Last Name First Name MI Student ID Number Total Score Chem 30A Spring 2005 Course Grade FINAL 180 Min 200 Thurs June 16th 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 24 Q4 16 Q7 30 Q2 30 Q5 32 Q8 20 Q3 18 Q6 40 Q9 20 Total 200 A professor is one who talks in someone else s sleep W H Auden I cannot teach anybody anything I can only make them think Socrates I fully realize that I have not succeeded in answering all of your questions Indeed I feel I have not answered any of them completely The answers I have found only serve to raise a whole new set of questions which only lead to more problems some of which we weren t even aware were problems To sum it all up In some ways I feel we are confused as ever but I believe we are confused on a higher level and about more important things Unknown In Memoriam Christopher Spencer Foote Scholar Teacher Professor Author 6 5 1935 6 13 2005 1 Q1 Cyclohexene A can be converted into 3 methoxycyclohexene D in a number of ways One pathway involves the reaction of A to give intermediate B which has the formula C7H13 BrO followed by a second reaction to give the desired product D Alternatively cyclohexane can be reacted to give intermediate C which has the formula C6H9 Br followed by a second reaction to give the desired product D Intermediates B and C as well as the final product D are formed as racemic mixtures Suggest possible structures for B and C in the appropriate boxes below For each reaction A B B D and A C C D provide the necessary reagents conditions in the appropriate box AND indicate what kind of reaction is happening in the case of substitution and elimination reactions indicate which mechanism is most likely operating your choices are listed in the box at the bottom of this page 24 points Reagents Conditions B Reaction Mechanism A Reagents Conditions C C7H13BrO Reaction Mechanism Reaction Mechanism Reagents Conditions Reagents Conditions OCH3 Reaction Mechanism C6H9Br D Reaction Types Mechanisms to choose from Addition Elimination E1 or E2 Substitution Radical SN1 SN2 Rearrangment 2 Q2 When alkene A is hydrated using EITHER acid catalyzed hydration H2 O H2SO4 cat OR hydroboration oxidation BH3 THF followed by NaOH H2O2 an approximately 1 1 mixture of the secondary alcohols B and C is obtained i e neither set of reagents gives any regioselectivity H2O OH H2SO4 cat OH OR i BH3 THF A B ii NaOH H2O2 1 1 mixture C a In contrast however when alkene D is hydrated separately under these two sets of conditions one reaction gives secondary alcohol E as the MAJOR product 98 whereas the other gives the secondary alcohol F as the MAJOR product 98 Indicate which set of conditions gives which product by writing the words HYDROBORATION OXIDATION in one arrowed box and ACID CATALYZED HYDRATION in the other You may want to answer parts b and c first 4 points OH OH E D F b In the box below draw the mechanism for the acid catalyzed hydration H2 O H2SO4 cat of alkene D and explain why the reaction is regioselective 8 points Question 2 is continued on the next page 3 c In the box below draw the mechanism for the VERY FIRST STEP of the hydroboration oxidation reaction of alkene D i e just show the mechanism for the first addition of alkene D to BH3 Draw the transition state for this step and explain why the addition is regioselective 8 points d Suggest a reason why no regioselectivity is observed in the hydration of alkene A no matter what conditions are chosen 4 points e The reaction of alkene D with Br2 in water gives a racemic mixture of two bromohydrins draw the structures of these two bromohydrins below 6 points Br2 H2O D 4 Q3 An optically active chiral compound A C11H18 reacts with hydrogen in the presence of a platinum Pt catalyst to give one SINGLE compound B with the formula C11H22 Compound B is optically inactive achiral When A undergoes an ozonolysis reaction O3 Me2S two new compounds are formed the ketodialdehyde C shown below and compound D in addition to the byproduct Me2S O Draw the structures of compounds A B and D in the boxes at the bottom of this page including any relevant stereochemistry 7 points each A and B 4 points for D H i O3 H2 Pt B A C11H22 C11H18 O C ii Me2S O both reagents used in excess O Space for working A H B D 5 D S O Q4 Propose a reasonable mechanism that accounts for the transformation of compound A into compound B shown below show all intermediates all appropriate lone pairs formal charges significant resonance forms and curly arrows Explain each step with a few words 16 points O OH H2SO4 cat O A O B 6 Q5 Ammonia NH3 undergoes an S N2 reaction with methyl iodide CH3 I in the presence of a base such as potassium carbonate K2CO3 to give methylamine CH3 NH2 Methylamine is still a good nucleophile and will react with another equivalent of CH3 I under the same conditions to give dimethylamine In turn dimethylamine will continue to react to form trimethylamine and finally trimethylamine will react to form tetramethylammonium iodide CH3 I NH3 CH3 I K2CO3 DMF H3C NH2 CH3 I K2CO3 DMF K2CO3 DMF H3C N CH3 CH3 H3C K2CO3 DMF CH3 H CH3 I H3C N CH3 I N CH3 Structure of K2CO3 Potassium carbonate O 2 K O O CH3 a In the box below draw the mechanism showing how NH3 reacts with CH3 I in the presence of a carbonate base to give methylamine CH3 NH2 i e the FIRST step of the sequence shown above show all intermediates all appropriate lone pairs formal charges and curly arrows 6 points b In the box below draw the mechanism showing how trimethylamine CH3 3 N reacts with CH3 I to give tetramethylammonium iodide CH3 4N I i e the LAST step of the sequence shown above show all intermediates all appropriate lone pairs formal charges and curly arrows 3 points c Briefly comment upon the role of the carbonate base in the reaction and suggest why it does not participate in the final step 3 points Question 5 is continued on the next page 7 d S Coniine is a toxic alkaloid found in the hemlock plant and is most infamously associated with the death of Socrates he was sentenced to death in 399 BC and made to drink a cup of hemlock juice You can ignore this bit of trivia inside these parentheses if you wish In man 3 mg of coniine is said to have produced symptoms but 15 mg have been tolerated without discomfort Perhaps 30 60 mg …