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Lab practicle Flashcards

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1
Q

Which of the following compounds used in the synthesis of thebromohydrin2-bromo-1,2-diphenylethanol is a permeator?

A

DMSO

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2
Q

What is the most common way turn an alkene into an epoxide?

A

By treating it with a proxy acid (m-CPBA) However, this proxy acids are explosive and hard to handle.

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3
Q

During the first portion of trans-stilbene experiment, what was the function of NBS?

A

NBS provided a bromide atom via bromohydration reaction, which created a bromonium ion on the trans-stilbene

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4
Q

What is a permeator? Provide an example of a chemical we used in class.

A

DMSO, a chemical that can pass through protective dermal layers and into the body.

Can expose us to toxic effects of a specific permeator or act as a carrier for other toxic/hazardous chemicals.

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5
Q

In the trans-stilbene experiment, a bromohydrin will be purified by which method?

A

Via recrystallization from hexanes

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6
Q

During the creation of bromohydrin, in the trans-stilbene experiment, most of the DMSO was removed from the product during which step?

A

the extraction

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7
Q

Finding the melting points in the trans-stilbene experiment were crucial because they told us what?

A

They told us the stereochemistry of our product.

trans vs. cis

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8
Q

When solid anhydrous MgSO4 is added to liquid, what is its function?

A

To remove any microscopic droplets of water.

It is a drying agent.

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9
Q

Why is DMSO difficult to remove from reaction mixtures? In the trans-stilbene experiment, how did we remove DMSO?

A

DMSO has a very high boiling point, which is why we removed it during our extraction process.

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10
Q

During recrystallization, what will happen if too much hot solvent is used to dissolve the crude compound?

A

Few or zero crystals will be isolated.

Crystals form may remain contaminated.

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11
Q

What are the three requirements to make a proper melting point sample?

A

1) Finely ground up solid
2) Compacted well into a capillary tube
3) sample should be about 2-3mm in height

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12
Q

What should you do if the baseline of your TLC plate dips below the level the solvent as you put the pate into the developing chamber?

A

Start over with a new TLC plate, dump out this solvent, and put less in the beaker next time.

Only need a small layer of solvent

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13
Q

How many layers of liquid should you have during the purification via extraction?

A

Two layers: aqueous (bottom layer) and organic (top layer)

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14
Q

What are the sample that come out the bottom of a chromatography column called?

A

Fractions

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15
Q

If you perform two chemical reactions in sequence, what is the overall percent yield for converting A to C?
A to B = 80% yield
B to C = 70%

A

0.8 0.7 100% = 56

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16
Q

Will the most polar or most non-polar compound come out of the chromatography column?

A

The most non-polar will elute first, as the polar compound will be stuck to the stationary phase due to hydrogen bonding.

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17
Q

When making a chromatography column with alumina or slice gel, why is hexane often used?

A

Because it will not dissolve the aluminum or silca gel and they will sink.

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18
Q

Why is sand used when a chromatography column is prepared?

A

The sand helps keep the bottom and top ends of the stationary phase flat and even

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19
Q

Trans-stilbene Experiment

If there is unreacted 2-bromo-1,2-diphenylehtanol left in your crude stilbene oxide, what will happen to this impurity during column chromatography?

A

The impurity will stay on the column longer than the epoxide product, thus the epoxide product will be purified.

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20
Q

When calculating the melting point of a final product how do you record it?

A

In a range. The first temperature will be when the sample starts to melt and the second value is when the sample is done melting

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21
Q

Define a reaction workup

A

a series of steps required to isolate the reaction product

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22
Q

Trans-Stilbene Experiment

If a carbocation intermediate is involved, what will the mp of the products be?

A

Lower than the mp provided by literature.

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23
Q

If a compound travels further up the TLC plate because its non-polar, will it have a higher or lower Rf value than the compound (polar) that didn’t make it very far?

A

The non-polar compound will have a higher Rf value.

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24
Q

When doing column chromatography, what is a slur?

A

A suspension of the stationary phase particles in the mobile phase

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25
Q

What will happen if a column chromatography separation is carried out but has one of these issues?

  • The top of the column is uneven (slants from one side to the other)
  • The column dries out for a few minutes during the separation
    -A column with air bubbles or cracks on the inside
A

The fractions will contain mixtures of products

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26
Q

When visualizing a TLC plate with 2,4-DNP dip, what does the orange color indicate.

A

Indicates aldehydes and ketones are present

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27
Q

What is the purpose of the vacuum on the rotary evaporator?

A

To lower the boiling point of the solvent

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28
Q

When shutting down the rotary evaporator, which valve must you close first?

A

First, turn off the vacuum at the main valve (blue) and then open the vacuum line before removing flask.

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29
Q

Vanillin Experiment

Why is NaBH4 used as reducing agent instead of LiAlH4?

A

Because LiALH4 is not selective and we don’t want all of our carbonyl groups converted to alcohols. NaBH4 is more selective and less reactive

B-H bond can reduce one carbonyl group, so in theory one equivalent of NaBH4 can react with four equivalents of carbonyl groups. Excess of NaBH4 is still used.

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30
Q

Vanillin Experiment

Why is reduction of vanillin acetate done at 0°C?

A

To avoid the ester group on vanillin acetate converting into an alcohol via base-catalyzed ester hydrolysis

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31
Q

What can one see when visualizing a TLC plate with UV light?

A

Chemicals with conjugated double bonds

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32
Q

Grignard Reaction Experiment

Crystal Violent and Malachite Green can be synthesized from what?

A

Grignard Reagent and ester

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33
Q

What is a Grignard Reaction?

A

A chemical reaction in which alkyl, vinyl, or aryl-magnesium halides (Grignard reagents) add to a carbonyl group in an aldehyde or ketone. This reaction is an important tool for the formation of carbon-carbon bonds.

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34
Q

What is a Grignard reagent?

A

R-MgX (hydrocarbon attached to metal and halide)

R = metal
x = Halide

Strong nucleophile and can be treated as a source of the carbanion R-

Also, strong bases

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35
Q

Grignard Reaction Experiment
The Mg-C bond formed from grignard reagent is describe how?

A

A polar covalent bond, with a large partial negative charge on the carbon atom

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36
Q

Grignard Reaction Experiment

Why must Grignard reactions done in anhydrous conditions?

A

Because Grignard reagents are strong bases and readily react even with weak acids like water. Thus, we must use anhydrous conditions to avoid decomposition of Grignard reagent.

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37
Q

Grignard Reaction Experiment

Why was 1-bromobutane used in this experiment?

A

It was used as a catalyst to speed up reaction between Mg and 4-bromo-N,N-dimethylaniline. The reaction can occur without catalyst but would require more time or refluxing at very high temperatures.

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38
Q

Grignard Reaction Experiment

The surface area of reactive magnesium metal was increase by doing what?

A

Grinding with mortar and pastel to remove layer of less reactive magnesium oxide and adding iodine

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39
Q

Grignard Reaction Experiment
What compounds will form when n-butylmagnesium bromide reacts with water?

A

Butane and HOMgBr (or some form of magnesium hydroxide)

40
Q

Why must you be cautious when working with diethyl ether?

A

It is highly flammable and volatile

41
Q

Why must you be cautious when working with magnesium?

A

1) When heated in the presence of water, it can release hydrogen (which is very flammable)
2) It might catch fire spontaneously, especially when heated

42
Q

Grignard Reaction Experiment

We avoided wrapping a damp pipe cleaner around the reflux apparatus in this experiment for what reason?

A

A drop of water could have dripped down the condenser through the rubber connector and into the reaction flask

Dangerous when working with magnesium

43
Q

Name the observed color for these color absorbances
Blue/Vio
Blue
Blue-Gre
Green
Orange
Purple

A

Blue/Vio -> Yellow
Blue -> Orange
Blue/Gre -> Red
Green -> Purple
Orange -> Blue
Purple -> Green

44
Q

What is the auxochrome?

A

A substituent that alters the wavelength and the intensity of the absorption

45
Q

When measuring the melting point for identification purposes, should you be concerned whether the sample is wet?

A

Yes, if the sample is wet, the observed melting point will likely be lower than the literature value.

46
Q

Boiling points measured in Boise will be ____________ compared with boiling points measure at see level. why?

A

Lower because the air pressure in Boise is lower than the air pressure at sea level

47
Q

During recrystallization, which chemicals are left in the mother liquor (the filtrate that gets separated from the crystals at the end)?

A

Impurities that were present in the crude compound and the target compound

48
Q

What can you learn about an unknown compound by titrating it with NaOH?

A

Molar Mass

49
Q

A boiling point collected in lab from distillation apparatus will be lower, equal, or higher than the literature value?

A

Lower

50
Q

Define the boiling point

A

the temperature at which vapor pressure of the liquid equals the atmospheric pressure

51
Q

What does the 2,4-DNP Test test for?

A

Determines whether we have a aldehyde/ketone or alcohol

(+) aldehyde/ketone present = Forms yellow-orangish-redish precipitate

52
Q
A

By looking at the density: A should be top C in the middle and B on the bottom

53
Q

what should you do if there is an insoluble impurity during recrystallization

A

do a hot filtration

54
Q

what happens to the solubility of the crude product as temperature increases during recrystallization

A

it increases

55
Q

how does carbocation effect melting point?

A

will cause the melting point to be lower

56
Q
A

Compound A would be more attracted to the silica because it has a hydrogen bond donor and acceptor coming from the OH group.
(it will have a lower RF value)

57
Q

what are the most common stationary phases in column chromatography

A

alumina(Al2O3) and silica gel (SiO2)

58
Q
A

Both spectra

59
Q

When doing column chromatography,
what is a slurry?

A

a solution of stationary phase suspended in mobile phase

60
Q
A

E first then K X and B

61
Q

What will change if you increase the polarity of the
mobile phase used in a column chromatography
separation

A

As you increase the polarity of the solvent the product will elute faster and the amount of mobile phase you need to use will be lower

62
Q

what is the purpose of visualizing TLC plates under UV lights

A
  • Works for chemicals with conjugated double bonds (all of the chemicals in this experiment).
  • Does not distinguish other functional groups
63
Q
A

B

64
Q
A

C

65
Q
A
66
Q

what kind of solvent is a grinard reagent made in

A

diethyl ether

67
Q

what is the stationary phase in GC

A

solid

68
Q

what is a polymer

A

A large molecule with a repetitive structure

69
Q

equation for atom economy

A
70
Q

equation for reaction efficiency

A
71
Q

what doess conjugation do to IR stretching frequency

A

it decreases it

72
Q

As the number of conjugated double bonds increases what happens to the energy and absorbed wave length

A

energy to excite electrons decreases and the absorbed wave length increases

73
Q
A

for each carboxylic acid functional group, you need to add in this example 3 equivalence of NaOH

74
Q
A
75
Q
A
76
Q
A

B because a catalyst only makes the reaction go faster

77
Q

what is the dean stark trap used for and what experiment was it used in

A

to remove water and it was used in esterificcation

78
Q

what causes overtones in IR spectrum

A

if you take the original cm-1 and multiply it by 2 you get the value of the functional group’s overtone

79
Q
A

no it will not dissolve because they will have strong intermolecular attractions w eachother

80
Q

what is the purose of TLC

A

identifying compounds, determining their purity and following the progress of a reaction

81
Q

which is more polar the stationary phase or mobile phase

A

the stationary phase is more polar. If you increase the polarity of the mobile phase then it’s retention time will be longer thus the fractions will elute faster. Note: polar molecules attracted polar molecules and vise versa

82
Q

Epoxides like stilbene oxide is generally considered what

A

carcinogenic

83
Q

what is the purpose of the reflux technique

A

it is used to keep the reaction held at a constant temperature

84
Q

what reagent is considered highly caustic (able to burn tissue) and hygroscopic (absorbs moisture from air)

A

NaOH

85
Q

In melting point determination, heating faster than 1-2 °C per minute, may lead to

A

the observed mp range higher than the correct one

86
Q

How is the equilibrium shifted in this esterification for a good yield of ester?

A

Water by-product is removed. (dean stark trap)

87
Q

two Methods that can be used to shift an equilibrium toward the product side of a reaction are:

A

A. Decreasing the quantity of one of the reactants.
C. Removal of the product as it is formed.

88
Q

Which of the following characteristics is necessary to make a Dean-Stark trap work properly? The chemicals that build up in the Dean-Stark trap must: ___________

A

be immiscible

89
Q

What characteristic must the solvents in a solvent extraction solvent system share with one another?

A

They must be immiscible in one another.

90
Q

What happens when nitric acid is mixed with an organic solvent like acetone, ethyl acetate, or diethyl ether?

A

heat and gas are released after a delay, and an explosion could result

91
Q

The GC-MS data will show us

A

what mixture of isomers were formed in the reaction

92
Q

Which of the following reagents used in this experiment is a strong oxidizer?

A

NaNO2

93
Q

It is important to avoid isolating the diazonium salt as a pure solid because:

A

solid diazonium salts can explode

94
Q

What does “solvolysis” mean?

A

It is a reaction between the solvent and the solute forming a new compound.

95
Q

sternutator”. What does this mean?

A

It means it may cause sneezing.

96
Q

The purpose of carrying out a reflux is to …

A

carry out a reaction or process atboiling temperatures without loss of volatile components.

97
Q

Slow cooling is advised during a recrystallization because…

A

purer crystals are obtained, as the soluble impurities are not bound within the crystal structure.

O-chem (3 decks)

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