Last Name First Name MI Student ID Number Total Score Chem 30A Fall 2004 Course Grade FINAL 180 Min 200 Fri Dec 17th 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 20 20 40 Q4 Q5 Q6 30 Q7 40 Q8 20 BONUS 15 Q9 30 BONUS Total 15 200 ATTEMPTED murder what is that Do they give a Nobel Prize for ATTEMPTED chemistry Well do they Sideshow Bob Q1 Five different cycloalkenes A E each with the molecular formula C6H10 will yield methylcyclopentane when subjected to catalytic hydrogenation H2 Pt catalyst as shown below Me H2 A B C D and E Pt cat a Two of these cycloalkenes constitute a pair of enantiomers the absolute configuration of the stereogenic center in compound A is R and in B it is S Draw these compounds below 2 points each A B R Isomer S Isomer b The other three cycloalkenes C D and E are achiral but when hydrogen gas H2 is replaced by deuterium gas D2 different results are observed 2 points for each structure C J i Compound C reacts to form a single product F draw these compounds below C F D2 Single Compound Pt cat ii Compound D reacts to form a pair of enantiomers G H draw these compounds below D G H D2 Enantiomers Pt cat iii Compound E reacts to form a pair of diastereoisomers I J draw these compounds below E I J D2 Pt cat 1 Diastereoisomers Q2 a When the tosylate derivative A is heated in a methanol solution compounds B and C are formed Propose a reasonable mechanism that accounts for the transformation of compound A into compound B SHOW ALL STEPS 10 points OMe OTs MeOH Heat A B C O R OTs R O S O Question 2 is continued on the next page 2 b This reaction also yields many compounds that retain seven membered ring structures i Draw the structure of the MOST ABUNDANT seven membered ring containing alkene D formed in this reaction and circle the mechanism responsible for forming this product ii Draw the structure of the MOST ABUNDANT seven membered ring containing methyl ether E formed in this reaction and circle the mechanism responsible for forming this product 2 1 2 points each D E Mechanism SN1 E1 SN2 E2 Mechanism SN1 E1 SN2 E2 c When the reaction conditions are changed and tosylate A is reacted with sodium methoxide in methanol yet another different product F is formed Draw the structure of this product and circle the mechanism responsible for its formation 2 1 2 points F OTs MeONa MeOH A Mechanism SN1 E1 SN2 E2 d When tosylate A is reacted with sodium cyanide in dimethyl sulfoxide DMSO product G is formed Draw the structure of this product and circle the mechanism responsible for its formation 2 1 2 points G OTs NaCN DMSO A Mechanism SN1 E1 SN2 E2 3 Q3 a Methylcyclohexane shown in the middle below can exist in two different chair conformations one of which is 1 8 kcal mol more stable than the other In each of the top two boxes below draw in a bond to one methyl Me group in the appropriate position In the bottom two boxes complete the Newman projections by filling in methyl Me groups AND hydrogen atoms H where appropriate 4 points 1 G 1 8 kcal mol 1 CH3 Least stable chair 1 6 Most stable chair 2 3 5 4 2 1 3 3 G 1 8 kcal mol 1 2 Least stable chair Most stable chair b trans 1 4 Dimethylcyclohexane shown below also exists in two different chair conformations one of which is 3 6 kcal mol more stable than the other In each of the boxes below draw in methyl Me groups in the appropriate positions 4 points CH3 CH3 G 3 6 kcal mol Least stable chair Most stable chair Question 3 is continued on the next page 4 c trans 1 2 Dimethylcyclohexane shown below also exists in two different chair conformations one of which is 2 7 kcal mol more stable than the other In each of the boxes below draw in methyl Me groups in the appropriate positions 4 points H3C G 2 7 kcal mol CH3 Most stable chair Least stable chair d In the box below explain using appropriate diagrams if you wish why the difference in energy between the two chair conformations of trans 1 2 dimethylcyclohexane is 0 9 kcal mol LESS than the difference in energy between the two chair conformations of trans 1 4 dimethylcyclohexane 8 points Question 3 is continued on the next page 5 For each of the questions below e h draw the most stable chair conformation for each compound and in each case give a succinct reason for your choice Hint the answers aren t perhaps as easy as you may think they are 2 2 points each e f OCH3 H3C CH3 CH3 reason g reason Br h CO2 NH3 I reason reason i When the compound in part h is treated with a strong acid a new compound is formed Draw the most stable chair conformation of this new product and justify your choice 4 points 6 Q4 Consider the reaction of 3 methyl 1 butene with borane THF BH3 THF a The very first step of the reaction proceeds regioselectively to give one major product A with the molecular formula C5H13B Draw the structure of A in the box below 2 points A BH3 THF C5H13B b Draw and briefly annotate with a few words the transition states that would lead to Markovnikov and anti Markovnikov addition of BH3 in the reaction shown above Indicate how both steric and electronic effects influence the observed regioselectivity in the hydroboration of such unsymmetrical alkenes Note Just drawing the transition states WILL NOT earn you full credit you must indicate how the electronics and or sterics either stabilize or destabilize each transition state structure 10 points Anti Markovnikov Addition Markovnikov Addition c Compound A can react with another equivalent of 3 methyl 1 butene to give compound B which can also react with another equivalent of 3 methyl 1 butene to give compound C Draw compounds B and C in the boxes below their molecular formulas are given to you 4 points B C A C10H23B C15H33B Question 4 is continued on the next page 7 d When compound C is reacted with sodium hydroxide and hydrogen peroxide the first product to be formed D is one in which ONE oxygen atom has been inserted into the structure Draw compound D in the box below 2 points D NaOH C H2O2 C15H33BO e In the box below propose a reasonable mechanism that accounts for the transformation of compound C into compound D 8 points f Compound D can react further with NaOH H2O2 to give compound E which can also react again to give …