CHEMISTRY 104 Hour Exam I I

Summer 2012 Page 1

M U L T I P L E C H O I C E - Three (3) points each.

Histidine, one of the 20 naturally occurring amino acids, has the following skeletal structure. Complete a Lewis structure for histidine and answer the following two questions.

\H C N H

H C H 2 1

H N C C O H

H H O

1. How many n bonds are in histidine?

a. 0 b. 1 c. 2 d. 3 e. 4

2. Which of the following statements is false concerning the structure of histidine?

a. There are four carbon atoms in histidine that are sp̂ hybridized. b. The bond angle about the oxygen atom labeled 1 is approximately 109''. c. The bond angles about the carbon atom labeled 2 is approximately 120°. d. There are 7 lone pairs of electrons in the complete Lewis structure. e. A l l of the nitrogen atoms are sp*̂ hybridized.

3. A student incorrectly named a compound 4-ethyl-2,3-diisopropylpentane. What is the correct lUPAC name for this compound?

a. 2,3-diisopropyl-4-methylhexane b. 4,5-diisopropyl-3-methylhexane c. 4-isopropyl-3,5,6-trimethylheptane d. 4-isopropyl-2,3,5-trimethylheptane e. 2,3,5-trimethyl-4-sec-butylhexane

4. When CsHg is combusted in a propane torch, how many moles of 02(g) are necessary for the complete combustion of one mole of CsHg?

a. 2 b. 4 c. 5 d. 6 e. 7

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5. Which of the following compounds has at least one carbon atom with sp hybridization?

a. 1 -chloro-4-methyl-2-heptyne b. cyclopropane c. 3 -methyl-1 -cyclopentene d. 2-hexene e. 3,4-dibromo-2,3,4,5-tetramethylhexane

6. Which of the following compounds has free rotation about every bond in the molecule?

a. 1 -chloro-4-methyl-2-heptyne b. cyclopropane c. 3-methyl-1 -cyclopentene d. 2-hexene e. 3,4-dibromo-2,3,4,5-tetramethylhexane

7. When C4H8 is treated with water and H"̂ , a tertiary alcohol is the major product. Which of the following structures could represent C4H8 in this reaction?

a. CH3CH=CHCH3 b. C H 3 C H 2 C H = C H 2

c. H3C -CH3 d. H2C CH 2

CH2 H2C CH2

e. none of these

8. Consider the four possible monochlorination products (C5H9CI) formed from the following reaction. How many of the monochlorination products can exhibit cis/trans isomerism?

CH,

^H + CI2 ^^^^^^ C5H9CI + HCl

a. 0 b. 1 c. 2 d. 3 e. 4 (all)

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9. Which of the following statements is false concerning benzene, C6H6?

a. Benzene rings are a predominate structural feature of aromatic compounds, b. Benzene exhibits 109° bond angles. c. Benzene is, in general, less reactive than alkenes due to the delocalized n electrons in

benzene. d. Benzene cannot exhibit cis/trans isomerism. e. Benzene has two equivalent (resonance) Lewis structures.

10. Which of the following are the same molecule (are conformations of each other)?

CH3 CH3 CH3

I . CH2CHCH2CHCH3 I I . CH3CHCH2CH2CHCH3 I I I . CH3CHCHCH2CH2

CH. CH, CH, CH, CH,

CH3

IV. CH3CHCH2

CH3CH2CHCH3

CH,

V. CH3CH

CH2CHCH3

CH2CH3

a. I and I I I b. I I and I I I

d. I , IV, and V e. I , I I , and IV

c. I , I I I and V

11. Which of the following compounds can exhibit cis-trans isomerism?

I . C H 2 = C H CH2CH2CH3 I I . C H 3 C H 2 — C = C CH3

I I I . C H 3 C H 2 — C H = C H CH2CH3 IV. C H 3 C H 2 — C H = C CH2CH3

a. I , I I , I I I , and IV

d. I l l only

3^n2-

b. I l l and IV c. I , I I I , and IV

e. I and IV

CH,

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12. Which of the following compounds contain two and only two chiral carbon atoms?

F CI H H

e. CI C C C C CI

H H CI H

13. When HCl is reacted with 1-pentene, two different products are possible. Which of the following statements best explains why 2-chloropentane is the major product of this reaction and 1 -chloropentane is the minor product?

a. The tertiary carbocation intermediate is more stable than the secondary carbocation intermediate.

b. The tertiary carbocation intermediate is more stable than the primary carbocation intermediate.

c. The secondary carbocation intermediate is more stable than the primary carbocation intermediate.

14. The boiling points for the following compounds are (in no particular order): 36°C, 80°C, 117°C and 141 °C. Which of the compounds (a-d) boils at 80°C?

a. 2-butanone b. 1-butanol c. propanoic acid d. pentane

CHEMISTRY 104 Hour Exam I I

Summer 2012 Pages

15. Which of the following aromatic compounds wil l be significantly more soluble in 1 M H C l than in pure water?

a. benzaldehyde b. benzoic acid c. phenol d. aniline e. toluene

16. The molecule below is a portion of angiotensin I I , a hormone which is present in blood plasma that regulates blood pressure. Which of the following functional groups is not present in the molecule?

O

H2N CH C NH CH

CH2

COOH

O

CHn

CHo

- N H CH-

a. a carboxylic acid

d. a primary amine

b. a ketone

e. an alcohol

H,C C H

C H ,

O

-NH CH-

c. an amide

CH.

OH

17. A postal employee discovered that an unlabeled bottle in a package is leaking a colorless liquid and has called you to analyze it. You run several tests on the liquid with the following results.

Test Result

Addition of CI2 no reaction pH of aqueous solution pH = 7 Addition of H2Cr04 no reaction

Which of the following compounds could be the liquid?

a. hexanal b. 2-propanone c. 1-butanol

d. 1-pentene e. ethanoic acid

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18. Which of the following compounds can form hydrogen bonding interactions with itself?

a. ethyl methyl propyl amine b. diethyl ether c. propanal d. propylethanoate e. None of the above compounds can H-bond with itself.

19. Below is a plot of vap̂ or pressure vs. temperature for two different substance A and B.

Which of the following statements is false concerning this plot?

a. As temperature increases, the vapor pressure of substance B increases. b. Substance A has stronger intermolecular forces than substance B. c. Substance A has a lower normal boiling point than substance B. d. For substance A, the boiling point at 2 atm external pressvire is higher than the boiling

point at 1 atm external pressure.

20. Consider the following initial rate data for the reaction:

Temperature

Cl2(aq) + 2 Fe^^(aq) 2 Fe'^(aq) + 2 Cr(aq)

[Cl2]o (mol/L) [Feno(mol/L) Initial Rate (mol/L»s)

0.10 0.50 0.10 0.60 0.50

0.30 0.10 0.40 1.00 0.40

1.8 3.0 2.4

36.0 12.0

Which of the following is the correct rate law for this reaction?

a. rate = k [ C l 2 f b. rate = k[Fe^^]^ c. rate = k[Cl2][Fen

d. rate = k[Cl2][Fe^1^ e. rate = k[Cl2]^ [Fe^l

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21. Consider the following initial rate data for the reaction:

2NO(g) -f Br2(g) -> 2N0Br(g)

Experiment [N0]o [Brijo Initial Rate (mol/L) (mol/L) (mol/L-s)

1 0.10 0.10 12 2 0.10 0.20 24 3 0.20 0.10 48 4 0.30 0.20 ?

What is the initial rate for experiment 4?

a. 192mol/L*s b. 144mol/L*s c. 96 mol/L*s

d. 108mol/L*s e) 216mol/L*s

22. The reaction

A B + C

is second order in A. When [A]o= 0.100 M, the reaction is 20.0% complete in 40.0 minutes. Calculate the value of the rate constant in units of L/mol»min.

a. 6.25x10"^ b. 5.58x10'^ c. 16.0 d. 1.00 e. 16.0

23. Consider the reaction:

2A -> D

Concentration of A vs time data is collected. I f a plot of [A] versus time is linear, then the reaction is order in A and the slope of the straight line in the plot is equal to

a. zero; k b. first; k c. second; k

d. zero; - k e. first; - k

CHEMISTRY 104 Hour Exam I I

Summer 2012 Pages

24. Consider the following general reaction mechanism:

A + B C

C + D ~> E + F

E -f A B + G

For the overall reaction, B is a and C is a(an)

a. reactant; product b. product; intermediate c. catalyst; product d. reactant; intermediate e. catalyst; intermediate

25. E a is a symbol used to designate activation energy. One of the characteristics of catalyzed reactions is that:

^- E a , forward ~ E a , reverse

b. Ea , catalyzed ~ E a , uncatalyzed

C. AHcatalyzed ~ AHuncatalyzed

26. Which of the following statements is true?

a. An increase in temperature decreases the rate of a forward reaction. b. At higher temperatures, collisions between gaseous reactants are more effective in

converting reactants to products. c. Al l collisions between reactant molecules result in product formation. d. The orders in a rate law always equal the coefficient in the balanced reaction. e. A catalyzed reaction at equilibrium produces more product than an uncatalyzed

27. In a reaction, increasing the concentration of a reactant by a factor of 4 causes the rate of reaction to increase by a factor of 64. What is the order of this substance in the rate law?

e. E a , catalyzed E a , uncatalyzed

reaction at equilibrium.

a. 0 b. 1 c. 2 d. 3 e. 4

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28. For the reaction 2 N205(g) 4 NOiCg) + 02(g), the following data were collected:

time (minutes) fNiOgI (mol/L)

0 1.240x 10"̂ 10.0 0.919 X 10"^ 20.0 0.681 X 10"^ 30.0 0.504 X 10"^ 40.0 0.373 X 10"^ 50.0 0.277 x 10"^ 70.0 0.152 x 10"̂

(12 pts) Assume this reaction is either zero, first, or second order in N2O5. Determine the order of the reaction with respect to N2O5, then answer the following questions.

a. Calculate the half-life for this experiment.

b. Calculate the initial rate of the reaction for this experiment.

c. The activation energy for this reaction is 250 kJ and A E for this reaction is 150 kJ. Sketch the energy profile (energy versus reaction progress) for this reaction showing the activation energy, E a , and A E on your plot.

d. Determine the activation energy for the reverse reaction.

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29. The reaction r (aq) + OCr (aq) IO~(aq) + CP (aq) is believed to occur by the following mechanism:

OCr + H2O ^ *• HOCl + OH" fast equilibrium

r + HOCl HOI + c r slow

HOI + OH" — ^ H2O + 10" fast

Derive the rate law for this reaction from the mechanism.

(6 pts)

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30. Sulfur exhibits two solid forms, rhombic and monoclinic. The complete phase diagram for sulfur is shown below. Consider the phase diagram when answering the following questions.

a. What is the normal melting point of monoclinic sulfur?

b. How many triple points are in the phase diagram?

c. Which is the densest phase?

d. At a pressure of 1.0 x 10 ^ atm, can rhombic sulfur sublime?

e. The pressure on a sample of sulfur at lOO^C is increased from 0 atm to 2000 atm. What phase changes wil l occur in this sample of sulfur as the pressure is increased?

(10 pts)

if!

u

Temperaturc

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31. The following compounds can be produced in a single step reaction. Indicate which reactants (including catalysts) are necessary to make the desired products. Only major products should be produced. For the organic reactant compound(s), draw the structural formula(s) and name it(them). Make sure your structural formulas contain all hydrogen atoms, e.g., butane should be drawn as CH3CH2CH2CH3 or CH3-CH2-CH2-CH3, not C-C-C~C.

(15 pts)

a. ethyl butanoate

b. chlorobenzene

c. 2,2-dichloropropane

d. -> hexanoic acid

e. 2-pentanol

CHEMISTRY 104 Hour Exam II

Summer 2012 Page 13

32. When H2O is reacted with cyclobutene (in the presence of H" )̂, an alcohol is produced. Propose a detailed mechanism for this reaction. Make sure your structures include all hydrogen atoms and lone pair electrons.

(9 pts)

33. a. How many ketones have the formula C5H10O? (6 pts)

b. Name the structural isomer of C5H12 which has the lowest boiling point.

c. Draw the structural formula for the isomer of C4H10O which is optically active.

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34. A student performed the following multistep conversions, taking the initial organic compound through several reactions. Assume the organic product after each reaction is a major product, which then becomes the reactant organic molecule in the next step. Draw the formula for the major organic product in each step. To save time you may omit the hydrogens attached to the carbon atoms in your structure.

(14 pts) a. 3-methyl-3-penten-2-ol = initial organic compound

Step 2: Reaction with H""

Step 3: Reaction with HBr ->

b. butanoic acid = initial organic compound

Stepl: Reaction with LiAlH4/H20

Step 2: Reaction with H^

Step 3: Reaction with H20/H^

Step ' l : Reaction with H2/Pt

Step 4: Reaction with H2Cr04 ->