NOT present in compound

CHEM 2OA3

Test 2 November 16, 2007

VERSION 4

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

Instructors: Drs. Harrison and Stöver

Instructions:

This examination paper consists of 20 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.

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. Then fill in your section number; section 01 is Dr. Harrison’s section, section 02 is Dr. Stöver’s section.

Questions 1-20; 2 marks each.

Questions 1 to 5 are about 3-aminoethoxyvinylglycine (1); this compound is used in the fruit industry to prevent fruits from ripening prematurely. It binds to an enzyme

that is involved in the ripening process, thus blocking the action of that enzyme.

1. Which of the following functional groups is NOT present in compound 1? A. Primary amine

B. Ketone

C. Carboxylic acid

D. Ether

E. Alkene

2. The correct stereochemical descriptors for the IUPAC name for compound 1 are: (A) 2R,3Z (B) 2R,3E (C) 2S,3Z (D) 2S,3E (E) 3S,2E

3. In an aqueous solution at a pH of 12, compound 1 exists predominantly as a species with a net charge of:

(A) -2 (B) -1 (C) 0, a neutral molecule (D) 0, a zwitterion (E) +1

4. Which drawing(s) represent(s) (a) resonance form(s) of 1 that obey(s) the rules for acceptable resonance structures?

O

O -O

NH₃+ N H₂ O O O H NH₂ N H₂ O O HO+ NH₂ N H₂

(i) (ii) (iii)

-+

(A) NONE (B) i and ii (C) ii only (D) ii and iii (E) ALL OF THEM

5. Which of the following statements is TRUE with respect to compound 1?

(A) Its enantiomer has the opposite configurations at the chiral centre and at the alkene

(B) The compound with the opposite configuration at the alkene is a constitutional isomer of 1

(C) Changing only the configuration at the chiral centre will probably result in a compound that has the same fruit-ripening activity

(D) Changing either or both of the configuration at the chiral centre and the configuration at the alkene will likely result in loss of fruit-ripening activity

Questions 6 and 7 refer to the diagram below, which shows several Newman projections of various conformations of 1-chloro-2-methyl-butane. Choose the appropriate conformations to match the descriptions below:

H Et Me H Cl H H Et Me H H Cl H Et Me Cl H H Et Me H H Cl H Et Me H Cl H H

i

ii

iii

iv

v

6. The most stable conformation and the least stable conformation are, respectively: (A) i and ii (B) i and iii (C) ii and iv (D) ii and v (E) i and v

7. The conformation that can most readily undergo an E2 elimination is: (A) i (B) ii (C) iii (D) iv (E) v

8. The following sentence has the format “Statement 1 BECAUSE Statement 2”. Decide whether statement 1 is true, whether statement 2 is true, and whether the REASONING (the ‘because’ relationship) between them is valid.

Statement 1: “In its most stable conformation, trans-1-tert -butyl-2-methyl-cyclohexane has BOTH the tert-butyl and methyl groups in equatorial positions” BECAUSE

Statement 2: “steric repulsion between the tert-butyl and the methyl groups forces them to have a dihedral angle (the angle Me3C-C-C-Me) of 180o”.

(A) Statement 1 and Statement 2 are both correct, and the reasoning is valid. (B) Statement 1 and Statement 2 are both correct, but the reasoning is NOT valid. (C) Statement 1 is correct, but Statement 2 is NOT correct.

9. The three structures below all represent 2,3-dichlorobutane. Me H Me H Cl Cl Cl H Me H Cl Me Me H Cl H Me Cl

i

ii

iii

Which of the following statements is TRUE with respect to these structures?

(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

10. In the molecular orbital view of a nucleophilic substitution reaction, the appropriate orbital containing the lone pair of the nucleophile interacts with the empty σ*

orbital of the C-X bond (where X is the leaving group) of the electrophile, e.g. the alkyl halide.

From the orbital diagrams below, select the diagram that shows the appropriate orbitals of the nucleophile (hydroxide) and the electrophile (CH3Cl) interacting in the correct way for a nucleophilic substitution:

O H H H H

Cl _{H O Cl}

H H H O H H H H

Cl _{H O}

11. Order the following six compounds in order of increasing ease of carbocation formation by the SN1 mechanism.

Cl

Br

Cl

Cl

Br Br

i ii iii

iv

v vi

(A) i < iv < v < ii < iii < vi (B) iv < i < ii < v < vi < iii (C) vi < iii < ii < v < iv < i (D) iii < vi < v < ii < i < iv (E) i < v < iii < iv < ii < vi

12. Which of the following statements about substitution and elimination reactions of alkyl halides are FALSE?

i) Primary alkyl halides undergo substitution by the SN2 mechanism, and elimination by the E2 mechanism

ii) Tertiary alkyl halides never react by SN2 or E2 mechanisms; they only react by SN1 or E1 mechanisms

iii) By adjusting the solvent, the order of nucleophilicity of halide ions can be reversed.

(A) None are false (B) i (C) ii (D) iii (E) All are false

13. Indicate the INCORRECT statements below regarding ring structures: i. Per methylene unit, cyclobutane has less ring strain than cyclopropane

ii. Cyclohexane prefers to adopt a chair conformation as this minimizes bond angle torsion and eclipsed arrangements

iii. Cyclopentane prefers a flat conformation in order to most closely approach an average bond angle of 109.5°

iv. E-Cyclobutene can adopt a flat conformation and is hence more stable than Z-cyclobutene

14. Indicate the CORRECT statements regarding the reaction of (S )-2-chloro-3-methyl-butane with alkoxides, described below:

i. Potassium t-butoxide is a suitable reagent to prepare predominantly alkene P2 ii. Sodium methoxide is a suitable reagent to prepare predominantly alkene P1 iii. The transition state energy for T1 is lower than that for T2, due to the influence of

the partly formed double bonds at T1 and T2

iv. This reaction follows an E1 mechanism, and hence produces a racemic mixture

(A) i, ii, iii (B) all of the above (C) i, ii, iv (D) i, ii (E) ii, iii, iv

15. Indicate the INCORRECT statement(s) with regards to the reaction diagram in question 14 above:

i. Carrying out these reactions at higher temperature will likely increase the reaction rate for both reactions

ii. Increasing the concentration of alkoxides will not increase the rate of reaction. iii. When using (S)-2-chlorobutane in these reactions the selectivity for the dominant

product will be reduced, compared to using (S)-2-chloro-3-methylbutane. iv. Using weaker bases than alkoxides could lead to formation of more substitution

products.

16. Indicate the CORRECT order of Lewis acid (LA) strength, and of Lewis base (LB) strengths, below:

LA: BCl3 CCl4 BF3

i ii iii

LB: NH2

NR3

N O

-

iv v vi

LA strengths; LB strengths

(A) iii > i > ii; iv > vi > v

(B) iii > i > ii; vi > v > iv

(C) ii > iii > i; iv > vi > v

(D) ii > i > iii; v > vi > iv

(E) i > ii > iii; v > iv > vi

17. Indicate the INCORRECT statement below:

i. SN1 reactions are favoured if the nucleophile is a weak base and the electrophile

(i.e. alkyl halide) is sterically hindered.

ii. SN2 reactions are disfavoured by sterically hindered nucleophiles and hindered

electrophiles

iii. E2 is the preferred mechanism for reaction between strong bases and sterically hindered electrophiles

iv. Polar aprotic solvents such as dimethylformamide promote bimolecular nucleophilic substitution reactions.

18. Indicate which of the following mechanisms correctly describes the cleavage of X

-

X

Y

X

Y

:

X

Y

:

X

Y

_X

_Y

(A) (B) (C) (D) (E)

19. Indicate the CORRECT number of resonance structures that exist for the following ionic compounds (including the ones drawn):

S O

O

O H2C

N

-+

C

(A) 3, 2, 2 (B) 4, 3, 3 (C) 3, 3, 2 (D) 3, 3, 3 (E) 4, 3, 2

20. Using coupling patterns and approximate chemical shifts, indicate which compounds correspond to the simulated proton NMR spectrum below (peak heights are approximate)

O

Br

Br O O

Br

Br

O O

Br

21. [20] This question is about the structure and reactivity of (1R,2S,4R )-2-bromo-1-chloro-1-methyl-4-tert-butyl-cyclohexane (compound 1).

(i) Indicate, using the template provided below, the structure of compound 1. You MUST use the carbon numbering scheme provided, and show ALL the bonds at carbon atoms 1 and 2 (including those to hydrogen), making sure all bonds are clearly shown in the correct orientation.

1

2

(ii) In ONE SENTENCE, explain why the structure above is not the most stable conformation. Draw the most stable conformation on the template below.

1

2

4

(iii) What is the relative stereochemistry of the bromine and chlorine atoms (e.g. E, Z, cis, etc.)?

(iv) Re-draw the structure of compound 1 from part (ii) on the left hand-side of the arrow below. Then show the major organic product(s) of its reaction with one molar equivalent of dilute, cold sodium cyanide solution. Use the templates provided (you may or may not need to use all product templates).

NaCN, DMSO

(v) Re-draw the structure of compound 1 from part (ii). Then show the major organic product(s) of the solvolysis reaction in cold methanol. Use the templates provided (you may or may not need to use all product templates).

MeOH

low temperature

(vi) Now consider treatment of compound 1 with a hot, concentrated solution of sodium t-butoxide in t-butanol. What mechanism will prevail under these conditions?

(vii) Will this process obey Zaitzev’s rule or Hoffmann’s? (If you can’t remember which is which, you can alternatively explain WHY the appropriate rule applies (one sentence)).

(viii) Draw the product of this process.

22. [20] Answer the questions below regarding an unknown compound with the following spectroscopic information: The unknown compound shows a molecular ion peak at m/z = 94, and an M+2 peak at m/z = 96, with an intensity ratio of about 3:1. The three major peaks in the infrared spectrum are at 3610, 2920, and 1440 cm-1. The proton and carbon-13 NMR spectra are shown below, with blow-ups showing coupling patterns and integration lines in the proton NMR spectrum.

(i) Is there likely to be an aromatic ring, and how could you tell from the two NMR spectra?

(iii) Do the NMR spectra show evidence that other (non-halogen) electron-withdrawing elements are present, and what is this evidence?

(iv) What functional group is likely present, based on the infrared data provided?

(v) What functional group family is likely NOT present, based on the infrared data provided?

(vi) How many different carbons are likely present, and how can you tell?

(vii) How many different types of protons are likely present, and how can you tell?

(viii) What is the total number of protons present in the unknown compound, and how do you know this?

(ix) Judging from the coupling patterns and the integrations in the proton NMR, which hydrocarbon group(s) (i.e. methyl, methylene, methine) are likely NOT present in the molecule? Give your reasoning.

23. [20] A CHEM 2OA3 student wanted to convert 1-chloro-3-bromo-3-methyl-butane (A) into the diol (G). Being knowledgeable about substitutions and eliminations, (s)he recognized several potential challenges in achieving this goal: for example, certain reagents would give any or all of compounds (B) – (F).

Br Cl Cl Cl Br OH Cl

Br OH OH OH

(A) (B) (C) (D) (E)

??

+

+

+

(F) (G)

+

(i) DRAW and NAME the mechanism that could give rise to compound (D). Remember in this and subsequent parts to show all charges, lone pairs that are involved in the reaction, curly arrows, intermediates etc.

(ii) Suggest a reagent and conditions that would give compound (E) from compound (A).

(iv) During formation of compound (E) from (A), what side-product(s) could reasonably result from (an) elimination reaction(s) under the conditions you chose? Select your answer(s) from compounds (B) – (G).

(v) Is there a reagent that would convert (A) to (G) directly, i.e. in one pot, in a reasonable yield (i.e. over 50%)? If so, what is it, and why does it work? If not, why not?

(vi) Suggest a reagent that would convert (E) to (G).

(vii) DRAW and NAME a mechanism for the proposed reaction in part (vi)

(viii) Taking the above consideration into account, provide a suitable two-step procedure to prepare (G) from (A) in good yield. Provide specific reagents and conditions for each step, and indicate the intermediate.

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