Chemistry 2211, Section 1 Name ______________________________ Exam 1 (100 pts) Wednesday, September 16, 2015 Chapters 1-4 Write and sign the VU Honor Pledge:

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Neatness counts

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Read each question carefully

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I. M. Honest

Chem 22

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xam 1,

F 2015

Name ________________________________ page 2 of 6

1 – 10. Multiple Choice. Choose the best answer for each of the following questions (40 pts). 1. Which of the following best depicts an sp3 atomic orbital?

2. Which of the following is the correct Lewis structure for the thiocyanate ion, SCN–

3. What is the hybridization of the carbon atom of thiocyanate, SCN– a) unhybridized b) linear c) sp2 d) sp 4. Which of the following is the correct bond-line (skeletal) structure of: CH3CHOH(CH2)2CH(CH2CH3)2

5. Below are the π-molecular orbital of 1,3-butadiene, H2C=CH-CH=CH2. Which is the highest energy molecular orbital of butadiene?

6. Which pair of structures is not related by resonance?

a) b) c) d)

S C N S C NS C Na) b) c) d)

S C N

a) b) c) d)OH

OH O

O

a) b) c) d)

O

H3C CH2C

OH

H3C CH3C

O

NH

O

NH

O

a)

b)

c)

d)

O

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xam 1,

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Name ________________________________ page 3 of 6

7. The equilibrium of the following reaction . . .

a. favors products.

b. favors reactants.

c. is approximately 1.

d. cannot be predicted based on the information given. 8. Which of the following is a Lewis acid?

a) BCl3

b) (H3C)3C+

c) H+

d) All of the above (i.e., a, b and c are all Lewis acids) 9. What is the correct order of acidity from lowest pKa value to the highest.

a) H3C-H < (H3C)2-NH < H3C-OH < H3C-SH

b) H3C-SH < H3C-OH < (H3C)2-NH < H3C-H

c) H3C-OH < (H3C)2-NH < H3C-H < H3C -SH

d) (H3C)2-NH < H3C-H < H3C-SH < H3C-OH 10. Which of the following is the highest energy conformation of cyclohexane?

a. twist boat

b. boat

c. half-chair

d. eclipsed

O

+ H OH2

OH

+ H2O

pKa = –1.7 pKa = –7.3

Chem 22

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xam 1,

F 2015

Name ________________________________ page 4 of 6

11. Tamiflu, shown below, is a synthetic molecule used to treat the avian flu. Other than alkane, identify (circle) and name the functional groups in Tamiflu. (10 pts)

12. a. Draw both chair conformations of cis-1-chloro-4-methylcyclohexane. b. A Cl–H 1,3-diaxial interaction is 2.0 KJ/mol per 1,3-diaxial interaction. A CH3–H 1,3-diaxial interaction is 3.8 KJ/mol per 1,3-diaxial interaction. Which conformer is more stable (10 pts)

13. The energy barrier for a chair-chair interconversion of chlorocyclohexane is 4.0 KJ/mol. The

rotational barrier of ethane is 12 KJ/mol. The rotational barrier of 1-chloroethane is 15 KJ/mol. The rotation barrier of propane is 14 KJ/mol. The rotation barrier of 1-chloropropane is 20 KJ/mol. a) Draw Newman projections for all the unique conformers of 1-chloropropane from rotation of the C1-C2 bond and calculate their relative energies. b) Which structure represents the rotational barrier. (15 pts)

chlorocyclohexane chair-chair interconversion : Cl-CH3 gauche interaction is 4.0/2 = 2.0 KJ/mol rotational barrier of ethane is 12 KJ/mol : H-H eclipsing interaction in 4.0 KJ/mol rotational barrier of 1-chloroethane is 15 KJ/mol: Cl-H eclipsing interaction is 15 – 2(4.0) = 7.0 KJ/mol rotation barrier of propane is 14 KJ/mol : H-CH3 eclipsing interaction is 14 – 2(4.0) = 6.0 KJ/mol

O

O

NH2

NH

O O

amide

ether

amine

esteralkene

H

Cl

HH3CH

CH3

H Cl

favored

H

H3C

H

H

Cl

H

H

H3C

H

Cl

H

H

0 KJ/mol 2 KJ.mol

H3C

HHH

H

Cl

4 KJ/mol4 KJ/mol

H3C

HHCl

H

H

4 KJ/mol

6 KJ/mol

7 KJ/mol

17 KJ.mol

2 KJ.mol

20 KJ/mol

12 KJ/mol

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Name ________________________________ page 5 of 6

14. a) Draw the mechanism of the acid-base reaction of phenol, placing the proper arrow between the reactants (shown) and products. b) Phenol (pKa ~10) is considerably more acidic than an aliphatic alcohol (pKa ~16) because its conjugate base (phenolate ion) is stabilized by resonance. Draw the resonance structures of the phenolate ion and show the mechanism by which the resonance forms interconvert. (15 pts).

15. The bond enthalpy for the C–H bond of methane is 435 KJ/mol. Draw a diagram showing the molecular orbitals of the C–H bond. (10 pts)

O H

phenol

+ H2O H3O+ +

O O

O

O

OO

C

sp3

H

1s

σ

σ∗

+ 435 KJ/mol

– 435 KJ/mol

Chem 22

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Name ________________________________ page 6 of 6

___________________________________________________________________________________

Problem 1-10:_______ (40 pts)

11:_______ (10 pts)

12:_______ (10 pts)

13:_______ (15 pts)

14:_______ (15 pts)

15:_______ (10 pts)

Total out of 100: ______________

Chem 22

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xam 1,

F 2015