Last Name First Name MI Total Score Student ID Number Circle the name of your TA HEATHER KAUSHIK CARI RYAN Discussion Section Day 100 Time Chem 30A Fall 2005 MIDTERM 2 50 Min Mon Nov 21st INTERPRETATION OF THE QUESTIONS IS PART OF THE EXAM DO NOT ASK FOR THE QUESTIONS TO BE EXPLAINED TO YOU ONLY ANSWERS WRITTEN IN THE BOXES PROVIDED WILL BE GRADED DO NOT OPEN THIS EXAM UNTIL INSTRUCTED TO DO SO Q1 Q2 20 36 Q3 20 Q4 Total 39 100 We didn t lose the game we just ran out of time Vince Lombardi All truth passes through three stages First it is ridiculed Second it is violently opposed Third it is accepted as being self evident Arthur Schopenhauer Q1 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 20 pt OH H2SO4 cat A O B 1 Q2 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 H2 3 atm A B C D and E CH3 Pt C cat a Two of these cycloalkenes constitute a pair of enantiomers the absolute configuration of the stereogenic center in compound A is S and in B it is R Draw these compounds below 6 pt A B S Isomer R Isomer b The other three cycloalkenes C D E are achiral When reacted with HCl in ether an inert solvent cycloalkenes C D give only the achiral chloroalkane F whereas cycloalkene E gives four stereoisomeric products G H I J Fill in the structures of E F G H I J in the boxes below note the labels G J are arbitrary i e any stereoisomer can go in any box 12 pt F Single achiral chloroalkane HCl C and D Ether G H I J E HCl Ether Four stereoisomeric chloroalkanes Question 2 is continued on the next page 2 c When cycloalkenes C D are reacted with deuterium gas D2 instead of hydrogen gas H2 different results are observed i Cycloalkene C reacts to form a single achiral product K draw these compounds in the appropriate boxes below 4 pt C K Single achiral compound D2 3 atm Pt C cat ii Cycloalkene D reacts to form a pair of enantiomers L M draw these compounds in the appropriate boxes below note the labels L M are arbitrary 6 pt D L M D2 3 atm Pt C cat Pair of Enantiomers d Cycloalkene E reacts with deuterium gas D2 to form two different ACHIRAL products N O draw these compounds in the appropriate boxes below note the labels N O are arbitrary 6 pt N E O D2 3 atm Pt C cat Two different ACHIRAL compounds e Circle ONE of the following words phrases that best describes the relationship between compounds N O 2 pt CONSTITUTIONAL ISOMERS THE SAME ENANTIOMERS CONFORMATIONAL ISOMERS DIASTEREOISOMERS 3 Q3 Compounds A B C D and E are all alkenes and their molecular formulae are shown in the appropriate boxes below Each alkene undergoes an ozonolysis reaction O3 followed by Me2S to give ONLY the compounds shown to the right of the reaction arrow in each case as well as the Me 2S O byproduct In the reactions that form more than one unique product D E the products are NOT necessarily formed in equal amounts Determine the structures of the alkenes A E and draw their structures in the appropriate boxes Hint for each compound it may be advantageous to calculate the hydrogen deficiency index number of double bond equivalents based upon the given formula 20 pt A i O3 O ii Me2S C10H16 B O i O3 ii Me2S O C8H14 C H i O3 O O ii Me2S H C9H14 D O i O3 ii Me2S O O H H C7H12 E O O i O3 ii Me2S O C13H22 4 O Q4 Phenol and potassium hydroxide undergo an acid base reaction as shown below OH KOH O H2O K pKa 10 pKa 16 a What is the equilibrium constant for the acid base reaction shown above 3 pt b Phenoxide anions react with 1 bromopropane to form ethers as shown below In the box below draw the energy profile for this reaction Draw the STRUCTURES of any proposed transition states or intermediates and label them as TS or INT as appropriate Also indicate activation barriers where applicable G the Gibbs free energy change associated with the reaction G and the rate determining step RDS 12 points Br O K O KBr EtOH E O K Br O KBr Reaction Coordinate Question 4 is continued on the next page 5 c The unsubstituted phenoxide anion X H below reacts with 1 bromopropane FIVE times faster than 4 nitrophenoxide X NO2 below to form the corresponding ethers as shown below In the box below using words AND pictures explain the difference in the observed rates of reaction 8 points Br O X K Relative rate of reaction O X EtOH KBr X H k 5 X NO2 k 1 d The reaction of 4 nitrocatechol with ONE equivalent of 1 bromopropane gives a DIFFERENT product depending upon how many equivalents of potassium hydroxide KOH are used in the reaction In each case however the product has the formula C9 H11NO4 Predict the products A B of the reaction sequences shown below and then explain your answers in the box underneath 16 pt A i 1 eq KOH O2N OH ii 1 eq Br OH iii dilute H3O work up C9H11NO4 4 nitrocatechol B i 2 eq KOH O2N OH ii 1 eq Br OH iii dilute H3O work up C9H11NO4 Explanation 6