CHEM241L - Final exam
At which pH is benzoic acid most soluble in organic solvent? (least polar, because organic solvent is non polar...)
pH of 2 where benzoic acid is all protonated (most anyways)
How will the first mL of distillate from the simple distillation differ from the first mL distillate of the fractional distillate?
the fractional distillate will be more pure
After your Grignard reaction is complete you will need to purify the carboxylic acid product. Outline the purification scheme that you plan to use (chromatography is not an option). If any part of your purification involves adding acids or bases, specify what your target pH is.
try to neutralize everything except for the carboxylic acid, and leave it in the aq layer. Add a fairly strong base that will protonate all other acids in the mixture and neutralize everything, but not the carboxylic acid product. Then remove the aqueous and re protonate the carboxylic acid by adding 6M HCl. Then dry with a buchner
Most charged organic compounds are more soluble in
water (polar)
List two features of a good solvent
1. has a lower melting point that the pure compound 2. has a wider range than the pure compound
If you removed the ammonium salt via acid wash, then what would you do with the organic phase?
Add NaOH Then you would separate the aqueous phase contain the carboxylate salt and the organic physe which would have the non-ionizable compound. Then you would re protonate
The products of the reaction are acetyl ferrocene and diacetylferrocene, why do the first and second acetyl groups end up on different ferrocene rings?
Because once one carbonyl group gets EAS to the ferrocene, it deactivates the ring so that no more can be added to that individual ring
The procedure states you should cool the reaction vial in an ice bath before adding ferrocene. Why is this necessary? (choose 1) To aid in the crystallization of products after the reaction is over To prevent the products from evaporating as they are formed Because the reaction is exothermic and might spontaneously boil away the solvent Because the hot plate is too large to control the temperature for such a small vial
Because the reaction is exothermic and might spontaneously boil away the solvent
If you have excess unreacted magnesium at the end of the lab, how should you dispose of it? (choose one) Throw it in the trash Put it in the solid waste container Leave it for the TA Dissolve it in 6M HCl
Dissolve it in 6M HCl
Friedel Crafts reaction- what type of reaction? What type of catalyst used? What time of reactants?
Electrophillic aromatic substitution reaction, acyl halide forms new c-c bond, aluminum chloride- chews acid catalyst
When two immiscible liquids are mixed what physical property determines which solvent layer is on the top?
Density, can check wihich is aqueous by adding small droplets of water
If benzene derivative is reactive enough, can brominate multiple times •Do bromines deactivate product enough to stop further brominations?
Depends on the derivative
Pure compound has what kind of MP
correct and a narrow range
EWG substituted benzenes give what kind of substitution effects?
meta examples: -COH, -COR, COOR
NMR- number of peaks
number of unique types of H
Most neutral organic compounds are more soluble in
organic solvent
EDG substituted benzenes give what kind of substitution effects?
ortho/para examples: NR2, -NH2, -OH, -
At which of the above pH is aniline the most soluble in organic solvent?
pH of 14 because it has no charge
What is the oxidation state the carbon bound to the oxygen of borneo, camphor, and isoborneol?
0, 2+, 0
If you are unsure which layer of your separatory funnel is the organic layer and which is the aqueous layer, which of these is the safest way to figure it out? (Choose one) Smell and/or taste each layer to see which smells like organic solvent Use a bunsen burner to see which layer is the flammable, organic layer Add a few drops of water to each layer to see if the water mixes in (aqueous layer) or forms a separate layer (organic) Dip your finger in to see which layer feels like water
Add a few drops of water to each layer to see if the water mixes in (aqueous layer) or forms a separate layer (organic)
If you accidentally measured out too much sulfuric or acetic acid, what should you do with the excess? Pour it back into the stock container Pour it down the drain Add the acid to water to dilute it, then pour it in the acid waste container Play a prank on your neighbor by pouring it in their water bottle
Add the acid to water to dilute it, then pour it in the acid waste container
AlCl3 and water?
Al(OH)3 and 3(HCl)
In this lab, you will use a variety of aldehydes and ketones, some of which are skin irritants. If you spill any of your starting material on yourself, what should you do? (choose all that apply) Go to the bathroom to clean up Let the chemical evaporate off your skin Alert your TA Assume the chemical is an irritant and wash the area with plenty of water
Alert your TA, Assume the chemical is an irritant and wash the area with plenty of water
Which of the following should you do if the contents of your separatory funnel spill on yourself? (choose all that apply) Go to the bathroom to clean up Alert your TA even if you have to shout Rinse the affected area with plenty of water Remove any affected clothing Blot the affected area with paper towels
Answer: Alert your TA even if you have to shout, Rinse the affected area with plenty of water, Remove any affected clothing
You are using sodium hypochlorite to oxidize borneol to camphor. What common household item is sodium hypochlorite found in? Toothpaste Dish soap Bleach Coca-cola
Answer: Bleach
What are some of the hazards of sodium hypochlorite? (choose all that apply) Chemically reacts to form toxic chlorine gas Corrosive if you spill it on your skin Poisonous if ingested
Answer: Chemically reacts to form toxic chlorine gas, Corrosive if you spill it on your skin, Poisonous if ingested
What are hazards of dry ice? (choose all that apply) It can cause cryogenic burns In sufficient quantity, it can displace oxygen and cause suffication It's flammable It's carcinogenic None, dry ice is as harmless as normal ice
Answer: It can cause cryogenic burns, In sufficient quantity, it can displace oxygen and cause suffication
Bromine must be removed from glassware before you rinse that glassware out with acetone. If acetone and bromine are mixed, they will produce bromoacetone. Why is bromoacetone very unpleasant? (choose one) It smells horrible It is explosive It is a lachrymator because it reacts with water in your eyeball to produce HBr, making you cry and causing a lot of pain It will dye your glassware and you'll never be able to get it fully clean again
Answer: It is a lachrymator because it reacts with water in your eyeball to produce HBr, making you cry and causing a lot of pain
What are some of the dangers of concentrated sulfuric acid? (choose all that apply) It is highly corrosive towards skin and clothing It releases a lot of heat when you add water to the acid, which risks the acid splattering and damaging the surroundings It smells bad It causes severe damage if it is ingested It is very reactive towards many other reagents, which risks the formation of other side-products with their own hazards
Answer: It is highly corrosive towards skin and clothing, It releases a lot of heat when you add water to the acid, which risks the acid splattering and damaging the surroundings, It causes severe damage if it is ingested, It is very reactive towards many other reagents, which risks the formation of other side-products with their own hazards
In this experiment you reflux your solvent. Why is that necessary rather then just heating an open flask? Refluxing lets you see the progress of the reaction Refluxing allows the reaction to be kept as hot as possible without solvent evaporating away Refluxing makes the fume hood more efficient by directing solvent vapors straight up Refluxing isn't necessary, it just looks cool
Answer: Refluxing allows the reaction to be kept as hot as possible without solvent evaporating away
If some of the bromine/hydrobromic acid mixture spills on you, what actions should you take? (choose all that apply) Remove your gloves and/or lab coat if any spilled Wash any affected skin with plenty of water If it got in your eyes, rinse them at the eye wash for 15 minutes Blot the mixture off your skin with a paper towel Alert your TA
Answer: Remove your gloves and/or lab coat if any spilled, Wash any affected skin with plenty of water, If it got in your eyes, rinse them at the eye wash for 15 minutes, Alert your TA
Why must all parts of the oxidation and reduction reactions be carried out in the fume hood? (choose all that apply) To protect you against any unplanned explosions To isolate any toxic gases produced such as chlorine gas In case any reactions accidentally ignite
Answer: To protect you against any unplanned explosions, To isolate any toxic gases produced such as chlorine gas, In case any reactions accidentally ignite
Why must the reaction temperature be carefully maintained at 50C instead of allowing the solution to reflux at 100C? (choose all that apply) At 100C, there is a higher risk of unwanted side reactions Sodium hypochlorite is unstable at higher temperatures The reaction will take longer at 100C meaning you will get a lower yield
At 100C, there is a higher risk of unwanted side reactions, Sodium hypochlorite is unstable at higher temperatures
In order to crystallize your product, you need to use the minimal amount of boiling hot organic solvent. What is the best method to add the solvent? (choose one) Hold the Erlenmeyer flask containing the boiling solvent in your hand and pour slowly into your crude material Transfer small amounts of solvent using a pipette until the crude product is fully dissolved Turn the heat down on the hot plate until the Erlenmeyer flask is cool enough to handle, then pour solvent into your crude material Instead of pouring hot solvent into your crude material, just scoop the crude product into the boiling hot solvent
Answer: Transfer small amounts of solvent using a pipette until the crude product is fully dissolved
IR salt plates are fairly expensive. What are some good techniques for handling them? (choose all that apply) Wear gloves when handling them so your sweat doesn't start dissolving them Hold them carefully so they don't fall on the floor and shatter When you're done with them, rinse them with bulk acetone (which contains a considerable amount of water) just like your other glassware When you're done with them, rinse them with a dry solvent like methylene chloride so they don't dissolve
Answer: Wear gloves when handling them so your sweat doesn't start dissolving them, Hold them carefully so they don't fall on the floor and shatter, When you're done with them, rinse them with a dry solvent like methylene chloride so they don't dissolve
If you added HCl and Ether what would be in the aq and what would be in the organic?
Aq- ammonium salt, save this/separate from the other mixture. Organic- carboxylic acid and the non ionizable
Acetophenone can undergo an aldol condensation with both benzaldehyde and cyclohexanecarboxaldehyde. Why would using cyclohexanecarboxaldehyde yield a product mixture with more products than using benzaldehyde?
Both of the two starting reactants have alpha carbons
There is an equilibrium between the carboxylic acid and ester for the Fischer esterification. Because esters and carboxylic acids have nearly identical stabilities, the equilibrium can be forced by doing what?
By using one of the reactants in excess, usually the cheaper reactant is chosen to be the reaction solvent, in this case acetic acid. And second, we will use a drying tube to move water form the reaction mixture, also serving to drive the reaction forward.
Why do you not see tri acetylation in the ferrocene friedel crafts experiment?
Carbonyls deactivate the ring
What are some of the hazards of dichloromethane (also known as methylene chloride)? (choose all that apply) Flammable Carcinogenic Explosive Can cause chemical burns upon skin contact Very volatile and easy to inhale
Carcinogenic, Can cause chemical burns upon skin contact, Very volatile and easy to inhale
Which of the following are true about mixing liquids in a separatory funnel? Everything should be done in your hood You should wear gloves Your hood sash should be between your face and the separatory funnel Don't aim the separatory funnel at anyone You should have a firm grip on the stopper and vent the funnel frequently by using the stopcock
Everything should be done in your hood, You should wear gloves, Your hood sash should be between your face and the separatory funnel, Don't aim the separatory funnel at anyone, You should have a firm grip on the stopper and vent the funnel frequently by using the stopcock
Often when quenching the reaction with water, a puff of corrosive smoke is seen. What is the origin of this smoke? (choose 1) HCl being released from the reaction Chlorine gas being released from the reaction The water igniting and combusting the unreacted starting materials Some of the ferrocene products evaporating
HCl being released from the reaction
Integration
How many of each unique type of H
What flammable gas is produced if sodium borohydride is mixed with water? (choose 1) Hydrogen Oxygen Borane (BH3) Hydrogen peroxide (H2O2)
Hydrogen
Splitting (n+1 rule)
If an atom has N H-atoms on neighboring carbon, it will be split into N+1 peak
If you spill bromine on the bench, what actions should you take? (choose all that apply) Inform your TA of the spill Wipe the liquid bromine up with a paper towel Quench the bromine with sodium bisulfite (a reducing agent) Pour water on the bromine to dilute it
Inform your TA of the spill, Quench the bromine with sodium bisulfite (a reducing agent)
What properties allow bromine to cause this health risk? (choose all that apply) It is a strong base It is a strong acid It is a strong oxidizing agent It is a strong reducing agent It is volatile and easily inhaled
It is a strong oxidizing agent, It is volatile and easily inhaled
What is the main health risk of liquid bromine? (choose one) It is flammable It smells bad It is corrosive and causes chemical burns It is explosive It is carcinogenic
It is corrosive and causes chemical burns
What actions should you take to reduce the health risk of silica gel? Keep it wet with solvent so less powder gets into the air Handle the silica gel in the fume hood If some silica gel spills, wipe it up with a wet paper towel, not a dry paper towel Wear personal protective equipment such as gloves and a lab coat to avoid getting silica gel on yourself
Keep it wet with solvent so less powder gets into the air, Handle the silica gel in the fume hood, If some silica gel spills, wipe it up with a wet paper towel, not a dry paper towel, Wear personal protective equipment such as gloves and a lab coat to avoid getting silica gel on yourself
Why slow cooling?
Large crystals, high purity, fast cooling, small crystals
What is the formula for sodium bisulfite? What is the use for this reagent in the experiment?
NaHSO3, to capture any excess bromine in the apparatus, stops it from escaping
When can diethyl ether and bunsen burnes be used together in lab? (choose one) You can flame dry your glassware while ether is in your round bottom flask You can't use a bunsen burner while you're using ether, but you can use it while other people are using ether No ether is allowed in lab until after everyone is finished with bunsen burners
No ether is allowed in lab until after everyone is finished with bunsen burner
Which of the following activities in this experiment can be performed outside the fume hood? (choose all that apply) The Friedel-Crafts reaction itself The TLC analysis of products The microscale extraction None of the above since they must all be carried out in the fume hood
None of the above since they must all be carried out in the fume hood
At what point in the procedure is the experiment no longer water sensitive, why can it be exposed to water after that point?
Once the reaction mix has formed a cloudy material or the solution is brown, the reaction has started. Once all Br has been replaced with the carboxylic acid/treated w/ CO2 it isn't sensitive to water, as there is no more Grignard reagent available to be oxidized and subjecting the desired intermediate to water adds on an H to form a carboxylic acid.
How do you avoid multiple products during an aldol condensation?
Only 1 carbonyl should have alpha protons, use a large excess of that carbonyl compound
what is the point of adding excess cyclo hexane to the bromination reaction?
Prevents bromine from reacting with anything else, just basically takes the volatile reactant out of the reaction after its gone to completion
You will use a water bath to heat the contents of your craig tube. Why not just heat the tube directly on the hot plate? (choose one)
Rapid heat transfer might crack the tube or cause the solvent to bump
If you spill concentrated sulfuric acid on your hand, what should you do FIRST? (choose one) Pour sodium hydroxide on your hand to neutralize the acid Run your hand under lots of cold water and then get the TA's attention Use a paper towel to rub as much of the sulfuric acid off your hand as possible Go to your TA and explain what happened
Run your hand under lots of cold water and then get the TA's attention
How do extractions work?
Separate compounds based on solubility in 2 immiscible solvents, usually water and organic, isolate layer that has your compound in it then remove the solvent
How should the crude compound MP compare to the crystalized product?
Should be a higher MP with a more narrow range
Principles of a TLC plate, how does it work?
Silica gel- very polar, plate placed into the jar of solvent- the less polar a compound is, the less it sticks to silica, the more it gets carried by the solvent. So if something is very polar it will not travel very far at all.
List two features of a good solvent for recrystallization
Solubility curve should be steep, material should be sparingly soluble at room temperature and very soluble at the solvent's boiling point
size of the peak is directly proportional to the number of H atoms
Start with relative areas, scale if necessary (ratios), round decimals
Whenever you heat liquids, especially near their boiling point, you should always use a stir bar or boiling stones. Why is this? (Choose one) Stirring causes the liquid to heat faster Stirring prevents the liquid from bumping out of the flask It looks cool to see the reaction stirring
Stirring prevents the liquid from bumping out of the flask
IF your impure sulfanilamide was dissolved in more than the minimum of hot ethanol, how would that effect the percent recovery? Why?
The % recover would be lower because the mother liquor would be larger, which will have more sulfanilamide that does not crystalize
Relative reactivity of brominated product of acetanilide, aniline, and anisole:
The anisole is reactive enough to add 2 bromine atoms to the benzyl ring. The acetanilide is reactive enough to add 1 bromine to the benzyl ring. The aniline is reactive to troibromate. The aniline is the most reactive, nitrogen is electron donating, not as electronegative as oxygen. Acetanilide is the least reactive compound, carbonyl group has electron withdrawing effects
What is the definition of "flash point"? (choose one) The lowest temperature at which a liquid can vaporize to form an ignitable mixture in the air The temperature at which the vapor pressure of a liquid equals the air pressure above the liquid The lowest temperature at which a liquid is capable of becoming a gas The lowest temperature at which a liquid can spontaneously ignite without a spark or flame.
The lowest temperature at which a liquid can vaporize to form an ignitable mixture in the air
The further downfield (higher chemical shift)
The more electronegative the environment
When assembling a simple or fractional distillation apparatus, where should clamps be placed? Every piece of glassware should be clamped Only the heaviest piece of glassware should be clamped The piece of glassware closest to the ground (the round bottom flask) should be clamped along with other glassware that's not directly above the round bottom flask such as the condenser Clamps aren't needed for the glassware setup
The piece of glassware closest to the ground (the round bottom flask) should be clamped along with other glassware that's not directly above the round bottom flask such as the condenser
Why should your disposal of excess magnesium take place in a fume hood? (choose all that apply) The quench released hydrogen gas, which is flammable and explosive The quench is highly exothermic and might cause the solvent to splash HCl is corrosive
The quench released hydrogen gas, which is flammable and explosive, The quench is highly exothermic and might cause the solvent to splash, HCl is corrosive
Which of the following is correct about the order of adding solvent to your round bottom flask? (choose one) The solvent should be added to your flask before you begin heating to ensure that the solvent doesn't ignite on the hot thermowell surface The solvent should be poured into your flask after you begin heating the distillation apparatus so the experiment goes quicker Since the solvent is flammable, you shouldn't heat the distillation apparatus at all during the experiment
The solvent should be added to your flask before you begin heating to ensure that the solvent doesn't ignite on the hot thermowell surface
A purified unknown has a MP of 121-122. The mixed melting point of this unknown and benzoic acid (121-122) is 105-114. The mixed MP of the unknown and succinimide (122-124) is 120-121. What can you conclude?
The unknown is most likely succinimide. When the unknown is mixed with benzoic acid it reaches an impure substances because the MP is lower with a broader range. When mixed with succinimide the MP is almost the same and has a small range so we can conclude it is a pure substances.
What is the main hazard present when using the GC? (choose 1) Exposure to the toxic carrier gas Thermal burns from the hot injector port and oven Health hazards from using large quantities of solvents Boredom since nothing could possibly be dangerous about using the GC
Thermal burns from the hot injector port and oven
If the thermometer bulb is placed too high how will this affect your results?
Thermometer placement: The thermometer should be placed into the glassware (distillation head) in such a way that the vapor touches the red/blue/green bulb of the thermometer as it passes through the side vent and into the condenser (see pictures on the next 2 pages and in PLKE)) for the most accurate reading. It should neither be placed too low into the distillation head to not see a mild reflux, nor too high for the vapor to touch the bulb. The top of the bulb should be even with the lower edge of the sidearmit will give an inaccurate temperature reading
Which of the following statements about waste disposal are correct? (Choose all that apply) Glass pipettes go in the trash Water from the water bath can go down the drain Solid chemicals should go in solid waste bins while filter paper and weighing paper go in the trash Water from the water bath can be drunk The mother liquor from your crystallization and other aqueous solutions go in the organic waste
Water from the water bath can go down the drain, Solid chemicals should go in solid waste bins while filter paper and weighing paper go in the trash
Silica gel is not flammable, nor is it chemically reactive. Why then is it considered hazardous, particularly with long term exposure? (choose 1) It binds to DNA making it carcinogenic When ingested it is highly poisonous, as seen on an episode of Seinfeld If it gets on your skin, it can't be washed off When inhaled it damages the respiratory tract
When inhaled it damages the respiratory tract
Ferrocene- aromatic compound, does it react EAS?
Yes it does, reacts the same way as benzene. The iron atom in the center is bonded equally to a ll 10 carbon atoms via the pi electrons of the aromatic rings
Possible side products of the reaction?
You could get two of the aromatic Br substituted rings joined together, you could also just get a substitution of a hydrogen where the Br was (if it interacts with water).
How would you do a separation with an amine, a carboxylic acid, and a non ionizable compound?
You would first add HCL and ether
Mechanism for reaction with ferrocene
acylium ion is created (triple bonded oxygen bonded to carbon that is also bonded to an R group) then there is an electrophilic attack by the ferrocene onto the cacylium cation- creating monoacetylferrocene
As solvent polarity increases...
al compounds move more
Which of the following common organic solvents are flammable (choose all that apply) Acetone Ethyl acetate Toluene Hexane Heptane
all
Bromobenzene is what...?
an o/p director but reacts slower than benzene
we predicted what kind of addition?
anti addition of the bromine, supported by the MP of the compound
What determines which compound comes off first in a distillation?
bioling point
Stereochemistry of bromine addition can be three ways:
bromonium ion (anti), concerted,(syn), arbocation (carbocation is planar, all diasteromers are formed)
Outcome of bromination experiment can be either only the threose enantiomers, only the erythro enantiomers, or a mixture of diasteromers. Match each kind of substitution to each type of outcome
carbocation is the mix of diasteromers, bromonium ion- erythreo, concerted- threose
Acetyl chloride and water?
carboxylic acid and HCl
Chemical shift
chemical environment for each H
What is the stereochemical relationship between borneo and isoborneol?
diasteromers
Crystallization solvents will
dissolve the substance when hot, but not when cold
Calculating retention factor
distance sspot travelled/distances solvent travelled
Equivalent H atoms
do not split each other, neighbors add together
If you used 100mg of ferrocene and 0.08mL of acetyl chloride what is your theoretical yield of mono acetyl ferrocene?
find moles of each, ends up being approximately 2:1 ration of acetyl chloride to ferrocene. So you would see both mono and di acetylation. the ferrocene is the limiting reagent, just multiply that by the MW of acmonoacetly ferrocene.
Splitting
how many neighbors for each H
Will the composition of the first mL of distillate collected be enriched in the lower or higher boiling point compound?
it is enriched in the lower boiling component
Why can't ethanol be used as a solvent for the grignard reaction?
it would participate in the reaction,, grignard reagents react with water and alcohols. The regains can decompose in the presence of O2, to produce products with new carbon-carbon bonds. Also reacts with the -OH group of alcohol/water.
Impure compound has what kind of MP
low and broad
How to calculate gc times
peak height x peak width at half height. Gives you the peak area, then divide by the correction factor, then addd the twthe total peak areas together (depends on how many samp types of sample) and then divide each individual peak by the total to get the % composition of each individual sample
The pKa of the anilium ion (protonated form of aniline) is 4.6. Would it be protonated or deprotonated at the pH of 1, 4.6, and 14?
protonated at 1, mixture oat 4.6, and deprotnated at 14
If the pKa of benzoic acid is 4.2, would it be protonated or deprotonated at pH of 2.0, 4.2, and 12?
protonated at 2.0. Mixture at 4.2 (1/2 and 1/2), and deprotonated at 12.
Predict the relative Rf values of biphenyl, benzoic acid, and benzyl alcohol (which will be slowest, which will be fastest?)
sort by polarity, the most polar will be the last to go through the column. So polarity order is benzoic acid (most polar), benzyl alcohol, and the biphenyl.
