Orgo Lab Finals
To synthesize 0.016 mol of n-butyl butanoate MW of 1-butanol = 74.1 g/mol density of 1-butanol = 0.810 g/mL MW of butanoic acid = 88.1 g/mol density of butanoic acid = 0.958 g/mL
1.19g or 1.146mL of 1-butanol 1.5g or 1.56mL of butanoic acid are needed Note that carboxylic acid is used in slight excess (mol alcohol + 0.001 mol)
A solid sample melted at 103.5-107.5°C. The compound was one of four possibilities, having the mp's shown below. Which was it most likely to be? A) 103.5 B) 105.5 C) 107.5 D) 109
109 Impure samples have a broader, lower melting temperature than pure samples. On the exam, choose the HIGHEST melting temperature
Hydrolysis of 0.018 mol of the fat, trimyristin, yields how many grams of myristic acid (MW = 228)?
12.3 grams grams of acid = 228*3*0.018 = 12.3
Decaffeinating coffee or tea represents the following type of extraction A) solid into a solvent B) solution into another solvent C) solvent into a solid D) solid into a solid
Solution into another solvent
The fat, trimyristin, when hydrolyzed with aqueous NaOH followed by acidification with HCl yields glycerol and myristic acid. If 0.015 mol of trimyristin is hydrolyzed, what is the theoretical yield of myristic acid in moles?
4.50E-2
A sterically unhindered alcohol and a sterically unhindered carboxylic acid are allowed to react in the presence of sulfuric acid. If a 1:1 mole ratio of carboxylic acid to alcohol is used, what is the maximum % yield of ester that may be isolated?
70%
What is the single most important variable that contributes to an effective separation in a distillation?
Distillation rate
Information about the number of neighboring hydrogens each hydrogen has can be obtained from the (choose one) A) number of signals B) positions of the signals C) multiplicity of the signals D) relative areas of the signals
Multiplicity of the signals
In this experiment a comparison of simple vs fractional distillation is done by comparing plots of _____________ vs _____________
Temperature vs. Volume
The Rf of ibuprofen was found to be 0.32 when neat t-butyl methyl ether was used as the development solvent. What effect would there be on the Rf of ibuprofen if acetone had been used to develop the TLC plate?
The Rf value would be higher since acetone is more polar than t-butyl methyl ether, and so it would pull the sample upwards
Briefly describe how soluble impurities are separated from the desired compound, at the molecular level
The impurities in the compounds exist in minute quantities, and remain in the solution when separated from the crystals. As a result, when the solvent and crystals are separated, the impurities remain in the solvent
In the bromine test, the presence of an alkene is indicated by a color change of A) reddish-orange to colorless B) colorless solution to a brown precipitate C) colorless to reddish-orange D) reddish-orange to purple E) purple to colorless
reddish-orange to colorless
The solubility of substance A in four different solvents at low temperature and high temperature are given below. Which solvent is the best for recrystallizing substance A? A) hexane; low temp: 114 g/ml; high temp: 132 g/ml B) acetone; low temp: 5 g/ml; high temp: 14 g/ml C) water; low temp: 47 g/ml; high temp: 84 g/ml D) toluene; low temp: 3 g/ml; high temp: 151 g/ml
toluene; low temp: 3 g/ml; high temp: 151 g/ml
If 0.036 mol of cyclohexanol reacts with 0.016 mol of 85% phosphoric acid, the theoretical yield of cyclohexene is _______ mol
0.036 mol In this reaction, the phosphoric acid is a catalyst, and its amount affects only the rate at which the reaction occurs. It does not enter into the overall stoichiometry of the reaction. The theoretical yield of cyclohexene is determined solely by the amount of cyclohexanol used. By looking at the balanced reaction it is seen that 1 molecule (or 1 mole) of cyclohexanol produces 1 molecule (or 1 mole) of cyclohexene. The number of moles of starting alcohol therefore determines the theoretical amount of alkene that can be produced.
In a TLC analysis, if the solvent was observed to travel 10.0 cm and the spot was observed to travel 8.40 cm, what is the Rf for that spot?
0.84
In a melting point determination, the heating rate as the solid is melting should be ____°C per minute
1°C per minute
In a micro scale distillation, the rate of distillation should be about one drop per ___________ to ____________ seconds.
20.0; 30.0 To achieve optimal separation in a distillation, a slow steady distillation rate must be maintained. For the set-up used in your experiment, this is accomplished by carefully adding hot sand to or removing it from the distillation flask.
The melting point of a sample of compound X was found to be 222-226°C. Compound X was one of four possible compounds having melting points of 222, 224, 226, and 228°C. Which was it most likely to be? A) 224 B) 222 C) 226 D) 228
228 Impure samples have a broader, lower melting temperature than pure samples. On the exam, choose the HIGHEST melting temperature
In this lab, a melting range of ____°C indicates that a compound is relatively pure
2°C
Name the alcohol and carboxylic acid (in that order) used to make the ester, 3-methylbutyl acetate.
3-methyl-1-butanol + acetic acid
The catalyst used in the dehydration of cyclohexanol is A) phosphorus tribromide B) concentrated sulfuric acid C) 85% phosphoric acid D) 15% phosphoric acid
85% phosphoric acid
A sterically unhindered alcohol and a sterically unhindered carboxylic acid are allowed to react in the presence of sulfuric acid. If a 3:1 or 1:3 mole ratio of carboxylic acid to alcohol is used, what is the maximum % yield of ester that may be isolated?
90%
An unknown which was either an alcohol, an aldehyde, or a ketone produced a reddish-orange precipitate upon reaction with 2,4-dinitrophenylhydrazine, gave a positive Schiff test, and a negative iodoform test. It can be concluded that the unknown is A) a conjugated methyl ketone B) an alcohol C) an unconjugated aldehyde D) a conjugated methyl aldehyde E) a conjugated aldehyde
A conjugated aldehyde
With respect to GC, what effect would raising the column temperature have on the retention time?
A higher column temperature would lead to a shorter retention time
In the iodoform test, formation of a yellow precipitate indicates the presence of A) a nonconjugated aldehyde or ketone B) an aldehyde group one bond away from another multiple bond C) a methyl group directly attached to the carbonyl of an aldehyde or ketone D) a methyl group anywhere in the molecule
A methyl group directly attached to the carbonyl of an aldehyde or ketone
In gc, retention times and thus peak separation is determined by A) column packing material B) carrier gas flow rate C) column length D) column temperature E) All of the above
All of the above
An unknown which is an alcohol, an aldehyde, or a ketone produces no precipitate upon reaction with 2,4-dinitrophenylhydrazine and causes ceric nitrate reagent to turn a reddish color. The unknown is most likely A) an aromatic ketone B) an unconjugated methyl ketone C) a conjugated methyl ketone D) a conjugated aldehyde E) an alcohol
An alcohol
In the Schiff test, a color change from colorless to magenta indicates the presence of A) an aldehyde B) a ketone C) a conjugated ketone D) a methyl ketone
An aldehyde
What will be the result of adding too much sample to the TLC plate?
An excess of sample will leave a trail and yield inaccurate results
An unknown which was either an alcohol, an aldehyde, or a ketone produced a yellow solid upon reaction with 2,4-dinitrophenylhydrazine, gave a negative Schiff test (no color formed), and a negative iodoform test. It can be concluded that the unknown is A) a conjugated ketone in which neither of the groups attached to the carbonyl in a methyl group B) an unconjugated aldehyde C) an alcohol D) an unconjugated ketone in which neither of the groups attached to the carbonyl is a methyl group E) an unconjugated methyl ketone
An unconjugated ketone in which neither of the groups attached to the carbonyl is a methyl group
Arrange the following compounds in order of increasing Rf in a TLC analysis: I) benzoic acid II) benzaldehyde III) 3-heptanone IV) nonane V) cyclohexanol
Benzoic acid < Cyclohexanol < Benzaldehyde < 3-heptanone < Nonane
After considering the results of the classification tests, the possibilities can be narrowed down further by determining the melting point of the A) triiodo compound B) Schiff addition product C) iodoform D) derivative
Derivative
What structural characteristic of thalidomide accounts for the fact that in one form it acts as a sedative and in another it acts as a teratogen? A) heat of formation B) polarity C) steric properties D) solubility in lipophilic solvents E) chirality
Chirality
True or False: In gc, if five peaks are observed, it can be assumed that there are five components in the sample
False Compounds having similar boiling points or other properties can have similar retention times. Such similar compounds may appear as one peak. It can therefore only be assumed that the number of peaks observed in gc is less than or equal to the number of components in the sample
The purity of the distilled cyclohexene is determined by A) gas chromatography B) thin layer chromatography C) infrared spectroscopy D) measuring the amount of dibromide formed in its reaction with bromine in dichloromethane E) nuclear magnetic resonance spectroscopy
Gas chromatography
In the purification of cyclohexene, the purpose of adding calcium chloride to the solution is to A) help remove water B) remove excess chaser solvent C) react with excess permanganate D) promote smooth boiling E) destroy excess bromine
Help remove water
In the purification of cyclohexene, the purpose of extracting with saturated aqueous sodium chloride solution is to A) decompose excess bromine B) react with calcium chloride C) decompose excess potassium permanganate D) prevent hold-up in the distillation apparatus E) help remove water from the solution
Help remove water from the solution
Which of the following organic solvent would be suitable for use in the extraction of an aqueous solution? A) ethanol B) hexane C) methanol D) acetone
Hexane One requirement of an extraction solvent is that it be mostly insoluble in water (the other solvent). Methanol, ethanol, and acetone are completely soluble in water. Hexane has a very low solubility in water
Give the three basic steps in TLC in the order in which they are done
I) spotting II) development III) visualization
What is mixed point determination?
If an unknown solid is known to be one of two possible known compounds, both having the same MP, the unknown can be mixed with one of the known compounds and a MP taken of the mixture. If the MP range is lowered and widened, it means that the two are different compounds. If the MP stays the same it means that the two compounds are likely identical
If you receive a minor burn from a hot object, the first thing to do is to A) Go to the infirmary B) Immediately place the burned tissue under cold water C) Immediately place the burned tissue under warm water D) Ask the TA for medication
Immediately place the burned tissue under cold water
Soap molecules dissolved in water form an aggregate called a A) globular cluster B) detergent C) scrubbing bubble D) carbonaceous chondrite E) micelle
Micelle
Information about functional groups may be obtained from examining the (choose one) A) positions of absorption of chemical shifts B) number of signals C) multiplicity of the signals D) relative areas of the signals
Positions of absorption or chemical shifts
In a distillation, the purpose of using a chase is to A) help remove water from the solution B) remove excess permanganate from the sample C) prevent loss of product due to hold-up in the apparatus D) remove excess bromine from the sample E) remove higher-boiling impurities
Prevent loss of product due to hold-up in the apparatus
When two liquids that are mostly insoluble in one another are mixed together, they separate out into two layers. Whether one liquid is the upper or lower layer depends upon the A) the solubilities of the two liquids B) relative densities of the two liquids C) functional groups present D) molecular weights of the two liquids
Relative densities of the two liquids
Reaction of an alcohol and a carboxylic acid to form an ester is an equilibrium reaction. In your experiment the method used to drive the equilibrium towards product and thus to obtain the maximum yield of ester is to A) use an excess of alcohol B) remove ester as it is formed C) use an excess of carboxylic acid D) use an excess of both alcohol and carboxylic acid E) remove water as it is formed
Remove water as it is formed
What class of fat is trimyristin?
Saturated fat (it has no alkenes)
Which test distinguishes between aldehydes and ketones? A) Schiff test B) 2,4-Dinitrophenylhydrazine test C) Iodoform test D) Conjugation test
Schiff test
What is the better nucleophile, sodium naphthoxide or naphthol? Why?
Sodium naphthoxide because it possesses oxygens that produce negative charges
The number of different hydrogen environments in a molecule can be inferred from (choose one) A) the number of signals in the spectrum B) the multiplicity of the signals C) the positions of the signals D) the areas of the signals
The number of signals in the spectrum
The relative number of hydrogens in each different environment can be determined from (choose one) A) the multiplicity of the signals B) the number of signals C) the positions of the signals D) the relative areas of the signals
The relative areas of the signals
If a second melting point determination must be taken for a sample, it is necessary to use a fresh sample and not the one that has already been used. Why?
The sample may have decomposed slightly
In a recrystallization, a solid is dissolved in a solvent and later the solvent is removed. If a MP of the sample is taken while the sample is still moist with solvent, what effect would that have on the MP of the sample?
The solvent would contribute to the impurity of the compound, making the melting point lower and wider
Why must the spot be applied to the TLC plate above the level of development solvent?
The spots should be above the level of development solvent so that the spots do not directly touch the solvent and wash off, affecting the results
In a TLC analysis of analgesics, what would be the result if a solvent of too low polarity is used to develop the plate?
The spots would not be pulled up the TLC plate, and so the Rf values would be very low
After visualization of a TLC plate, four spots were observed. What can be concluded about the number of components in the original mixture? A) There are more than four components in the mixture B) There are at least four components in the mixture C) There are four components in the mixture D) No conclusion can be made
There are at least four components in the mixture
A TLC analysis was run on an unknown mixture. After visualization by two methods, three spots were observed. What can be concluded? A) There are at least three components in the mixture B) No conclusion may be drawn C) There are three components in the mixture D) Six components are present in the mixture
There are at least three components in the mixture All that can be concluded is that the number of components in a mixture is greater than or equal to the number of spots observed in a TLC analysis
What was the purpose of adding NaOH to the 2-naphtol in the SN2 lab?
To form a napthoxide ion (which is highly nucleophilic), and consequentially it will be attacked by the n-butyl iodide
Another name for a fat is A) the sodium salt of a carboxylic acid B) triglyceride C) glycerol D) cholesterol
Triglyceride
In your experimental set-up, to maximize the yield of ester A) water is allowed to evaporate B) water is trapped in a side-arm C) water is removed with sulfuric-acid D) ester is trapped in a side-arm
Water is trapped in a side-arm
In a TLC analysis if the Rf's of the spots are too small, A) a different method of visualization should be used B) a spotting solvent of lower polarity should be used C) a spotting solvent of higher polarity should be used D) a development solvent of higher polarity should be used E) a development solvent of lower polarity should be used
a development solvent of higher polarity should be used In general, to increase the Rf of a spot, use a development solvent of higher polarity. The spotting solvent has no effect on the separation. It is used simply to help transfer the sample to the TLC plate
For a 2,4-dinitrophenylhydrazone a yellow color indicates the presence of A) an aldehyde B) a methyl ketone C) a conjugated carbonyl group D) an unconjugated carbonyl group
an unconjugated carbonyl group
If the gc column temperature were decreased, the retention time of a peak would _______________________ A) become longer B) become shorter C) not change
become longer
If the carrier gas flow rate in a gc experiment were increased, the retention time of a peak would _________ A) become longer B) become shorter C) not change
become shorter
In a TLC analysis, if the Rf of a compound was found to be too large, a _____________ (spotting or development?) solvent having a ____________ (lower or higher?) polarity should be chosen.
development, lower
A sample of naphthalene was mixed with water and tert-butyl methyl ether. The naphthalene dissolved mostly in the (water or ether?) _______________ layer. The ether layer was the (upper or lower?) _______________ layer
ether, upper Naphthalene, being relatively nonpolar, will be more soluble in ether than in water. tert-Butyl methyl ether, with a density of 0.74, will float on top of water (density = 1.0)
In the gc used in your laboratory, the carrier gas is A) nitrogen B) argon C) helium D) sulfur hexafluoride E) oxygen
helium
After removing the crystallization solvent from the crystals, the crystals are rinsed with fresh solvent to remove impurities clinging to the surface of the crystals. Which statement is most correct? A) the crystals should be rinsed with a minimum amount of warm solvent B) the crystals should be rinsed with a minimum amount of ice-cold solvent C) the amount of rinse solvent does not matter as long as it is ice-cold D) the temperature of the rinse solvent does not matter as long as a minimal amount is used
the crystals should be rinsed with a minimum amount of ice-cold solvent Even at low temperatures, the desired compound has some solubility in the crystallization solvent. If rinse solvent is warm (even at room temperature) or if too much is used, some of the crystals will be dissolved and lost
The correct amount of solvent to use in crystallization is A) the minimum needed to dissolve the solid near the boiling point of the solution B) the minimum needed to dissolve the solid at room temperature C) twice the minimum needed to dissolve the solid near the boiling point of the solution D) five mL per gram of solid
the minimum needed to dissolve the solid near the boiling point of the solution
A sample of glucose is added to a mixture of water and tert-butyl methyl ether. The glucose will dissolve mostly in the (ether or water?) ____________ layer. The water later will be the (upper or lower?) ______________ layer
water, lower Glucose, with its -OH groups, is very polar and is also capable of forming hydrogen bonds. It will therefore be more soluble in water than in the relatively less polar ether. tert-Butyl methyl ether (density = 0.74) will float on water (density = 1.0)
A mixture of which two compounds is distilled in the first part of the experiment? I) Cyclohexane II) Xylene III) Toluene IV) Cyclopentane V) Octane
•Cyclohexane •Toluene
Melting points can provide the following information about a sample (select all correct answers) I) The functional groups present in the compound II) The crystal structure III) The identity IV) The heat formation of the substance V) The purity
•Identity •Purity
Select the four characteristics of a proton NMR spectrum that are used to help interpret the spectrum I) Positions of absorption II) Multiplicity of signals III) Number of signals IV) Area of signals V) Height of signals VI) Width of signals
•Positions of absorption •Multiplicity of signals •Number of signals •Area of signals
In a distillation, what two pieces of information can be obtained? (select two) A) The boiling point of each component B) The ratio of the amounts of the components in the original mixture C) The density of each component D) The melting point of each component E) The heat of vaporization of each component
•The boiling point of each component •The ratio of the amounts of the components in the original mixture
In the permanganate test, the presence of an alkene group is indicated by (choose all that apply) I) a dibromide formation II) a color change from purple to colorless III) a formation of a brown precipitate IV) a color change from colorless to purple V) a color change from reddish-orange to colorless
•a color change from purple to colorless •formation of a brown precipitate
Which of the following would be considered to be chemical properties? (check all correct answers) I) Melting point of cholesterol II) Acidity of 2-chlorobenzoic acid III) Rate of the SN2 reaction of 1-bromobutane and potassium tert-butoxide IV) Solubility of caffeine in dichloromethane V) Boiling point of 2-methylnonane
•acidity of 2-chlorobenzoic acid •rate of the SN2 reaction of 1-bromobutane and potassium tert-butoxide
Two obvious structural features that may affect the solubility of a compound are I) its ability to react with hydrogen II) its polarity III) its refractive index IV) its ability to form hydrogen bonds V) its inner electron configuration
•its polarity •its ability to form hydrogen bonds
Which the following would be considered to be physical properties? (check all correct answers) I) rate of the SN2 reaction of 1-bromobutane and potassium tert-butoxide II) solubility of caffeine in dichloromethane III) melting point of cholesterol IV) acidity of 2-chlorobenzoic acid V) boiling point of 2-methylnonane
•solubility of caffeine in dichloromethane •melting point of cholesterol •boiling point of 2-methylnonane
The three general types of impurities that may contaminate a solid sample are: I) soluble impurities II) colored impurities III) insoluble impurities IV) semi-soluble impurities V) phenolic impurities
•soluble impurities •colored impurities •insoluble impurities
Thin layer chromatography can be used to help determine (select all correct answers) I) the purity of a compound II) the density of a compound III) the melting point of a compound IV) the number of components in a mixture V) the identity of a compound VI) the boiling point of a compound
•the purity of a compound •the number of components in a mixture •the identity of a compound