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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
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
The fractions will contain mixtures of products
26
When visualizing a TLC plate with 2,4-DNP dip, what does the orange color indicate.
Indicates aldehydes and ketones are present
27
What is the purpose of the vacuum on the rotary evaporator?
To lower the boiling point of the solvent
28
When shutting down the rotary evaporator, which valve must you close first?
First, turn off the vacuum at the main valve (blue) and then open the vacuum line before removing flask.
29
Vanillin Experiment Why is NaBH4 used as reducing agent instead of LiAlH4?
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.
30
Vanillin Experiment Why is reduction of vanillin acetate done at 0°C?
To avoid the ester group on vanillin acetate converting into an alcohol via base-catalyzed ester hydrolysis
31
What can one see when visualizing a TLC plate with UV light?
Chemicals with conjugated double bonds
32
Grignard Reaction Experiment Crystal Violent and Malachite Green can be synthesized from what?
Grignard Reagent and ester
33
What is a Grignard Reaction?
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.
34
What is a Grignard reagent?
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
35
Grignard Reaction Experiment The Mg-C bond formed from grignard reagent is describe how?
A polar covalent bond, with a large partial negative charge on the carbon atom
36
Grignard Reaction Experiment Why must Grignard reactions done in anhydrous conditions?
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.
37
Grignard Reaction Experiment Why was 1-bromobutane used in this experiment?
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.
38
Grignard Reaction Experiment The surface area of reactive magnesium metal was increase by doing what?
Grinding with mortar and pastel to remove layer of less reactive magnesium oxide and adding iodine
39
Grignard Reaction Experiment What compounds will form when n-butylmagnesium bromide reacts with water?
Butane and HOMgBr (or some form of magnesium hydroxide)
40
Why must you be cautious when working with diethyl ether?
It is highly flammable and volatile
41
Why must you be cautious when working with magnesium?
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
Grignard Reaction Experiment We avoided wrapping a damp pipe cleaner around the reflux apparatus in this experiment for what reason?
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
Name the observed color for these color absorbances Blue/Vio Blue Blue-Gre Green Orange Purple
Blue/Vio -> Yellow Blue -> Orange Blue/Gre -> Red Green -> Purple Orange -> Blue Purple -> Green
44
What is the auxochrome?
A substituent that alters the wavelength and the intensity of the absorption
45
When measuring the melting point for identification purposes, should you be concerned whether the sample is wet?
Yes, if the sample is wet, the observed melting point will likely be lower than the literature value.
46
Boiling points measured in Boise will be ____________ compared with boiling points measure at see level. why?
Lower because the air pressure in Boise is lower than the air pressure at sea level
47
During recrystallization, which chemicals are left in the mother liquor (the filtrate that gets separated from the crystals at the end)?
Impurities that were present in the crude compound and the target compound
48
What can you learn about an unknown compound by titrating it with NaOH?
Molar Mass
49
A boiling point collected in lab from distillation apparatus will be lower, equal, or higher than the literature value?
Lower
50
Define the boiling point
the temperature at which vapor pressure of the liquid equals the atmospheric pressure
51
What does the 2,4-DNP Test test for?
Determines whether we have a aldehyde/ketone or alcohol (+) aldehyde/ketone present = Forms yellow-orangish-redish precipitate
52
By looking at the density: A should be top C in the middle and B on the bottom
53
what should you do if there is an insoluble impurity during recrystallization
do a hot filtration
54
what happens to the solubility of the crude product as temperature increases during recrystallization
it increases
55
how does carbocation effect melting point?
will cause the melting point to be lower
56
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
what are the most common stationary phases in column chromatography
alumina(Al2O3) and silica gel (SiO2)
58
Both spectra
59
When doing column chromatography, what is a slurry?
a solution of stationary phase suspended in mobile phase
60
E first then K X and B
61
What will change if you increase the polarity of the mobile phase used in a column chromatography separation
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
what is the purpose of visualizing TLC plates under UV lights
* Works for chemicals with conjugated double bonds (all of the chemicals in this experiment). * Does not distinguish other functional groups
63
B
64
C
65
66
what kind of solvent is a grinard reagent made in
diethyl ether
67
what is the stationary phase in GC
solid
68
what is a polymer
A large molecule with a repetitive structure
69
equation for atom economy
70
equation for reaction efficiency
71
what doess conjugation do to IR stretching frequency
it decreases it
72
As the number of conjugated double bonds increases what happens to the energy and absorbed wave length
energy to excite electrons decreases and the absorbed wave length increases
73
for each carboxylic acid functional group, you need to add in this example 3 equivalence of NaOH
74
75
76
B because a catalyst only makes the reaction go faster
77
what is the dean stark trap used for and what experiment was it used in
to remove water and it was used in esterificcation
78
what causes overtones in IR spectrum
if you take the original cm-1 and multiply it by 2 you get the value of the functional group's overtone
79
no it will not dissolve because they will have strong intermolecular attractions w eachother
80
what is the purose of TLC
identifying compounds, determining their purity and following the progress of a reaction
81
which is more polar the stationary phase or mobile phase
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
Epoxides like stilbene oxide is generally considered what
carcinogenic
83
what is the purpose of the reflux technique
it is used to keep the reaction held at a constant temperature
84
what reagent is considered highly caustic (able to burn tissue) and hygroscopic (absorbs moisture from air)
NaOH
85
In melting point determination, heating faster than 1-2 °C per minute, may lead to
the observed mp range higher than the correct one
86
How is the equilibrium shifted in this esterification for a good yield of ester?
Water by-product is removed. (dean stark trap)
87
two Methods that can be used to shift an equilibrium toward the product side of a reaction are:
A. Decreasing the quantity of one of the reactants. C. Removal of the product as it is formed.
88
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: ___________
be immiscible
89
What characteristic must the solvents in a solvent extraction solvent system share with one another?
They must be immiscible in one another.
90
What happens when nitric acid is mixed with an organic solvent like acetone, ethyl acetate, or diethyl ether?
heat and gas are released after a delay, and an explosion could result
91
The GC-MS data will show us
what mixture of isomers were formed in the reaction
92
Which of the following reagents used in this experiment is a strong oxidizer?
NaNO2
93
It is important to avoid isolating the diazonium salt as a pure solid because:
solid diazonium salts can explode
94
What does "solvolysis" mean?
It is a reaction between the solvent and the solute forming a new compound.
95
sternutator". What does this mean?
It means it may cause sneezing.
96
The purpose of carrying out a reflux is to ...
carry out a reaction or process at boiling temperatures without loss of volatile components.
97
Slow cooling is advised during a recrystallization because...
purer crystals are obtained, as the soluble impurities are not bound within the crystal structure.

O-chem (3 decks)

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