ochem lab final Flashcards
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.
1.8680
Calculate % recovery of your essential oil you obtained experimentally, show calculations. We recovered 1.7705g of oil from 11.2341g of cinnamon sticks
1.7705g / 11.2341 * 100 = 15.7601
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?
oil will dissolve in ethyl acetate and be present in the top layer
(exp PL 1) Choose ALL the compounds that are NOT LIMONENE and NOT AN ISOMER of limonene.
D
% recovery formula
( actual yield / theoretical ) * 100
Based on the structure of piperine, do you expect it to have better solubility in water or in dichloromethane?
In DCM, because polarity of the molecule matches polarity of DCM
(exp 2 PL) Given structures of the following molecule, also found in black pepper, what is the relationship between this molecule and piperine?
stereoisomers
(exp 2 PL) What is molecular fromula for the another compound that can be isolated from black pepper shown below?
C19H21NO3
Molecule of piperine contains amide functional group in its structure (T/F)
True
(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.
A and D
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.
Both Rf values will decrease, due to hexanes being less polar solvent than ethyl acetate.
(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).
0.76
(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.
R and S ibuprofen
Mixtures can be easily identified by TLC method due to:
mixture will result in multiple spots on TLC plate
(exp 4 PL) Which of the following compounds is the most polar based on the TLC plate shown below?
3
Does Rf of the compound’s spot depend on the solvent system used as eluent?
yes
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
What do you expect your calculated [α] value be for 50% to 50% mixture of D and L arabinoses?
answer
How many asymmetric carbon atoms does the following molecule have?
0
(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.
C
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
1-bromoheptane
(2-bromoethyl)cyclohexane
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
2-chloro-2-methylhexane
1-bromo-1-methylcyclopentane
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)?
chlorocyclohexane
(exp 7 PL) Select all compounds for which you would expect to see a positive result (disappearance of color) in Bromine test?
A, C
(exp 7 PL) Choose a major product that will result from the dehydration reaction of the following compound.
C
What feature in the structure of carotenoids is responsible for their colorful appearance?
Presence of conjugated double bonds
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)?
chlorophyll is more polar - it interacts with silica gel more than carotene and thus elutes slower from the column
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
polarity
How many π-bonds are there in the structure of β-carotene
11
Which method will you use to analyze the obtained pigments from today’s experiment? (extraction of spinach lab)
UV-vis spectroscopy
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
DCM, ethyl acetate
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?
top, ether
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.
- Dissolve mixture in organic solvent, such as DCM
- Conduct liquid-liquid extraction with NaOH solution
- Acidify aqueous layer with HCl to obtain pure para-toluic acid as precipitate
- Isolate para-toluic acid using vacuum filtration
(exp 10 PL) Select a TLC plate that will signify that the reduction reaction is complete.
B
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?
change solvent system to 10:1 hexanes:ethyl acetate
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
C=C stretch at ~1500 cm-1
sp2 C-H stretch at ~3050 cm-1
O-H stretch at ~3300 cm-1
(exp 10 PL) Choose all the compounds that can be reduced using NaBH4 into corresponding alcohols.
B, D
what reagents for isolation of essential oils
DCM, limon or cinamon, cyclohexane, cyclohexene, KMnO4
reagents for piperine extraction
piperine, DCM, diethyl ether
reagents for caffeine extraction
caffeine, sodium carbonate, DCM, ethyl acetate, petroleum ether(hexanes)
unknown analgesic reagents
acetaminophen
ibuprofen
caffeine
acetylsalicilic acid
ethyl acetate
hexanes
polarimetry reagents
sucrose 10%, D and L arabinose, mix of D and L
alkyl halides reagents
HCl
Tert butanol
NaI
AgNO3
1 chlorobutane
2 chlorobutane
tert butyl chloride
1 bromobutane
2 bromobutane
tert butyl bromide
alcohol dehydration reagents
cyclohexanol
cyclohexene
phosphoric acid
sulfuric acid
ethyl acetate
bromine
KMnO4
Extraction of Spinach Pigments reagents
acetone
hexanes
reagents acid base extraction
benzoic acid
3 nitroalinine
napthalene
diethyl ether
ketone reduction reagents
benzophenone
methanol
sodium borohydride NaBH4
Which method(s) will you use to determine purity of the isolated piperine?
Melting Point Comparison
What role does reflux condenser play in the reflux set up?
water that runs through the condenser cools down solvent vapors so that they condense and return to the reaction flask
When today’s reaction mixture is heated to a reflux, the temperature of the system is kept nearly constant at: (piperine extraction)
~40 C, boiling temperature of dichloromethane
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
filter paper
buchner funnel
rubber sleeve
filtering flask
Erlenmeyer flask
(pre lab 3)Based on the following TLC plate (silica gel coating), which compound (A or B) is more polar?
B
Acetone is miscible with water. Would it be better or worse to use acetone (rather than CH2Cl2) for extraction of caffeine from water?
It would be worse due to acetone mixing into one layer with water
Which method(s) will you use to determine purity of the isolated caffeine?
thin Layer Chromatography
What is the molecular formula for caffeine
C8H10N4O2
(pre lab 3) Rf of the product shown on this TLC is:
0.6
Which of the solvents available to you is the most polar and which is the least polar. hexanes, ethyl acetate, ethanol
Ethanol is most polar and hexanes is least polar
In most cases, melting point of impure compound is
Lower and broader than melting point of a pure compound
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?
Decrease polarity of solvent system by adding more hexanes
(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?
A and D
(pre lab 4) Which of the following TLC plates represent pure compound? (Select all that apply)
c, d
How much does observable rotation, α-αblank, differ for 2 M and 4 M solution of sucrose?
Rotation for 4 M is twice as big
Which one is chiral object in everyday life
shoes
Which of the following molecules are chiral? (pre lab 5)
a and c
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?
-xo
What is the purpose of a polarimeter?
To measure optical rotation of molecules
What is the purpose of adding anhydrous sodium sulfate to the final product?
To remove traces of water from the product
(prelab 6) Given the following structures of alcohols, arrange them in increasing rate of substitution via SN1 mechanism
tertiary carbocations are the most stable, thus SN1 proceeds fastest with tertiary substrates and does not go with primary substartes.
Which reagent is used as a qualitative chemical test for tertiary alkyl halide?
silver nitrate in ethanol
Which reagent is used as a qualitative chemical test for primary alkyl halide?
sodium iodide in acetone
What is the major product of the reaction of tert-butanol with concentrated HCl at room temperature? (pre lab 6)
Cl on top
what will likely happen if you reacted cyclohexanol with HBr instead of heating it with H2SO4?
substitution reaction will likely happen producing an alkyl bromide
What is the major product of today’s experiment of dehydration of cyclohexanol?
cyclohexene
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)
by removing the product from the reaction mixture
what is the reason for shaking the distilled crude product with sodium bicarbonate solution?
to neutalize any remaining acid
What is the purpose of running today’s reaction in distillation apparatus?
to be able to boil away products from the reaction mixture as they form
what feature in the structure of carotenoids is responsible for their colorful appearance?
Presence of conjugated double bonds
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)?
chlorophyll is more polar - it interacts with silica gel more than carotene and thus elutes slower from the column
Which method will you use to analyze the obtained pigments from today’s experiment? (spinach extraction)
UV-vis spectroscopy
Why ammonium salts are more soluble in water and amines are more soluble in organic solvents (e.g. dichloromethane)?
Due to “like dissolves like” principle (polar water can stabilize charged salt cations and anions better than uncharged amines)
What is the product that forms after benzoic acid is extracted with sodium hydroxide solution? (acid base extraction)
PhCO2Na
Diethyl ether is a highly volatile and flammable solvent. What precautions will you take during today’s experiment? (acid base extraction)
Keep it away from open flames and hot plates, work in a fume hood
What functional group is responsible for basic properties of 3-nitroaniline?
The amino group
How will you obtain pure naphthalene from the solution of naphthalene in diethyl ether
use rotary evaporator to remove diethyl ether
Aldehydes can be successfully reduced to corresponding primary alcohols using NaBH4 (t/f)
true
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
O-H stretch at ~3300 cm-1
During the work up , the reaction mixture is poured into the beaker containing crushed ice and HCl. What does this step accomplish (reduction lab)
cold HCl is needed to acidify the alkoxide ion and break down excess NaBH4 reagent.
What is the role of NaBH4 in today’s experiment: (reduction lab)
reducing agent
As a result of the reaction with NaBH4 or LiAlH4 carbonyl group is converted into: (reduction lab)
alcohol group
NaBH4 is not able to convert ester group to a corresponding alcohol. (t/f)
true
