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(chem101)[200X](f)final~946^_10035.pdf
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CHEMISTRY 101: FUNDAMENTALS OF ORGANIC CHEMISTRY

Final Examination Sample Questions Answer Key

Thursday 10 December 20xx
12:30-15:30 LG4204

Time allowed: 180 minutes
Instructions:



i. Write your name and ID number on the examination booklet. If you use more than one examination booklet, be sure to enter your name and ID number on all booklets.
ii. Read the questions carefully. If you get stuck on a problem, go on to the next question.
iii. There are a total of 180 marks. You have 180 minutes for this exam paper.






Data

i. Use Integral masses for MS 1H; 12C; 14N; 16O; 35Cl; 37Cl; 79Br; 81Br
ii. Some chemical shift ranges: H-C(sp3)-R (R = alkyl) 0.9-1.8 ppm; H-C(sp3)-C(=O) 2.1-2.5; H-C(sp3)-NR 2.2-2.9; H-C(sp3)-Cl 3.1-4.1; H-C(sp3)-O- 3.3-3.7; H-OC(=O) [carboxylic acid H] 10-13 ppm. Note: C(sp3) refers to sp3 C attached to other H or sp3 C only.
iii. IR stretching absorptions: O-H 2500-3600; N-H 3350-3500; C-H 2850-3320; C=O 1680-1750 cm-1.






DO NOT OPEN THIS EXAMINATION QUESTION BOOKLET UNTIL YOU ARE INSTRUCTED TO DO SO.
1 i. (S)-2-Iodopentane 1a is treated with the sodium salt of (R)-2-methyl-2-phenylethane-1-thiol 1b in methanol at room temperature. Carefully draw the stereostructure of the organic product, and assign configuration to each of the relevant centres as R or S. (6 pts)




Reaction is strictly SN2 process with a powerful thiolate nucleophile; reaction proceeds with inversion; this must be clearly indicated in the structural diagram in your answer. Configuration at the carbon bearing the iodide leaving group undergoes inversion. This must be clearly indicated, and the stereostructure of the product must be correctly indicated.




ii. If instead of (S)-2-iodopentane and (R)- 2-methy-2-phenylethane-1-thiol, each of racemic 2-iodopentane and racemic 2-methyl-2-phenylethane-1-thiol are used in the foregoing reaction, how many products will be formed? Give a brief reason for your answer. (6 pts)
Racemic reactants mean that there are the two enantiomers of the nucleophilic thiolate present in equal amounts, and two enantiomers of the electrophilic iodo compound present in equal amounts, in the reaction mixture, which will result in the formation of four products. Structures of the products, or an indication of the stereochemistries of each of the products, by means of the descriptors (R)- or (S)-should be given C e.g. (R,R), (R,S), (S,R), (S,S).




iii. Indicate carefully the reagents and conditions required to prepare the compound 1c via SN2 reaction from 1,5-dibromopentane. (6 pts)
The reaction is an example of a 'double' nucleophilic substitution reaction involving a 'bifunctional' nucleophile and 'bifunctional' electrophile as described in Slide 35, Chapters 3-5,8, Nucleophilic Substitution and Elimination Reactions. Na2S can be used in (aqueous) methanol or ethanol solvent at