OChem Final Study - Quiz and Test
In a thin layer chromatography experiment, a sample was spotted 1.0 cm from the bottom of a plate that was 10 cm long. When developed, the solvent was allowed to rise 9 cm above the bottom edge. Two spots were observed which had moved 3 cm and 5 cm from the point of origin. Their respective Rf values are: (Hint: draw the TLC plate)
0.38 and 0.63
(Molecular Models [Post]) Identify the atoms that participate in 1,3-diaxial interactions in the shown conformation of cis-1,2-dimethylcyclohexane. How many total 1,3-diaxial interactions are present in this molecule?
2
An sp carbon typically has ___ atoms attached to it with bond angles of about ____.
2 180°
A mixture of benzoic acid, benzyl chloride and cyclohexyl amine is dissolved in dichloromethane. The solution is extracted with dilute aqueous HCl and the layers separated. The dichloromethane layer contains: 1.cyclohexyl amine 2.benzoic acid 3. benzyl chloride
2 and 3
Which of the following statements about steam distillation is/are true? 1. A steam bath is used as a heat source. 2. Steam distillation is only effective for compounds that are not very water soluble. 3. The boiling point of the mixture being distilled will be lower than any of the components of the mixture.
2 and 3
A strong IR absorbance in the 1670‐1830 cm‐1 range is present in which of the following: 1. alkenes 2. esters 5. alcohols 3. aldehydes 4. carboxylic acids
2,3,and4
(Recrystallization of Acetanilide) None of the following molecules display much solubility in water at room temperature. however, two of the molecules display appreciable solubility in boiling water. Based on it structure, which molecule will be the least soluble in hot water?
2-naphthol
What is the volume range of a typical injection for the Preparative Gas Chromatography experiment?
25-100μL
Arrange the following substituted cyclohexanes in order of increasing total steric strain (lowest strain energy first). You may need to see Table below. 1. Chair conformation with both CH3 on pointing up on top. 2. Chair conformation with one CH3 pointing down in the middle and other to the side on right 3. Chair conformation with pointing on opposite ends 4. Chair conformation pointing up and down
3-2-4-1
(Molecular Models [Post]) Considering that gauche interactions and 1,3-diaxial interactions both contribute 3.8 kJ/mol to the strain energy for a conformation, calculate the total strain energy for the shown conformation of trans-1,2-dimethylcyclohexane. EQUITORIAL. What is the total strain energy in this molecule?
3.8 kJ/mol
The William ether synthesis between 2-napthol and allyl bromide in the presence of strong base and benzyltriphenylammonium chloride as a phase transfer catalyst in dichloromethane solution is know to proceed in reasonable yield. The need for a phase transfer catalyst would be removed if a polar aprotic solvent such as DMSO were used as a reaction solvent. Why is DMSO not used as a solvent for this reaction?
Because of the risks associated with toxicity.
Which of the following items is not true of the mini-column used in the phase transfer catalysis?
Any leftover starting material eluted off the column before the product.
A phenol (ArOH) that is deprotonated by NaOH will become _______.
ArO- Na+
Steam distillation is useful for isolating compounds that:
Are water immiscible with low vapor pressure at room temperature
Which of the following statements is true?
As the temperature of a liquid increases, the vapor pressure increases.
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.
("Who Has My Compound?") Why is it good practice to perform a mixed melting point determination at two different ratios of unknown to known materials in the melting point capillary?
Because it is possible that one particular combination of materials generates a eutectic.
How does a change in dipole moment effect IR absorption?
Bond stretching, causing a change in dipole moment, results in an IR absorption peak.
Which statement is NOT true about bromide, Br2
Br2 is a reducing agent
Which reagent is not an oxidizing agent?
CaSO4
Common TLC stationary phases include all of the following except:
Calcium chloride
The reaction performed in the dehydrohalogenation experiment was an E2 reaction. Which of the following statements about E2 reactions is false?
Carbocation intermediates are common in E2 elimination reactions.
A positive bromine test indicates the presence of what?
Carbon-carbon double bonds
Which structure below will have the highest strain energy when calculated by molecular mechanics?
Chair with 6 axial and 3 axial
In the oxidation of cyclohexanol to cyclohexanone with bleach solution, the oxidation state of what element is reduced?
Cl
Which of these statements about the column with a typical GC is false?
Column contents are volatile.
To dry the reaction product
Combine the organic layers over anhydrous potassium carbonate
The IR spectra of a compound reveals absorptions around 3400 cm-1 and 1600 cm-1. Which of the following could be the compound
H2NCH2CH2CH=CH2
In the kinetic study of SN1 solvolysis, the nucleophile in the reaction is?
H2O
Which reagent is not an oxidizing agent?
H2O
To form a salt of an amine, R-NH2, you must add which reagent?
HCl
Why would concentrated hydrochloric acid be a poor choice as the acid catalyst for formation of cyclohexene by dehydration of cyclohexanol?
HCl is a poor depronater, so it wouldn't be able to get rid of the positive charge or make a = bond
Which of the following statements about gas chromatography is false?
If the stationary phase is polymeric alcohol, a nonpolar compound would move more slowly than a polar compound with the same boiling point.
What effect would decreasing carrier gas flow due to the retention time?
Retention time increases
The preparation of 3‐chloro‐3,7‐dimethyloctane from 3,7‐dimethyl‐3‐octanol, is an:
SN1 reaction in which formation of tertiary carbocation is the rate determining slow step.
In the preparation of 3-chloro-3,7-dimethyloctane, 3,7-dimethyl-3-octanol is treated with concentrated HCl to give the alkyl chloride. By which of the following pathways does this reaction proceed?
SN1 through a carbocation intermediate
("Who Has My Compound?") Which of the following statements about melting point determination are true? Select all that apply.
The lower limit of the melting temperature range occurs when the first crystal starts to melt. & The melting point is a physical measure of the forces holding the material into its crystal lattice. & The upper limit of the melting temperature range occurs when the last remaining crystal melts.
To avoid making the reaction mix become an emulsion.
The reaction was stirred at a moderate, not rapid, pace.
Which one of the following statements would not be desired in a good recrystallization solvent?
The recrystallization solvent is nonvolatile.
Which statement is false for the phase transfer catalysis experiment?
The role of the phase transfer catalyst, benzyltri-n-butyl ammonium chloride is to carry the naphtholate anion into the water
Which statement is true about thin layer chromatography?
The solvent moves through the stationary phase by capillary action.
Over time, the amount of the most volatile component in the distillate increases. T/F
True
The first step in utilizing a separatory funnel is to make sure the funnel stopcock is closed and then carefully pour the liquid to be extracted into the funnel. T/F
True
The rate of heating affects the number of theoretical plates in the column. T/F
True
The stopcock can be used to vent excess pressure if either of the liquids are warm to the touch and has a low boiling point. T/F
True
To avoid a build up of pressure from the dichloromethane
Vent the separatory funnel occasionally through the stopcock.
To avoid dangerous vibration due to imbalance
Vials placed into the centrifuge in pairs, 180 degrees apart
To preserve the purity of the sample
Wait for the second peak to be on the rise before beginning its collection
The dehydrohalogenation of 3-chloro-3,7-dimethyloctane (an E2 reaction) is favored over substitution because:
a tertiary halide is used
Arrange the following solvents for least dense to most dense
hexanes > diethyl ether > water > dichloromethane > chloroform
To get effective mixing in a separatory funnel, the combined level of liquids should not exceed:
higher than the widest part of the separatory funnel
What is the type of em radiation associated with these peaks:
infrared radiation
Before returning your bin of glassware to the stockroom, you are required to rinse the glassware with acetone to:
insure that all traces of water have been removed & insure that no traces of organic soluble material has remained in the flasks & insure that no unwanted reaction will occur the next time the glassware is used, owing to the presence of a contaminant
In IR what kind of absorption can help you identify the cyclohexene formation for certain?
presence of a peak around 1650 cm-1 and 3010-3100 cm-1
The rate law: rate = k[RCl][‐OH] is representative of what type of kinetics?
second order
The raising of the oven temperature in GC will _____ the retention times of two compounds and _____ their separation.
shorten, decrease
Which one of the following tests cannot be used to detect the presence of eugenol?
silver nitrate test
In a thin layer chromatography experiment, a compound is found to have an Rf close to unity (1.0). The spot for this compound on a TLC plate is most likely to appear:
slightly below the solvent front
Eugenol can be isolated by steam distillation because it is insoluble in water and has a much higher boiling point than water (254 degrees C versus 100). What temperature will a mixture of eugenol and water boil at?
slightly less than 100C
A compound to be recrystallized should be:
slightly soluble at low temperature and highly soluble at high temperature
In the recrystallization of acetanilide, you were asked to allow the hot solution to cool slowly to form crystals. What happens if the solution is cooled rapidly?
small crystals form and adsorb impurities.
When a solution is cooled very rapidly in recrystallization:
small crystals form that have a large surface area on which impurities will be absorbed
When the solution is cooled very rapidly in recrystallization
small crystals form that have a large surface area on which impurities will be adsorbed.
In a distillation, one vaporization and condensation step is usually called a(n):
theoretical plate
Which of the following is one of the criteria used to determine whether compounds can be purified by gas chromatography?
thermal stability
In the phase transfer catalysis experiment, what type of analysis was used to determine the progress of the reaction?
thin layer chromatography
Rates of reactions. Rate in rate equation, always have units of mole L-1 sec-1. In the above equation, what are the units of the rate constant, k?
time-1
In the phase transfer catalysis experiment, the role of benzyltri-n-butylammonium chloride is:
to carry the naphtholate anion to the organic phase.
Why do you add boiling chips to a solution that will be heated?
to promote even boiling
In the solvolysis reaction of 1-chloro-1-phenylethane what is the nucleophile?
water
Which of the following is the most polar compound?
water
For Sn1 nsolvolysis of t-butyl chloride, rank the solvents from fastest reaction to slowest reaction.
water > formic acid > methanol > ethanol > acetone > acetic acid
A student's kinetic study of the SN1 solvolysis reaction of 1‐phenyl‐1‐chloroethane (using dilute NaOH to neutralize the HCl formed) gave a rate constant k=5.0 x 10‐4sec‐1, using a 70% H2O, 30% ethanol mixture for solvent. Steam distillation is used to isolate:
water insoluble oils
Which of the following statements describe why moisture must be excluded from any sample injected into the G.C.
water is very slow to elute from the column and water contains dissolved salts that can degrade the column
(Recrystallization of Acetanilide) When is recrystallization not a suitable method to purify an organic material?
when the organic material is a liquid instead of a solid
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 that 140°C
(Recrystallization of Acetanilide) During the recrystallization of an impure solid sample of acetanilide, the sample is dissolved in hot water then filtered while hot. The filtrate is allowed to cool and the mixture is filtered a second time. Which of the following actions will increase the percent recovery of the acetanide solute?
after the first filtration, place the solution in an ice-water bath for about 10 minutes
Which of the following would not be a role of the phase transfer catalyst?
aids in the separation of the products of the reaction
What products can be prepared through the oxidation of primary alcohols?
aldehydes and carboxylic acids
At the end of the phase transfer catalysis experiment, what molecule had the highest Rf value when you ran the TLC?
ally 2‐naphthyl ether
During a solvent extraction between water and an immiscible solvent, a student has two layers in their separatory funnel and then shakes it. A single, milky liquid develops and no real sign of any layers are visible. What has occurred and what should the student do?
an emulsion has formed, the student should first, add a small quantity of water. if that does not work, then add solvent
In considering rotation about the C2-C3 bond of butane, how many conformations are encountered?
an infinite number
The reaction that converts 2‐heptanol to a carbonyl compound is best described as:
an oxidation
Which of the following statements are true concerning azeotropes?
an unknown liquid that boils at a constant temp. could be an azeotrope
What are commonly used oxidizing agents?
chromic acid and sodium dichromate
Most organic compounds are less dense than water and will be on top of the aqueous phase in a separatory funnel. Which of the following organic phases breaks this rule and will be on the bottom?
dichloromethane
An ideal recrystallization solvent will
dissolve little of the compound at room temperature and lots at high temperatures
(Molecular Modeling) Which statement about equatorial and axial positions in cyclohexane is correct?
each carbon in cyclohexane is attached to one axial and one equatorial hydrogen
The solubility data table shows that both benzoic acid and benzocaine are significantly more soluble in ethanol than they are in water. Why is ethanol not a suitable solvent for the solvent extraction of benzoic acid and benzocaine from aqueous solution?
ethanol is miscible with water
Which of the following variations of 1,2‐dimethylcyclohexane in the chair conformation is the most stable?
methyl groups are diequatorial
In the fractional distillation of an ideal solution of two miscible liquids, the vapor contain:
more of the more volatile component
What ion did the benzyltri-n-butylammonium cation transport from the aqueous to organic phase in the phase-transfer catalysis experiment?
naphtholate anion
If concentrated sulfuric acid is spilled during the experiment, what is the proper procedure for cleaning the spill?
neutralize the spill with sodium bicarbonate
In the Who Has My Compound experiment, how did the inorganic sand affect the melting point benzoic acid?
no effect on the melting point
In simple distillation, the temperature frequently drops after the main fractions have distilled because:
not enough vapor and condensate are present in the head to keep the thermometer bulb hot
(Recrystallization of Acetanilide) The solvent should dissolve the compound while cold. T/F
False
(Recrystallization of Acetanilide) The solvent should not dissolve the compound while hot. T/F
False
(Who Has My Compound?) Mark the plate after applying the sample. T/F
False
(Who Has My Compound?) Polar compounds will have higher Rf values than non polar compounds under the same developing conditions. T/F
False
(Who Has My Compound?) Polar compounds will have higher Rf values than nonpolar compounds under the same developing conditions. T/F
False
(Who Has My Compound?) Rf is not dependent on polarity. T/F
False
(Who Has My Compound?) The less polar the solvent, the higher the Rf values. T/F
False
(Who Has My Compound?) Use a pencil or pen to mark the position of a spot on the TLC plate. T/F
False
Hold your thumb firmly over the hole in the top of the funnel during shaking T/F
False
It is acceptable to handle TLC plates with bare hands T/F
False
Methylene chloride is flammable T/F
False
Over time, the amount of the most volatile component in the distillation flask increases. T/F
False
Pipets that contain only water can be disposed of in the trash T/F
False
Rapid heating can drive heated vapor up the column, preventing the formation of an equilibrium that allows the lower boiling component to separate. As a result, this will increase the number of theoretical plates and increase the separation. T/F
False
Silica is toxic T/F
False
Simpel distillation is effective at separating mixtures of liquids with very similar volatilites. T/F
False
Students should throw away the first and acid washes. T/F
False
The smaller the boiling point difference, the easier it is to separate two liquids and fewer theoretical plates are required. T/F
False
(Recrystallization of Acetanilide) Identify the apparatus used in a vacuum filtration by dragging and dropping the labels into the appropriate boxes.
Filter paper is placed in the Buchner funnel to collect all the big particles. The Buchner funnel is held down by a vacuum seal by filter adapter (or Filtervac). The filtrate runs into the filter flask. The clamp, usually attached to a ring stand, holds the entire apparatus if it's securely tightened around the neck of the filter flask.
An example of sp2 hybridization on the central atom is:
Formaldehyde
If two compounds are close in boiling points, which might be a good technique to separate them?
Gas Chromatography because it can separate compounds based on polarity.
(Recrystallization of Acetanilide) A student was given a sample of crude acetanilide to recrystallize. The initial mass of the the crude acetanilide was 146 mg. The mass after recrystallization was 115 mg. Calculate the percent recovery from recrystallization.
% recovery = final mass / initial mass 100% = 115/146 100% = 78.8%
(Molecular Models [Post]) Identify the atoms that participate in 1,3-diaxial interactions interactions in the shown conformation of trans-1,2-dimethylcyclohexane. EQUITORIAL. How many total 1,3-diaxial interactions are present in this molecule?
0
(Molecular Models [Post]) Identify the gauche interactions between methyl groups in the shown conformation of trans-1,2-dimethylcyclohexane. AXIAL. How many gauche interactions are there between methyl substituents in this molecule?
0
(Molecular Models [Post]) Identify the gauche interactions between methyl groups in the shown conformation of cis-1,2-dimethylcyclohexane. How many gauche interactions are there between methyl substituents in this molecule?
1
(Molecular Models [Post]) Identify the gauche interactions between methyl groups in the shown conformation of trans-1,2-dimethylcyclohexane. EQUITORIAL. How many gauche interactions are there between methyl substituents in this molecule?
1
("Who Has My Compound?") TLC Procedure:
1. Add just enough developing solvent to cover the bottom 3 mm of the TLC chamber. Cover with a watch glass. 2. Make a pencil mark on the TLC plate 10 mm from the bottom. 3. Use a capillary to deliver a 2 mm diameter spot onto the pencil mark. 4. Stand the TLC plate upright in the chamber, and replace the lid. 5. Remove the TLC plate when solvent is near the top of the plate. 6. Gently mark the position of the solvent front using a pencil before the TLC plate dries completely. 7. Measure the distance that the spot and solvent have moved.
List the procedural steps that are required to convert 2-naphthol and allyl bromide into allyl 2-naphthyl ether.
1. Fit a conical vial with a stirring vane and add 2-napthol, allyl bromide, and benzyltriammonium chloride in dichloromethane. 2. Add NaOH to the reaction flask. 3. Cover the reaction vial and stir. 4. Periodically stop the stirring, allow the layers to settle, and spot the organic layer on a TLC plate. 5. Remove the bottom layer and dry over CaCl. 6. Run the reaction solution through a silica chromatography column. 7. Evaporate dichloromethane solvent to dryness.
(Recrystallization of Acetanilide) Procedure:
1. Place the finely divided mixture and a boiling chip into an Erlenmeyer flask on a steam bath. 2. Add the minimum amount of hot water to dissolve the solid. 3. Rapidly filter the hot solution through a pre-warmed funnel. 4. Wash the filter with hot solvent and transfer the filtrate to a clean flask. 5. Allow the filtrate to cool slowly, then cool in an ice bath to force precipitation. 6. Vacuum filter the cold suspension. 7. Air dry the purified solid on the filter.
"Who Has My Compound?" M.P. Determination Procedure:
1. Press the open end of a capillary tube into the solid sample. 2. Invert the tube and tap gently to move the solid to the bottom of the capillary. 3. Place the loaded tube into the hole in the melting point apparatus, and heat at 10 degrees per minute. 4. Observe the material through the complete melting process to get a rough estimate of the melting point range. 5. Turn off and allow to cool by 15 degrees. 6. Replace the existing tube with a new sample. 7. Heat at 2 degrees per minute through the expected range.
Select the proper set of reagents to complete the following two reactions: 1-cyclohexanone-4,4-dimethyl -1-> 1-OH,H-cyclohexane-4,4-dimethyl -2-> Back to one
1. reaction with sodium borohydride 2. reaction with HOCl
LIst the procedural steps that are required to perform a steam distillation of limonene from orange peel
1.)Place citrus peel into a preweighed round round bottom flask 2.)add water until the level is past the midpoint of the flask 3.)attach a condenser and recieving flask with greased joints, then distill the mixture 4.)add ethyl acetate to the recieving flask to extract the droplets of oil 5.)separate the layers, and dry the organic layer over calcium chloride 6.)filter off the drying agent, and then remove the ethyl acetate solvent by microdistillation 7.)collect and weigh the residue of pure limonene
List the procedural steps that are required to perform an extraction of eugenol from a solution of clove oil in dichloromethane:
1.)Place the dichloromethane solution of clove oil into a separatory funnel 2.)Add sodium hydroxide solution. Separate and collect the aqueous layer 3.)Acidify the aqueous later with hydrochloric acid 4,)Extract the acidic solution into dichloromethane. Collect the organic layer 5.)Dry the dichloromethane solution over calcium chloride 6.)Remove the dichloromethane solvent by microdistillation 7.)collect and weigh the residue of pure eugenol
List the procedural steps, from start to finish, that are required to separate and collect a two-liquid mixture using preparative gas chromatography.
1.Each unknown sample is labeled with a number that represent the oven temperature of a particular preparative gas chromatograph. 2. Inject the sample into the Prep GC whose number matches your sample. 3. Place a curved collcetion tube on the exit port of the GC, and collect the sample just after it is detected. 4. Replace the tube so that pure sample of the next fraction can be collected. 5. Transfer the collection tubes to conical vials, and centrifuge to collect the pure samples. 6. The full procedure is listed in the lab manual.
List the procedural steps, from start to finish, that are required to perform a chemically active solvent extraction of a three-component mixture composed of benzoic acid, benzocaine, and a neutral organic molecule all dissolved in dichloromethane.
1.dissolve the solid three-component mixture in dichloromethane and place in a separatory funnel. Add 6M Hal to the solution. Shake and allow to settle into layers 2. add water to dissolve the brown emulsion between the layers 3. separate and collect the aqueous layer in a flask, and add base 4. place the dichloromehtane layer back in the separatory funnel and extract it with 3M NaOH. allow layers to settle 5. add water to dissolve the white gel-like emulsion 6. separate and collect the aqueous layer in a flask, and add acid 7. collect and dry the solids in both Erlenmeyer flasks by filtration
(Molecular Models [Post]) Considering that gauche interactions and 1,3-diaxial interactions both contribute 3.8 kJ/mol to the strain energy for a conformation, calculate the total strain energy for the shown conformation of cis-1,2-dimethylcyclohexane. What is the total strain energy in this molecule?
11.4 kJ/mol
What region of an infrared spectrum is most useful for distinguishing between isomers that contain the same functional group?
1400-400 cm-1
(Molecular Models [Post]) Considering that gauche interactions and 1,3-diaxial interactions both contribute 3.8 kJ/mol to the strain energy for a conformation, calculate the total strain energy for the shown conformation of trans-1,2-dimethylcyclohexane. AXIAL. What is the total strain energy in this molecule?
15.2 kJ/mol
Benzoic acid and phenol can be differentiated in the infrared because benzoic acid shows an absorption near ______ and phenol does not.
1700 cm‐1
Butyl butyrate, an ester, differs from p-dioxane, an ether, by showing a strong infrared absorbance at:
1745 cm-1
What is the appoximate wavenumber of that band?
3500
(Molecular Models [Post]) Identify the atoms that participate in 1,3-diaxial interactions in the shown conformation of trans-1,2-dimethylcyclohexane. AXIAL. How many total 1,3-diaxial interactions are present in this molecule?
4
The infrared spectrum displays the wavelengths at which specific functional groups absorb energy. Match the functional group to the region of the spectrum that it is most likely to absorb energy. The scale is shown in wavenumbers, cm-1.
4000-3000=O-H alcohol 1800-1640=C=O aldehyge 1600=C=C alkene
Considering the reaction of 2A + 3B goes to 1C + 3D, with molecular weights being 150, 200, 200, and 233 for A, B, C and D respectively, what would the theoretical yield for C be if you started with an excess of B and 75 grams of A.
50g
The computer calculated that the local minimum for the gauche butane conformation had a dihedral angle of:
65
The computer calculated that the local minimum for the gauche butane conformation had a dihedral angle of:
65°
You have treated 10.0 g of 2‐methyl‐2‐butanol (MW = 88.15 density = 0.805 g/mL) with concentrated HCl and purified the product by extraction and distillation. Your product is 9.0 g of 2‐chloro‐2‐methylbutane (MW = 106.60 density = 0.865 g/mL). The percent yield is:
74%
Which of the following functional groups has sp hybridization?
Alkyne
Which of the following statements about gas chromatography is true?
Polar compounds are retained more by polar columns
In the dehydration of cyclohexanol experiment, there is a possibility that the intermediate cyclohexyl cation (carbonium ion) might undergo a condensation reaction with a starting cyclohexanol molecule to produce dicyclohexyl ether as a byproduct (see reaction below). If this condensation reaction had taken place during your experiment and gave you a mixture of cyclohexene and dicyclohexyl ether in 8:1 mole ratio as a result, what would be the percent yield of cyclohexene, considering all of cyclohexanol was converted to these two products? cyclohexanol -H2O+-> cyclohexene + two cyclohexane connected with an O
80%
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? Cyclohexanol with MW: 100 g/mol -h+-> Cyclohexene with MW: 82 g/mol + H2O
81.3%
The distillate collected whilst dehydrating cyclohexanol is an azeotropic mixture of cyclohexene and water. What is the composition ratio of cyclohexene to water?
90:10
By plotting the natural logarithm (ln) of the initial concentration of alkyl halide ([RCl]0) over the concentration of alkyl halide at any time ([RCl]t) as function of time for a first order reaction, the plot will yield:
A Straight line with slope equals the rate constant k
During a melting point determination, it is normal to first take a rapid rough measurement followed by a slower more accurate measurement. Why is it important to allow the Mel-Temp to cool 15 °C before placing the second capillary tube in, and to set the voltage generate 1-2 °C temperature increase per minute?
A rapid temperature increase will give a melting point range that is too high.
Which of the following statements concerning the infrared spectroscopy experiment is WRONG?
A thick layer (> 10 ) of sample is required to run ATR‐IR.
During Thin Layer Chromatography, what method is typically used to apply the dilute solution of the sample to a TLC plate?
A thin glass spotter or capillary tube.
Which of the following molecules are expected to be sp3 hybridized at all multi-bonded atoms? A - N surrounded by 3 ethyl's B - C surrounded by 4 CH3 C - C surrounded by 4 Cl D - Cl-C=C-Cl
A,B,C
To keep the time for the reaction to go to completion under an hour.
Allyl bromide was used in excess.
Compounds A, B and C are three unknown compounds. Compound A melts at 130-133°C, Compound B melts at 132-134°C and Compound C melts at 140-143°C. Compound D is a known compound who melts at 131-134°C. The mmp A+B is 131-133°C. The mmp A+C is 138-142°C. The mmp B+C is 139-144°C. The mmp A+D is 130-134°C. The mmp C+D is 134-140°C. What can you conclude about your unknowns?
A=B=D
According to the Merck Index, the amount of solvent necessary to dissolve 1.0 g of m- 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 m-nitrobenzoic acid from water?
Acetone is soluble in water.
According to the Merck Index, the amount of solvent necessary to dissolve 1.0 g of m‐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 m‐nitrobenzoic acid from water?
Acetone is soluble in water.
Convert the benzocaine into a water-soluble salt.
Add acid to the three-component mixture
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, and vacuum filter the crystals.
Generate the oxidizing agent
Add bleach drowse into a flask containing acetic acid
Destroy the oxidizing agent
Add sodium bisulfite solution
Sodium hypochlorite and glacial acetic acid combine to make hypochlorous acid. Hypochlorous acid (HOCl) oxidizes cyclohexanol to cyclohexanone. At the end of the reaction, any excess hypochlorous acid must be neutralized. How is the neutralization of HOCl accomplished?
Add sodium bisulfite, NaHSO3
To precipitate the benzocaine
Addable to the aqueous acidic layer mixture
In reference to TLC, which statement best describes the change in Rf caused by a change in solvent polarity?
Adding a polar solvent causes the Rf of the compound to increase.
The reaction of bromide and of permanganate with cyclohexene both belong to which of the four general kinds of reaction?
Addition
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
What is the similarity with E2 elimination and SN2 substitution?
Concentration of nucleophile affects the rate of the reactions
To avoid the loss of sample
Detector fitted to the prep GC is a TCD not an FID
If you have a sample that is known to be either adipic acid or acetanilide, what is a quick way to distinguish the two?
Determine the solubility of each in sodium bicarbonate
Which compound below would you expect to have a greater than zero dipole moment?
Dichloromethane
To avoid the introduction of a spurious peak into the GC trace
Do not rinse the syringe with acetone, rinse it with sample instead
The experiment states that a distillation should never be continued until the distilling flask is dry. Does dry mean 'no water present' as when using a drying agent on an organic solution? Explain.
Dry means no liquid in the distillation head as well as no water in an organic product
To remove dissolved water is from the reaction mixture.
Enough calcium chloride to cover half the bottom of the flask was added.
In the natural product isolation experiment, which of the following statements is false?
Eugenol and limonene are a steroid and a terpene, respectively.
In the Who Has My Compound? experiment (among other experiments) you performed thin layer chromatography on a number of compounds and used the Rf values to help determine who else had the same compound as you had. Based on the structures of the following molecules, which would you expect to have the lowest Rf value when run in 50/50 EtOAc and Hexanes.
F-Phenyl-O=CH-OH
T/F - Lachrymators like allyl bromide are specifically dangerous because of their explosion hazard.
FALSE
T/F - The primary risk associated with dichloromethane is its flammability.
FALSE
TRUE OR FALSE: Gloves and goggles are not required when handling sodium hydroxide.
FALSE
TRUE OR FALSE: Unused allyl bromide can be disposed of in the aqueous waste.
FALSE
(Molecular Modeling) The twist boat conformation of cyclohexane has angle strain but is almost free of steric strain. T/F
False
(Recrystallization of Acetanilide) For hot vacuum filtration, the filter paper should be completely dry when pouring the hot solution into the Buchner funnel to filter. T/F
False
(Recrystallization of Acetanilide) For recrystallization, rapid cooling gives the best crystals. T/F
False
(Recrystallization of Acetanilide) The solvent should chemicals react with the compound. T/F
False
When hexane was used as the solvent for your Analgesics TLC lab, why didn't the spots move?
Hexane is not able to disrupt the polar-polar interactions between the analgesics and the silica gel
Rank the following conformations of 2-methylbutane in the increasing order of energy strain Newman Projections I - CH3 all near each other II - CH3 on top, and two near on bottom III- Two of the CH3 on top and near, one on bottom IV - Only one that is tilted
II and III, I, IV
Identify what type of spectra it is:
IR
What observation would be most conclusive in determining that the following compound was successfully oxidized to it carbonyl product? 3-HEPTANOL(bp=156) --> oxidation = product
IR band at 1710 cm-1
which of the following statements about infrared spectroscopy is not true?
IR can be used to analyze almost any kind of sample
Which is the least polar molecular
Ibuprofen
Rank in Rf values
Ibuprofen > aspirin > acetaminophen
What experimental observation on the initial dissolution of compound with with hot solvent would let you known that a hot filtration was not needed?
If after the initial dissolution of ht compound there are no solids left, then that would demonstrate that hot filtration was not needed
Thin Layer Chromatography (TLC) is a common technique that is routinely used in organic chemistry lab. It is simple, inexpensive, and very useful. Select the TRUE statement.
If compound A has a smaller Rf value than compound B, we can conclude that compound A is more polar than B.
Which of the following statements is false for recrystallization as a method for purification of organic compounds?
If the impurities are soluble, they may be removed by filtration at high temperatures.
What does the Bromine test for? and which product will it be positive for?
It tests for carbon-carbon double bonds and eugenol, limonene and cyclohexene would be positive
What does the Potassium Permanganate for? and which products will it be positive for?
It tests for carbon-carbon double bonds and eugenol, limonene and cyclohexene would be postive
What does the Ferric Chloride test for? and which product will it be positive for?
It tests for phenols and only eugenol would be positive
Why is it important to wash your flask and collected crystals with ice cold solvent after a recrystallization? What would happen if you used room temperature or warm solvent instead?
It's important to use ice cold solvent after recrystallization because room temperature or warm solvent could possibly dissolve part of the crystals
A student is comparing two samples of crystalline organic solids. A TLC analysis shows a single spot for each sample and the co-spot with the same Rf value. Which of the following would provide the most conclusive evidence that the two samples are the same compound?
Perform a mixture melting point
What is the chemical formula of the precipitate formed in the Baeyer's test?
MnO2
Which chemical was used to destroy excess oxidant in the oxidation of a 2° alcohol experiment?
NaHSO3r
To avoid spilling chemicals on other students or yourself
Never point the separatory funnel at anyone, including yourself.
The vibration of which bond gives an IR absorption that distinguishes between the following two compounds? CH3CH2CH2OH CH3CH2OCH3
O-H
To coontrol the rate of reaction
Place the reaction flask in an ice-water bath
Which of the following statements concerning GC is true?
Preparative GC allows purification and recovery of a compound after passing it through a GC column. & The moving phase in GC is an inert gas.
Infrared spectroscopy may be used to distinguish a primary amine from a secondary amine because:
Primary amines show two absorptions at 3400-3100 cm-1 and secondary amines show only one absorption at 3400-3100 cm-1
Write the rate expression for an SN1 reaction of R-Cl.
Rate = ln [RCl]o/[RCl]t = kt
In attempting to recrystallize impure benzoic acid, it was found that the benzoic acid formed a layer of oil on top of the recrystallizing solvent as the solution cooled. How could this problem be solved?
Reheat the solution to completely dissolve the oil, add a small portion of hot solvent, and allow the solution to cool slowly.
What effect would increasing the column temp. due to the retention time?
Retention time decreases
(Recrystallization of Acetanilide) What happens if the solution is called too rapidly?
Small impure crystals will form.
Consider the following reaction: What type of mechanism is this? alcohol -HBr-> back-alkanebromide and front-alkanebromide
Sn1
To deprotonate alcohols to become good alkoxide nucleophiles.
Solid sodium hydroxide was added to 2-naphthol.
Which of the following is a limitation to recrystallization?
Some product will be lost
T/F - Sodium hydroxide can cause severe damage to skin and eyes.
TRUE
In the extraction of eugenol from clove oil, the clove oil is treated with NaOH. Two layers form, an aqueous and a methylene chloride phase. Which of the following statements is true?
The OH‐ removes the phenolic hydrogen. The eugenol salt will be found in the top layer.
When analyzing the IR of your product from the Oxidation of a Secondary Alcohol you were looking for what in the spectra?
The appearance of a peak at approximately 1700 cm‐1 and disappearance of broad peak at approximately 3300 cm‐1.
Increasing the length of the column and packing the column with glass beads or rings are methods that produce more theoretical plates. T/F
True
("Who Has My Compound?") Which of the following statements best describes a eutectic composition?
The composition of a mixture of two components that generates the lowest possible melting point.
Which of the following statements best describes a eutectic mixture?
The composition of mixtures of two elements that makes a lowest possible melting point
Why would an organic substance dissolve in a basic sodium bicarbonate solution which is mostly water?
The compound reacts to make a charged compound
Assume your sample spots are 1 cm above the bottom of the TLC plate. What happens if you put the plate in a developing chamber that has 1.2 cm of developing solvent?
The compounds to be analyzed will end up in the developing solvent.
To separate the non-polar ether product from the polar by-products.
The contents of the reaction flask were passed through a column of silica.
During the extraction lab you extracted benzocaine out of CH2Cl2. What was the reactive functional group and what reagent was used to make this happen?
The functional group was an amine and the reagent was an acid
1-Phenyl-1-chloroethane is a secondary halide. Most secondary halides undergo SN1 reaction quite slowly. Explain why 1-phenyl-chloro-ethane undergoes Sn1 nsolvolysis quite readily.
The intermediate carbocation is not stable in an aqueous environment and is rapidly hydrated to yield a protonated alcohol
(Molecular Modeling) The gauche conformation of butane occurs when the dihedral angle between the C1-C2 bond and the C3-C4 bond is 60°. There is steric strain in the molecule because of the proximity of the two methyl groups. Would the magnitude of this steric strain increase or decrease if the dihedral angle was increased from 60° to 65°?
The magnitude of the steric strain will decrease because the groups are moving further apart
("Who Has My Compound?") How would the melting range of a pure organic material be changed if there was a tiny shard of broken glass inside the melting point capillary?
The melting range would not be affected.
Which of the following statements about melting point determination is not true?
The presence of impurities introduces entropy, which raises the energy required to melt the substance
What is the purpose of a hot filtration when performing a recrystallization?
The purpose of hot filtration is for the insoluble particles to dissolve
In the kinetics experiment, two different solvent mixtures were used. One mixture was 50% water-50% ethanol, the other was 60% water-40% ethanol. What would you predict about the rates in the two solvent mixtures?
The rate in the 60% water-40% ethanol mixture would be faster because the solvent better stabilizes the cation
A 0.7 mL mixture of pentanol and heptanol are separated and collected using preparative gas chromatography on a GC fitted with a polar column and a TCD detector. During the separation, why are the injection port and detector heated to a higher temperature than the column?
The wire in the thermal conductivity detector needs to be cooled by the eluent in order to register a signal. and c. A heated injector creates flash vaporization which allows separation at temperatures lower than the boiling point of the sample.
Why is the reaction of cyclohexene with HBr (a rapid, simple reaction) not useful as a characterization reaction?
There is no color change, so you can't view the reaction
What type of detector is used in the GC instruments used in the A&M Organic Labs?
Thermal conductivity detector
What are the two main properties of compounds necessary to do a successful gas chromatography?
Thermal stability and volatility
Which of the following is not true about phase transfer catalysts?
They are insoluble in water
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.
When would a hot filtration step NOT be necessary or useful in a purification by recrystallization?
This step would. not be necessary for recrystallization when there is no more solids in the solution
The suggested procedure for spotting a sample on a TLC plate involves transferring a droplet of concentrated solution from a capillary onto the plate, allowing it to dry, then repeating the process over the existing spot. Why is it advised to spot multiple times?
To facilitate visualization by having a higher compound concentration.
During the developing of a TLC plate, it is common to place a cover on the chromatography chamber and have a piece of moist filter paper line the walls of the TLC chamber. Why is the moist filter paper in the TLC chamber of importance during thin-layer chromatography?
To prevent evaporation from the TLC plate during development. To ensure that the air in the chamber is saturated with solvent vapor.
Methylene chloride is a probable human carcinogen T/F
True
(Recrystallization of Acetanilide) What is the purpose of using hot vacuum filtration?
To remove insoluble solid impurities such as dust, inorganic salts, polymeric material, or other unidentifiable unsoluble material.
To test for the presence of oxidizing agent
Touch a drop of the reaction mix onto a piece of KI-starch paper
(Molecular Modeling) After a ring flip, an axial substituent in one chair form becomes an equatorial substituent. T/F
True
(Molecular Modeling) Each carbon in cyclohexane is bonded to one axial and one equatorial hydrogen. T/F
True
(Molecular Modeling) Substituents larger than hydrogen prefer to adopt equatorial positions due largely to a smaller amount of steric strain. T/F
True
(Molecular Modeling) The different geometries that a molecule can attain by bond rotations and bends are called conformations. T/F
True
(Recrystallization of Acetanilide) 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. T/F
True
(Recrystallization of Acetanilide) Recrystallization requires the material that is to be purified is a solid. T/F
True
(Recrystallization of Acetanilide) The solvent should dissolve the compound while hot. T/F
True
(Recrystallization of Acetanilide) The solvent should either dissolve the impurities at all temperatures or not dissolve the impurities at all. T/F
True
(Recrystallization of Acetanilide) The solvent should not chemically react with the compound. T/F
True
(Recrystallization of Acetanilide) The solvent should not dissolve the compound when cold. T/F
True
(Recrystallization of Acetanilide) Use clamps to secure the filter flask to avoid tipping and unnecessary exposure to hot liquids or the solute. T/F
True
(Who Has My Compound?) Only touch the edges of the plate. T/F
True
(Who Has My Compound?) Rf is dependent on polarity. T/F
True
(Who Has My Compound?) Rf values should be kept in the range of 0.2 to 0.8 for the most effective separation when more than one compound is present in the sample. T/F
True
(Who Has My Compound?) Spot the plate on the dull, not shiny side of the plate. T/F
True
(Who Has My Compound?) Spots should be 1 or 2 mm in diameter T/F
True
(Who Has My Compound?) The Rf value is defined as the ratio between the distance the spot moved and the distance the solvent moved. T/F
True
(Who Has My Compound?) The distance the solvent moved is where the spot started to where the solvent front ended up. T/F
True
(Who Has My Compound?) The distance the spot moved is where the spot started to the center it ended up. T/F
True
Acetone is flammable T/F
True
Concentrated acetic acid is corrosive T/F
True
Distillation is a physical separation, not a chemical reaction. T/F
True
Each vaporization-condensation is called a theoretical plate. T/F
True
Ethyl Acetate is flammable T/F
True
Hexane is flammable T/F
True
Hypochlorous acid is an oxidizing agent T/F
True
If one is going to re-extract the upper layer with another volume of liquid, the upper layer can be left in the separatory funnel and fresh solvent added to the funnel
True
(Recrystallization of Acetanilide) The proper solvent choice is crucial for effective recrystallization. What are the features of a good recrystallization solvent? Select all that apply.
We should be able to easily remove the solvent from the purified product. & The solvent should not react with the target substance. & The solvent should dissolve a moderate quantity of the target substance near its boiling point but only a small quantity near 0 °C.
(Recrystallization of Acetanilide) When is recrystallization not a suitable method to purify an organic material?
When the organic material is not a solid.
Which statement(s) below are advantages for the purification of compounds by preparative GC versus distillation?
You may be able to separate different compounds which have exactly the same boiling point. & You can isolate a compound at temperatures well below its boiling point once it has been vaporized. & Some compounds which cannot survive the extended heating necessary for distillation may be stable enough to purify by GC.
What characteristic bond stretching does an aldehyde have in its IR spectrum that makes it easy to differentiate it from a ketone, a carboxylic acid, or an amide?
a C-H stretch at approximately 2700 cm-1
Which structure(s) represent an alcohol? a. CH3CH2-OHO b. H-C-OHOH c. CH3CH2CH2CH2CHCH3
a and c
Which of the following is an indication of a positive test for the permanganate test(Bayer's Test)?
a brown precipitate of manganese dioxide is formed
Which of the following compounds would be indicated by a strong, sharp infrared absorption in the 1680-1830 cm-1 region and a strong, broad absorption in the 2500-3300 region?
a carboxylic acid
In attempting to recrystallize impure benzoic acid, it was found that the benzoic acid formed a layer of oil on top of the recrystallizing solvent as the solution cooled. How could this problem be solved?
a. Reheat the solution to completely dissolve the oil, add a small portion of hot solvent, and allow the solution to cool slowly.
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.
acetone, ethyl acetate, benzene
During a solvent extraction, a student lost track of which layer was the aqueous layer and which was the organic layer. What simple, non-destructive test could be used to determine which layer is which?
add a little distilled water to see which layer the water adds to
(Recrystallization of Acetanilide) During the recrystallization of an impure solid sample, the sample is dissolved in hot water then filtered while hot. The filtrate is allowed to cool and the mixture is filtered a second time. Which procedure should a student NOT do if they observe an oil forming as the solution cools?
add a small amount of ice-cold water
Eugenol and limonene:
are an acetogenin and a terpene, respectively & are natural products
Infrared Spectra are recorded using an ATR detector? What does ATR stand for?
attenuated total reflectance
Upon simple distillation a mixture of CH3CH2OH and H2O distills at a constant boiling point and with a constant composition. This mixture is called a(n):
azeotrope
When you tested mixture melting point temperatures in the lab, your records showed that:
b and c only
In "Who Has My Compound," the lab included a solubility test for the unknown compounds in sodium bicarbonate. What purification technique uses the same chemical properties as the solubility test?
base extraction
To separate two compounds by liquid-liquid extraction, the compounds must
be distributed unevenly between the two immiscible liquids.
In an SN2 reaction, if the concentration of the nucleophile is doubled, the rate of the reaction will:
be doubled
Volatile organic compounds should:
be transferred in the hood
Eugenol, the essential oil found in cloves, is insoluble in water. The alcohol group in eugenol is dramatically more acidic than regular straight-chain alcohols. How could eugenol (shown below) be separated from a mixture of other non-acidic molecules?
dissolve the mixture in dichloromethane, shake with sodium hydroxide, collect the aqueous layer, and reacidify to force precipitation of the eugenol
A dichloromethane solution contains three compounds: A, B, and C. When this dichloromethane solution is extracted with aqueous sodium hydroxide, one obtains a basic aqueous solution of Compound A and a dichloromethane solution of compounds B and C. If this latter dichloromethane solution containing B and C is extracted with aqueous hydrochloric acid, one obtains an acidic aqueous solution containing the salt of compound B and a dichloromethane solution containing compound C. Of the following, Compound B is most probably:
benzocaine
You are given a dichloromethane solution containing compounds A, B, and C. You first extract with 3M NaOH and find that A is in the aqueous layer. Re-extraction of the organic layer with 3M HCl leaves only C in the organic layer. Of the following, compound B is probably:
benzocaine
In the Who Has My Compound experiment, which technique did you not use to determine your compound?
boiling point determination
1-chloro-1-phenylethane undergoes solvolysis in water by sn1 mechanism to make 1-phenylethanol, the reaction is followed with bromothymol blue indicator sodium hydroxide base, true statements about reaction?
carbocations are stabilized by protic solvents like water
(Molecular Modeling) Which is NOT true about the chair conformation of cyclohexane?
it contains six equatorial hydrogens that are perpendicular to the ring
What effect on the rate of an SN1 type reaction would there be if you doubled the concentration of the nucleophile?
it would have no effect on the rate
What effect on the rate of an SN1 type reaction would there be if you doubled the concentration of the nucleophile?
it would have no effect on the rate
What change in naphthol's structure upon forming naphthyl ether will allow you to determine if the reaction is complete by IR?
loss of O-H stretch
There is a maximum quantity of sample that should be injected for preparative gas chromatography separations. This maximum quantity is determined by:
loss of resolution (separation) with increasing injection size.
Which of the following is not a criterion for the selection of a good recrystallization solvent?
low volatility
If you take the melting point of an impure substance, the observed melting point range will be ______ relative to the melting point range observed for the pure substance.
lower and broader
The melting point of an impure compound is
lower and has a wider range
Rank the following molecules in terms of their carbonyl stretching frequency, v(C=O) in the infrared spectrum. a. benzaldehyde b. pentanal c. cinnamaldehyde
pentanal > benzaldehyde > cinnamaldehyde
Which of the structures shown below would exhibit the lowest IR energy absorption for the carbonyl functionality?
phenyl acetate
During the purification of allyl-2-naphthyl either in the phase transfer catalysis experiment, some products were retained the in the silica gel mini-column. What is the nature of these retained products?
polar
In normal phase thin layer chromatography, the stationary phase is:
polar
For the selection of an appropriate solvent in thin layer chromatography one must consider:
polarity of absorbent polarity of solvent polarity of compounds, if known
Absorption of infrared radiation by a molecule a. causes excitation of the outer electrons
produces changes in the amplitude of molecular vibrations
A nonvolatile impurity dissolved in a liquid:
raises the boiling point and lowers the vapor pressure
1-chloro-1-phenylethane undergoes solvolysis in water by sn1 mechanism to make 1-phenylethanol, the reaction is followed with bromothymol blue indicator sodium hydroxide base, true statements about reaction?
rate of gain of acid is equal tot he rate of loss of alkyl halide
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
Compared to dichromate oxidizing agents, hypochlorous acid is _____________.
safer & less expensive & environmentally friendly
(Recrystallization of Acetanilide) 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
You have carried out a synthesis and the pot contains your product (a liquid which you plan to distill) and one impurity. You will have to carry out a fractional distillation in order to recover the product in good purity if the impurity is:
soluble in the product and volatile
What is the hybridization of the oxygen in ethanol?
sp3
What is the predicted hybridization of the oxygen in ethanol?
sp3
Based on VSEPR theory, what is the hybridization of the nitrogen atom and the approximate bond angles around nitrogen in methyl amine, CH3NH2?
sp3 and 109.5
What is the hybridization of the oxygen atom and the approximate bond angles around oxygen in methanol, CH3OH?
sp3 and 109.5°
(Molecular Modeling) The gauche conformation of butane occurs when the dihedral angle between the C1-C2 bond and the C3-C4 bond is 60°. There is steric strain in the molecule because of the proximity of the two methyl groups. Would the steric strain in this molecule increase or decrease if the C1-C2-C3 bond angle (and the C2-C3-C4 bond angle) was increased to more than 109.5°?
steric strain will decrease because groups are moving further apart
Steam distillation is a good method for the isolation of high boiling compounds because the vapor pressure for an immiscible mixture is equal to the _________ of the two compounds' vapor pressures.
sum
Compounds such as -pinene and (+)-limonene are members of the class of natural products known as:
terpenes
In which of the following ways is the use of an infrared spectrophotometer fitted with an ATR sample advantageous over a beam-through-sample spectrophotometer?
the ATR crystal is not degraded by the presence of water and & the same ATR sample holder may be used for liquid samples and solid samples
The term antiperiplanar means:
the abstracted proton and the leaving group have a dihedral angle of 180°
In the dehydrohalogenation of 3-chloro-3,7-dimethyloctane there are three positional alkene isomers produced because:
the alkyl halide contains three different types of hydrogens that can be attacked by the base
The William ether synthesis between 2-napthol and allyl bromide in the presence of strong base and benzyltriphenylammonium chloride as a phase transfer catalyst in dichloromethane solution is know to proceed in reasonable yield. Why will the reaction fail to work if the phase transfer catalyst is switched to ammonium chloride while retaining the same reactants, solvent and base?
the bromo group is a poor leaving group when attached to an aromatic rings
When performing preparative gas chromatography,
the collection tube must be uncapped to allow free passage of vapor through the tube
Retention time in gas chromatography is not affected by:
the concentration of the sample
Which of the following does not influence the separation of a mixture of compounds in gas chromatography?
the densities of the compounds in the sample
In preparative gas chromatography, as the amount of sample injected increases
the peak overlap increases
In preparative gas chromatography, as the amount of sample injected increases
the peak overlap increases and becomes unacceptable
The fingerprint region of the IR refers to:
the portion of the spectrum from 1500‐400 cm‐1 that is unique for nearly every compound
The boiling point of a liquid is not affected by:
the rate of heating
Which of the following statements best describes density?
the ratio of a substance's mass to its volume, measured in g/mL and also equivalent to g/cm3
In TLC, a Rf value is:
the ratio of the distance the compound moved divided by the distance the solvent moved
Both Br2 and HCl undego electophilic addition to alkenes. Why is Br2 used as a test for unsaturation instead of HCl?
the reaction speed with bromine is slower than with HCl
What error is introduced if the bulb of the thermometer, or the thermocouple, is too high in the distillation apparatus?
the recorded boiling point will be lower than actual because the bulb is not exposed to the hot vapor
Why is it important not to distill a flask/vial to dryness?
the residue in the flask could explode
Preparative gas chromatography would be the best method for:
the separation of 0.5 g of a mixture of two liquids (bp 150 C and 160 C).
For a first order reaction, the specific rate constant is found by which of the following techniques?
the slope of a line found by plotting ln([A]o/[A]t) versus time
In a Gas Chromatograph, the liquid adsorbed on to the column packing is usually referred to as:
the stationary phase
Which of the following statements about the collection of a GC trace is true?
the stationary phase is a very high-boiling liquid adsorbed onto fire brick
How is it possible to separate two liquids with the exact same boiling point by gas chromatography (GC) when it cannot be done by fractional distillation?
the use of a polar GC column will separate the liquids based on differences in polar interactions and volatility
(Recrystallization of Acetanilide) 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
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 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.
top, bottom, bottom
(Molecular Modeling) The gauche conformation of butane occurs when the dihedral angle between the C1-C2 bond and the C3-C4 bond is 60°. There is steric strain in the molecule because of the proximity of the two methyl groups. When you consider that E(strain) = E(stretch) E(angle) E(torsion) E(steric), would E(torsion) increase or decrease when the dihedral angle of gauche butane is increased from 60° to 65°?
torsional strain increases
In gas chromatography, the efficiency of separation does not depend on the:
type of detector used
What is measured in this spectroscopic method?
vibrational frequency of a bond
Your experimentally determined melting point is 10 degrees low and has a 4 melting point range. This indicates that:
your compound is impure
