Chem 269 lab final (orgo)
MP For question 1, if the sample is one of four possible compounds the melting points of which are 133°, 135°, 137°, and 139°C, which is it most likely to be? Why?
139, impurities boil at lower temperatures
In this lab a melting range of ____° C indicates that a compound is relatively pure.
2
The catalyst used in the dehydration of cyclohexanol is phosphorus tribromide 15% phosphoric acid concentrated sulfuric acid 85% 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%
ESTER Write out the detailed step-wise mechanism for this reaction.(Fischer esterification)
Addition of a Lewis acid leads to a more reactive electrophile. Nucleophilic attack of the alcohol gives a tetrahedral intermediate in which there are two equivalent hydroxyl groups. One of these hydroxyl groups (the protonated one) leaves and there is a proton shift (tautomerism) to give water and the ester.
An unknown sample produces a precipitate upon reaction with 2,4-dinitrophenylhydrazine reagent. Draw the structure of a compound that would give this result.
An aldehyde or a ketone
ESTER During which step or steps is most of the excess carboxylic acid removed?
Carboxylic acid is soluble in water and reacts with sodium bicarbonate, so it is removed during the extraction phase of this experiment.
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? steric properties solubility in lipophilic solvents polarity chirality heat of formation
Chirality
CYCLOHEXANE Looking at the fractional distillation curve above, draw a gas chromatogram for a one drop sample taken at the 60 drop mark. Label each peak clearly with the compound associated with that peak, and the relative amounts and relative retention times of each component.
Cyclohexene 0.703min A=95.8 Toulene 2.08 min A=4.17
ACID BASE A mixture of benzoic acid and a neutral nonpolar compound is dissolved in ether and mixed thoroughly with aqueous sodium bicarbonate. What is the organic chemical species that is present in the ether layer? In the aqueous layer?
Ether layer: neutral non-polar compound. Water layer: sodium benzoate.
Soap molecules dissolved in water form an aggregate called a globular cluster. micelle. scrubbing bubble. detergent.
Micelle
Which test distinguishes between aldehydes and ketones? Schiff test 2,4-Dinitrophenylhydrazine test Conjugation test Iodoform test
Schiff test
Give the three basic steps in TLC in the order in which they are done.
Spotting development visualization
What is the purpose of making derivatives of unknowns?
The derivatives are created to help further identify the compound by allowing us to create a solid in order to find the melting point
ETHER Can you predict an undesirable side reaction that might occur involving the deprotonated ethanol (sodium ethoxide)?
The undesirable side reaction involving ethoxide ion (NaOH, EtOH) is its conversion to ethanol. Also Sodium ethoxide favors elimination reaction instead of substitution reaction in presence of alkyl halide. Hence n-butyl iodide will undergo elimination reaction to give butene.
ESTERDuring a distillation, how does one know when to collect pure product?
You know when to collect pure product when the temperature rises to about 5 °C below the boiling point. At this point switch out the vials, and collect the pure product across the boiling point plateau.
In the Schiff test, a color change from colorless to magenta indicates the presence of a methyl ketone. a conjugatged ketone. an aldehyde. a ketone.
an aldehyde
Which of the following would be considered to be physical properties? (check all correct answers) Acidity of 2-chlorobenzoic acid. Solubility of caffeine in dichloromethane. Rate of the SN2 reaction of 1-bromobutane and potassium tert-butoxide. Boiling point of 2-methylnonane. Melting point of cholesterol.
boiling point melting point solubility
A mixture of which two compounds is distilled in the first part of the experiment? cyclohexane toluene octane xylene cyclopentane
cyclohexane and toluene
In the gc used in your laboratory, the carrier gas is argon. sulfur hexafluoride. nitrogen. oxygen. helium.
helium
In the purification of cyclohexene, the purpose of adding calcium chloride to the solution is to remove excess chaser solvent. help remove water. react with excess permanganate. promote smooth boiling. destroy excess bromine.
help remove water
Which of the following organic solvents would be suitable for use in the extraction of an aqueous solution? ethanol methanol hexane acetone
hexane. One requirement of an extraction solvent is that it be mostly insoluble in water
THIN LAYER Arrange the following compounds in order of increasing Rf in a TLC analysis: benzoic acid, benzaldehyde, 3-heptanone, nonane, and cyclohexanol.
increasing order is :Benzoic acid( most polar), cyclohexanol, benzaldehyde, 3-heptanone, nonane(less polar)
Information about functional groups may be obtained from examining the (choose one) positions of absorption or chemical shifts. multiplicity of the signals. relative areas of the signals. number of signals.
positions of absorption or chemical shifts.
In the bromine test, the presence of an alkene is indicated by a color change of reddish-orange to colorless. reddish-orange to purple. colorless to reddish-orange. colorless solution to a brown precipitate. purple to colorless.
reddish orange to colorless
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 functional groups present. molecular weights of the two liquids. the solubilities of the two liquids. relative densities of the two liquids.
relative density of the 2 liquids
ACID BASE The ether solution is extracted with saturated aqueous sodium chloride. What is the purpose of this?
remove the water
The three general types of impurities that may contaminate a solid sample are
soluble insoluble colored
Another name for a fat is glycerol the sodium salt of a carboxylic acid triglyceride. cholesterol.
triglyceride.
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
RECRYSTALLIZATION Draw a solubility (y) vs temperature (x) plot showing the three common solubility behaviors and indicate which one is that of a good recrystallization solvent.
high solubility at high temps, and low solubility at low temps
Melting points can provide the following information about a sample.
identity and purity
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 layer will be the (upper or lower?) layer?
water lower
In a melting point determination, the heating rate as the solid is melting should be _____° C per minute.
1
Give three reasons why acetone might interfere with your results
1)It may give as false negative schiff reading if acetone is present 2)If trying to determine a methyl ketone or aldehyde, could give a false positive when doing the iodine test 3)Could create a false positive test for 2.4 DNP test
Name the alcohol and carboxylic acid (in that order) used to make the ester, n-propyl butanoate. + n-propyl butanoate + HOH
1-propanol butanoic acid
Hydrolysis of 0.016 mol of the fat, tripalmitin, yields how many grams of palmitic acid (MW = 256)? grams.
One mole of fat yields three moles of carboxylic acid, so grams of carboxylic acid = MW(acid)*mol(fat)*3, or specifically for this case grams of acid = 256*3*0.016 = 12.3
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 will be drier after it has been left for a longer time. The crystal structure may have changed. A less pure sample may have been used the first time. The sample may have decomposed slightly.
The sample may have decomposed slightly
TRI One triglyceride present in animal fats is tristearin (glycerol trioctadecanoate). What is the theoretical yield, in grams, of stearic acid upon hydrolysis of 1.8 g of tristearin?
(1.8g)(1mol/891.48g)=0.0020 moles tristearin (0.0020moles)(3)=0.0060moles (0.0060 moles)(284.5/mol)=1.7g
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%
MP A solid sample has a MP of 133 - 137°C. What can one conclude about the sample?
The 4 degree difference concludes that there is impurities in the sample
In the permanganate test, the presence of an alkene group is indicated by (choose all that apply) a color change from colorless to purple. a color change from purple to colorless. formation of a brown precipitate. a color change from reddish-orange to colorless. dibromide formation.
a color change from purple to colorless. formation of a brown precipitate.
For a 2,4-dinitrophenylhydrazone, a reddish-orange color indicates the presence of a conjugated aldehyde or ketone. an unconjugated carbonyl group. a methyl group one bond from the carbonyl. a double bond anywhere in the molecule.
a conjugated aldehyde or ketone.
In a micro scale distillation, the rate of distillation should be about one drop per _____ to ____ seconds.
20/30 Seconds
TRI If the mixture were heated at 40° for 45 minutes, what would be the result?
If the mixture were heated at 40° for 45 minutes, the complex compounds would separate. Hydrolysis would yield trimyristin and small amounts of myristic acid.
ESTER What is the purpose of the sulfuric acid?
Sulfuric acid acts as a catalyst. This causes the carboxylic acid to be a better nucleophile
A TLC analysis was run on an unknown mixture. After visualization by two methods, three spots were observed. What can be concluded? No conclusion may be drawn. Six components are present in the mixture. There are at least three components in the mixture. There are three components in the mixture.
There are AT LEAST 3 components in the mixture
TRI In the first recrystallization, after the solid has been dissolved in warm acetone, the solution is allowed to cool slowly to room temperature. In an older procedure the warm solution was placed directly into an ice bath. How does this older procedure differ from a normal recrystallization and what might be the consequences?
This older procedure differs from a normal recrystallization in that most of the other numerous ether soluble components of nutmeg remain in the acetone solution. They must be allowed to dissolve further before the solution is put into an ice bath.
An unknown sample produces a reddish precipitate upon reaction with 2,4-dinitrophenylhydrazine reagent, no color change with Schiff's reagent, and a yellow precipitate when mixed with iodine and base. Draw the structure of a compound that would give this result.
methyl ketone
DISTILL What is the single most important variable that contributes to an effective separation in a distillation?
slow and steady. 1 drop per 20-30 seconds
THIN LAYER What will be the result of adding too much sample to the TLC plate?
there may be so many spots so large spots will be possible. we could not able to identify identify rF value.
In a distillation what two pieces of information can be obtained? (select two) The boiling point of each component. The ratio of the amounts of the components in the original mixture. The heat of vaporization of each component. The melting point of each component. The density of each component.
-The boiling point of each component. -The ratio of the amounts of the components in the original mixture.
If 0.021 mol of cyclohexanol reacts with 0.016 mol of 85% phosphoric acid, the theoretical yield of cyclohexene is _______ mol.
0.021 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.
Note that carboxylic acid is used in slight excess (mol alcohol + 0.001 mol). To synthesize 0.011 mol of n-butyl pentanoate, _____ grams, or ______ mL of 1-butanol and ______ grams, or _______ mL of pentanoic acid are needed. MW of 1-butanol = 74.1 g/mol density of 1-butanol = 0.810 g/mL MW of pentanoic acid = 102 g/mol density of pentanoic acid = 0.939 g/mL
0.815g, 1.01ml 1.23g, 1.30 ml You were asked to synthesize 0.011 mol of n-butyl pentanoate. Although the balanced reaction shows that 1 mole of alcohol reacts with 1 mole of carboxylic acid to yield 1 mole of ester plus 1 mole of water, a slight excess of carboxylic acid is used (an additional 0.001 mole). To make 0.011 moles of ester therefore, 0.011 moles of alcohol and 0.012 moles of carboxylic acid are needed. To convert moles to grams and grams to milliliters: grams = MW x mol mL = grams/density
The melting point of a sample of compound X was found to be 199 - 203 ° C. Compound X was one of four possible compounds having melting points of 199, 201, 203, and 205 ° C. Which was it most likely to be?
205
RECRYSTALLIZATION If the resulting solution in question 3 were cooled to 14° C, how many grams of phthalic acid would crystallize out? What would be the percent recovery?
3) first we should take the solubility data from text book 18 gram will dissolve in 100 mL of water so fro 4.2 gram how much boiled water =100 x 4.2/18 = 420/18 = 23.34 boiling water again from text book at 14 degree 0.54 gram will dissolve in 100 mL water 0.54 x 23.34 / 100 = 0.126 4.2 - 0.126 = 4.074 gram thalic acid will recrystalize
The fat, triolein, when hydrolyzed with aqueous NaOH followed by acidification with HCl yields glycerol and oleic acid. If 0.012 mol of triolein is hydrolyzed, what is the theoretical yield of oleic acid in moles?
3.6E-2
Which of the following would be considered to be chemical properties? (check all correct answers) Rate of the SN2 reaction of 1-bromobutane and potassium tert-butoxide. Solubility of caffeine in dichloromethane. Melting point of cholesterol. Boiling point of 2-methylnonane. Acidity of 2-chlorobenzoic acid.
Acidity rate of SN2 reaction
DISTILL From the boiling point vs volume graph for your simple distillation, what can you conclude about the purity of each of the two components in the distillate (hint: how can one tell that a pure liquid is dripping into the collection vial?)?
Bubble point is definsd as the temperature at which the first drop of liqudi vaporizes and dew point is defined as the temperatue at which last drop of liquid vaporizes. The conce During the addition of volume of liquid, if the temperature remains relatively stable, it suggest that the pure component is getting distilled. As the volume increases, the liquid having highest vapour pressure boils and remains constant. This plateau represents the boiling point of less volatile component. Even after increase in volume, the boiling point remains constant and at a particular volume of liquid, it starts to rise. This volume is designated as x. Further increase in volume has to be carried out since one sees the second plateau (the point where the boiling point of second component takes place The ratio of purity of products is x:y where x is the volume of liquid where first plateau ends and y is the difference in volume of final volume and volume at which second plateau appears. , the plateaus of boiling point vs volume can more easilty be distinguished in case of fractional distillation compared to simple distillation and as a result, the boiling point are more accurate and hence there is every possibilty whether pure liquid is collected ot not Hence purity of the products can easilty be known in caae of fractional distillation as compared to simple distillation.
In gc, if five peaks are observed it can be assumed that there are five components in the sample. True False
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.
Using chemical tests how would you distinguish among 1-pentanol, 2-pentanone, 3-pentanone, and pentanal?
First use 2,4 DMP to determine alcohol from the group -1 pentanol will have a positive result Use stiffs test to determine between the ketones and aldehydes -magenta=pentanal -no color= 2 pentanone or 3 pentagon Determine the different ketones I2/OH test -2 pentanone will give a yellow precipitate, 3 pentagon will give negative results
The purity of the distilled cyclohexene is determined by measuring the amount of dibromide formed in its reaction with bromine in dichloromethane. infrared spectroscopy. gas chromatography. thin layer chromatography. nuclear magnetic resonance spectroscopy.
Gas chromatography
CYCLOHEXANE With respect to GC, what effect would raising the column temperature have on the retention time?
Higher temperature in the GC analysis column would result in a shorter retention time. This is due to the liquid vaporizing faster, causing the vapor to reach the detector faster, and shortening the retention time
CYCLOHEXANE Examining your two chromatographs, how do you know you have prepared cyclohexene? What would happen if you spiked your sample with a small amount of known cyclohexene and re-ran the GC?
I know that cyclohexane was synthesized because on the chromatogram we can see that the retention time was shorter that that of the other component in the the product, which we can assume is toluene. If I spiked my sample with cyclohexane I would see a shorter retention for the first peak, as well as a large area underneath it
MP Two test tubes contain compounds having the same MP. Using MPs, how could you determine whether the two test tubes contain the same or different compounds?
If a mixture of A+B, A+C, or B+C is made, a depression of melting point will prove whether or not two compounds having the same melting points are identical. If the two substances in the mixture are identical, the mixture will have the same melting point. If the two substances in the mixture are different, the mixture will have a reduced melting point.
THIN LAYER 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?
If the TLC plate is run with Acetone then RF value is more,because Acetone is more polar than t-butyl methyl ether ,so Acetone carriers the ibuprofen to more distance than t-butyl methyl ether.the distance travelled by the ibuprofen is more ,so RF increases.
TRI What is the structural difference between saturated, monounsaturated, and polyunsaturated fats? Of which kind is trimyristin?
If the carboxylic acid portion of the fat contains no alkene groups, the fat is said to be saturated. If one alkene group is present the fat is monounsaturated. If more than one alkene is present the fat is polyunsaturated. In a monounsaturated fat, if the alkene is one carbon in from the far end of the long chain (away from the ester group), the fat is said to contain omega-1 (read as omega minus one - omega refers to the end of the chain so omega-1 refers to one carbon in from the end) fatty acids. Trimyristin is a saturated fat.
In a TLC analysis if the Rf's of the spots are too small, a spotting solvent of higher polarity should be used. a development solvent of lower polarity should be used. a development solvent of higher polarity should be used. a spotting solvent of lower polarity should be used. a different method of visualization should be used.
In general, to increase the Rf of a spot, use a development solvent of higher polarity.
MP In a recrystallization (a technique that you will encounter later in the semester), 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?
Incomplete drying of a sample may result in the presence of impurities. When impurities remain present in a sample, the melting point is both lowered and broadened.
ETHER Why is it important to fully cool the product in an ice bath prior to isolation by suction filtration? Why do you need to rinse your product with ice water instead of room temperature water?
It is important because ice water helps in the crystallization of the product butyl naphthyl ether and is easily isolated by crystallization. But if we use room water for crystallization, the product will be lost with other liquids.
Starting with 1.20 g of cyclohexanol, what is the theoretical yield of cyclohexene in mol (do not add the units to these answers)? mol What is the theoretical yield in g?_____ g The amount of product obtained after the final distillation is 0.836. Assuming that the distillate is pure cyclohexene, what is the % yield of product?______ % If gas chromatography of the distillate showed that the purity of product was 0.720, what is the % yield of pure cyclohexene? ______%
Mw of hyclohexene: 100.2 MW of cyclohexanol: 82.1
ETHER Why does naphthol react with sodium hydroxide? Why does ethanol not react to the extent that naphthol does with sodium hydroxide?
Naphthol is aromatic compound when the NaOH reacts with it then OH- takes the proton from the hydroxyl group of the naphthol and forms oxygen anion. This anion is stabilized by the resonance stabilization by the pi electrons of the aromatic ring therefore it is more stable. But such resonance is not possible in ethanol. Therefore the naphthol reacts faster than ethanol with NaOH.
Decaffeinating coffee or tea represents the following type of extraction: solution into another solvent solid into a solvent solvent into a solid solid into a solid
Solution into another solvent
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? The amount of rinse solvent does not matter as long as it is ice-cold. The crystals should be rinsed with a minimum amount of ice-cold solvent. The crystals should be rinsed with a minimum amount of warm solvent. 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.
Thin layer chromatography can be used to help determine (select all correct answers) the melting point of a compound. the identity of a compound. the purity of a compound. the density of a compound. the number of components in a mixture. the boiling point of a compound.
The identity the purity and the number of components in a mixture
ETHER Why is it important to mix the naphthol with sodium hydroxide before adding the n-butyl iodide? What happens during this time?
The naphthoxide ion needed for this reaction to proceed is highly reactive and hence need to be prepared immediately prior to the reaction. So before adding the n-butyl iodide, naphthol is treated with NaOH to get the naphthoxide ion needed for this reaction to proceed.
TRI In the hydrolysis of trimyristin the reaction mixture is heated at about 75° for 45 minutes. What is the purpose of heating a reaction mixture?
The purpose of heating the reaction to its boiling point was to accelerate the reaction that occurred, and mix the reagents.
RECRYSTALLIZATION Briefly describe how soluble impurities are separated from the desired compound, at the molecular level.
To remove soluble impurities, first, by doing solubility tests, a suitable solvent is chosen (high solubility in hot solvent, low solubility in cold solvent). The soluble impurities are then removed as follows: the desired compound along with the soluble impurities are dissolved in a MINIMUM of near or at BOILING solvent. The solution is then allowed to cool slowly and without interruption. As the solution cools, the solubility of the compound (and of the soluble impurities) decreases, the solution becomes saturated with the desired compound, and the compound begins to crystallize. Because formation of crystals is a highly selective process that usually excludes foreign molecules, only crystals of the desired compound form. Because the soluble impurities are present in smaller amounts, the solution never becomes saturated with the impurities, so the impurities remain in solution even after the solution has cooled. Removing the solution from the crystals thus removes the solvent and the soluble impurities from the desired crystals. A final rinse with a MINIMUM of ICE- COLD solvent, followed by its removal, cleans off any residual soluble impurities clinging to the surface of the desired crystals.
ESTERThis is an equilibrium reaction. For the esters in this experiment, equimolar amounts of carboxylic acid and alcohol in the presence of acid catalyst will produce only about 70% ester. In this experiment how is the equilibrium driven towards product to produce a higher yield of ester?
Water is continuously removed throughout the experiment and this causes a disruption in the equilibrium, which forces the system to restore equilibrium by making more products. This drives the reaction forward.
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 an alcohol. a conjugated aldehyde. a conjugated methyl aldehyde. an unconjugated aldehyde. a conjugated methyl ketone.
a conjugated aldehyde.Precipitate upon reaction with 2,4-dinitrophenylhydrazine means it is an aldehyde or ketone. Reddish-orange color of precipitate indicates probable conjugation of carbonyl. Positive Schiff means it's an aldehyde, negative iodoform means it does not contain a methyl group directly attached to the carbonyl (not a methyl aldehyde).
In the iodoform test, formation of a yellow precipitate indicates the presence of a nonconjugated aldehyde or ketone. a methyl group anywhere in the molecule. an aldehyde group one bond away from another multiple bond. a methyl group directly attached to the carbonyl of an aldehyde or ketone.
a methyl group directly attached to the carbonyl of an aldehyde or ketone
IR
alcohol O-H carboxylic acid O-H water O-H ester C=O carboxylic acid C=O alkyl C-H aryl, alkenyl C-H 3300 cm-1 3000 cm-1 3700 cm-1 1740 cm-1 1710 cm-1 just below just above 3000 cm-1 3000 cm-1 broad peak, medium to strong intensity very broad (3400-2400), med/str intensity, overlaps C-H strong, broad sharp, strong peak sharp, strong peak sharp, strength depends upon number of C-H bonds present sharp, strength depends upon number of C-H bonds present
In gc, retention times and thus peak separation is determined by carrier gas flow rate. column packing material. column temperature. column length. All of the Above
all of the above
An unknown sample does not react with 2,4-dinitrophenylhydrazine reagent, but a color change is observed on reaction with ceric nitrate reagent. Draw the structure of a compound that would give this result
an alcohol
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 an aromatic ketone. an unconjugated methyl ketone. a conjugated methyl ketone. an alcohol. a conjugated aldehyde.
an alcohol
For a 2,4-dinitrophenylhydrazone a yellow color indicates the presence of an unconjugated carbonyl group. an aldehyde. a methyl ketone. a conjugated carbonyl group.
an unconjugated carbonyl group.
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 an unconjugated methyl ketone. an unconjugated ketone in which neither of the groups attached to the carbonyl is a methyl group. a conjugated ketone in which neither of the groups attached to the carbonyl is a methyl group. an unconjugated aldehyde. an alcohol.
an unconjugated ketone in which neither of the groups attached to the carbonyl is a methyl group.
Select the four characteristics of a proton NMR spectrum that are used to help interpret the spectrum. area of signals multiplicity of signals width of signals positions of absorption height of signals number of signals
area position multiplicity number of signal
If the carrier gas flow rate in a gc experiment were decreased, the retention time of a peak would ("become longer", "become shorter", or "not change"?) ANSWER MUST BE WRITTEN EXACTLY AS SHOWN.
become longer. In gas chromatography, increasing the carrier gas flow rate through the column will cause all compounds to travel through the column more quickly. Decreasing the flow rate will cause all compounds to travel through more slowly. Flow rate is adjusted so that peaks will be sufficiently separated within a reasonable amount of time. Too high a flow rate will cause all compounds to travel through too rapidly with little or no separation.
If the gc column temperature were increased, the retention time of a peak would ("become longer", "become shorter", or "not change"?) ANSWER MUST BE WRITTEN EXACTLY AS SHOWN.
become shorter. In gas chromatography, increasing the temperature of the column will cause all compounds to travel through the column more quickly. Decreasing the temperature will cause all compounds to travel through more slowly. Column temperature is adjusted so that peaks will be sufficiently separated within a reasonable amount of time. Too high a temperature will cause all compounds to travel through too rapidly with little or no separation.
After considering the results of the classification tests, the possibilities can be narrowed down further by determining the melting point of the iodoform. triiodo compound. derivative. Schiff addition product.
derivative
In the purification of cyclohexene, the purpose of extracting with saturated aqueous sodium chloride solution is to react with calcium chloride. prevent hold-up in the distillation apparatus. decompose excess bromine. decompose excess potassium permanganate. help remove water from the solution.
help remove water from the solution
THIN LAYER Why must the spot be applied to the TLC plate above the level of development solvent?
if it is below th level of solvent the compounds may dissolve in that solvent.
THIN LAYER In a TLC analysis of analgesics, what would be the result if a solvent of too low polarity is used to develop the plate?
if solvent s are too low polarity all compounds will get same rf value.
Two obvious structural features that may affect the solubility of a compound are
its polarity its ability to form hydrogen bonds
Information about the number of neighboring hydrogens each hydrogen has can be obtained from the (choose one) multiplicity of the signals. number of signals. relative areas of the signals. positions of the signals.
multiplicity of the signals.
ETHER What is the better nucleophile, sodium naphthoxide or naphthol? Why?
naphthoxide ion is the conjugate base of naphthanol and a conjugate base is always a stronger nucleophile. This is due to aromaticity .Hence, sodium naphthoxide is a better nucleophile than nahthol.
In a distillation the purpose of using a chaser is to prevent loss of product due to hold-up in the apparatus. help remove water from the solution. remove excess permanganate from the sample. remove excess bromine from the sample. remove higher-boiling impurities.
prevent loss of product due to hold-up in the apparatus.
CYCLOHEXANE Mixing cyclohexanol with phosphoric acid is an exothermic process, whereas the overall reaction from cyclohexanol to cyclohexene is endothermic. Referring to the mechanism above, construct an energy diagram showing the course of the reaction. Label the diagram with the starting alcohol, the protonated alcohol, the carbocation, and the product.
protonated cyclohexanol is low up to carbocation. Up again to cyclohexene
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 use an excess of both alcohol and carboxylic acid. use an excess of alcohol. remove water as it it is formed. remove ester as it is formed. use an excess of carboxylic acid.
remove water as it it is formed.
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 use an excess of carboxylic acid. use an excess of both alcohol and carboxylic acid. remove water as it it is formed. remove ester as it is formed. use an excess of alcohol.
remove water as it it is formed.
In this experiment a comparison of simple vs fractional distillation is done by comparing plots of ________ vs _______
temperature vs volume
MP What two pieces of information can a MP determination provide?
the identity and the purity
The correct amount of solvent to use in a crystallization is five mL per gram of solid. twice the minimum needed to dissolve the solid near the boiling point of the solution. the minimum needed to dissolve the solid near the boiling point of the solution. the minimum needed to dissolve the solid at room temperature.
the minimum needed to dissolve the solid near the boiling point of the solution.
The number of different hydrogen environments in a molecule can be inferred from (choose one) the areas of the signals. the multiplicity of the signals. the positions of the signals. the number of signals in the spectrum.
the number of signals in the spectrum
The relative number of hydrogens in each different environment can be determined from (choose one) the number of signals. the multiplicity of the signals. the relative areas of the signals. the positions of the signals.
the relative area of the signals
RECRYSTALLIZATION What structural property of sodium 4-amino-1-naphthalenesulfonate makes it very soluble in water? You will have to look up the structure of this compound and comment on why it is water-soluble. Simply stating that it's polar will get no credit.
this is the sodium salt of the 4-amino-1-naphthalenesulfonic acid so generally salts will get soluble in water
In your experimental set-up, to maximize the yield of ester water is trapped in a side-arm. water is removed with sulfuric acid. ester is trapped in a side-arm. water is allowed to evaporate
water is trapped in a side-arm.
