CHEM 238 - Lab Final
Would you predict the heat of formation of a cis isomer to be more or less negative than a trans isomer?
The cis isomer's heat of formation would be less negative than the trans isomer because steric hinderance makes it less stable meaning the heat of formation will be less negative
LD-50
The dose found to be lethal in 50% of a group of test animals when administered by the specified route
High toxicity
Those chemicals having an acute toxicity of either (1) Median Lethal Dose, single oral dose or (2) Median Lethal Concentration, four-hour inhalation exposure or (3) Median Lethal Dose, dermal exposure
Low Toxicity
Those substances that have been shown to produce low toxicity or irritation, or those chemicals having an acute toxicity of either (1) Median Lethal Dose, single oral dose or (2) Median Lethal Concentration, four-hour inhalation exposure or (3) Median Lethal Doe, dermal exposure
Benzene and its derivatives undergo a type of substitution reaction in which a hydrogen atom is replaced by a substituent, but the stable aromatic benzene ring is regenerated at the end of the mechanism.
True
Carbocations are stabilized by resonance
True
Esters have low boiling points and evaporate easily
True
Esters react with two moles of Grignard
True
For recrystallization, the material that is to be purified must be a solid.
True
Heating reaction mixture under reflux prevents the loss of volatile reactants and products
True
If a molecule has an unprotected alcohol, phenol, or terminal acetylene, you have to use at least two equivalents of the Grignard reagent
True
LiAlH4 will reduce esters
True
Methanol is flammable.
True
NaBH4 will reduce ketones
True
Recrystallization is the process of dissolving a solid material into a suitable solvent or mixture of solvents and allowing the material to crystallize from this solution.
True
The solvent should dissolve the compound while hot.
True
The solvent should either dissolve the impurities at all temperatures or not dissolve the impurities at all.
True
The solvent should not chemically react with the compound.
True
The solvent should not dissolve the compound when cold.
True
Use clamps to secure the filter flask to avoid tipping and unnecessary exposure to hot liquids or the solute.
True
Water wash helps ester to separate alcohol and acid to obtain a pure ester
True
Teratogenic agent
a substance or agent that can interfere with normal embryonic development
Ultraviolet B
causes skin cancer
As the concentration of the solution increases, the absorbance of the solution
increases
-SO3H
meta deactivator
carboxylic acid
meta deactivator
ketone
meta deactivator
nitrile
meta deactivator
nitro
meta deactivator
tertiary amine
meta deactivator
Benzenes
ortho, para activating
Amide
ortho, para activating group
Carboxylic acid anhydrides
reactive derivatives of carboxylic acids, but generally are less reactive than the acid chloride
Mixed anhydrides
similar in reactivity to the acid chloride
Minimal Erythemal Dose (MED)
the amount of time one can stay in the sun before getting sunburn
During the recrystallization of a solid, the sample is dissolved in hot solvent then filtered while hot. The filtrate is allowed to cool and the mixture is filtered a second time. What is the purpose of the initial hot vacuum filtration in the recrystallization process?
to remove insoluble solid impurities
When is recrystallization not a suitable method to purify an organic material?
when the organic material is a liquid instead of a solid
Beer's Law
𝐴=𝜖⋅l⋅𝐶 C = sample concentration (mmol/mL) l = path length (cm) 𝜖 = molar extinction coefficient
Bottom Layer
-Aqueous layer -Sulfuric acid -Carboxylic acid -Alcohol
UVC health problems
-Can be lethal, but is almost totally absorbed by ozone in the earth's atmosphere
UVB health problems
-Delayed, more intense sunburn -Skin cancer, skin aging, cataracts, immunosuppression; somewhat absorbed by earth's atmosphere (most intense at noon)
Diethyl ether
-Extremely volatile -Highly flammable -Very low miscibility with water
Which of the given statements best represent what to do in the event of a spill of concentrated sulfuric acid.
-First, rinse the affected area with copious amount of water. -Second, treat the area with aqueous sodium bicarbonate solution.
The carbon-magnesium bond in a Grignard reagent is covalent and highly-polarized such that the carbon is negatively charged. Which of the following statements can be used to describe the Grignard carbanion?
-Grignard reagents are strong bases -Grignard reagents are strong nucleophiles
Which of the following is the best choice of acid catalyst in an acid-catalyzed esterification reaction? C6H5COOH+CH3OH↽−−⇀C6H5COOCH3+H2O
A few drops of concentrated sulfuric acid.
Which of the following statements relates the value and magnitude of ΔHf to stability of a product?
A large negative value of ΔHf indicates a stable product.
Molar extinction coefficient (e)
A measure of how strongly the sample absorbs light at that wavelength, λ
What indicates a positive Tollens test?
A mirror will form on the test tube or black precipitate will form if impurities are still present
Sun Protective Factor (SPF)
A number that indicates the amount of sun protection a product will offer = (MED for skin with sunscreen) / (MED for skin without sunscreen) -only refers to product effectiveness against the UVB rays of the sun
What compounds give a positive Tollens test?
Aliphatic and aromatic aldehydes
Least reactive
Amides
What compounds give a positive Schiff's test?
An aliphatic aldehyde
What indicates a positive Schiff's test?
An immediate purple/wine color
Reduction
An increase in the electron ownership of a carbon atom that is achieved either by the breaking of a bond to an electronegative element or the formation of a C-H bond -Hydrogen gas -Catalyst -Pressure/heat
Semiempirical
Based in part upon scientific tests or observations; a close approximation that is obtained partly with carefully determined measurements and partly by estimates based upon observations, semiempirical methods or calculations are refined as further observations are made
Sodium Borohydride reacts slowly with water (and even more slowly with ethanol) to generate H2. What observation would allow you to deduce that H2 is being generated either during your reaction or when you pour the reaction mixture into water?
Bubbles will form
What should you do if the reaction begins to reflux too vigorously?
Cool the reaction briefly using an ice-water bath
Hydrochloric acid
Corrosive irritant
Sodium hypochlorite
Corrosive irritant
Macrolide
Cyclic esters containing more than nine carbons
Flammable
Defined as a liquid with a flash point below 100 degrees F
Which statement does not identify a safety concern associated with the use of diethyl ether in the lab?
Diethyl ether has a very low miscibility in water.
Acid chlorides
Frequently used as intermediates for the synthesis of esters and amides -produces much higher yields, and no excess of alcohol is required
Select the group that is ortho‑, para‑ directing, but also deactivating in electrophilic aromatic substitution reactions.
Halogen
During the preparation of a tertiary alcohol by a Grignard reaction, the reaction mixture was shaken with saturated sodium chloride solution. What is the purpose of the saturated sodium chloride solution?
Saturated sodium chloride decreases the solubility of the organic product in water.
Alcohols
Second strongest ortho, para activating group
During the recrystallization of a solid, the sample is dissolved in hot solvent then filtered while hot. The filtrate is allowed to cool and the mixture is filtered a second time. What effect will result if the filtrate solution is cooled too rapidly?
Small impure crystals will form.
Grignard reactions are highly exothermic and are performed in ether solvent. There is a real risk of fire during this reaction. In the case that a fire should occur in your distillation apparatus, what is the best course of action?
Smother the flames with a watch glass or beaker.
Contents of iodoform test reagnet.
Sodium hydroxide, iodine
Sodium iodide
Irritant
UVA health problems
-Immediate sunburns -Penetrates deeply and may lead to premature skin aging; may contribute to skin cancer and cataracts
THF
-Less volatile -Less flammable -Completely soluble in water -Readily absorb water from the atmosphere
Top Layer
-Organic layer -Ester
Which of the following statements about semi-empirical methods are true:
-Some experimentally measured parameters are substituted into the calculation. -It is good at predicting structural properties that arise from subtle interactions of orbitals.
Which of the following statements about the ratio of products formed by a reaction under kinetic control are true?
-The ratio of products is determined by the relative energies of transition states. -The ratio of products is not determined by the energies of products.
Which of the following statements are true of the ratio of products formed by a reaction under thermodynamic control?
-The ratio of products is not determined by relative energies of transition states. -The ratio of products is determined by energies of products.
Reduction of camphor
-addition of hydride to the carbonyl group of camphor can occur at either the endo or exo face of the carbonyl -the two possible products have the same configuration at all but one stereo center -Since camphor contains a single simple ketone, sodium borohydride will be used for the reduction
Ultraviolet C
-highest energy wave -totally absorbed by Earth's ozone layer -potentially lethal
Ultraviolet A
-lowest energy wave -causes mild skin aging
What are two methods to clean the magnesium?
1) Physically clean by crushing the magnesium with a stir rod 2) Chemically clean by adding a chemical such as iodine
What are the two steps that can be taken to drive the reaction toward completion?
1) Use an excess of the alcohol 2) One or both of the products can be removed as it is formed to drive the reaction to completion
What is the major product of allylic halogenation at low temperatures?
1,2-adduct -kinetic product -forms more rapidly because transition state #1 is lower in energy
What is the major product of allylic halogenation at high temperatures?
1,4-adduct -thermodynamic -product is more stable (lower energy)
The spectral data that are most characteristic of a sample are:
1. wavelength of maximum absorbance, called λmax 2. value of the molar absorptivity, 𝜖, at each maximum
Rearrange the Beer's law equation to solve for the molar absorptivity, 𝜖. 𝐴=𝜖⋅𝑏⋅𝐶 What are the units of molar absorptivity?
1/(cm⋅M)
Minimum wavelength (UVC):
100 nm
What indicates a positive Iodoform test?
A bright yellow precipitate forms
Maximum wavelength (UVC):
290 nm
Minimum wavelength (UVB):
290 nm
Based on its structure, which molecule will be the least soluble in hot water?
2‑naphthol
Maximum wavelength (UVB):
315 nm
Minimum wavelength (UVA)
315 nm
Maximum wavelength (UVA)
400 nm
Optimum temperature for esterification
50 - 60 degrees Celsius
monosubstituted
770-715 cm-1
1,2 disubstituted
770-730 cm-1
1,2,3-trisubstituted
790-750 cm-1
1,3 disubstituted
820-760 cm-1
1,2,4-trisubstituted
850-800 cm-1
1,4 disubstituted
870-800 cm-1
1,3,5-trisubstituted
910-830 cm-1
Cancer Suspect agent
A substance suspected of inducing cancer based on human evidence or demonstration by appropriate methods of carcinogenesis in two or more animal species or strains
Lachrymator
A substance with vapors that irritate the eye, causing shedding of tears
What is likely to be observed for a positive test for the 2,4‑dintrophenylhydrazine (2,4‑DNP) test?
A yellow to orange/red precipitate is formed.
Only one aldehyde gives a positive test with the iodoform test reagent. Give the name and draw the structure of that aldehyde in the boxes below.
Acetaldehyde
Second most reactive
Acid anhydrides
Most reactive
Acid chlorides
Third most reactive
Esters
Amides
Even more resistant than esters to hydrolysis
The safety hazard warning for acetyl chloride labels it as a lachrymator. Which of the given statements best defines what a lachrymator is?
Exposure to the chemical vapors make you cry.
10% sodium carbonate solution must be used in the fume hood.
False
Benzoic acid is a lachrymator.
False
Dichloromethane is flammable.
False
For hot vacuum filtration, the filter paper should be completely dry when pouring the hot solution into the Buchner funnel to filter.
False
For recrystallization, rapid cooling gives the best crystals.
False
NaBH4 will reduce amides
False
The solvent should chemically react with the compound.
False
The solvent should dissolve the compound while cold.
False
The solvent should not dissolve the compound while hot
False
When you take your IR spectra next week, what evidence would indicate that some unreacted camphor was still present in your isolated product?
If there was still unreacted camphor, it would show up as a peak around 1700-1800 cm-1 on the IR spectra
Sodium hypochlorite (household bleach) solution is a strong oxidizing agent. Bleach solutions can also emit chlorine gas, which is a respiratory and eye irritant. Which of the following actions should you follow if you spill bleach on your arm?
Immediately flush the affected area with running water and notify your TA.
What should you do if the transparent liquid becomes cloudy?
Immediately turn off the heat
The use of rinse acetone to remove traces of water from glassware is a very common laboratory technique. When performing qualitative tests in glass test tubes, such as the iodoform test or dinitrophenylhydrazine test, why should you avoid rinsing the glassware with acetone prior this experiment?
It will give a false positive for some carbonyl classification tests.
What might happen if a low molecular weight carboxylic acid is exposed to a slightly acidic aqueous environment such as skin?
It will produce burns.
What can give a false positive Tollens' test
Ketones with an a-hydroxy group and some conjugated ketones which exist predominantly as the enol form of the tautomer
Aromatic acid chloride
Less reactive, but will react slowly with water at room temperature
Corrosive
Liquid or solid that causes visible destruction or irreversible alterations in skin tissue at site of contact, or, in the case of leakage from its packaging, liquid that has severe corrosion rate on steel
Aldehydes
Meta deactivator
Esters
Meta deactivator
NaBH4
Milder reducing agent capable of reducing only aldehydes and ketones -corrosive irritant
A reaction was performed, and the dichloromethane solvent was dried by adding magnesium sulfate drying agent. When the reaction flask was shaken, it was observed that the magnesium sulfate clumped together at the bottom of the flask. What does this observation indicate?
Not enough drying agent has been added.
Organometallic compounds
Organic compounds that have a carbon-metal bond
Alkyl (-CH3)
Ortho, para activating group
What type of carbocation has the highest energy?
Primary
Almost all low molecular weight ester are pleasant smelling while their acid counterparts are acrid and repellant
True
Ammonia is corrosive.
True
Procedure: The flask was fitted with a condenser and heated for twenty minutes.
Purpose: Heating under reflux keeps the reaction temperature high without evaporation.
Procedure: Concentrated sulfuric acid was added to the flask containing carboxylic acid and alcohol.
Purpose: The Fischer esterification is catalyzed by acid, but water will push the equilibrium back to the reactant side.
Procedure: The UV spectrum was obtained within 30 seconds of preparing the solution.
Purpose: The product has a very high molar extinction coefficient, and is sparingly soluble in hexane.
Procedure: Boiling chips were added to the round bottom flask prior to the reaction being heated under reflux.
Purpose: The reaction solvent is methanol, which bumps violently when heated.
Procedure: The reaction mix was washed with sodium carbonate solution.
Purpose: The unreacted carboxylic acid was neutralized under mild conditions.
Procedure: Grease all ground glass joints prior to heating under reflux.
Purpose: To avoid potassium hydroxide from seizing the glass pieces together.
Procedure: The hydroxide pellets were dissolved in absolute ethanol.
Purpose: To exclude water from the reaction.
Procedure: The reaction flask was heated under reflux on a steam bath.
Purpose: To minimize the flammability risk associated with ethanol.
How are grignard reagents prepared?
Reaction of alkyl or aryl halides with magnesium using an ether solvent such as either diethyl ether or tetrahydrofuran to produce alcohols
LiAlH4
Readily reduces aldehydes, ketones, carboxylic acids, esters, and amides
Ester reactivity
Relatively inert to water, as demonstrated by most oils and waxes
Primary amines
Strongest ortho, para activating group
Which of the given techniques is not one of the four most common methods for separation and purification?
Sublimation
Carcinogen
Substance or agent capable of causing or producing cancer in mammals
Irritant
Substance which, by contact in sufficient concentration for a sufficient period of time, will cause an inflammatory response or reaction of the eye, skin, or respiratory system
Toxicity
Sum of adverse effects resulting from exposure to a material, generally by the mouth, skin, or respiratory tract
Flash point
Temperature at which a liquid will give off enough flammable vapor to ignite with an ignition source such as a spark
What type of carbocation has the lowest energy?
Tertiary
Benzene and its derivatives tend to undergo electrophilic aromatic substitution reactions.
True
Camphor is reduced to isoborneol by sodium borohydride in ethanol. The instructions for safe disposal of the chemical waste generated by this reaction state that the lids should not be screwed back onto the waste containers. Why should the lids not be put back on the waste containers?
The reaction waste is still generating hydrogen gas that would get trapped in the container.
What is sublimation?
The transition directly from the solid phase to gas phase
-OCH3
Third strongest ortho, para activating group
Moderate Toxicity
Those substances that have been shown to produce moderate toxicity following exposure or have been demonstrated to produce carcinogenic, mutagenic, or teratogenic action in a single animal species with little or no human evidence of carcinogenic, mutagenic, or teratogenic action, or those chemicals having an acute toxicity of either (1) Median Lethal Dose, single oral dose or (2) Median Lethal Concentration, four-hour inhalation exposure or (3) Median Lethal Dose, dermal exposure
An integration of 3.19 is a signal from how many hydrogens?
Three
Why is heat used in this reaction?
To liberate the water molecule, aids in evaporation of water
What is the purpose of drying the glassware with a heat gun?
To remove excess water (and acetone)
What is the purpose of applying a small amount of external heat to the reaction?
To try to initiate this reaction
Salicylamide
Toxic irritant
Addition reactions with benzenes lead to the loss of aromaticity.
True
Sodium borohydride and lithium aluminum hydride are two of the most commonly used reducing agents. Match each given property to the correct reducing agent by dragging the property into the appropriate box. If both reducing agents match the statement then drag the statement into the box labeled "True for both hydrides."
True for only lithium aluminum hydride -Reduces esters -Reduces carboxylic acids to primary alcohols True for only sodium borohydride -Is the least reactive of the two hydrides -Is the safest to use -Can be used in reactions with methanol solvent True for both hydrides -Reduces aldehydes to primary alcohols -Reduces ketones to secondary alcohols
An integration of 1.94 is a signal from how many hydrogens?
Two
Alkyl chloride
Very exothermic reaction with water
Consider the reactants benzoic acid and methanol. Could these undergo a Fischer esterification reaction? If so, what else is needed for this reaction to occur?
Yes, if the carboxylic acid is heated in the alcohol solution and a small amount of H2SO4 is used as a catalyst.
Fischer esterification
an equilibrium process in which the carboxylic acid is mixed with an excess of the alcohol and a trace of mineral acid acts as the catalyst
What compounds give a positive Iodoform test?
compounds with a methyl group attached to the functional carbon in methyl ketones and in primary or secondary methyl carbinols
Lactone
cyclic carboxylic esters containing six or fewer carbons
E = hv = hc/λ
h = Planck's constant c = speed of light v = frequency λ = wavelength
