CHE 3238 Final Pre+Post Lab Qs

True or False: Melting point should be recorded as an exact temperature.

False, should be a range

What influences melting point?

Purity of sample

When doing a rough melting point, you want to set the ramp rate to _. After this measurement is finishes, you should set the start temperature _ your observed rough melting point and chose a ramp rate of _ to obtain your precise melting point measurement.

10ºC/min; slightly closer to, 1ºC/min

The low temperature of a melting point measurement corresponds to the...

moistening point

I run a melting point experiment in the lab. In my fast measurement, I observe my solid slightly changing at 123 °C, then liquid sample appears at 124 °C. I see a meniscus form at 126°C and the sample melts completely at 127 °C. Then, I run a slow measurement where I observe slight change and liquid appearing at 123 °C. A meniscus forms at 124 °C and the sample becomes clear at 125 °C.

What should I mark down as the accurate melting point of this sample?

123-125

The melting point range of a impure compound will be

lower and broader

True or False: You can dispose of used melting point capillaries in the normal trashcan.

False- goes into glass waste

True or False: You cannot reuse melting point samples.

True

What is the primary purpose of infrared (FTIR) spectroscopy in chemical analysis?

To identify functional groups in a molecule

Fourrier Transform Infrared Spectroscopy (FTIR) observes what kind of molecular motion?

Vibrations

FTIR spectra are given in what units?

wavenumbers (cm-1)

When you are done with your IR, you should clean your plates with

_ and kimwipes.

acetone

Water in your sample would show as....

A large, broad peak at 3500 cm-1

What is the difference between the "fingerprint region" and the "functional group region" in an IR spectrum?

The fingerprint region is unique to each molecule and shows complex, overlapping absorptions, while the functional group region shows characteristic absorption bands for functional groups.

The salt plates used in this experiment do not absorb IR radiation

True

True or false: FTIR can visualize ALL covalent bond vibrations.

False

What is the primary purpose of 1H NMR Spectroscopy?

To elucidate the structure of organic compounds

All types of atoms are visible by NMR

False

Which of these functional groups would be most deshielded (high ppm value):

aldehyde

-CH2Cl (the H2)

benzene ring

alkene

aldehyde

Which of the following affect a 1H nucleus' chemical shift, in ppm.

Resonance structures, electronegative atoms, aromatic rings

What does the integration of a peak in a 1H NMR Spectrum represent?

The number of protons contributing to that peak

You can use normal chloroform (CHCl3) as the solvent for your NMR sample

False- can't have any H's or else they will interfere with the results

You find in the lab two liquid samples with their labels erased! You know one is an aldehyde and one is a ketone. Which of the techniques that you used in the Compound ID lab would be the most accurate in helping you figure out which sample is which?

NMR

True or false: The C-O bond vibration in isopropanol is a broad peak around 3300 cm-1

False- the -O-H bond would be at 3300 cm-1, not the C-O

You attempt to synthesize ibuprofen in the lab. You obtain a white solid which looks like ibuprofen, and melts at the correct melting point (75-77 °C). You mix the synthesized sample with pure ibuprofen, then take a melting point analysis of that mixed sample. Which of the following observations would prove to you that your synthesized sample is indeed ibuprofen?

The melting point of the mixed sample would remain 75-77 °C

A diethyl ether organic phase would

be above the aqueous layer (density of diethyl ether is smaller than water therefore would float)

A chloroform organic phase would

be below the aqueous layer (density of chloroform is heavier than water therefore would sink)

I have a mixture of 3 compounds: A is acidic, B is basic and N is nonacidic. If I treat my mixture with aqueous NaOH, which compound(s) will remain in the organic phase?

B and N (A would react and be in the aqueous phase)

I want to extract N-methylpyrrolidine from an organic solution that also contains methyl benzyl ether. I can achieve this separation by treating the organic phase with aqueous 1 M NaOH.

False (N-methyl pyrrolidine is a base and must be protonated to be separated from the nonreactive ether. Sodium hydroxide will not protonate as it is a basic solution.)

I can deprotonate phenol with a solution of sodium bicarbonate of pH 8.5.

False (phenol has a pKA of 10 and therefore the pH of the aqueous solution must be higher than 10 to achieve deprotonation. The pH of sodium bicarbonate is not basic enough.)

Which of the following are correct when using a separatory funnel for an aqueous extraction?

Vent regularly after shaking, point the funnel towards the back of the hood while venting, remove the stopper before turning the stopcock to pour out the solution, rest the funnel on a ring stand/c clamp

Predict whether the organic compounds below would be majoritarily protonated or deprotonated at the given pH.:

Acetic acid in a solution of pH 2

Aniline in a solution of pH 12

Salicylic acid in a solution of pH 4

Piperidine in a solution of pH 7

Protonated

Deprotonated

Deprotonated

Protonated

Organic bases generally contain which functional group?

Amine

You are looking at extracting a phenol-containing compound (pKA =10.5) from an organic phase and transfer it to the aqueous phase. Which of the following aqueous solutions can you use to perform this extraction?

1% aqueous NaHCO3, pH 8.5

1M NaOH, pH 14

water, pH 7

saturated NH4Cl, pH 5

1M NaOH, pH 14 (pH needs to be greater than 10.5)

You are looking at extracting a pyridine-bearing compound (conjugate acid pKA = 4) from an organic phase and transfer it to the aqueous phase. Which of the following aqueous solutions can you use to do so?

1M NaOH, pH 14

water, pH 7

saturated NH4Cl, pH 5

1 M HCl, pH 1

1 M HCl, pH 1 (pH needs to be less than 4)

I can take my separatory funnel out of the fume hood to shake it.

False

I don't know which of my layers is water and which is my organic phase, and I've forgotten what solvent I used!

Which of the following observations would tell me that my top phase is my organic phase:

-I add a few drops of water to the top of my separatory funnel. The droplets pass through the top phase without mixing, then mix with the bottom phase

-My top phase is yellow colored

-I add a few drops of water to the top of my separatory funnel. The droplets mix with the top phase

-My top phase looks slightly cloudy

I add a few drops of water to the top of my separatory funnel. The droplets pass through the top phase without mixing, then mix with the bottom phase

Column Chromatography using silica gel separates compounds by...

Polarity

As opposed to a TLC, the eluent moves ..... in a chromatography column

downwards

A flash column is faster than a normal gravity column thanks to the application of

air pressure

The construction of your column should include

A short plug of cotton

A top layer of sand

A layer of silica gel

A bottom layer of sand

Each time you add eluent, you should elute the solvent completely out of the silica gel so it becomes dry again before adding more eluent.

False

When doing a gradient elution you start your column with a ___ eluent mixture and progressively ___ polarity until your target eluent mixture is reached

nonpolar; increase

You are evaluating a gradient elution eluent for use in a column by TLC. In order for your compound to elute when you reach the end of the gradient, the TLC RF of your desired compound in that eluent should be...

0.3-0.5

Order these solvent mixtures from least polar (1) to most polar (4)

Least polar

1:1 Hexanes/Ethyl acetate

5:2 Hexanes/Ethyl acetate

9:1 Hexanes/Ethyl acetate

2:3 Ethyl acetate/Hexanes

Most polar

9:1 Hexanes/Ethyl acetate

5:2 Hexanes/Ethyl acetate

2:3 Ethyl acetate/Hexanes

1:1 Hexanes/Ethyl acetate

In flash column chromatography, the silica gel is the stationary phase and the eluent is the mobile phase.

True

The cotton plug and bottom layer of sand in a column serves what purpose?

It creates a flat surface for the silica get layer to rest on; it prevents silica gel from flowing out of the column

If, during your experiment, instead of regular silica gel you had used reverse phase silica gel, which compound would have eluted out of the column the fastest?

acetaminophen, asprin, caffeine

caffeine

(Reverse phase silica gel is coated with hydrophobic chains. Polar compounds therefore interact less with the stationary phase, while non-polar compounds will interact with it strongly. The order seen in regular silica gel chromatography will be reversed: caffeine is the most polar compound and will elute out first, followed by acetaminophen and finally caffeine.)

Flash column chromatography is a special type of column chromatography that uses ___ to increase efficiency.

compressed gas

Equilibration of the silica gel column...

Removes air bubbles and cracks from the silica gel layer

Must be done before loading the sample mixture onto the column

Chromatography columns are packed with silica gel, which consists of microscopic beads of silica. The size of the beads in most chromatography-grade silica gel is 60 to 200 mesh. Higher mesh means smaller, finer particles, similarly to sandpaper grit.

If you changed the silica gel to a higher mesh, would that affect the separation?

It would slow the eluent flow rate but improve separation

When at reflux, the temperature inside the reaction flask is constant

True

Reflux is observed when

the solvent drips steadily back into the reaction

If I run a reaction at reflux in toluene, what temperature would my reaction be at?

110ºC (boiling point of toluene)

The reaction I am running reacts A and B together to make product C. In my flask, I have 15 mmol of A and 20 mmol of B. How many equivalents of B are there compared to A? round to 2 decimal places

1.33

I am using 5 mL of a 2.5 M solution of NaOH. How many millimoles of NaOH does this correspond to? (use 3 significant figures)

12.5

I calculated that my reaction could give me 250 mg of product, but only isolated 175 mg. What is my percent yield?

70%

I have to use 382 mg of phthalic acid in a reaction. Using molecular weight, calculate the millimoles of phthalic acid this corresponds to, with 3 significant figures

2.30

True or False: you can use an acid-base extraction to separate your tetracyclone from leftover benzil or dibenzylketone.

False (neither are soluble in water and neither react as acids or bases)

How many millimoles of KOH would be present in 1.2 mL of a 1.1 M solution of KOH in ethanol? Use one decimal place.

1.3

You plan a synthesis of tetracyclone using different quantities of Benzil and Dibenzylketone. 282.1 mg is the mass of benzil while 408.2 mg is the mass of dibenzylketone. What is the theoretical yield of the reaction, in milligrams? Use 1 decimal place.

515.2

You used an eluent mixture of 9:1 hexanes/ethyl acetate for your TLC. What would happen to your RF values if you changed the eluent to 7:1 hexanes/ethyl acetate

all RF values would increase

Hydrogen is the only atom that can be analyzed by NMR

False (can do F as well as others)

In this experiment, you are using a solution of azulene in hexanes of known concentration. What weight of azulene, in milligrams, would you be using if you were starting with 1.5 mL of solution? Use 3 significant figures.

10.5

Trifluoroacetic anhydride is a liquid. What volume, in milliliters, would you need to measure to obtain a 1 g sample of trifluoroacetic anhydride? Use 2 decimal places.

0.66

You have a mixture of your EAS starting material (azulene) and your product (trifluoroacetyl azulene) that you want to analyze by TLC. Which of the two compounds would have the lowest RF?

Trifluoroacyl azulene product (more polar than azulene and wont travel up the tlc as much)

When I add water to my reaction, the water phase will be on top of the organic phase (solvent is hexane)

False

If I need to wash my glassware with water, I can do so in the sink.

False (wash it with DI water into waste beakers)

In what region(s) of the NMR spectrum do you expect peaks for trifluoroacetyl azulene?

6.5-8.5 ppm (benzene Hs)

If you were to take an IR spectrum of your trifluoroacetyl azulene product, in what region(s) of the spectrum do you expect to see relevant peaks?

3000 cm-1 and 1700 cm-1

If the EAS experiment I am running goes to completion, I would have leftover azulene.

False (limiting reagent, TFAA was in excess)

You forgot to put your vial in the oven! What could be the main consequence of this error?

The trifluoroacetic anhydride could react with leftover moisture and affect yield

One product of your reaction is the red product, trifluoroacetyl azulene. Another chemical is produced during the EAS reaction: which of the following would it be?

trifluoroacetic acid (TFAA)

In the EAS experiment, you added water to your reaction after observing the color change. What could be the role of water?

it reacts with any excess trifluoroacetic anhydride to form trifluoroacetic acid

it makes an aqueous phase that trifluoroacetic acid will dissolve in

If you had tested the pH of the aqueous phase you removed, what result would you expect? Assume the DI water is pH 7.

Acidic pH (<6)

The melting point of the recrystallized product should be a _ and a _ compared to the melting point of the crude product.

higher temperature; narrower range

T or F: Precipitates can be mixtures, while crystals are pure compounds.

True

T or F: My procedure tells me to add up to 8 mL of boiling ethanol to recrystallize my solid. I can add the whole amount at one time without affecting my yield.

False

True or false: in the reaction, cinnamaldehyde is deprotonated by sodium hydroxide.

False- its the phosphonium salt that naoh deprotonates

You find 2 samples with erased labels that look like cinnamaldehyde. You know one is benzaldehyde and one is cinnamaldehyde. Which of the following NMR signals would show you your sample is cinnamaldehyde?

there is a doublet at 9.7 ppm (aldehyde)

there is a doublet of doublets at 6.7 ppm (benzene)

In one of your NMR spectra, the doublet at 9.7 ppm has a J value of 7.5 Hz. Similarly, the doublet of doublets at 6.7 ppm has two J values: 15.7 Hz and 7.5 Hz (one for each "split"). What does that information tell you about the two hydrogens that correspond to those peaks?

the two hydrogens are neighbors and are coupling to each other

True or false: if you had leftover cinnamaldehyde in your product, an acid-base extraction can be used to deprotonate the unwanted starting material and purify your product.

False

You are looking to setup a Wittig reaction with 0.63 mL of cinnamaldehyde. Using the same proportions as the experiment you did in the lab, what mass of benzyltriphenylphosphonium chloride, in grams, would you require? Round the final amount to two decimal places.

2.10

In the Wittig reaction lab, why was your recrystallized product washed with cold ethanol and not room temperature or hot ethanol?

to minimize the solubility of the product in that solvent

T or F: You accidentally used 1.0 g of benzyltriphenylphosphonium chloride instead of the 1.61 g indicated in the procedure. This wouldn't affect yield as the reagent is still in large excess.

False

I run a new Wittig reaction, and calculate that my theoretical yield of 1,4-diphenylbutadiene is 0.43 grams. How much triphenylphosphine oxide would the reaction also produce, in grams? Round your result to two decimal places.

0.58

You used 9:1 hexanes/ethyl acetate as eluent for your TLC. What would happen to your Rf values if you had run the same TLC samples in 8:1 hexanes/ethyl acetate?

The Rf of all spots would increase

What are the key physical processes involved in distillation?

Boiling and condensation

What is the primary difference between simple distillation and fractional distillation?

Fractional distillation uses a fractionating column, simple distillation does not

What is the role of a fractionating column?

To increase the number of repeated condensation and vaporization cycles

What is a theoretical plate?

-a representation of one condensation and vaporization cycle

-a measure of the separation efficiency of the column

T or F: A catalyst gets consumed in a reaction

False

According to Le Chatelier's principle, which of the following are ways to manipulate equilibrium?

-increase the proportion of one of the reagents

-remove or sequester one of the products

Which of the following techniques could be used to modify the position of the equilibrium by removing or sequestering a product?

-Using a Dean-Stark trap and toluene azeotrope

-Use of a drying agent to remove water

What are examples of catalysts?

-KOH in the synthesis of tetracyclone

-H2SO4 in the Fischer esterification

My reaction calls for 20 mol% of catalyst. If I use 15 mmol of limiting reagent, how many mmol of catalyst should I be using?

3

TLC is able to separate diastereomers of the same compound. If you had started with a 50/50 mixture of cis and trans cinnamic acid, you would have seen two spots in your cinnamic acid standard lane.

True

You monitored the completion of your esterification reaction by TLC. If you had to monitor the completion of the reaction by NMR, which peak could you use to quickly identify presence of the methyl cinnamate product

a singlet at approx. 4 ppm

You obtain two unlabeled printouts relating to this experiment. One is methyl cinnamate while the other is cinnamic acid. Which IR vibration peak would tell you this spectrum shows cinnamic acid.

a medium intensity, very broad peak at 3000 cm-1 that resembles a V

If you had used dichloromethane instead of diethyl ether for your extraction, which of your phases would be the aqueous phase?

the top phase