Ochem Lab Final
In the phase transfer catalysis experiment the product of the reaction, allyl 2-naphthyl ether, was easily separated from the starting material and other impurities using the silica gel mini-column because:
allyl 2-naphthyl ether is much less polar than other compounds in the reaction mixture
Which is a positive test result for the presence of an oxidant using the potassium iodide-starch test paper?
appearance of a blue-black color
Which compound below would you expect to have a greater than zero dipole moment?
b. dichloromethane
You are given a dichloromethane solution containing compounds A, B, and C. You first extract with 3N NaOH and find that a salt of A is in the aqueous layer. Re-extraction of the organic layer with 3N HCl leaves only C in the organic layer. Of the following, compound B is probably:
benzocaine
If a methylene chloride solution of benzoic acid and benzocaine is shaken with aqueous hydrochloric acid, _____ will be protonated to form the _____.
benzocaine; hydrochloride salt
If you were to extract a solution of p-toluidine (an amine) and benzoic acid in methylene chloride with aqueous base and then acidify the water layer, the solid you would isolate would be:
benzoic acid
In the developing chamber, solvent rises up the TLC plate owing to:
capillary action
Which of the following is not a requirement for an efficient fractional distillation?
careful heating of the pot
The purpose of the phase transfer catalyst in the phase transfer catalysis experiment was to:
carry the naphtholate anion into the organic phase where the reaction can occur.
Phase transfer catalysts promote certain reactions by
changing the solubilities of one of the reactants and thus increasing its concentration in the other phase
Why is sodium hypochlorite preferred over chromic acid as an oxidizing agent?
chromic acid forms toxic salts
During the dehydration of cyclohexanol experiment, the desired product was distilled as an azeotrope (a mixture that behaves as a pure component and has a single boiling point), what two compounds comprised this azeotropic mixture?
cyclohexene and water
In the solution Who Has My Compound? experiment, the solubility of your sample was tested in what
dilute sodium bicarbonate
When a simple distillation is carried out on a liquid containing a nonvolatile impurity, the distillation head temperature at the top of the column is:
equal to the boiling point of the pure liquid
Three possible products are shown below from a steam distillation of common spices. You run an IR of an isolated substance and notice you have a small peak at 3050 cm-1, a medium intensity peak at 1640 cm-1, and a strong peak at 1720 cm-1. Which of these compounds did you most likely isolate?
eugenol
Which of the following steps is not used in the application of the technique of solution recrystallization?
filtration of the purified crystals from the cooled supernatant solution
Assuming you had a mixture of the following compounds, which one would elute first on a GC that contains a polar poly-alcohol (Carbowax 20m) column?
hexane
In the distillation of hexane/heptane and hexane/octane mixtures, the early distillation fractions contain higher percentages of hexane because:
hexane has a higher vapor pressure
In the Natural Products Isolation experiment, steam distillation was used to isolate limonene from orange peels. Which of the following properties of the natural product to be steam distilled are desired for rapid distillation with giving larger amounts of the natural product?
high vapor pressure and high molecular weight
The reaction of sodium hypochlorite and an acid (i), are used to generate an oxidizing agent (ii). What are (i) and (ii)?
i) acetic acid, (ii) hypochlorous acid
A kinetic study of the SN1 solvolysis of 1-chloro-1-phenylethane showed a rate constant of 4.0 x 10-1 sec-1 in a solvent system that was 50:50 H2O/EtOH. With a solution of the same concentration except in a solvent system of 70:30 H2O/EtOH, one would expect the rate constant to be:
larger because an increased amount of polar H2O stabilizes the formation of the cation
Which of the alcohols below cannot undergo a dehydration reaction using the experimental conditions used in the dehydration experiment?
methanol
The solvent chosen to recrystallize a compound should
not react chemically with the compound, but should dissolve a large amount of the impure compound at temperatures near the boiling point of the solvent.
A phase transfer catalyst was used in the preparation of allyl naphthyl ether because:
one reactant was soluble in the aqueous phase and one reactant was soluble in the organic phase
For a simple distillation to work,
only I and II are correct
You allow a hot recrystallizing solution to cool slowly because:
otherwise small crystals form rapidly, adsorbing impurities
In preparative gas chromatography, increasing the quantity of injected sample will produce:
poorer separation
Absorption of infrared radiation by a molecule,produces changes in the amplitude of molecular vibrations
produces changes in the amplitude of molecular vibrations
Which of the following statements is true of thin layer chromatography?
produces changes in the amplitude of molecular vibrations
Which is the rate expression for the SN1 solvolysis of 1-chloro-1-phenylethane?
rate = k[R-Cl]
In the purification technique of recrystallization, a hot filtration is sometimes carried out to:
remove insoluble solid impurities
If you spill sulfuric acid on your hand, you should rinse the area with large amounts of water followed by a solution of:
sodium bicarbonate
In preparative gas chromatography, very slow injection of a sample results in a poor separation because
some of the sample has started moving through the column before all of the sample is injected.
Based on VSEPR theory, what is the hybridization of the nitrogen atom and the approximate bond angles around nitrogen in methylamine, CH3NH2?
sp3 and 109.5 degrees
Which of the following will increase the efficiency of a liquid-liquid extraction procedure?
subdividing the solvent into smaller portions and doing several smaller extractions.
Which is the correct procedure for isolating benzocaine crystals from a solution of benzoic acid and benzocaine in methylene chloride?
Add aqueous HCl, remove aqueous layer, add NaOH to the aqueous layer, collect crystals by vacuum filtration.
Which of the following is true about melting point determination?
At the eutectic point, the melting point of a mixture of two compounds is sharp.
Gas Chromatography can separate compounds based on their______? I. boiling point II. melting point III. polarity IV. size
I and III
Which of the following pairs of structures below are representations of the same molecule?
I and III
What is the main building block for terpenes?
Isoprene
Which of the following shows correct mechanism for the reaction of sodium naphtholate with allyl bromide to produce corresponding allyl 2-naphthyl ether?
Mechanism #2
Which of the following reagents is not an oxidizing agent?
NaBH4
Which statement is NOT correct about simple distillation and gas chromatography?
Neither can be used to separate organic compounds that have the same boiling point.
The functionality that absorbs IR radiation of the highest energy is
O-H
When taking a melting point, which of the following is not a consideration?
Pack each capillary with 1-2 cm of the solid
Which test is used to assure excess oxidant in the reaction of the experiment "the oxidation of secondary alcohols" and what is the positive result?
Potassium iodide-starch paper, get blue-black color from the triiodide-starch
All the following statements about Kinetic Study of SN1 Solvolysis experiment are correct except
Temperature does not have effect on the reaction rate.
For thin layer chromatography, which of the following statements is wrong?
The farther the developing solvent travels, the bigger Rf of a certain compound
Which of the following statements about an SN1 Solvolysis Experiment is false?
The reaction involves a single-step mechanism.
IR Spectroscopy is useful in the analysis of carbonyl compounds because:
the C=O bond is a strong absorber of particular frequencies of infrared radiation
In gas determined by: chromatography, the temperature at which the chromatograph must be operated is
the volatility of the mixture to be separated
In considering the conformations of n-butane generated by 360 rotation about the C2-C3 bond, how many different energy values will be encountered as energy minima?
Two
Which of the following is not correct for the preparative gas chromatography experiment?
While collecting and handling the tubes with sample in them, keep them positioned with both ends down.
In the oxidation reaction of secondary alcohols such as cyclohexanol, the major product would be:
a ketone
Stearic acid and limonene are two natural products which are classified respectively as:
acetogenin, terpene
The word(s) that describes one vaporization and condensation step in a distillation is:
theoretical plate
You are performing a solvent extraction of a neutral, basic, and an acidic compound. All are very soluble in CH2Cl2 (dichloromethane) and slightly soluble in H2O. You have added aqueous HCl to the separation funnel and shaken the funnel. The basic compound is in the ______ layer, the acidic compound is in the ______ layer, and the neutral component is in the ______ layer. bottom, top, top
top, bottom, bottom
Thin layer chromatography is:
useful for detecting impurities in a compound.
The absorption of infrared radiation involves changes in what type of molecular energy states?
vibrational
Compounds A and B both have melting points of 140 C. If A is mixed with B at a ratio which leads to melting at the eutectic point, the melting point of the mixture
will be less than 140 C
You have a mixture of all of the compounds below in toluene. You extract the toluene with 2 M aqueous HCl. Which compounds will stay in the toluene?
1 and 4
In phase transfer catalysis, which of the following structure(s) is(are) soluble in the organic phase?
1, 3 and 4
During an extraction procedure you add equal amounts of the following: water (Density = 1g/mL) dichloromethane (Density = 1.3266 g/mL) ethyl acetate (Density = 0.897 g/mL) 5% NaOH solution (Density = 1.055 g/mL)How many layers do you expected to see in the funnel and which one will be the bottom layer?
2 layers, organic phase
Which of the following alcohols undergoes dehydration reaction (E1) most rapidly?
2-methyl-2-butanol
If you started with 10 g of 75% pure crystals, and recovered 5 g of 100% pure crystals after a recrystallization, how much of the product did you lose?
2.5 grams
In the following reactions, what conditions were used to isolate eugenol from clove oil?
3 N NaOH
Which of the following alcohols would not react via a bleach oxidation?
3-methyl-3-pentanol
3-pentanol has an O-H peak from alcohol at:
3200-3600 cm-1
The dihedral angle (torsion angle) between the methyl groups in the structure, is expected to be about:
60 degrees
The theoretical yield of cyclohexene from the dehydration of 10 grams of cyclohexanol would be
8.2 grams
In the boiling point-composition diagram below, boiling a mixture of 60% methanol and 40% water will yield a vapor which is:
80% Methanol
For the following reaction, the starting material weighs 3.00 g and the final product weighs 2.00 g. What is the percent yield for this reaction?
81.3%
When you determine the melting point of a compound, what is indicative of an impure compound?
A broad melting range and a lower melting point.
Which of the following statements is true for thin layer chromatography (TLC) on silica gel?
A compound will move further if the solvent is changed from hexane to ethyl acetate.
Which statement concerning molecular geometries is correct?
A low energy structure may not necessarily be the global minimum of lowest possible energy.
Having completed the Thin Layer Chromatography experiment, you find that caffeine gives an Rf of 0.75 in the 75% ethyl acetate - 25% hexane solution. Out of curiosity, you decide to run a second TLC plate in hexanes. What should you expect to see and why?
A lower Rf because the hexanes are a less polar solvent system
Which of the following statements concerning the infrared spectroscopy experiment is WRONG?
A thick layer (> 10 m) of sample is required to run ATR-IR.
If you do a kinetic study of SN1 solvolysis, which graph is correct?
C
In order to get a the most pure fraction of Fraction II, when should you start to collect the second fraction according to the following GC?
C
In IR, which of the following functional groups absorb at 1600-1800 cm-1?
C=O
An analysis of which stretching region will be the most helpful in distinguishing between the following two compounds with infrared spectroscopy?
C=O stretching region
In the oxidation reaction with sodium hypochlorite, the oxidant is reduced into _____.
Cl-
Essential oils from which of the following spices would give you a positive Ferric Chloride test?
Clove and Allspice
What is the mechanism of acid-catalyzed dehydration of cyclohexanol?
E1
The strain energy of a molecule can be broken down into four terms. What is the last one? Estrain = Estretch + Eangle + Etorsion + ____ .
Esteric
Which type of strain energy in a molecule accounts for van der Waals interactions and dipole repulsions present in a conformation?
Esteric
Which of the following statements is false?
Eugenol will give a negative ferric chloride test.
Steam distillation allows for the distillation of water-immiscible compounds in solution at temperatures __________ their normal boiling points because their net vapor pressure is equal to __________ both vapor pressures.
Far below, the sum of
Which of the following statements about melting points is incorrect?
Rapid heating results in a narrower melting point range.
When recrystallizing a solid, the solvent must initially be hot because
Some solids are highly soluble in hot solvents but not so soluble in cold solvents
For an E1 reaction (unimolecular elimination), the reaction rate does not depend upon:
The strength of the nucleophile or base.
When using a non-polar column in a gas chromatographic analysis, what plays the major role in the separation of the components?
The vapor pressures of the compounds.
Which of the following is essential for the separation of two compounds in a mixture by preparative GC?
They have different distribution in the stationary phase.
In determining the rate of SN1 solvolysis of 1-chloro-2-phenylethane, which of the following had to be measured to determine the rate constant?
the change in concentration of a reactant or a product during a measured time interval
In order to determine the rate of a reaction one must know:
the change in concentration of either reactants or products with time
Which of the following criteria for recrystallization solvents is false?
the compound should be soluble in both hot and cold solvent
After we have completed an organic reaction, we often "workup" the reaction. The term "workup" refers to:
the general method of purification that uses aqueous-organic extraction
In the phase transfer experiment, a very short liquid chromatography column was sufficient to obtain pure product because:
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
In the reaction of allyl bromide with naphthol using phase transfer catalysis:
the reaction mechanism was SN2
In the SN1 hydrolysis of 1-chloro-1-phenylethane:
the reaction rate is monitored by the rate of HCl formation.
