237-Fall

Organic Chemistry Laboratory Final Exam Chemistry 237Exam Version A Fall 2009

Chemistry 237 Exam Version A Page 3 of 12

Choose the most correct answer: (4 points each)

_____ 1. E If two compounds are close in boiling points, which might be a good technique to separatethem?a. Simple Distillation because it offers a high number of theoretical platesb. Simple Distillation because it offers a low number of theoretical platesc. Gas Chromatography because it separates compounds based on molecular weightd. Both Simple Distillation and Gas Chromatography are valid techniquese. Gas Chromatography because it can separate compounds based on polarity

_____ 2. D For the following reaction:

If 23.2g of 1-propanol is treated with an excess of phosphorous tribromide and35.6 g of 1-bromopropane is isolated, what is the percent yield for the reaction? [Atomic Weights: C-12; O-16; H-1; Br-80; P-31]a. 24%b. 50%

c. 65%d. 75%

e. 93%

_____ 3. C In the Who Has My Compound? experiment, how did the inorganic sand affect the meltingpoint of the benzoic acid?a. increased the melting pointb. decreased the melting pointc. no effect on the melting pointd. broadened the melting point rangee. decreased the melting point range

_____ 4. D To purify a solid by recrystallization, it is desirable that the desired compound have adifferent _____ from the impurities.a. melting pointb. densityc. retention timed. solubilitye. molecular weight

_____ 5. B In considering the conformations of n-butane generated by rotation about the C2-C3 bond,how many different energy values will be encountered as energy minima?a. Oneb. Twoc. Three

d. Foure. An infinite number

_____ 6. C The area of the peak recorded on a gas chromatogram is related to:a. the boiling point of the compoundb. the shape of the compoundc. the relative amount of the compoundd. the molecular weight of the compounde. the retention time of the compound

CH3 CH2 CH2 OH CH3 CH2 CH2 BrPBr3



_____ 7. B Which of the following statements about thin layer chromatography is true?a. Rf values can be used to positively identify a compound without the use of a standard.b. It can be used to separate a mixture.c. Two or more solvents cannot be used.d. UV light is the only way spots can be detected.e. Thin layer is the most easily quantitated chromatographic technique.

_____ 8. E In the dehydrohalogenation of 3-chloro-3,7-dimethyloctane there are three positional alkeneisomers produced because:a. the alkyl halide is impureb. hydrolysis, a competing reaction, is also taking placec. the initially formed product rearrangesd. the ethanol used as a solvent contains a small percentage of watere. the alkyl halide contains three different types of hydrogens that can be attacked by the

base

_____ 9. C Which of the following statements is true about eugenol?I. It is an acetogenin.

II. It is a terpene.

III. It will give a positive Baeyer test.

IV. It will give a positive ferric chloride test.a. all of these are trueb. I, II, and IIIc. I, III, and IV

d. I and IVe. II and III

_____ 10. C IR Spectroscopy is useful in the analysis of carbonyl compounds because:a. the carbonyl group is chiralb. carbonyl compounds are brightly coloredc. the C=O bond is a good absorber of particular frequencies of infrared radiationd. carbonyl groups emit characteristic frequencies of infrared radiatione. carbonyl rotational states are closely packed

_____ 11. E A kinetic study of the SN1 solvolysis of 1-chloro-1-phenylethane showed a rate constant of4.0 x 10-1sec-1 in a solvent system that was 50:50 H2O/EtOH. With a solution of the sameconcentration except in a solvent system of 70:30 H2O/EtOH, one would expect the rateconstant to be:a. larger because of an increasing amount of less polar H2Ob. smaller because of the polar interactions between the alkyl halide and the increased

amount of H2Oc. smaller because an increase in H2O means that the cation will be better solvated and less

able to reactd. the same because the rate in an SN1 reaction depends only on the concentration of alkyl

halidee. larger because an increased amount of polar H2O stabilizes the formation of the cation

_____ 12. A The reaction of an alcohol with hydrogen halide to give an alkyl halide works best witha. tertiary alcoholsb. primary alcoholsc. cyclic alcohols

d. secondary alcoholse. phenols



_____ 13. B Use the vapor-liquidcomposition diagrambelow to estimate thevapor composition uponboiling of a liquid mixturewhich is 40%B. Thevapor will contain about:a. 25% Bb. 12% Bc. 80% Bd. 88% Be. 86E

_____ 14. A The best method for theseparation of 100 g of a 50:50 mixture of mesitylene (1,3,5-tri-methylbenzene) (mp -45EC;bp 162EC) and tri-N-propylamine (mp -93.5EC: bp 161.5EC) is:a. extraction with 6M HClb. fractional distillationc. preparative gas chromatographyd. recrystallizatione. thin layer chromatography

_____ 15. B At its melting point, an organic compound is:a. in the solid phase onlyb. in both the liquid and solid phasesc. in the liquid and gas phased. in the liquid phase onlye. an oily liquid

_____ 16. E In crystallization, if an oil forms what step(s) should be taken:a. continue to cool the solutionb. bring the solution to a boil and coolc. boil away part of the solventd. heat solution and filtere. heat the solution to dissolve the oil and add a little more solvent

I IIII I I II

_

_

_

_

_

__

_

__

_

__

_

__

_

_

_

_

_

_

_

_

_

_

_

100% A 0% A0% B 100% B

TemperatureOC

Vapor

Liquid

40% A60% B

Figure 1. Vapor-Liquid Composition for an Ideal Mixture of Two Liquids

80

90

100



_____ 17. A Suggest the most efficient extraction sequence to isolate compound III from the followingmixture in dichloromethane

a. 3 N aqueous NaOH, 6 N aqueous HClb. 6 N aqueous HCl, 3 N aqueous NaOHc. 3 N aqueous NaOHd. 6 N aqueous HCl, 3 N aqueous NaOH, 6 N aqueous HCle. 6 N aqueous HCl

_____ 18. D Which structure below will have the highest strain energy when calculated by molecularmechanics?

a.CH3

CH3

b.

CH3

CH3

c.

CH3

CH3

d.

CH3

CH3

e.

CH3

CH3

_____ 19. C In preparative gas chromatography, increasing the quantity of injected sample will produce:a. better separationb. longer retention timesc. poorer separationd. sharper peak shapese. no effect on separation or retention

_____ 20. E Which of the following statements are false for limonene and eugenol?a. limonene is a terpene and eugenol is an acetogeninb. limonene is obtained by isolation from citrus peelc. eugenol is one of the compounds contained in clove oil which may be obtained by steam

distillation of clovesd. eugenol reacts with FeCl3 reagent to give a dark green solutione. both are phenols, so we could separate them by base extraction

NH2NH2

EtO2CHO

OCH3

I III IVII



O

+ CH2CHBr CH2R

elat

ive

Tran

smitt

ance

.2

.4

.6

.8

1

1741 cm-1

_____ 21. B The organic product(s) of the following reaction is(are):

a.

O Br

+ CH3CH CH2

b.

O CH2CH CH2

c.

OH

+ CH3CH CH2

d.

CH2CH CH2

e. no reaction occurs

_____ 22. D The peak located at 1741 cm-1 wavenumbers corresponds to the vibrational frequency of whatfunctional group?

IR SpectraWavenumber (cm-1)

a. alcoholb. alkene

c. alkyned. carbonyl

e. aromatic



_____ 23. D The rate law: rate = k[RCl][-OH] is representative of what type of kinetics?a. third orderb. first order

c. fourth orderd. second order

e. zero order

_____ 24. B In the oxidation reaction of cyclohexanol to cyclohexanone, how many hydrogens areeffectively removed?

a. 1b. 2

c. 3d. 4

e. 5

_____ 25. A A silver nitrate test is positive ifa. a white precipitate appearsb. the purple color vanishesc. a color change from yellow to green is observedd. a black precipitate appearse. a color change from brown to clear is observed

_____ 26. C Which of the following is not an important requirement for the satisfactory separation of twoliquids by fractional distillation?a. sufficient column lengthb. extensive contact between the liquid and vapor phasesc. sufficient difference in densities of componentsd. maintenance of the proper temperature gradient in the columne. sufficient difference in boiling points of components

_____ 27. A After we have completed an organic reaction, we often “workup” the reaction. The term“workup” refers to: a. the general method of purification that uses aqueous-organic extractionb. collection of crystalsc. the process of distillation d. concentration or removal of the solvent from a reactione. the addition of a drying agent to a solution of the product

_____ 28. D What is the hybridization of the carbon atom and associated bond angles around carbon informaldehyde, CH2O?a. sp and 120Eb. sp and 180Ec. sp2 and 109.5E

d. sp2 and 120Ee. sp3 and 109.5E

_____ 29. A If you have narrowed your search for your compound down to adipic acid and acetanilide,what is a quick way to distinguish the two?a. Determine its solubility in sodium bicarbonateb. Perform a mixed melting point with bothc. Spot all three on a TLC plate and elute itd. Perform the bromine teste. Perform a mixed GC analysis with both

OH Ooxidation



CO2H NH2Cl

CH CHCO2H

_____ 30. B If you started with 10g of 75% pure crystals, and recovered 5g of 100% pure crystals after arecrystallization, how much of the product did you lose?a. 2 gramsb. 2.5 grams

c. 20%d. 50%

e. none

_____ 31. B The strain energy of a molecule can be broken down into four term. What is the last one? Estrain = Estretch + Eangle + Etorsion + ____ .a. Esizeb. Esteric

c. Evibrationd. Estrength

e. Emechanics

_____ 32. C The following compounds are dissolved in dichloromethane;

1. 4.

2. 5.

3.

The solution is extracted with 3M sodium hydroxide. The compounds present as salts in theaqueous layer are:a. 1 onlyb. 3 and 5

c. 2 and 4d. 3 and 4

e. 1 and 3

_____ 33. E Having just completed the Thin Layer Chromatography experiment, you find that caffeinegives an Rf of 0.75 in the 75% ethyl acetate – 25% hexane solution. Out of curiosity, youdecide to run a second TLC plate in hexanes. What should you expect to see and why? a. A lower Rf because the hexanes are a more polar solvent systemb. A higher Rf because the hexanes travel up the TLC plate fasterc. A higher Rf because the hexanes are a less polar solvent systemd. A lower Rf because the hexanes travel up the TLC plate fastere. A lower Rf because the hexanes are a less polar solvent system

_____ 34. D Steam distillation is a good method for the isolation of high boiling compounds because thevapor pressure for an immiscible mixture is equal to the ____________ of the twocompounds’ vapor pressures.a. quotientb. productc. differenced. sume. square

_____ 35. C The role of benzyltri-n-butylammonium chloride in the phase transfer catalyst experiment isa. to carry allyl naphthyl ether into the organic phaseb. to carry NaOH into the organic phasec. to carry the naphtholate anion into the organic phased. to carry the allyl bromide into the organic phasee. to raise the temperature of the reaction

NH2H3C



_____ 36. C What is expected as the major product from the following reaction?

a. H3C C

CH3

CH3

O Na + NaCl

b. H3C C

CH3

CH3

OH + NaCl

c. + H2O + NaClCH2 CCH3

CH3

d. H3C C

CH3

CH3

O + NaClC

CH3

CH3

CH3

e. H3C C

CH3

CH3

OCH2CH3 + NaCl

_____ 37. A By plotting the natural logarithm (ln) of the initial concentration of alkyl halide ([RCl]0) overthe concentration of alkyl halide at any time ([RCl]t) as function of time for a first orderreaction, the plot will yield:a. A Straight line with slope equals the rate constant kb. A straight line with slope equals the initial concentration of alkyl halide ([RCl]0)c. A hyperbola with slope equals the rate constant kd. A hyperbola with slope equals initial concentration of alkyl halide ([RCl]0)e. A straight line with slope equals zero

_____ 38. E Why is sodium hypochlorite preferred over chromic acid as an oxidizing agent?a. chromic acid is too strong an oxidizing agentb. chromic acid is too expensivec. chromic acid is too weak an oxidizing agentd. sodium hypochlorite is a better reducing agente. chromic acid forms toxic salts

_____ 39. A The preparation of 3-chloro-3,7-dimethyloctane is achieved via a(n) _____ reaction.a. SN1b. SN2

c. E1d. E2

e. a and c

H3C C

CH3

CH3

Cl + NaOH ethanol ?heat



_____ 40. B Which of the following statements concerning the preparative gas chromatographyexperiment is WRONG?a. IR was used to analyze unknowns.b. A flame ionization detector was the detector used.c. Samples must be thermally stable and volatile for running GC.d. Peak area is sometimes proportional to sample amount.e. Compounds with the same boiling points may be separated by prep GC.

_____ 41. A Which of the following molecules are expected to be sp3 hybridized?

A B C Da. A, B, Cb. A, Cc. B, Cd. B, C, De. A, B, C, D

_____ 42. A Which technique would be best for the purification of a mixture which contained a largeamount of a solid material with a small amount of liquid contamination. Both the liquid andsolid are soluble in organic solvent.a. recrystallizationb. simple distillationc. extractiond. preparative gas chromatographye. fractional distillation

_____ 43. D In the Who Has My Compound? experiment, the solubility of your sample was tested in whatsolution?a. dilute hydrochloric acidb. dilute sodium hydroxidec. saturated sodium chlorided. dilute sodium bicarbonatee. saturated sodium carbonate

_____ 44. D The global minimum energy for conformations of butane occurs whena. The dihedral angle is less than 60°b. C1 and C4 are eclipsedc. The C2-C3-C4 bond is less than the ideal 109.5°d. C1 and C4 are in an anti conformatione. This molecule cannot adopt a global minimum geometry



_____ 45. E During an extraction procedure you add equal amounts of the following:• water (Density = 1g/mL)• dichloromethane (Density = 1.3266 g/mL)• ethyl acetate (Density = 0.897 g/mL)• 5% NaOH solution (Density = 1.055 g/mL)

How many layers do you expected to see in the funnel and which one will be the bottom layer?a. 3 layers, aqueous phaseb. 3 layers, organic phasec. 2 layers, aqueous phase

d. 4 layers, organic phasee. 2 layers, organic phase

_____ 46. D To obtain best results when performing thin layer chromatography, one must: a. wash the TLC jar with water to make sure it is clean before beginning the experiment.b. make sure that the solvent line develops to the top of the TLC plate so maximum

separation can be achieved.c. make sure the developing solvent covers the sample spots at the origin when the TLC

plate is placed in the jar.d. Make sure that the top of the TLC jar is capped so it is air tight.e. While the TLC plate is developing, be sure to move the plate around in the jar so that the

solvent line develops evenly.

_____ 47. E You used phase transfer catalysis to carry out which of the following types of reactions?a. E1 eliminationb. E2 eliminationc. electrophilic substitution

d. SN1 substitutione. SN2 substitution

_____ 48. E The dehydrohalogenation of 3-chloro-3,7-dimethyloctane with KOH in ethanola. gives a mixture of four alkanesb. involves competing elimination and substitution reactions, with the substitution being

favored over eliminationc. is an example of an SN1 reactiond. is an example of a electrophilic substitution reactione. is an example of a E2 reaction

_____ 49. B 3-pentanol has an O-H peak from alcohol at? (All numbers are in cm-1)a. 1050-1300b. 3200-3600c. 2500-3300

d. 1670-1830e. 600-800

_____ 50. C In the oxidation of cyclohexanol to cyclohexanone with bleach solution, the oxidation state ofwhat element is reduced?a. Crb. hydrogenc. Cld. O (of hypochlorous acid)e. C (attached to C=O of acetic acid)

— — — — — THIS IS THE END OF THE EXAM — — — — —

Documents

237-Fall