Download Chemistry Exam 2 - 220a, October 15, 2004 and more Exams Organic Chemistry in PDF only on Docsity! EXAM 2 CHEMISTRY 220a Friday, October 15, 2004 NAME (print): ___________________________________________________ TA:_____________________ Day:_________________ Time:__________ Take a few moments to look over the exam. Answer each question on the exam paper. Important clues, points, and structures are in bold. Do all preliminary drawing or computations on the work sheets at the end of the exam. The work sheets will not be graded. The exam is 55 minutes. STOP writing and hand in your exam when you are asked to do so. REMEMBER: Neatness is to your advantage. 1. Thermochemistry (28 pts) ______ 2. Reactions (24 pts, Do 4 of 5) ______ 3. Potpourri (24 pts, Do 4 of 5) ______ 4. Mostly Mechanisms (24 pts, Do 4 of 5) ______ ______________________________________________ Total (100 pts) Name:______________________________________ 2 1. Thermochemistry: (28 pts.) a) (18 pts) Provide the propagation steps and overall reaction for the gas phase, room temperature, free radical monobromination of cycloheptane. Place the alkane in the first box on the left. Place the other reactants and products in the remaining boxes with their BDEs on the appropriate lines. See the last page 11 for BDEs. kcal/mol Propagation step 1 kcal/mol Overall reaction + + kcal/mol Propagation step 2 + + + + b) (10 pts) Determine the heat of formation of the monobromination product in part a), given the following data: ΔHfo (kcal/mol): cycloheptane (-28.2), HBr (-8.7), Br2 (+7.4), HCl (-22.1), and Cl2 (0). Name:______________________________________ 5 3. Potpourri: (4 x 6 pts. = 24 pts.) Do 4 of 5. If you do all five, be sure to cross out the one that you do not want graded. a) “One of these things (Fischer projections) is not like the others. One of these things doesn’t belong.” Circle it. CH3 H CO2H HO H3C OH CO2H H CH3 H OH CO2H CH3 H CO2H HO CH3 H CO2H OH b) A 3/2 mixture of enantiomers has an observed [α] = +16o. What is the best answer for the rotation of the major enantiomer? Circle it. Show work. -80o +16o 78o +3o 0o c) Name the following optically active by IUPAC rules. BrH H d) Free radical chlorination of (R)-1-chloro-2-methylbutane leads to five constitutional isomers, one of which has a stereoisomer present (A), one of which is achiral (B), and one of which is a racemate (C). Label A and its stereoisomer A', B, and, C below. [Note: A and A' are not distinguishable with the information provided.] Cl ClCl ClCl Cl Cl Cl Cl Cl e) Why is the heat of formation of bromine given in 1b equal to its heat of vaporization? Be brief. Name:______________________________________ 6 4. Mostly Mechanisms: (4 x 6 pts. = 24 pts.) Provide the structures or requested information in 4 of 5 of the following problems. Comment briefly. If you do all five, be sure to cross out the one that you do not want graded. [Note: Questions a-d are from the questions at the end of Chapters 5 and 6.] a) A CH3ONa CH3OH D H H H H H + major minor b) D3C CD3 Br D2C CD3 D3C CD3 OH + Provide reaction conditions so that the rate of formation of the products is no different from the reaction with protio 2-bromopropane. c) CH2Br CH3OH, heat OCH3 + OCH3 A + C + D + E Provide a mechanism for the formation of A or B. B Ag+ Name:______________________________________ 7 Continued on the next page … Name:______________________________________ 10 Work Sheets Name:______________________________________ 11 Work Sheets Name:______________________________________ 12
