Midterm I Key Chem 2312-003 F '12

8/13/2019 Midterm I Key Chem 2312-003 F '12

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Chem 2312-003 Midterm I F12 Page 1 of 6

Chemistry 2312-003

Organic Chemistry I

Midterm Examination I

11:00 12:20 pm

September 25, 2012

J. Jeon

Name: ____________Answer Key_____________ Total /100

please print

ID #: ______________________________________

There are 100 points on this exam and the six exam pages. For the multiple choice questions 1-20, select the best answerand darken completelywith

a pencilthe space corresponding to that answer in scantron (form # 882-E).

You are free to use molecular models during the exam.Have fun!


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1. (5 pts) Five atoms in the molecule below are labeled as Ato E. Which of the following is correct

regarding i) valence, ii) hybridization, iii) electronic arrangement of the each numbered atom?

B

N

H

H H

E

A

B

C

DO

i) valence ii) hybridizationiii) electronic

arrangement

a) A

b) B

c) C

d) D

e) E

3

3

4

3

3

sp2

sp

sp3

sp2

sp2

bent

linear

trigonal planar

tetrahedral

trigonal planar

2. (5 pts) Which statement concerning the length of bonds indicated in the molecule below is correct?

III

B

N

H

H H

O

II

I

a) II is the shortest and I is the longest

b) II is the shortest and III is the longest

c) III is the shortest and II is the longest

d) III is the shortest and I is the longest

e) I is the shortest and III is the longest

3. (5 pts) The dipole moments (if any) of each of the following molecules are given. Which of the

following is notcorrectly indicated.

a)

F

F

b)

O C O

c)

O

d)

O

4-9. Questions 4/5and 6/7are related to each other.

4. (5 pts) Select the major resonance contributor.

O

N

O

N

1a 1b

Br Br

CH3 CH3

a) 1a

b)1b

c) same

5. (5 pts) Select the best explanation regarding your choice above (1a vs. 1b in question 4).

a) charges b) octet rule c) atom size d) electronegativity e) molecular geometry


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6. (5 pts) Select the major resonance contributor.

H2C N

H H2CN

H

2a 2b

CH3 CH3

a) 2a

b)2b

c)same

7. (5 pts) Select the best explanation regarding your choice above (2a vs. 3b in question 6).

a) charges b) octet rule c) atom size d) electronegativity e) molecular geometry

8-10. Question 8to 10are about isomerism.

8. (5 pts) What is the relationship of the following pairs (3aand 3b)?

O

H3C CH3

FH

O FH

H3C

H3C

3a 3b

a) constitutional isomers

b) conformational isomers

c) enantiomers

d) identical

e) cis-transisomers


Cl

H2N

NH2

Cl

4a 4b



c) enantiomers

d) identical

e) cis-transisomers


CH3

H

H

Cl

CH3

H

Cl

H

5a 5b



c) enantiomers

d) identical

e) cis-transisomers


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11. (5 pts) Select the molecule with the lowest pKa (6a and 6b).

P

H

P

H

vs.

CH3

CH3

CH3

CH3

6a 6b

a) 6a

b)6b

c) same

12. (5 pts) Select the best explanation regarding your choice above (in question 11).

a) electronegativity of atoms b) atom size c) resonance d) inductive effect e) orbitals

13. (5 pts) Acid-base (proton transfer) reaction is shown below. Which of the following statements is

correct?

CH3

O

HO

O

+

O

+

H

H

H

H

H

7 8 9 10

CH3

O

O

a) 8 is acid

b) 10 is base

c) the reactants will be favored at equilibrium (Keq< 1).d) the products will be favored at equilibrium (Keq> 1).

e) this reaction is completely at equilibrium (Keq= 1).

14.(5 pts) This problem is about the IUPAC (International Union of Pure and Applied Chemistry)

nomenclature of organic compounds. Select the best name for the following molecule 11. (ignore the

relative stereochemistry.)

11

a) (4-Cyclopropyl-3-ethyl-5-methyl)octane

b) (3-Ethyl-5-methyl-4-octyl)cyclopropane

c) (6-Ethyl-5-cyclopropyl-4-methyl)octane

d) (5-Cyclopropyl-6-ethyl-4-methyl)octane

e) (6-Ethyl-4-methyl-5-octyl)cyclopropane


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18-20. Consider the molecule pentane, viewing the C2-C3 bond.

H

H

Et

HH

Me

Et

H H

HH

Me

H

Et

H

HH

Me

Potential

Energy

Dihedral Angle

H

Et H

HH

Me

60 120 180 240 300

D

C

A

B

Interaction

methyl/methyl gauche

methyl/ethyl gauche

methyl/H eclipse

ethyl/H eclipse

methyl/methyl eclipse

methyl/ethyl eclipse

H/H eclipse

Energy cost

(KJ/mol)

3.8

4.2

6.0

6.4

11.0

12.0

4.0

CB DA

2

3

2 22 2

?

18.(5 pts) Which of the following conformations is the leaststable conformation?

a) A b) B c) C d) D e) all

19.(5 pts) Based on the table regarding energy costs, what is the total energy cost of the conformation C?

a) 3.8 KJ/mol b) 4.2 KJ/mol c) 12 KJ/mol d) 15.8 KJ/mol e) 16.4 KJ/mol

20.(5 pts) Based on the table regarding total energy costs, what is the total energy cost of the

conformation D?

a) 12 KJ/mol b) 15.8 KJ/mol c) 16.4 KJ/mol d) 17.4 KJ/mol e) 20 KJ/mol

***** End of Exam *****

You may pick up your exam on Tuesday, October 2 (in class).

Midterm I Key Chem 2312-003 F '12

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