolate para-toluic acid using vacuum filtration

Question 34

(exp 10 PL) Select a TLC plate that will signify that the reduction reaction is complete.

Answer 34

B

Question 35

If after running TLC experiment in 1:1 hexanes:ethyl acetate mixture Rf of your product was 0.95 what could you do to obtain a smaller Rf value in a consecutive TLC experiment?

Answer 35

change solvent system to 10:1 hexanes:ethyl acetate

Question 36

Select all peaks that you expect to see in IR for your isolated product. (reduction lab 10) C=C stretch at ~1500 cm-1 C=O stretch at ~1700 cm-1 sp2 C-H stretch at ~3050 cm-1 O-H stretch at ~3300 cm-1

Answer 36

C=C stretch at ~1500 cm-1 sp2 C-H stretch at ~3050 cm-1 O-H stretch at ~3300 cm-1

Question 37

(exp 10 PL) Choose all the compounds that can be reduced using NaBH4 into corresponding alcohols.

Answer 37

B, D

Question 38

what reagents for isolation of essential oils

Answer 38

DCM, limon or cinamon, cyclohexane, cyclohexene, KMnO4

Question 39

reagents for piperine extraction

Answer 39

piperine, DCM, diethyl ether

Question 40

reagents for caffeine extraction

Answer 40

caffeine, sodium carbonate, DCM, ethyl acetate, petroleum ether(hexanes)

Question 41

unknown analgesic reagents

Answer 41

acetaminophen ibuprofen caffeine acetylsalicilic acid ethyl acetate hexanes

Question 42

polarimetry reagents

Answer 42

sucrose 10%, D and L arabinose, mix of D and L

Question 43

alkyl halides reagents

Answer 43

HCl Tert butanol NaI AgNO3 1 chlorobutane 2 chlorobutane tert butyl chloride 1 bromobutane 2 bromobutane tert butyl bromide

Question 44

alcohol dehydration reagents

Answer 44

cyclohexanol cyclohexene phosphoric acid sulfuric acid ethyl acetate bromine KMnO4

Question 45

Extraction of Spinach Pigments reagents

Answer 45

acetone hexanes

Question 46

reagents acid base extraction

Answer 46

benzoic acid 3 nitroalinine napthalene diethyl ether

Question 47

ketone reduction reagents

Answer 47

benzophenone methanol sodium borohydride NaBH4

Question 48

Which method(s) will you use to determine purity of the isolated piperine?

Answer 48

Melting Point Comparison

Question 49

What role does reflux condenser play in the reflux set up?

Answer 49

water that runs through the condenser cools down solvent vapors so that they condense and return to the reaction flask

Question 50

When today's reaction mixture is heated to a reflux, the temperature of the system is kept nearly constant at: (piperine extraction)

Answer 50

~40 C, boiling temperature of dichloromethane

Question 51

Choose all applicable piece of glassware and equipmet that are needed for a typical vacuum filtration set up filter paper beaker buchner funnel rubber sleeve filtering flask Erlenmeyer flask

Answer 51

filter paper buchner funnel rubber sleeve filtering flask Erlenmeyer flask

Question 52

(pre lab 3)Based on the following TLC plate (silica gel coating), which compound (A or B) is more polar?

Answer 52

B

Question 53

Acetone is miscible with water. Would it be better or worse to use acetone (rather than CH2Cl2) for extraction of caffeine from water?

Answer 53

It would be worse due to acetone mixing into one layer with water

Question 54

Which method(s) will you use to determine purity of the isolated caffeine?

Answer 54

thin Layer Chromatography

Question 55

What is the molecular formula for caffeine

Answer 55

C8H10N4O2

Question 56

(pre lab 3) Rf of the product shown on this TLC is:

Answer 56

0.6

Question 57

Which of the solvents available to you is the most polar and which is the least polar. hexanes, ethyl acetate, ethanol

Answer 57

Ethanol is most polar and hexanes is least polar

Question 58

In most cases, melting point of impure compound is

Answer 58

Lower and broader than melting point of a pure compound

Question 59

Imagine you’re running a TLC in hexanes/ethyl acetate 1/1 mixture, and all of your compounds move all the way with the solvent front. What will you do with the solvent system to make the compounds separate and move in the middle of TLC?

Answer 59

Decrease polarity of solvent system by adding more hexanes

Question 60

(pre lab 4) The following picture is of a TLC for mixture X (spot on the left) with four known compound as reference (A, B, C and D). Based on this TLC which components (A,B,C,D) are present in the mixture?

Answer 60

A and D

Question 61

(pre lab 4) Which of the following TLC plates represent pure compound? (Select all that apply)

Answer 61

c, d

Question 62

How much does observable rotation, α-αblank, differ for 2 M and 4 M solution of sucrose?

Answer 62

Rotation for 4 M is twice as big

Question 63

Which one is chiral object in everyday life

Answer 63

shoes

Question 64

Which of the following molecules are chiral? (pre lab 5)

Answer 64

a and c

Question 65

If specific rotation, [α], of 1 M D-arabinose solution is +xo, what specific rotation would you expect for a 2 M L-arabinose solution?

Answer 65

-xo

Question 66

What is the purpose of a polarimeter?

Answer 66

To measure optical rotation of molecules

Question 67

What is the purpose of adding anhydrous sodium sulfate to the final product?

Answer 67

To remove traces of water from the product

Question 68

(prelab 6) Given the following structures of alcohols, arrange them in increasing rate of substitution via SN1 mechanism

Answer 68

tertiary carbocations are the most stable, thus SN1 proceeds fastest with tertiary substrates and does not go with primary substartes.

Question 69

Which reagent is used as a qualitative chemical test for tertiary alkyl halide?

Answer 69

silver nitrate in ethanol

Question 70

Which reagent is used as a qualitative chemical test for primary alkyl halide?

Answer 70

sodium iodide in acetone

Question 71

What is the major product of the reaction of tert-butanol with concentrated HCl at room temperature? (pre lab 6)

Answer 71

Cl on top

Question 72

what will likely happen if you reacted cyclohexanol with HBr instead of heating it with H2SO4?

Answer 72

substitution reaction will likely happen producing an alkyl bromide

Question 73

What is the major product of today’s experiment of dehydration of cyclohexanol?

Answer 73

cyclohexene

Question 74

In today’s reaction of dehydration of 4-methylcyclohexanol, a certain equilibrium is established. How will you disturb this equilibrium and shift the reaction to the side of the products, utilizing Le Châtelier’s principle? (dehydration of alcohols)

Answer 74

by removing the product from the reaction mixture

Question 75

what is the reason for shaking the distilled crude product with sodium bicarbonate solution?

Answer 75

to neutalize any remaining acid

Question 76

What is the purpose of running today's reaction in distillation apparatus?

Answer 76

to be able to boil away products from the reaction mixture as they form

Question 77

what feature in the structure of carotenoids is responsible for their colorful appearance?

Answer 77

Presence of conjugated double bonds

Question 78

If the “yellow” component of spinach should elute in hexane (mixtures of C6H14), and the “green” component in acetone (CH3COCH3), which of the components is more polar – β-carotene (yellow) or chlorophyll (green)?

Answer 78

chlorophyll is more polar - it interacts with silica gel more than carotene and thus elutes slower from the column

Question 79

Which method will you use to analyze the obtained pigments from today’s experiment? (spinach extraction)

Answer 79

UV-vis spectroscopy

Question 80

Why ammonium salts are more soluble in water and amines are more soluble in organic solvents (e.g. dichloromethane)?

Answer 80

Due to “like dissolves like” principle (polar water can stabilize charged salt cations and anions better than uncharged amines)

Question 81

What is the product that forms after benzoic acid is extracted with sodium hydroxide solution? (acid base extraction)

Answer 81

PhCO2Na

Question 82

Diethyl ether is a highly volatile and flammable solvent. What precautions will you take during today’s experiment? (acid base extraction)

Answer 82

Keep it away from open flames and hot plates, work in a fume hood

Question 83

What functional group is responsible for basic properties of 3-nitroaniline?

Answer 83

The amino group

Question 84

How will you obtain pure naphthalene from the solution of naphthalene in diethyl ether

Answer 84

use rotary evaporator to remove diethyl ether

Question 85

Aldehydes can be successfully reduced to corresponding primary alcohols using NaBH4 (t/f)

Answer 85

true

Question 86

Appearance of which peak in IR will signify that today's reduction reaction was successful? sp2 C-H stretch at ~3050 cm-1 C=O stretch at ~1700 cm-1 O-H stretch at ~3300 cm-1 C=C stretch at ~ 1500 cm-1

Answer 86

O-H stretch at ~3300 cm-1

Question 87

During the work up , the reaction mixture is poured into the beaker containing crushed ice and HCl. What does this step accomplish (reduction lab)

Answer 87

cold HCl is needed to acidify the alkoxide ion and break down excess NaBH4 reagent.

Question 88

What is the role of NaBH­4 in today’s experiment: (reduction lab)

Answer 88

reducing agent

Question 89

As a result of the reaction with NaBH4 or LiAlH4 carbonyl group is converted into: (reduction lab)

Answer 89

alcohol group

Question 90

NaBH4 is not able to convert ester group to a corresponding alcohol. (t/f)

Answer 90

true