Exam1-00

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)

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.

b) (10 pts) Determine the heat of formation of the monobromination product in part a), given the following data: DH_f^o (kcal/mol): cycloheptane (-28.2), HBr (-8.7), Br₂ (+7.4), HCl (-22.1), and Cl₂ (0).

2. Reactions: (4 x 6 pts. = 24 pts.) Provide reasonable structures for the products in 4 of 5 of the following reactions. If you do all five, be sure to cross out the one that you do not want graded. Comment very briefly. Pay attention to stereochemistry and absolute (R vs. S) configuration.

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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.

b) A 3/2 mixture of enantiomers has an observed [a] = +16^o. What is the best answer for the rotation of the major enantiomer? Circle it. Show work.

-80^o +16^o 78^o +3^o 0^o

c) Name the following optically active by IUPAC rules.

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.]

e) Why is the heat of formation of bromine given in 1b equal to its heat of vaporization? Be brief.

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.]

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Work Sheets