You MUST also complete ALL the information at the top of this page.

CHEM 2OA3 Midterm Test October 24, 2008 VERSION 1

NAME (First & Last): _____________________ ID#: _______________

Lab Station: ______

(Print ‘E’ if you are exempt from the labs)

Please circle your lab section in the table below.

Group Monday Tuesday Wednesday Thursday Friday I L01 L02 L03 L04 L05

II L06 L07 L08 L09 L10

Duration: 90 minutes Instructor: Harald Stöver

Instructions:

This examination paper consists of 22 pages, containing 20 (twenty) multiple choice (MC) questions, and 3 short-answer questions. You are responsible for ensuring your copy of the question paper is complete. A mini-periodic table and spectral correlation charts 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 all answers are in the correct place, and that you follow the correct procedure for filling out the scan sheet.

Mark your student number in the space provided on the sheet on Side 1 AND FILL IN THE CORRESPONDING BUBBLES UNDERNEATH. Now enter your version number, which can be found on the top right hand corner of this page, by filling in the BUBBLE in the “version” column provided. You MUST sign the sheet in the space provided.

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.  

MC

Written Section

Q21 Q22 Q23

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.

 

1. Indicate in which structure(s) below the oxygen has a formal charge of +1 O C H H O H O H H H O H₃C C ₃

CH₃

II III IV

I . . . . . . . . : . . H H

A) I only B) II only C) I and III D) I and IV E) I, III, and IV Ans: E

2. Indicate the approximate bond angles in PH3 A) 60º

B) 90º C) 105º D) 110º E) 120º Ans: C

3. Indicate which of the following structures represent pairs of constitutional isomers?

O OH O O and A) Br Br and B)  Br Br and C)

4. Indicate which of the compounds below has the lowest boiling point.

A) NH2

B)

NH₂

C) N

H

D) N

E) NH₂

Ans: D

5. Indicate the correct order of elution (first to last) of the three compounds below if they are separated on a silica chromatography column using methanol as the solvent.

  A) 2, 3, 1

B) 1, 2, 3 C) 2, 1, 3 D) 3, 2, 1 E) 3, 1, 2

6. You are using TLC to identify an unknown mixture, containing up to four possible

ingredients (1, 2, 3, 4). Shown below are several silica TLC plates after development. Use the TLC results to identify the unknown mixture.

   

Ingredients

1 2 3 4

Mixture A X X X

Mixture B X X X

Mixture C X X

Mixture D X X X X

 

4 3

2 1

Unknown Unknown Unknown

Indicate the unknown mixture A) Mixture A

B) Mixture B C) Mixture C D) Mixture D

7. Indicate which functional group is not contained in prostaglandin E1, shown below.

OH

O

O

HO

OH

H

_H

H

H

Prostaglandin E1 A) Ketone B) 2 º alcohol C) 3 º alcohol D) Carboxylic acid E) Alkene

Ans: C  

 

8. Indicate which of the compound(s) below contain(s) tertiary carbon atom(s).

F

Br

OH OH

I

II

IV

V

III

A) I B) I, II, III C) II, III D) I, IV E) V

9. Which acid-base reaction(s) would not take place as written? I. CH3Li + CH3CH2OH ⎯⎯⎯⎯→ CH4 + CH3CH2OLi II. H2C=CH2 + NaOH ⎯⎯⎯⎯→ H2C=CHNa + H2O III. CH3C≡CNa + H2O ⎯⎯⎯⎯→ CH3C≡CH + NaOH IV. (CH3)2CHOH + NaH ⎯⎯⎯⎯→ (CH3)2CHONa + H2 V. CH3CO2H + CH3ONa ⎯⎯⎯⎯→ CH3CO2Na + CH3OH A) I

B) II C) III D) II, IV E) III, V Ans: B

10. Indicate the correct statement(s) below. I. The stronger the acid, the larger its pKa.

II. The conjugate base of a strong acid is a strong base.

III. Acid-base reactions always favor the formation of the weaker acid and the weaker base. IV. Strong acids can have negative pKa values.

V. Hydrogen need not be present in the molecular formula of a Bronsted-Lowry acid.

11. Indicate the molecule(s) to which the “energy versus angle of rotation” graph below could apply.

0

o

60

o

120

o

180

o

240

o

300

o

360

o

R

el

at

iv

e

en

er

gy

Angle of rotation

I. Ethane II. Propane

III. 1-Bromobutane (C2-C3 rotation) IV. 1,2-dichloroethane (C1-C2 rotation) V. Butane (C1-C2 rotation)

12. Indicate which of the disubstituted cyclohexanes shown below has (have) trans configuration?

O

H Br Cl

F

Br

O H

I

_II

_III

IV

_V

A) I B) II, V C) III, IV D) I, III and IV

E) None of the above are trans isomers. Ans: D

13. Identify the most stable isomer of cis-1,3-dimethylcyclohexane.

H

H

H

H H

H

H

H

H

H

I

_II

III

IV

_V

A) I, II B) I, V C) II D) III E) IV

14. Indicate which of the compounds below do(es) not possess a plane of symmetry? H F H F

I

H CH₃ Cl H

II

Br H H Br

III

Br Br CH3

H₃C

IV

V

A) I, II and V B) I, III and IV C) II, III and IV D) III and IV E) V

Ans: D

15. The three structures below all represent 2,3-dichlorobutane. Indicate the correct statements with respect to these structures.

Me H Me H Cl Cl Cl H Me H Cl Me Me H Cl H Me Cl

i

ii

iii

A) i and ii are enantiomers, while iii is a meso compound B) i and iii are enantiomers, while ii is a meso compound C) ii and iii are enantiomers, while i is a meso compound

D) ii and iii are identical compounds, while i is a meso compound E) i, ii and iii are all identical structures

16. Indicate the correct relationship between the structures below. H Cl H CH₃ H CH₃ H Cl

A) constitutional isomers. B) enantiomers.

C) diastereomers. D) identical. E) None of these

Ans: B

17. Indicate which of the structures below represent (R)-2-butanol.

H

CH₂CH₃ OH H₃C

I

CH₃

CH₂CH₃ OH H

II

H

CH₂CH₃ CH₃ HO

III

CH₃

CH₂CH₃ H HO

IV

CH₂CH₃

CH₃ OH H

V

A) III and V B) I, III, IV and V C) I, IV and V D) I and III E) I, II, IV and V

Ans: C

18. Indicate the correct systematic name for the structure below:

H

Cl

H

Cl

Ans: D

19. Indicate the correct number of stereogenic centers in Lovastatin, a cholesterol-lowering drug.

O HO

O

O

(Lovastatin)

A) 4 B) 5 C) 6 D) 7 E) 8 Ans: E  

   

20. Indicate the correct statement(s) regarding an SN2 reaction of (R)-2-bromobutane with hydroxide ion.

A) Doubling the hydroxide ion concentration would double the rate of the reaction. (Assume that all other experimental conditions are unchanged.)

B) The major product would be (S)-2-butanol.

C) Doubling the concentration of (R)-2-bromobutane would double the rate of the reaction. (Assume that all other experimental conditions are unchanged.) D) All of the above

Three Short Answer Questions (each worth 20 points): 21.[22] There are two subquestions, (i) and (ii).

(i)

This question relates to isomers of

C

6

H

12

O

.

(a) Draw the bond-line structures of all constitutional isomers of

C

6

H

12

O

that are

aldehydes (ignore stereochemistry).

O O O O

O O O

:

O

(b) Select the C6H12O isomer above which best fits the carbon-13 NMR spectrum shown below, and draw it right in the C-13 spectrum. Label the carbons in the structure with the numbers 1 through 4 as shown in the spectrum, to indicate which NMR signal they correspond to.

 

O

3  4 

4  3 

(ii)

The reaction of 5-chloro-1-pentanol with sodium hydride (NaH) in diethyl ether proceeds in two steps to give a product with the molecular formula

C

5

H

10

O

. Answer the following

questions about this reaction, using bond-line structures throughout: (a) Draw the bond-line structure of the starting material, 5-chloro-1-pentanol

OH Cl

(b) Draw the mechanism of the first step (the initial reaction of 5-chloro-1-pentanol with sodium hydride). Use curly arrows and show all lone pairs, formal charges, and side products.

(Note: these solutions do not contain all the lone pairs requested )

Cl O

H

Cl O- Na+

(c) Draw the mechanism for the second step (the actual SN2 reaction), again using curly arrows and showing all lone pairs, formal charges, and side products. Label the nucleophile and

electrophile with NP and EP, respectively.

O Cl

O

Cl _O +

Na+Cl-(d) Below are shown the carbon-13 and proton NMR spectra of the final product. Draw the bond-line structure of your product into each spectrum, and label all carbons, and all sets of protons, with the labels shown in the spectra. 

O

O

b 3 

b 

b 

2  2 

22.[22] Answer the questions about the compound

C

6

H

12

O

2 whose spectra are shown

(i) Indicate the degree of unsaturation (index of hydrogen deficiency, IHD) of

C

6

H

12

O

2.

(recall: a IHD of n indicates the molecule can absorb n equivalents of H2 upon hydrogenation) -Æ 1

(ii) What is the (one) major vibrational frequency indicating a chemical functional group? ~1750, carbonyl

(iii) List two specific functional groups containing oxygen that might be present in your molecule, and that could cause the IR signal listed in (ii).

Ester, ketone (not aldehyde as it only goes up to 1740, not acid, as there is no H-O stretch)

(iv) List three specific functional groups containing oxygen that are likely absent according to the IR spectrum.

Any three out of: Hydroxy, phenol, carboxylic acid, amide, 1° and 2° amine, aldehyde

(v) Indicate how many distinct types of carbon atoms your molecule contains. 6

(vi) Indicate the approximate carbon-13 NMR chemical shifts (in ppm) of the carbons directly attached to oxygen, and draw the corresponding functional group fragments.

O

C O-CHn

(vii) The proton NMR shows five signals, corresponding to five sets of protons, which we may call a through e, from left to right in the spectrum. In the first row of the table below, write the actual number of protons for each of these sets of protons. In the second row of the table, write the number of protons coupling to each of these sets.

a (3.9ppm) b c d e (0.78ppm)

Number of

protons in this set of protons

2 3 2 2 3

Number of protons coupling to this set of protons

2 0 4 5 2

(viii) Draw a large scale bond-line structure of the unknown compound.

e  d 

c  b 

a 

23. [16] Acetylene (ethyne, C2H2) carries two reasonably acidic protons, and can undergo

chemical reactions. Answer the questions listed below.

-Na+

H2

Cl

(S)

NaCl

S 

NaH or   NaNH2  or BuLi… 

Cl

(R)

-Na+

(R)  _(S) 

(S) NaCl 

+ H2 (if NaH)

(i) Complete the above scheme by drawing the missing reagents/intermediates in the above scheme, in the boxes provided. Include any side products, lone pairs and formal charges. (ii)Label all five chiral reagents and products in the scheme above with their correct

stereochemistry, using the (R), (S) nomenclature. Ans (R),(S)

(iii)Would the final product 3, 8-dimethyldecyne be optically active? Explain in one sentence.

Ans: No – it would be a meso compound.

 

Acid

p

K

_a

H

I

H

Br

H

Cl

H

₂

SO

₄

H

₃

O

+

H

₃

PO

₄

CH

₃

CO

₂

H

H

₂

CO

₃

N

H

₄+

H

CO

₃

-H

₂

O

CH

₃

CH

₂

O

H

C

H

₃

C=OMe

HC C

H

H

₂

N

H

₃

CH

₂

=C

H

₂

CH

₃

C

H

₃

-9

-8

-7

-5.2

2.1

9.24

10.33

15.9

20

38

-1.74

4.76

6.36

15.7

25

35

 

 

IR correlation chart: