1 Chemistry 301 Fall, 2018 THIRD EXAMINATION 7:30 PM, DECEMBER 10, 2018 Duration: 2.0 hr Name____________________________________________________________ Name (as registered on Blackboard) This is an "open book" examination; you may use anything that is not alive or connected to the internet. No computers, cell phones, calculators, nor drawing templates are allowed to be used in the examination room. Note: if you do not know the complete or specific answer, give a partial or general answer-- WRITE SOMETHING If you are using a resonance argument in your answer, draw the relevant resonance structures. If you need to show resonance with a benzene ring, you need show only the critical resonance structure to make your point. Your cyclohexane chair forms must be drawn carefully, making clear the axial and equatorial relationships. NOTE: You will be asked to write mechanisms. That implies using the arrow formalism. Please use it precisely, carefully, and correctly. Show charges carefully. Distinguish between an intermediate and a transition state. A "good" mechanism is short and proceeds through lower energy intermediates/transition states. Write only in the space provided for each question. Score: p2______/11 p3_______/14 p4_______/16 p5______/10 p6_______/13 p7_______/15 p8______/12 p9______/09 Lab:________/14 Lecture total: ________/100 There are 11 pages in this exam. Page 11 is Table 3.2 from the text, with axial substituent effects in cyclohexane, and a glossary of names of common reagents and solvents. PLEDGE:________________________________________________________________2 I. (11 pts). Note the formation of diethyl ether from ethanol in the presence of sulfuric acid. A. (06 pts). Write the best mechanism for this process. Show all intermediates; you need not show transition states. If any of your steps are examples of SN1, SN2, E1, or E2 reactions, name those steps. Is the reaction catalytic in acid (H+)? yes no cannot tell (circle best answer) B. (05 pts). Draw the reaction coordinate diagram which describes this reaction; include all protonation and deprotonation steps (if any). Draw each intermediate at the appropriate position on the chart. Identify the rate-determining transition state. CH3CH2OHH2SO4CH3CH2OCH2CH3 + H2O3 II. (14 pts). Note the series of related bromides, A-E, and the relative rate data, comparing A (rate = 1) to each of the others, for the reaction shown in part (A). A. (05 pts). Write the best mechanism for the conversion of A to F. Show all intermediates; you need not show transition states. Label the rate-determining step (RDS). B. (03 pts). Explain carefully why the rate for B under the same conditions is 103 higher than for A. Give the single most important reason. C. (03 pts). Explain carefully why the rate for C under the same conditions is 0.02, compared to that for A. Give the single most important reason. D. (03 pts). Explain carefully why the rate for E under the same conditions is104 higher than for A. Give the single most important reason. BrOBrOBrOBrOBrrate: 1 103 0.02 0.2 104AB CD EAgMeOHOMeBrAF4 III. (11 pts). Consider the relative rate of the pair of reactions here, one run in DMSO solution and the other in hexane. A. (04 pts). Circle the faster reaction above and write the mechanism, showing clearly the transition state for the rate-determining step, and the product. B. (07 pts). Draw a reaction coordinate diagram that describes both reactions and use it to explain clearly why one reaction is faster than the other. Identify DG‡ for each solvent on your diagram. IV. (05 pts). For the following pair of reactions, choose that member of the pair which has the higher rate. Draw the most likely product for that reaction. Give the name of the mechanism (you need not write the mechanism). Explain why the reaction you chose is the faster one. 1.(CH3)3N: + CH3IDMSO2.(CH3)3N: + CH3Ihexane1. + CH3ICH3OH2.(CH3)2NH + CH3I CH3OHN:5 V. (10 pts). Here are four reactions that might be imagined to produce the alkyne A. Only one of them actually works. A. (05 pts). Choose the reaction that should work and write the mechanism here (you need not show transition states). Name the mechanism. B. (05 pts). Choose one of the reactions that will not work and explain why. +HBr[ A ][ A ]3.4.??+HHO !A +BrBr+[ A ][ A ]1.2.??6 VI. (13 pts). Consider the simple SN1 reaction (no rearrangements) of the secondary p-toluenesulfonate esters represented by X, and the relative rate data for the case where R = phenyl and the case where R = cyclohexyl. A. (05 pts). Draw the mechanism for the reaction involving R = cyclohexyl. Draw the product(s) carefully, indicating stereochemistry where relevant. Identify the rate-determining step. B. (04 pts). Explain why the reaction with R = phenyl is much faster compared to the reaction with R = cyclohexyl . C. (04 pts). Now consider the SN1 reaction of substrate Y under the same conditions with a very different outcome in relative rates. Explain why Y with R = tert-butyl is much slower than Y with R = Me. Pictures will be required. 50 0CH2ORMeOTsXSN1R = Ph 1000R = cyclohexyl 1rateproductH 50 0CH2OROTsYSN1R = Me 600R = tert-butyl 1rateproductH7 VII. (15 pts). Consider the trisubstituted cyclohexanes, H and J, and the E2 reaction in the presence of strong base. A. (04 pts). Draw here the most stable chair form of H and call it H-1. Then draw the other chair isomer of H and call it H-2. Now, do the same for J, drawing J-1 (most stable) and J-2 (less stable). B. (02 pts). Which is more stable, H-1 or J-1? Explain. C. (02 pts). Why is H-1 more stable than H-2? Explain. D. (02 pts). What is the torsional strain energy in H-1? Show your work. E. (05