Chem 241 Fall 2008 Chapter 7 Practice Problem Question 1 A student had carefully prepared pure R 2 iodopentane but in his her haste had left the compound in solution overnight When that student came back in the morning and took an optical rotation the compound was racemic It was also discovered that a small amount of sodium iodide was present in the solution What happened 1 Chem 241 Fall 2008 Question 2 For each reaction shown below provide the mechanism i e draw in the curved arrows showing the movement of electrons and identify the expected major product S Na a b excess NaI H3C Br Br Br Br c KCN H Br d NaOH Br HO 2 C4H8O Chem 241 Fall 2008 LiOH e I O OH f NaOH C7H10O2 I H3C O S O g O Me LiSEt 3 Chem 241 Fall 2008 Question 3 As mentioned in class methyl tert butyl ether MBTE is a common gasoline additive used to boost octane rating Below are two reactions that are both attempts to form MBTE Which reaction will be successful Which reaction will fail to produce MBTE Why will it fail 1 CH3 3COK CH3Br H3C H3C H3C 2 CH3 3CBr CH3OK 4 O CH3 MBTE Chem 241 Fall 2008 Question 4 Below are a series of reactions that fail to give the indicated SN2 products Explain why each reaction fails CH3 a NaOH OH X CN Br b KCN X I Cl c NaI H3C X CH3 Me d NMe3 H3C CH3 Me Br X 5 NMe3 Chem 241 Fall 2008 Question 5 Rank the following sets of carbocations from most to least stable Careful part c is tricky Me Me Me a Me b c The carbocation formed from ionization of the following iodides Me Me Me I I I 6 Chem 241 Fall 2008 Question 6 Starting with S 3 methyl 2 propanol provide structures A G for the following reactions Pay attention to stereochemistry where appropriate G C H DMF dimethyl formamide a polar aprotic solvent NaCN HBr OH CH3 H3C TsCl NaI acetone pyridine CH3 A B CH3 H2SO4 aqueous H3C OK tert butanol CH3 D E C5H10 Note The conjugate base of sulfuric acid is not very nucleophilic 7 CH3SNa DMSO dimthylsulfoxide a polar aprotic solvent F C6H14S Chem 241 Fall 2008 Question 7 The reaction below does not proceed as written but an SN2 reaction does take place What is the major product formed H3C S H3C CH3 CN NaCN H3C CH3 CH3 B A 8 SMe2 Chem 241 Fall 2008 Question 8 When cis 1 iodo 2 methylcyclohexane A is treated with potassium tertbutoxide 1 methylcyclohexene B is formed as the major product reaction 1 However when trans 1 iodo 2 methylcyclohexane C is treated with potassium tertbutoxide 3 methylcyclohexene D is formed reaction 2 and the reaction proceeds more slowly than does reaction 1 Explain why the observed products are formed in reaction 1 and 2 and why reaction 2 proceeds more slowly CH3 Me H3C OK Me CH3 1 faster I A B CH3 H3C Me OK Me CH3 2 slower I D C 9 Chem 241 Fall 2008 Question 9 a Explain why heating in primary bromide A in methanol does not produce the direct substitution product Br OMe MeOH A 10 Chem 241 Fall 2008 b When the reaction above is carried out a complex mixture of products results as shown below Br Me MeOH Me OMe A OMe Provide a mechanism showing how each of the above products is formed Label each product as resulting from SN2 SN1 E2 or E1 11 Chem 241 Fall 2008 Question 10 Explain the major difference in reactivity between the following pair of reactions NH4OH NH2 I NH4Br Br I Question 11 Explain the major difference in reactivity between the following pair of reactions I NaOH I NaBr 12 Br