CHEM 2OA3 Midterm Test May 27, 2010 VERSION 1

CHEM 2OA3 Midterm Test May 27, 2010 VERSION 1 NAME (First & Last): ___ _____________ ID#: _______________ Lab Station: ______ (1-72 )

Please circle your lab section in the table below.

Group Monday Tuesday Wednesday Thursday Friday Exempt

I L01 L02 L03 L04 L05 E

Duration: 120 minutes Instructor: Teri Gullon

Instructions:

This examination paper consists of 21 pages, containing 20 (twenty) multiple choice (MC) questions, and 5 short-answer questions. You are responsible for ensuring your copy of the question paper is complete and no pages are missing. A mini-periodic table, spectral correlation charts and scrap paper are provided on the last two pages. Feel free to detach these last pages for easier use.

Answer all the MC questions on optical scan sheets. Each MC question is worth two marks and you will not be penalized for incorrect answers. Follow the instructions on the optical scan sheets, and the University rules for OMR exams which are reproduced on page 2. Failure to follow instructions may result in loss of credit.

You are responsible for ensuring your copy of the test is complete, no pages are missing, that all answers are in the correct place, and that you follow the correct procedure for filling out the scan sheet.

All McMaster rules and procedures relating to Academic Dishonesty and Academic Integrity apply to this exam; all violations will result in a penalty. Students must do their own work. A program designed to detect similar answers will be used for this exam.

You MUST also complete ALL the information at the top of this page. Failure to do so may result in a loss of marks.

Markers Only:

Written Section

Q1 Q2 Q3 Q4 Q5 Written Total

OMR EXAMINATION – STUDENT INSTRUCTIONS

NOTE: IT IS YOUR RESPONSIBILITY TO ENSURE THAT THE ANSWER SHEET IS PROPERLY COMPLETED. YOUR EXAMINATION RESULT DEPENDS UPON

PROPER ATTENTION TO THESE INSTRUCTIONS.

The scanner, which reads the sheets, senses the bubble shaded areas by their non-reflection of light. A heavy mark must be made, completely filling the circular bubble, with an HB pencil. Marks made with a pen will NOT be sensed. Erasures must be thorough or the scanner will still sense a mark. Do NOT use correction fluid on the sheets. Do NOT put any unnecessary marks or writing on the sheet.

1. On SIDE 1 (red side) of the form, in the top box, print your student number, name, course name, and the date in the spaces provided, in pen. Then you MUST write your signature, in the space marked SIGNATURE.

2. In the second box, mark your student number and test or exam version number (1, 2, 3 …) by filling in the corresponding bubbles underneath, in pencil.

Written Section (Marks in square brackets)

1. [12] In the space provided below:

a. Draw the valence shell _{molecular orbital diagram for F2 (difluorine)}

b. Include an energy scale, and indicate the relative energies of AOs and MOs (assume relative molecular orbital energies to be the same as in O2).

c. Draw the appropriate number of electrons in the AOs and in the formed MOs, using single headed arrows.

d. Label the AOs and MOs according to the conventional nomenclature for MO diagrams.

e. Calculate the bond order (show calculation)

MO Diagram:

2. [10] A) Synthesis: Complete the following reaction equations by putting in appropriate reagents/conditions/structures in the boxes below:

A)

H

H NaNH₂ 1 eq

H

Na+

I

-B)

H

, Pt

Pressure

C) I

OH NaOH

3. A) [4] Circle the correct structure (i or ii) which corresponds to the IR spectrum below:

B) [3] If a mixture of these two compounds in A were spotted on a silica TLC plate and eluted using a 1:1 hexane/ether mixture, which would have the largest Rf value? Circle the answer:

i or ii

C) [3] IR absorption signals of alcohols are typically broad. However, IR spectra of gaseous alcohol containing samples show sharp peaks. Briefly explain why this would be the case in the box below.

HO

O i

4. This question relates to (1S,2S)-1-bromo-2-ethylcyclohexane.

A) [4] Using the template below, draw the structure of (1S,2S

)-1-bromo-2-ethylcyclohexane by adding the appropriate substituent(s) using dashes and wedges at position 1 and 2.

B) [6] Complete the templates below for (1S,2S)-1-bromo-2-ethylcyclohexane in the chair conformations.

1 2

i ii

C) [3] Which of the structures above is more stable (circle correct answer): i or ii

5. [12] Draw a complete reaction mechanism (curly arrows) to give the product(s) for the following SN1reaction in the box below. Make sure to include all lone pairs, formal charges, intermediates and stereochemistry if relevant.

I

Multiple Choice Section (Each question worth 2 Marks): Answers must be completed on the scantron provided

1. Which of the following pairs of compounds are geometric (cis, trans, E, Z)isomers?

Br Br Br Br H Br Br H Cl Cl i iii iv ii v

A) i B) ii C) iii D) iv E) v

2. Which orbital drawing best represents the π* orbital of ethanal (acetaldehyde)?

C C H O H H H C C H O H H H C C H O H H H C C H O H H H C C H O H H H

.. ..

.. ..

.. ..

..

..

.. ..

A B C

3. In which structure(s) below does nitrogen have a formal charge of +1?

N

H3C CH3

CH3

N

H3C CH2

H

N

H3C H H3C NH2

IV III

II

I V

N H

OH H

. .

. . . .

. .

. . . .

. .

A) I

B) II and IV

C) III and V

D) I and V

E) V

4. How many 2p atomic orbitals from boron must be mixed with a 2s atomic orbital to yield the bonding hybrid atomic orbitals in BF3?

A) 1

B) 2

C) 3

D) 4

E) 5

5. Which of the following compounds has the highest ring strain?

6. Which of the following are resonance structures of compound 1?

N H

N

O N

H N

O NH

N

O NH

N O

NH N

O

NH N

O

1 i ii iii

iv v

+ _

+ _

_ +

_

+ _

A) i and iv B) ii and iii C) i only D) iii only E) iv and v

7. Which of these potential acid/ base reactions does not occur to any appreciable degree due to an unfavorable equilibrium?

A) NaOH (aq) + CH3CH2CH2CO2H

B) CH3CH2ONain ethanol + ethene

C) CH3Li in hexane + ethyne

D) NaNH2 in liq. NH3 + ethanol

8. Which compound would you expect to have the lowest boiling point? A)

NH₂ O

B) H

N

O

C)

N O

D)

NH₂

O

E)

O N

H

9. Which of the following best describes the net dipole in a carboxylate anion (RCO2-)?

R

O O

R

O O R

O O R

O

O _(B) (C) (D) (E) no dipole

10. Which of the following statements are false?

i. SN2 reactions only occur with primary alkyl halides and methyl halides ii. the ease with which an SN1 reaction occurs depends on the stability of the

intermediate carbocation

iii. steric bulk near the electrophilic centre does not affect the overall rate of the SN1 reaction

iv. steric bulk near the electrophilic centre does not affect the overall rate of the SN2 reaction

v. a secondary alkyl halide could react either via an SN1 or an SN2 reaction

A) i only B) i, iii and iv C) i and iv only D) ii and v only E) v only

11. Drawn below is Atropine, found in Atropa belladonna, sometimes used in dilating pupils during an eye-exam. Which of the following functional groups is NOT in atropine?

N _O

O OH

Atropine

A) Amine

B) Ester

C) Alcohol

D) Phenyl

12. Which of the following statements is true?

A These compounds are

enantiomers H

F Br

H Br

F

B These compounds are enantiomers

F

F

C These compounds are diastereomers

H _FBr

H

BrF Br F

F Br

D These compounds are constitutional isomers

Cl Cl

E These compounds are diastereomers

F F

13. Which of the assignments of R and S is correct in the compound below:

CO₂H

OH OH

HO₂C

CO₂H

OH OH

HO₂C

CO₂H

OH OH

HO₂C

CO₂H

OH OH

HO₂C

A B C D

E The centers are not chiral

R

R S S _R S

14. Which of the following equilibria lie to the left (higher concentration of the compounds on the left)

O O Cl Cl Cl NH₄ OH O Cl Cl Cl

NH₃ +

C

H₃C-H

CH₃ _ O Cl Cl Cl OH Cl Cl

Cl O OH

H O H S

H

S

H OH2

iv

+

+

+

+

+

+

+

15. Consider the graph below, which is a plot of the relative energies of the various conformations of 2,3-dimethylbutane, viewed through the C2-C3 bond. The conformations corresponding to the 120o and 240o are:

0o 60o 120o 180o 240o 300o 360o

R

el

at

iv

e

e

n

er

g

y

Angle of rotation

A) Eclipsed, more stable than the conformation at 0o

B) Eclipsed, more stable than the conformation at 180o

C) Staggered, more stable than the conformation at 0o

D) Staggered, less stable than the conformation at 180o

E) Two of the above are true

16. Which of the following will have the same energy after undergoing a ring flip?

CH₂CH₃

CH₂CH₃ Cl

CH₃ OH

HO

CH₃ HO

Br

F

I

II

III

IV

V

A B C

17. Pairs of enantiomers are:

CH₂CH₂CH₃ H₃C Cl

CH₃

CH₂CH₂CH₃

Cl CH₃

CH₃

I II

H H₃C Cl

CH₂CH₂CH₃

CH₂CH₂CH₃

H H

CH₂Cl

IV V

CH₂CH₂CH₃ H₃C Cl

H

III

A) I, II and III, IV

B) I, II

C) III, IV

D) IV, V

E) None of the structures

18. Which of the following compounds are chiral?

CO₂H

OH OH

HO₂C

Br

Cl

Br

Cl

i ii iii iv

19. Which nucleophile and solvent combination will give rise to the fastest substitution reaction with chloroethane?

(A) sodium ethoxide/ ethanol

(B) sodium ethoxide/ water

(C) sodium ethoxide/ DMSO

(D) sodium ethanethiolate/ ethanol

(E) sodium ethanethiolate/ DMSO

NOTE: sodium ethoxide = NaOCH2CH3; sodium ethanethiolate = NaSCH2CH3; DMSO = S O

20. Consider the reaction of 1-chloro-5-methylhexane with the CN- ion below:

Cl NaCN CN NaCl

Assuming no other changes, what effect on the rate would result from

simultaneously doubling the concentrations of both 1-chloro-5-methylhexane and CN- ion?

A) No effect.

B) It would double the rate.

C) It would triple the rate.

D) It would increase the rate four times.

Acid

p

K

H

I

H

Br

H

Cl

H

SO

H

O

H

PO

CH

CO

H

H

CO

N

H

H

CO

-H

O

CH

CH

O

H

C

H

C=OMe

HC C

H

H

N

H

CH

=C

H

CH

C

H

-9

-8

-7

-5.2

2.1

9.24

10.33

15.9

20

38

-1.74

25

35

4.76

6.36

15.7