Chemistry 231 Exam

Flashcard maker : Lily Taylor
Limonene from orange peel belongs to which of the following classes of natural products?
A) Terpenes
B) Alkaloids
C) Acetogenins
D) Steroids
E) Carbohydrates
A) Terpenes
Eugenol belongs to the Acetogenins class of natural products
Which of the following is NOT essential for a suitable extraction solvent for aqueous extraction?
A) It must be immiscible with water
B) It must have a different density than water
C) It must have a lower boiling point than water
D) Compounds to be extracted must have favorable distribution coefficients in the solvent
E) All of these are essential requirements
C) It must have a lower boiling point than water
The boiling/melting points difference does not effect whether the extraction is suitable or not
In the phase transfer experiment (10), a very short liquid chromatography column was sufficient to obtain pure product because:
A) The silica gel used in the column caused impurities to decompose
B) The silica gel has great affinity for aromatic ethers and so they elute rapidly
C) The product molecule is smaller than any of the reactant molecules or side products so it can travel through the silica gel very rapidly
D) The reactant 2-naphthol is much more volatile than the naphthol ether and so it evaporates as it moves through the column
E) The naphthyl ether is so much less polar than the non-volatile reactants or side products that the ether can move through the highly polar silica gel more rapidly than reactants, catalysts, or side products
E) The naphthyl ether is so much less polar than the non-volatile reactants or side products that the ether can move through the highly plar silica gel more rapidly than reactants, catalysts, or side products
When you tested mixture melting point temperatures in the lab, your records showed that:
A) The melting point of your unknown compound will not change no matter what you are mixing it with, so the melting point range will always stay narrowed and not depressed
B) The melting point of your unknown compound will be lower and the range broader if you mixed it with an organic compound different from your unknown
C) Organic compounds and insoluble inorganic compounds that do not mix when melted give a melting range that is sharp, even though there are inorganic impurities in the sample
D) B and C only
E) A and C only
D) B and C only
Benzoic acid and phenol can be differentiated in the infrared because benzoic acid shows an absorption near _____ and phenol does not
A) 3400 cm-1
B) 2100 cm-1
C) 1050 cm-1
D) 2950 cm-1
E) 1700 cm-1
E) 1700 cm-1
In the mechanism for the dehydrohalogenation of 3-chloro-3,7-dimethyloctane, what is the dihedral angle between the hydrogen and chlorine atoms that are eliminated?
A) 0°
B) 45°
C) 90°
D) 135°
E) 180°
E) 180°
Which of the following factors does not affect the retention time of a given component in a gas chromatographic analysis?
A) The temperature at which the column is maintained
B) The nature of the stationary liquid phase
C) The rate of flow of the inert gas
D) The length of the column
E) The retention time of the other components
E) The retention time of the other components
Which is the rate expression for the SN1 solvolysis of 1-phenyl-1-chloroethane?
A) Rate = k[R-Cl][HCl]
B) Rate = k[R-Cl][H2O]
C) Rate = k[R-OH]
D) Rate = k[H2O]
E) Rate = k[R-Cl]
E) Rate = k[R-Cl]
For the TLC experiment, which of the following is correct?
A) Under UV light, we can visualize the location of many compounds because the compounds can give out UV light
B) Under UV light, we can visualize the location of many compounds because the compounds absorb the UV light
C) TLC can be used to analyze the functional groups
D) The liquid in the jar can rise up the plate because of its evaporation
E) We can separate the compounds with TLC because the evaporation rates differ under the same conditions
B) Under UV light, we can visualize the location of many compounds because the compounds absorb the UV light
When performing preparative gas chromatography,
A) the collection tube must be capped while collecting to avoid the loss of the volatile solute
B) the collection tube must be capped while collecting to avoid contamination of the collected sample by impurities in the air
C) the collection tube must be capped while collecting to avoid the absorption of water by the collected sample which would ruin the acquired IR spectra
D) the collection tube must be uncapped to allow free passage of vapor through the tube
E) during collection of a solute, the sample tube must be maintained in a downward slope to keep the GC port from plugging up
D) the collection tube must be uncapped to allow free passage of vapor through the tube
In the following reactions, what conditions were used to isolate eugenol from clove oil?
A) 1 M HCl
B) 3 M NaOH
C) Methylene chloride and water
D) 6 M HCl
E) A steam bath
B) 3 M NaOH
The following compounds are dissolved in dichloromethane;
1. CH 2. CO 3. NH2 4. CHCO2H 5. 2HNH2Cl
The solution is extracted with 3 M sodium hydroxide. The compounds removed from the dichloromethane are:
A) 2 and 4
B) 2 and 5
C) 3 and 5
D) 1 and 2
E) 1 and 5
A) 2 and 4
In the phase transfer catalysis experiment (10), what type of analysis was used to determine the progress of the reaction?
A) Extraction
B) Thin Layer Chromatography
C) Gas Chromatography
D) Distillation
E) Recrystallization
B) Thin Layer Chromatography
An ideal recrystallization solvent will:
A) Dissolve lots of the compound at room temperature and little at high temperatures
B) Dissolve lots of the compound at room termperature and lots at high temperatures
C) Dissolve little of the compound at any temperature
D) Dissolve little of the compound at room temperature and lots at high temperatures
E) React with the compound being recrystallized
D) Dissolve little of the compund at room temperature and lots at high temperatures
Which of the following statements concerning the infrared spectroscopy experiment is WRONG?
A) ATR stands for “attenuated total reflectance”
B) ZnSe is the most commonly used crystal for ATR
C) Normal IR spectra show absorptions around 400-4000 cm-1
D) Absorptions below 1400 cm-1 are usually considered as the fingerprint region
E) A thick layer (>10 u) of sample is required to run ATR-IR
E) A thick layer (>10 u) of sample is required to run ATR-IR
In performing a simple distillation,
A) it is better to distill rapidly
B) the higher boiling compound distills first
C) the temperature should be held below 100°C
D) two compounds can be separated completely if they have a boiling point difference of less than 10°C
E) the distallate contains a progressively larger percentage of the higher boiling compound as the distillation proceeds
E) the distillate contains a progressively larger percentage of the higher boiling compound as the distillation proceeds
Joe Aggie performed a kinetic study of the SN1 solvolysis reaction (11) of 1-phenyl-1-chloroethane using a 40% H20, 60% ethanoll mixture for the solvent. What effect would occur if he uses an 80% H2O, 20% ethanol mixture?
A) The rate would decrease
B) The rate would increase
C) The rate would remain unchanged
D) The solution would remain acidic longer
E) The acidity of the solution would double
B) The rate would increase
The reaction that converts 2-ethyl-1,3-hexanediol to a carbonyl compound is best described as:
A) Condensation
B) Reduction
C) Hydrolysis
D) Ammonolysis
E) Oxidation
E) Oxidation
Which of the following descriptions is correct?
A) Limonene has a characteristic absorption peak for the -OH group
B) Eugenol should give a positive result in the ferric chloride test
C) The purpose of adding NaOH in the eugenol extraction is to make the solution basic
D) A black precipitate is formed in the presence of an alkene for the Baeyer test
E) The compound must be miscible in water for steam distillation
B) Eugenol should give a positive result in the ferric chloride test
The dihedral angel (torsion angle) between the methyl groups in the structure, is expected to be about:
A) 60°
B) 120°
C) 30°
D) 45°
E) 0°
A) 60°
The reaction of naphtholate anion and allyl bromide involved the use of a catalyst, benzyl tri-n-butyl ammonium chloride. The catalyst:
A) Carries the water-soluble naphtholate anion into the organic phase
B) Carries the hydrophobic naphtholate anion into the aqueous phase
C) Slows the rate of the reaction
D) Carries the water-soluble allyl bromide into the organic phase
E) Carries the hydrophobic allyl bromide into the aqueous phase
A) Carries the water-soluble naphtholate anion into the organic phase
We run a hot vacuum filtration in crystallization in order to ________
A) Save solvent
B) Avoid the formation of oil
C) Prevent crystals from forming too rapidly
D) Remove insoluble impurities
E) Increase the recovery
D) Remove insoluble impurities
Your experimentally determined melting point is 10 degrees low and has a 4° melting point range. This indicates that:
A) Your compound is impure
B) Your put too much material in the melting point capillary
C) Your compound is pure
D) The Mel-Temp thermometer is poorly calibrated
E) You set the voltage on the Mel-Temp too high
A) Your compound is impure
In the distillation of hexane/heptane and hexane/octane mixtures, the early distillation fractions contain higher percentages of hexane because:
A) Hexane reacts with oxygen faster
B) Heptane and octane stick to the distillation vial
C) Hexane has a higher vapor pressure
D) The vapors of heptane or octane escaped and did not condense
E) Heptane and octane have higher vapor pressures
C) Hexane has a higher vapor pressure
What would you do if you spilled sulfuric acid on your hand?
A) Wash it with water and apply .6 M sodium thiosulfate solution
B) Wash it with water and apply .6 M sodium sulfate solution
C) Wash it with cold water and apply .6 M sodium bicarbonate solution
D) Wash it with cold water and apply .6 M sodium hydroxide solution
E) Wash it with cold water and dilute acetic acid solution
C) Wash it with cold water and apply .6 M sodium bicarbonate solution
You used hypochlorous acid (generated from sodium hypochlorite and acetic acid) to oxidize a secondary alcohol. What is the oxidation state of the chlorine in hypochlorous acid, HOCl?
A) +2
B) -1
C) 0
D) -2
E) +1
E) +1
The preparation of 3-chloro-3,7-dimethyloctane from 3,7-3-octanol is an example of:
A) An SN1 reaction
B) A halogenation reaction
C) An oxidation reaction
D) An elimination reaction
E) An SN2 reaction
A) An SN1 reaction
Which of the following statements concerning GC is true?
A) Injecting larger sample volumes leads to greater sensitivity (resolution)
B) Preparative GC allows purification and recovery of a compound after passing it through a GC column
C) The moving phase in GC is an inert gas
D) A, B, and C
E) B and C
E) B and C
According to the Merck Index, the amount of solvent necessary to dissove 1.0 g of n-nitrobenzoic acid is: water- 146 mL, ethanol- 3 mL, chloroform- 220 mL, ether- 4.5 mL, acetone- 2.5 mL. Why wouldn’t acetone be the best solvent to extract n-nitrobenzoic acid from water?
A) The acid is not soluble enough in acetone
B) The acid is more soluble in water than in acetone
C) Acetone is soluble in water
D) 2.5 mL of acetone is not enough to do an extraction
E) Acetone has a lower density than water
C) Acetone is soluble in water
Which compound will form bubbles and dissolve in aqueous sodium bicarbonate?
A) Benzocaine
B) Benzyl Alcohol
C) Benzoic Acid
D) Benzene
E) Benzyl Chloride
C) Benzoic Acid
It is possible to tell the difference between cyclohexanol and cyclohexanone in the IR spectrum by the presence or absence of a peak at:
A) 1000 cm-1
B) 1650 cm-1
C) 3010-3100 cm-1
D) 3200-3600 cm-1
E) 2850-2960 cm-1
D) 3200-3600 cm-1
You inject a mixture of these three compounds on a non-polar column: acetone, bp 56°C; ethyl acetate, bp 77°C; benzene, bp 80°C. Order the three compounds by increasing retention time.
A) Benzene, acetone, ethyl acetate
B) Ethyl acetate, acetone, benzene
C) Benzene, ethyl acetate, acetone
D) Acetone, ethyl acetate, benzene
E) Acetone, benzene, ethyl acetate
D) Acetone, ethyl acetate, benzene
Which of the following statement(s) is/are true about the SN1 reaction of 1-phenyl-1-chloroethane?
I. Carbocation formation is the rate-determining step
II. Addition of water is the rate-determining step
III. The product is a mixture of enantiomers
A) I only
B) II and III only
C) II only
D) I and III only
E) III only
D) I and III only
The dehydrohalogenation of 3-chloro-3,7-dimethyloctane (an E2 reaction) is favored over substituion because:
A) A tertiary halide is used
B) A slightly basic nucleophile is used
C) A highly polarizable nucleophile is used
D) A primary halide is used
E) A strongly acidic nucleophile is used
A) A tertiary halide is used
A sample mixture containing naphthalene, naphthol, and 2-ethoxynaphthalene was run on a TLC plate. Indicate the order of Rf’s from highest (closest to 1) to lowest (closest to 0), of these compounds.
*Shown*
A) I, II, III
B) I, III, II
C) II, I, III
D) II, III, I
E) III, II, I
B) I, III, II
Which of the following reagents can be used as a classification test to detect the existence of limonene? (Choose all correct answers)
I. Bromine solution
II. Permanganate solution
III. Silver Nitrate solution
IV. Concentrated Hydrochloric Acid
A) I only
B) I and II
C) I, II, and IV
D) II and III
E) All four reagents can be used
B) I and II
Which statement concerning molecular geometries is correct?
A) Chemical bonds must be broken for a molecule to interconvert among different conformers
B) Lower energy structures are achieved by distorting bond angles and bringing atoms into close contact
C) The gauche conformation of butane is a global minimum
D) A low energy structure may not necessarily be the global minimum of the lowest possible energy
E) Bond stretching and torsion do not contribute to the overall strain energy of a molecule
D) A low energy structure may not necessarily be the global minimum of the lowest possible energy
You are given a dichloromethane solution containing compounds A, B, and C. You first extract with 3 M NaOH and find that A is in the aqueous layer. Re-extraction of the organic layer with 3 M HCl leaves only C in the organic layer. Of the following, compound B is probably:
A) Pentane
B) Benzoic Acid
C) Toluene
D) Sodium Sulfate
E) Benzocaine
E) Benzocaine
When a solution is cooled very rapidly in recrystallization:
A) No crystals will form
B) Small crystals form that have a large surface area on which impurities will be absorbed
C) Ideal recrystallization takes place
D) The impurities don’t have time to stick to the crystals
E) None of these
B) Small crystals form that have a large surface area on which impurities will be absorbed
Compounds A, B, and C are three unknown compounds. Compound A melts at 130°C-133°C, compound B melts at 132°C-134°C, and compound C melts at 140°C-143°C. Compound D is a known compound who melts at 131°C-134°C. The mp of A+B is 131°C-133°C. The mp of B+C is 139°C-144°C. The mp of A+C is 138°C-142°C. The mp of A+D is 130°C-134°C. The mp of C+D is 134°C-140°C. What can you conclude about your unknowns?
A) A=B=D
B) B=C=D
C) A=B=C
D) B=C
E) C=D
A) A=B=D
Butyl butyrate, an ester, differs from p-dioxane, an ether, by showing a strong infrared absorbance at:
A) 3500 cm-1
B) 2950 cm-1
C) 2250 cm-1
D) 1745 cm-1
E) 1212 cm-1
D) 1745 cm-1
Why do you add boiling chip to a solution that will be heated?
A) To keep the solution homogenous
B) To increase the rate of reflux
C) To promote even boiling
D) To lower the boiling point
E) All of these
C) To promote even boiling
When analyzing the IR of your product from the Oxidation of a Secondary Alcohol you were looking at what in the spectra?
A) The disappearance of a peak at approximately 1700 cm-1 and appearance of broad peak at approximately 3300 cm-1
B) The appearance of a peak at approximately 1700 cm-1 and disappearance of broad peak at approximately 3300 cm-1
C) The appearance of a strong peak at approximately 2200 cm-1 and disappearance of strong peak at approximately 1700 cm-1
D) The disappearance of a strong peak at approximately 2200 cm-1 and appearance of strong peak at approximately 1700 cm-1
E) None of theses cases are correct, we didn’t monitor the product by IR
B) The appearance of a peak at approximately 1700 cm-1 and disappearance of broad peak at approximately 3300 cm-1
Tert-pentyl alcohol (.25 moles) was treated with a 300% excess of concentrated HCl yielding the chloro-subsituted compound. If 15.4 mL of pure product was obtained, what was the reaction yield?
A) 50%
B) 73%
C) 59%
D) 67%
E) None of these
A) 50%
A drug analyzed by normal phase silica gel TLC gave the following chromatogram. Which of the following statements is false?
A) Rf values A< B< C B) The drug probably contains acetaminophen C) The drug does not contain caffeine D) Compound C is more polar than compound A E) The drug contains at least 3 different compounds
A) Rf values A< B< C
Which of the following is NOT a property that an organic extraction solvent must have to be suitable for a liquid-liquid extraction?
A) It must readily dissolve the substance being extracted but must not dissolve to any appreciable extent in the solvent from which the desired substance is being extracted
B) It should not extract starting reagents or byproducts present in the mixture
C) It dissolves a reasonable amount of the organic compound at high temperatures and very little at low temperatures
D) Except in the case of reaction solvents, it should not react with the substance being extracted
E) It should be readily separated from the desired solute after extraction
C) It dissolves a reasonable amount of the organic compound at high temperatures and very little at low temperatures
In the following E2 reaction, what would the expected product(s) be? *Molecules will be listed*
B) 1 and 3
The absorption of infrared radiation changes what mode of molecular motion?
Vibrational
The pieces of glassware labeled A and B respecitively are called:
A) Buchner funnel and B) filter flask
Compounds such as a-pinene and limonene are members of the class of natural products known as:
Terpenes
In thin layer chromatography, the R value is calculated to:
Compare with the known R value of standards
In the purification technique of recrystallization, a hot filtration is sometimes carried out to
Remove insoluble solid impurities
Which of the following statements about melting points is incorrect?
Rapid heating results in a narrower melting point range
In the solvolysis of the 1-phenyl-1-chloroethane (R-Cl) with water, the reaction is:
Independent of the amount of water
3-chloro-3,7-dimethyloctane is a _____ halide, so the rate of competing nucleophilic subsitution in the dehydrohalogenation experiment will be very ______
Tertiary, slow
Preparative gas chromatography would be the best method for:
The separation of .5 g of a mixture of two liquids (bp 150° and 160°)
The computer calculated that the local minimum for the gauche butane conformation had a dihedral angle of
65°
Which of the following is the conjugate acid of bleach?
HOCl
Phase transfer catalysts promote certain reactions by
changing the solubilities of one of the reactants and thus increasing its concentration in the other phase
In the preparation of 3-chloro-3,7-dimethyloctane, the organic layer was washed with sodium bicarbonate solution. This washing was for the purpose of:
removing the remaining acid
The boiling point of a liquid is not affected by
The rate of heating
If you were to extract a solution of p-toluidine (an amine) and benzoic acid in methylene chloride with aqueous base and the acidify the water layer, the solid you would isolate would be:
Benzoic Acid
You have performed all of the following classification tests this semester except
Ninhydrin test
Eugenol, an aromatic phenol, may be easily isolated from clove oil by which of the following methods?
Base extraction and neutralization
You have carried out a thin layer chromatography of a sample of benzoic acid. Measuring from the bottom of the sheet, the origin was at 10 mm, the solvent front at 90 mm and the center of the benzoic acid spot was 30 mm. If you rerun it on a larger sheet so that the origin is at 10 mm and the solvent at 130 mm, where will the benzoic acid spot be?
40 mm
Which of the following techniques would not induce crystallization?
Slowly warming the cold solution
When benzoic acid is mixed with inorganic sand, what happens to the melting point of benzoic acid?
Stays the same
Solvolysis of 1-phenyl-1-chloroethane follows an SN1 mechanism to give a mixture of ______
Enantiomers
You can separate different compounds with the same boiling point by prep GC when
They have different polarities
Of the three mono-subsituted cyclohexanes shown, the trimethyltin substituent in A has the smallest steric strain because
It has a longer axial bond length
In the oxidation reaction with sodium hypochlorite, the oxidant is reduced into
Cl
At the end of the phase transfer catalysis experiment, what molecule had the highest R value when you ran the TLC?
Allyl 2-naphthyl ether
25.00 g of 2,4-dimethyl-2-pentanol (mw:116.2) is shaken with an excess of concentrated HCl (mw: 36.53). After work up, 18.36 g of pure 2,4-dimethyl-2-chloropentane (mw: 134.65) aer isolated. What is the percent yield?
63.4%
The fingerprint region of the IR refers to:
the portion of the spectrum from 1500-500 cm-1 that is unique for nearly every compound
Select the best method of separation in order to separate the two components of a solution of a non-volatile solid dissolved in a volatile liquid?
Simple Distillation
When you performed simple distillation upon a 50/50 mixture of hexane and heptane, you later analyzed your fractions using GC. What was the purpose of performing the GC experiment?
To determine the proportions of hexane and heptane in your samples
Steam distillation is used to isolate
water insoluble oils
Considering thin layer chromatography, which of the following statements is correct?
TLC allows separation of components in a mixture if individual components distribute differently between the solid stationary phase and the mobile liquid phase
The dehydrohalogenation of 3-chloro-3,7-dimethyloctane proceeded according to what mechanism?
E2
A student was given 2.00 g of a very impure solid. After recrystalization and drying the student obtained 2.00 g of recovered material. Which of the following statements is true?
Since all of the material was recovered, no purification occured
Normally a mixture of two different solid compounds will melt over a broader range than a pure solid. However, they will show a sharp melting point if:
They form a eutectic
All the following statements about Kinetic Study of SN1 solvolysis experiment are correct except
Temperature does not have effect on the reaction rate
Which of the following is not a requirement for preparative gas chromatography?
The sample size must be less than 5 uL
Which of the following C-C-C-C dihedral angles was calculated as the butane conformer of lowest energy?
180°
Which reagent is not an oxidizing agent?
CaSO
In the preparation of 3-chloro-3,7-dimethyloctane, you performed a silver nitrate test on the product. Hopefully, you witnessed the immediate formation of a white precipitate. What was the precipitate?
AgCl
For a simple distillation to separate compounds effectively,
I. the difference in boiling points has to be at least 40°
II. all compounds have to be thermally stable
III. the compounds have to be chemically similar
I and II are correct
IR is a useful spectroscopic technique for identifying compounds because
I. A particular frequency indicates a specific functional group
II. It is rapid
III. It is destructive
IV. Only a small amount is required
V. It establishes stereochemistry
I, II, and IV
What is the hybridization of the oxygen atom and the approximate bond angles around 3 oxygen in methanol, CH-OH?
Sp3 and 109.5°
Which of the following statements is untrue regarding recrystallization?
A lot of the compound being purified should remain in solution at low temperatures
Which of the following shows correct mechinistic steps for the reaction of sodium naphtholate with allyl bromide to produce coresponding allyl 2-naphthyl ether?
Mechanism #2

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