KWANTLEN UNIVERSITY COLLEGE CHEMISTRY R10 Organic Chemistry I

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1 KWANTLEN UNIVERSITY LLEGE EMISTRY R10 rganic hemistry I ecember 14, Total Marks Time: 3 hours (180 minutes) Budget your time and good luck!! NAME: This paper consists of 12 pages (11 questions) (including this title page). Ensure that you have a complete paper (data pages will be provided). Molecular models may be used during this examination. 1 2 Grading Scheme F The Exam Question Mark Maximum Total Percent 180 %

2 Question 1. (14 Marks) ircle the crect answer f each of the following: a) F the following three constitutional isomers (all 49): (5) X Y Z Which would give the fastest reaction with I - in acetone (solvent)? X Y Z Which would require the lowest temperature f solvolysis (2)? X Y Z Which could produce the largest number of E2 products? X Y Z Which could be fmed from an alkene with /22? X Y Z Which could not be fmed from an alkane with 2/_? X Y Z Which could not be easily fmed from an alcohol with P3? X Y Z b) This question is based upon the three compounds (B, and F) shown below: B F Which compound would have the: (4) highest boiling point: B F highest vapour pressure: B F lowest water solubility: B F largest pka value: B F c) F the reaction below: (5) X Nu Solvent i) Which leaving group (X) would yield the fastest reaction? l I ii) Which would be the better nucleophile? iii) Which nucleophile would give the greatest yield of SN2 product? Nu - - N - iv) Which nucleophile would give the greatest yield of E2 product? - - v) Which solvent would be better f solvolysis; i.e., no other Nu present? N -

3 Question 2. (18 Marks) The following optically pure compound was treated with 2 in the presence of UV radiation to produce a mixture of monobrominated compounds. Provide the crect number f each of the terms indicated. (4.5) pair(s) of enatiomers UV 2 optically pure compound(s) meso compound(s) The products were fmed as a result of a { concerted / non-concerted } process best described as { regioselective / stereoselective } in which the { intermediate / transition state } was most likely a { bromonium ion / free radical / carbocation }. (4) The following compound A was isolated from a similar bromination process. (4.5) omplete structure B so that it is the enantiomer of compound A. omplete structure so that it is a confmational isomer of compound A. omplete structure so that it is a diastereomer of compound A. A 3 B 3 In compound A, the carbon atom containing the atom is best labelled as: (1) R S In compound A, the carbon atom containing the atom is best labelled as: (1) R S omplete the structure of the maj product and the min product fmed in the E2 reaction of compound A with NaN2. (3) A 3 NaN 2 ether maj min

4 Question 3. (18 Marks) Provide/complete the structures to illustrate the following: a) keto-enol tautomerism b) a resonance stabilized cation c) an achiral dimethylcyclohexane which d) a gauche confmer of hexane (3 to 4) requires no stereochemical prefixes e) an unsaturated 612 isomer which f) a saturated 6102 isomer which contains only allylic atoms is a meso compound g) an isomer of 511 which could h) a stronger base than 32 - not undergo an E2 reaction with - N2 i) a chlobicyclo[2.2.1]heptan-2-one j) a methylbicyclo[4.2.1]nonene isomer that requires the prefix endo isomer that requires the prefix anti k) an unsaturated isomer of 46F2 l) the E,Z stereoisomer of 3,5-dichlo-2,4- which is non-polar pentadienal

5 Question 4. (18 Marks) a) omplete the structures of compounds B and, each fmed from the reaction of compound A excess 3Mg followed by an acidic wk-up. (3) A 1. 3 Mg 2. 3 B ompound A is a meso compound: (1) Yes No ompounds B and are: (1) diastereomers enantiomers confmers ompounds B and are each: (1) optically pure achiral racemic The reaction with 3Mg is best described as a(n): (1) electrophilic addition of 3 nucleophilic addition of 3 electrophilic addition of 3 - nucleophilic addition of 3 - b) omplete the structures of compounds E and F, each fmed from the reaction of the optically pure compound with dilute acid. Assume that no rearrangements occur. (3) E F Which compound is optically pure? (1) E F The reaction is best described as the: (1) electrophilic addition of nucleophilic addition of c) omplete the structures of compounds and I, each fmed from the reaction of compound G with l2. NTE: The t-butyl group is much larger than a l atom. (3) 3 3 l 2 3 G l 4 I Which compound is me stable? (1) I This reaction is best described as a { regioselective / stereoselective } { syn / anti } addition. (2)

6 Question 5. (13 Marks) a) Using structural fmulas and reaction arrows, including the use of "electron arrows", clearly show the steps of a reasonable mechanism f the following transfmation. (5) concentrated S heat 3 b) lever alvin, that renowned EM 2320 graduate, set out to prepare benzyl t-butyl ether. e tried the following two methods; but unftunately, only one of them gave good yields of the desired product. Indicate which process would give the best yield (giving the structure of the benzyl t-butyl ether), and f the other one, give the structure of the maj product(s) which would have been isolated instead. (4) c) Propose a structure f the maj product fmed in each of the following reactions. (4) NaI (1 equivalent) 2 2 Na 2 S acetone 2 3 acetone 5 10 I 4 8 S

7 Question 6. (16 Marks) In many reactions where me than one product MIGT be fmed, it is quite often found that one compound may be fmed to a greater extent than others. F each of the following reactions, circle the compound that would be the maj product. I ( 3 ) 3 - ( 3 ) 3 warm S N 1 conditions I F NaI 2 I 2 F 2 acetone 2 2 I 3 l NaN ether R 3-2 l 1 mole l l

8 Question 7. (24 Marks) Provide the structure of the maj product expected in each of the following reactions. Include any pertinent stereochemistry where imptant. P P 3 ether 2 uli NaN 2 1. Tsl I 3 1. s 4 ether 2. NaS 3 2 S 4 2 g 2 2 Lindlar catalyst KMn 4 acidic Zn/ 2 R 3 2 Pt high P high T 2 2

9 Question 8. (20 Marks) Each of the following reactions produces two maj products. omplete the structure of each product (clearly showing any pertinent stereochemistry) and indicate the relationship between the two compounds; i.e., enantiomers, diastereomers, positional isomers, tautomers, not isomers, etc.... Provide the name of the type of reactive intermediate involved in the process (if there isn't any, put none) intermediate: relationship: 1. B / - intermediate: relationship: = 2 excess 2 Pt intermediate: relationship: I S N 1 conditions 3 3 intermediate: relationship: UV intermediate: relationship:

10 Question 9. (14 Marks) Sidney Smart is having a really bad day at AME hemicals. e has treated isobutyl benzene with l2 in the presence of UV radiation and then boiled a ption of the resulting mixture of monochlide products in a mixture of ethanol and water. After isolating several compounds, he arranged to have their 1 NMR spectra taken. As you can guess, he has fgotten everything he once knew about chemical shifts, splitting patterns etc... elp out po Sidney by assigning the ptions of the molecule responsible f the signals in the 1 NMR spectrum of isobutylbenzene (1014), and then complete the structures of the compounds A (1013l), B (1012), (1014) and (1218).

11 Question 10. (10 Marks) lever alvin needs your help again, this time with a synthetic problem. e has a rush der f the two alcohols A and B below (constitutional isomers of each other). Propose suitable sequences of reactions (including the necessary reagents/solvents etc..) to prepare each of the two alcohols. You may use any inganic reagents in addition to the iginal starting materials (which you can use as many times as you need to). Show the structure of the maj product fmed after each reaction. 3 A 3 and 3 as the only B sources of carbon

12 Question 11. (15 Marks) The optically pure compound A (614) had a strong band in the IR around 3400 cm -1, and could be converted to the optically pure compound B (612) with P. ompound B had a strong band in the IR around 1700 cm -1. Treatment of compound B with 2/Pt at high temperature and high pressure refmed compound A as a mixture of two diastereomers. Treatment of optically pure compound A ( the mixture of diastereomers) with concentrated 2S4 lead to the fmation of the achiral diastereomers and (both 612) as maj products. Treatment of compound with dilute acid produced the same achiral compound E (614) which had a strong band in the IR around 3400 cm -1. ompound E gave no reaction with P. Propose complete structures f compounds A ---> E in the boxes below. Make certain that any pertinent stereochemistry is clearly shown. A B E