Last Name First Name MI Student ID Number Total Score Chem 30A Winter 2005 Course Grade FINAL 180 Min 200 Mon March 21st DO NOT OPEN THIS EXAM UNTIL INSTRUCTED TO DO SO ONLY ANSWERS WRITTEN IN THE BOXES PROVIDED WILL BE GRADED INTERPRETATION OF THE QUESTIONS IS PART OF THE EXAM DO NOT ASK FOR THE QUESTIONS TO BE EXPLAINED TO YOU Q1 Q2 Q3 Q4 20 15 30 25 Q5 Q6 Q7 Q8 20 40 30 20 Q9 BONUS Q10 BONUS 15 15 Total 200 Organic chemistry just now is enough to drive one mad It gives me the impression of a primeval forest full of the most remarkable things a monstrous and boundless thicket with no way of escape into which one may well dread to enter Friedrich W hler 1835 Q1 Using the appropriate reagents and conditions 2 2 dimethylbutane A can be transformed into compound B which in turn can be converted into compound C Three constitutionally isomeric alcohols D E and F can then be made separately from compound C depending upon what reaction conditions are chosen Draw appropriate structures for compounds B and C and suggest the reagents and conditions that are necessary for each transformation shown on the page boxes 1 through 5 Note some boxes require two step reactions and the reagents and conditions you choose must yield the desired compound as the MAJOR product 20 points B 1 A 2 C 3 4 5 HO D E F OH 1 OH Q2 Propose a reasonable mechanism that accounts for the transformation of 2 cyclobutylpropene A into 1 chloro 1 2 dimethylcyclopentane B as depicted in the box below SHOW ALL STEPS AND EXPLAIN EACH ONE WITH A FEW WORDS 15 points HCl A B ether 2 Cl Q3 Consider the reactions A and B of trans and cis 1 chloro 2 thiophenylcyclohexane with water in ethanolic solution The reaction A of the trans isomer is a million times faster than the reaction B of the cis isomer and perhaps somewhat surprisingly both reactions give the same product namely a racemic mixture of the trans diastereoisomer of 1 thiophenylcyclohexan 2 ol in neither reaction is any of the cis diastereoisomer formed A B Cl H2O S Cl OH EtOH Ph H2O S EtOH Ph krel 106 S Ph krel 1 a From the significant difference in reaction rate it is apparent that reactions A and B proceed through different mechanisms DESPITE THE FACT THAT THEY SHARE A COMMON INTERMEDIATE In the box to the right draw the structure of the intermediate that is common to both pathways 3 points Common Intermediate b Starting from the MOST STABLE CHAIR CONFORMATION of trans 1 chloro 2 thiophenylcyclohexane draw a mechanism showing how reaction A arrives at the reaction intermediate you drew above Briefly explain each step with a few words 8 points Question 3 is continued on the next page 3 c Starting from a simple flat representation of cis 1 chloro 2 thiophenylcyclohexane as drawn in the reactions at the top of the previous page draw a mechanism showing how reaction B arrives at the reaction intermediate you drew above Briefly explain each step with a few words 8 points d Draw a mechanism showing how the intermediate common to reactions A and B is converted into a racemic mixture of trans 1 thiophenylcyclohexan 2 ol 6 points e Using words and illustrations as appropriate explain why reaction A is a million times faster than reaction B i e why can t the cis isomer of the starting material react via the same mechanism as the trans isomer 5 points 4 Q4 Answer the following questions about ELIMINATION REACTIONS 4 1 points each a For each of the three reactions shown below predict the MAJOR ELIMINATION PRODUCT In each case indicate if the reaction proceeds via an E1 or E2 mechanism in the small box to the right CH3 CH3 tert BuOK Br tert BuOH CH3 CH3 EtONa Br EtOH CH3 CH3 EtOH Br Heat b For both of the reactions shown below predict the MAJOR ELIMINATION PRODUCT carefully indicating the position of the deuterium atom if present In each case indicate if the reaction proceeds with SYN ANTI or NO stereospecificity in the small box to the right Br NaOH D H2O Br NaOH D H2O H Br D H H 5 Q5 You are given a sample vial that is labeled achiral alkyl halide A and are told to determine the identity of the compound and some of its derivatives A combustion analysis of A shows the molecular formula to be C10H17 Br 20 points Treatment of A with ethanolic potassium hydroxide gives two different compounds B and C each with the formula C10 H16 KOH A C10H17Br B C10H16 EtOH C C10H16 Ozonolysis of A gives a product mixture containing some 2 propanone acetone i O3 O A Unidentified halogen containing material ii Me2S Dissolving A in H2O EtOH rapidly gives an acidic solution that contains bromide ions AgBr precipitates upon addition of AgNO3 Bromination of A Br2 CCl4 gives two compounds D and E that can be separated and each shown to be achiral Catalytic hydrogenation of either B or C results in a mixture of cis and trans 1 methyl 4isopropylcyclohexane H2 B or C Pt Ozonolysis of B gives a product mixture containing some 1 4 cyclohexanedione but ozonolysis of C gives a mixture of products that DOES NOT contain any of this compound i O3 B O O Other products O Other products ii Me2S i O3 C O ii Me2S X What are the structures of compounds A B C D and E A B C D 6 E Q6 For each of the reactions shown below draw the MAJOR PRODUCT paying particular attention to any appropriate stereochemical relationships in the boxes provided Note for two step reactions just give the final product DO NOT draw intermediates Some of these reactions may yield a pair of enantiomers and in these cases draw both of them If a reaction produces a single enantiomer assign its configuration as either R or S depending upon which enantiomer is formed 40 points a N Heat HO HBr b Cl ether i HBr ether c ii NaOEt EtOH i BH3 THF d ii NaOH H2O2 e Br R NaSMe DMSO Question 6 is continued on the next page 7 i OsO4 f ii NaHSO3 g excess D2 Pt h 1 eq Br2 CCl4 Product contains C C i i O3 ii Me2S j HgSO4 H H2SO4 H2O 8 Q7 Answer the following questions about SUBSTITUTION REACTIONS 30 points a The rates of the SN1 solvolysis reactions of the three alkyl bromides shown below A B and C differ dramatically C reacts a million times faster than B which in turn reacts a million times faster than A which reacts so slowly it essentially doesn t happen at all Explain this trend in the box below A B C H2O R R Br OH EtOH Br Br 10 13 Br 10 6 1 krel b Tertiary amines R3 N react with ethyl iodide in S N2 reactions to form quaternary …