Ochem lab 2325

Acetic anhydride will show two carbonyl stretching frequencies in the IR spectrum.

True

Learning organic chemistry with chemical structure drawings and not just words (names) is required for this course.

True

Which item is missing from our lab? A copy of the Safety Agreement is linked on the main page.

fire blanket

The desired product from this experiment is...

is soluble in hexanes.

The product of each reaction should be:

labeled and stored for use in subsequent reactions

Which is the best analogy of how trituration works?

separating salt and sand by adding water

What is the formal oxidation state of the indicated carbons? Answers may be repeated.

the carbon that is attached to oxygen --> +1 the carbon on the benzene ring with no hydrogens attached --> 0 the carbon that is attached to oxygens --> +3 any carbon on the benzene ring with a hydrogen attached --> -1

Match each use to a reagent that will be used in this experiment.

the compound that is to be purified --> Benzaldehyde the major contaminant of the compound that is to be purified --> benzoic acid used to convert the major contaminant to a salt that is more soluable in water --> % 10 (g/v) aqueous sodium carbonate used to remove excess base --> water used to remove water --> anhydrrous magnesium sulfate used to prevent the product from oxidizing easily --> hydroquininone

Why must we wait for our reaction flask to cool to room temperature before adding water in this experiment?

to avoid breaking the flask

Though not stated in the procedure, what is the best reason why we should clamp the Erlenmeyer flask while heating the reaction?

to avoid burning our hands

Match each use to the piece that was used in your vacuum distillation setup. Exact matching.

used to keep up the heater in case the heater needs to be removed quickly --> ring clamp used to create constant agitation --> boiling chips used to connect the round bottom flasks --> clamps used to prevent large bubbles from bumping over --> Claisen adapter used to plug the unused connection of the Claisen adapter --> glass stopper used to connect the side arm of the Claisen adapter to the condenser --> distillation head used to record the boiling point --> thermometer used to cool hot vapors --> condenser used to connect the distillation setup to the vacuum --> vacuum adapter used to prevent oxidation --> hydroquinone

The major purification technique that we will learn in this experiment will be?

vacuum distillation

As you observed, benzaldehyde is immiscible in water. Looking up the density of benzaldehyde, match each condition to what you were most likely to observe in "washing" benzaldehyde with different liquids.

washing with too little deionized water --> an emulsion washing with plenty of deionized water --> water floating on benzaldehyde washing with 10 % sodium carbonate --> benzaldehyde floating on water

In today's reaction you will be making a mixture of (Z) and (E) stilbene. The ratio of E-stilbene to Z-stilbene in the product mixture is 2:1. If you start from 7.8 g benzyltriphenylphosphonium chloride and 2 mL benzaldehyde, then how much Z-stilbene you will be making if your reaction yield is 78%.

0.89 g

How many mL are required to get 13 g of a liquid with density 1.26? Give 2 significant digits in your answer.

10

The Clausius-Clapeyron Equation (hopefully introduced to you in General Chemistry) can be used to relate the temperature and vapor pressure of a pure liquid given its heat of vaporization. It can be used to create a specialized nomograph for each compound as shown in Figure 6.1 of your text for hydrocarbons and carboxylic acids. In a simplified form it is given in Equation 6.1 of your book for nitrobenzene. At what temperature in °C should benzaldehyde distill if your vacuum pressure is [[p]] mm Hg? Provide 2 significant digits in your answers, for instance, 559 should be rounded to 560.

110

How many grams are in 94.0 mL of a liquid with density 1.33? Give 2 significant digits in your answer.

130

According to the text, how many mL of the starting material will be used in this experiment?

15

How many hydrogens are in benzyltriphenylphosphonium chloride?

22

Using Hooke's law, calculate the stretching frequency of a C-D bond if the stretching frequency of a C-H bond is 3040 cm-1

2230 cm^-1

How many carbons are in benzyltriphenylphosphonium chloride?

25

How much sodium carbonate do you need to make a 75mL 5 wt% aqueous sodium carbonate solution?

3.75 g

How many stereoisomers of stilbene dibromide are possible in today's reaction if you start from a mixture of (Z)- and (E)-stilbene?

4

What is the percent recovery if you started with 9.3 mL of benzaldehyde and ended with 4.1 g of benzaldehyde after distillation? Give 2 significant figures in your answer. Assume the density of benzaldehyde is 1.044.

42

In this lab, sometimes we use benzyltriphenylphosphonium bromide instead of the chloride because of availability. Using the following atomic weights, what is the formula weight of benzyltriphenylphosphonium bromide? Give a whole number answer. C = 12, H = 1, O = 16, N = 14, P = 31, Br = 80, Cl = 35.5

433

Which regions is considered fingerprint region in IR spectra?

500-1500 cm^-1

At the text scale, how much hexanes will be used to triturate with in this experiment of purification of stilbene?

6 x 50 mL

In case of minor accidents which may require medical treatment, we must always call which number?

747-5611 (University Police)

Using the formula weight of benzyltriphenylphosphonium bromide that you calculated in the previous question, how many grams (to the nearest tenth) of this substance will we use in this experiment if used instead of the chloride? Assume the amount of chloride listed in the book.

8.7

The Clausius-Clapeyron Equation (hopefully introduced to you in General Chemistry) can be used to relate the temperature and vapor pressure of a pure liquid given its heat of vaporization. It can be used to create a specialized nomograph for each compound as shown in Figure 6.1 of your text for hydrocarbons and carboxylic acids. In a simplified form it is given in Equation 6.1 of your book for nitrobenzene. If benzaldehyde in your vacuum distillation boiled at [[c]] °C, how good was your vacuum in mm Hg? Provide 2 significant digits in your answers, for instance, 559 should be rounded to 560.

82

Let's assume you were given 3.4 g of stilbene dibromide, 1.75 g of KOH and 20 mL of triethylene glycol to do today's reaction. At the end of the reaction, you isolated 1.5 g of diphenylacetylene. What is the % yield of this reaction?

84.0%

Which of the following structures could be the resonance structures of benzylidenetriphenylphosphorane (drawn below)? Note that this compound is the Wittig reagent in your experiment. Hint: You need to move the pi-electrons around to figure out the correct answers. Remember that the resonance structures should be chemically meaningful. (Negative credits will be applied to incorrect answers. Select 4 correct answers to get full credits.)

A1 A2 A4 A6

Which of the following dibromide compounds is NOT capable of undergoing double elimination reaction to produce diphenylacetylene type compound when reacts with strong base? (Negative credits will be applied to incorrect answers. Select 2 correct answers to get full credits.)

A1 A4

As both Na2CO3 and NaHCO3 are weak base, NaHCO3 solution can be used in place of Na2CO3 solution to do the washing of benzaldehyde in today's experiment. Keeping this information in mind, predict the end products of the washing step. Here 'washing step' refers to the washing of benzaldehyde with NaHCO3 solution.

A2

Oxaphosphetane is a four-membered ring compound that forms as an intermediate in a Wittig reaction. Which of the following oxaphosphetane will be formed if you perform following Wittig reaction?

A2

Predict the structure of the bromonium ion intermediate in the following bromination reaction.

A2

What would be the major product of the following reaction? Keep in mind that only one equivalent of KOH is present in the reaction.

A2

You have learned the bromination reaction of stilbene, associated mechanism and stereochemistry. Using that knowledge, predict the products for the following bromination reaction. (Negative credits will be applied to incorrect answers. Select 2 correct answers to get full credits.)

A2

Which of the following compounds are considered Wittig reagent? Remember, Wittig reagent can be expressed in two resonance forms. (Negative credits will be applied to incorrect answers. Select 2 correct answers to get full credits.)

A2 A3

Predict the intermediate in the following reaction. (Negative credits will be applied to incorrect answers. Select 2 correct answers to get full credits.)

A2 A4

What type of reaction are you going to perform today? (Stilbene dibromide PostLab)

Addition reaction

Match each structure to its place in the mechanism of the autooxidation of ethanal (acetaldehyde). Exact match.

Aldehyde --> Starting Material Radical --> First Intermediate Peracid --> Second intermediate Criegee Intermediate --> Third intermediate Ethanoic Acid --> Final product Oxygen --> Oxidizing agent Alcohol --> Not part of the mechanism but a precursor that is oxidized by bacterial to ethanal in liquor

What are we doing with all the isomers of stilbene dibromide?

All of them are equally useful for the next reaction.

Match the precautions on the left to a particular substance on the right. Exact match. (pt. 1)

Although not mentioned in the MSDS sheet, students have reported itchiness when they rest their wrists (exposed skin between the gloves and lab coat sleeves) on the front edge of the hood and someone has spilled this substance there. --> benzyltriphenylphosphonium chloride Though very volatile and thus relatively safe to use in a hood, this substance is a non-polar and thus can permeate your gloves and skin. Anything (chemicals, radiation, mechanical damage) that does cell damage is a potential carcinogen. To be safe (although your body heat will volatilize most of it), remove your gloves, wash and dry your hands, and use new gloves if you spill this substance on your gloves. --> dichloromethane This substance can dissolve your skin and convert it to soap. Fortunately, because it is so polar, it will not permeate your gloves. If you spill it on your gloves, wash it off with water. If you spill it on your skin, wash with copious amounts of water and soap. --> 50 % aqueous sodium hydroxide This substance must be applied lightly to all the joints of your equipment especially because the non-polar solvents will leach it. --> silicon grease Though present in perfumes, too much of anything is bad especially because it is also non-polar and permeates the skin. --> benzaldehyde

The boiling point of this final product of this experiment should be:

Below 180°C

The night after the vacuum distillation experiment, many condensers start forming a white solid inside them. What is this white solid?

Benzoic Acid

Which of the following compounds forms as an intermediate in the autoxidation of benzaldehyde to benzoic acid?

C4

You have learnt about the oxidation of benzaldehyde and the nature of common impurity in a bottle of benzaldehyde. Using that knowledge, answer the following question. Which of the following compounds is the most common impurity in a bottle of para-tolualdehyde?

C4

Which of the following types of bonds produce strongest absorptions in the IR spectra for sure? (Negative credits will be applied to incorrect answers. Select 2 correct answers to get full credits.)

Carbon oxygen double bond of Acetone N-N-N bond of sodium azide

What compound is the precursor to the fizzing that was observed in the washing of benzaldehyde with 10 % sodium carbonate? Sadly, this compound is the reason why the oceans are acidifying.

Carbonic Acid

What are "hexanes"?

a mixture of hydrocarbons that has the approximate boiling point to that of normal hexane

Match the unit to the symbol in the following equation: E = hv = (hc)/λ

E - kJ h - Js c - ms^-1 λ - cm v - s^-1

What type of reaction are you going to perform today? (Diphenylacetylene Post Lab)

Elimination Reaction

What activities can endanger your laboratory environment? (Negative credits will be applied to incorrect answers. Select all the correct answers to get full credits.)

Entering lab if you don't see your TA in the lab Entering lab without long pant Entering lab without lab coat Entering lab without safety goggles Not asking your TA if you are unsure of your waste treatment Pouring down a clear, water-like liquid to the sink without knowing the identity of the liquid Walking around the lab wearing a flip flop Pipetting any liquid by your mouth Leaving the chemical bottle uncapped in the balance room Quickly throwing away the broken glass after breaking an glassware, without telling your TA Smelling your product as it smells good Using a round bottom flask with a visible crack for a high heat refluxing experiment Following your TA's instructions even if you don't understand fully

You will be turned away from the lab and a receive a zero in attendance for missing all but one item?

Experimental Organic Chemistry A Small-Scale Approach, 2nd Edition, Wilcox & Wilcox

C=C stretching frequency of a trans-alkene will be stronger than that of a cis-alkene.

False

It is only necessary to read the experimental section of the textbook and not the full chapter for background information.

False

Which compound is generated "in situ" in this lab? This is why your reagents should only be mixed in the hood.

bromine

For this experiment you should start heating water in a large beaker but under no circumstance should you place any hexanes near the heater! In fact, you should not get the total quantity of hexanes that you will use in the experiment, only the small amount you need for each trituration and keep it on the opposite side of the hood as the heater. You should weigh out the largest round bottom flask that you have with the aid of a cork ring. You will then clamp the flask that contains the dried products from the previous lab, add the appropriate amount of hexanes away from the heater, heat the mixture a short time on the hot water bath (Bain-Marie or Baño Maria) until the hexanes start boiling (you are not trying to evaporate it), and decant off the supernatant carefully into your largest round bottom flask away from the heater with the aid of a funnel suspended on a ring clamp. Since you are repeating the trituration a few times you should not try to pour off all the supernatant at the risk of pouring over solid. The hexanes will be evaporated off on a rotary evaporator. Once evaporated and cooled off you should weigh the flask and remove your product for the next reaction. What is our major concern for this experiment?

Fire Exposure to fumes

How can we best maintain the temperature of our reaction between 160 and 170 °C?

clamping the flask and raising or lowering it off the heating well

Which of the following molecules will not give any IR spectrum? (Negative credits will be applied to incorrect answers. Select 3 correct answers to get full credits.)

H2 O2 N2

The infrared frequencies can be estimated from atomic weight using which law?

Hooke's Law

Why you should add a small crystal of hydroquinone while storing your pure benzaldehyde for future use? (Negative credits will be applied to incorrect answers. Select 2 correct answers to get full credits.)

Hydroquinone is easier to oxidize than benzaldehyde Hydroquinone reacts with O2 to form benzoquinone

What is the role of triethylene glycol in today's reaction? (Negative credits will be applied to incorrect answers. Select 3 correct answers to get full credits.)

It acts as a solvent It acts as a reagent and reacts with KOH It produces a much stronger base than KOH

Predict the solubility of stilbene dibromide according to the experimental procedure described in the lecture. (Negative credits will be applied to incorrect answers. Select 2 correct answers to get full credits.)

It is almost insoluble in cold acetic acid It is partially soluble in cold 1:1 methanol/water mixture

How does pyridium tribromide act as brominating reagent?

It provides bromine molecule in the reaction.

Which of the following compounds is frequently used to prepare IR pellet?

KBr

Predict the byproducts of today's reaction. (Negative credits will be applied to incorrect answers. Select 2 correct answers to get full credits.)

KBr Water

Anhydrous MgSO4 is a common drying agent that is used in Organic Laboratory to remove trace amount of water from organic solution. How do you think the anhydrous MgSO4 work as drying agent?

MgSO4 + 6H2O = [Mg(H2O)6]SO4

To convert stilbene dibromide to diphenylacetylene, you need strong base like KOH. In place of KOH, which of the following bases you can also use to promote this reaction? (Negative credits will be applied to incorrect answers. Select 2 correct answers to get full credits.)

NaOH NaOtBu

Which of the following compounds will be used as brominating reagent in today's reaction?

None of the above

You have learnt about the mechanism of Baeyer-Villiger oxidation. Now apply that mechanism on para-tolualdehyde and fill in the box with correct compound.

P3

Match the following materials to its proper waste disposal treatment:

Paper towel that you used to dry your hands after washing --> Trash can You spilled some benzoic acid and need to dispose it --> Solid waste container Some unused benzaldehyde from your laboratory experiment --> Non-halogenated waste container Saturated sodium bicarbonate aqueous solution portion after a liquid-liquid extraction --> Aqueous waste container You accidentally broke a round-bottom flask and need to dispose the broken glasses --> Broken glass waste container The NMR tube that you used to take NMR spectrum of your synthesized compound --> You should not dispose it. Some unused dichloromethane from your laboratory experiment --> Halogenated waste container

To prepare a Wittig reagent, you will be using NaOH in today's lab. If you do not find NaOH, what other reagents you can use in place of NaOH to make the Wittig reagent? Hint: Think about the role of NaOH in preparation of Wittig reagent. The alternative reagents should play similar role. (Negative credits will be applied to incorrect answers. Select 3 correct answers to get full credits.)

Phenyllithium Potassium hydroxide Potassium tert-butoxide

Match each types of electromagnetic radiation to its effect on a molecule.

Radio Wave - Realignment of nuclear spin Microwave - Rotation of molecules Infrared - Stretching and bending of chemical bonds Visible and Ultraviolet - Promotion of electron from filled to unfilled orbitals X-ray and gamma ray - Ionization of atom, breaking chemical bonds

Predict the products of the following Wittig reaction. (Negative credits will be applied to incorrect answers. Select 2 correct answers to get full credits.)

S1 S3

What type of isomers are (E)-stilbene and (Z)-stilbene? (Negative credits will be applied to incorrect answers. Select 2 correct answers to get full credits.)

Stereoisomer Cis-trans isomer

What is the limiting reagent in today's experiment?

Stilbene

What is the major reason why for such a small reaction we use such a large round bottom flask for this experiment?

The fumes of triethylene glycol can catch on fire.

Considering the procedure, time, and volatility of solvents; which paragraph represents a good starting point for the next lab?

The one that starts with "Triturate the residue"

Why should the funnel not be shaken vigorously during the extraction?

The organic and aqueous phases will form an emulsion and will not separate.

What is the best reason why we should only use a little ice-cold methanol and water to wash our final product?

The product is more soluble in methanol-water mixture at room temperature.

How do we know how much anhydrous magnesium sulfate to add to a liquid to dry it?

enough so that some powder is left over

Match the precautions on the left to a particular substance on the right. Exact match. (pt. 2)

This hydrocarbon is more flammable than gasoline and also a non-polar solvent that permeates the skin all the way to the brain. --> hexanes Though relatively safe and non-toxic, this substance can kill you if you keep your head in it for prolonged periods and thus is listed as dangerous in its MSDS sheet. --> water This substance will not be necessary for our lab procedure because our lab will be divided into two periods. --> anhydrous magnesium sulfate This is the desired product of this lab. --> (E)-stilbene This is the undesired by-product of this lab. --> triphenylphosphine oxide