Penn 241e1-06 ans

Penn 241e1-06 ans - CHEM 241-601, U. Penn Hour Exam I...

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CHEM 241-601, U. Penn Name______________________________ Hour Exam I answers October 17, 2006 Signature___________________________ 1.(20) Draw Newman projections for each of the unique rotational conformations of 1,1,2-tribromobutane (look down C 1 -C 2 , 60 o rotations) and plot the potential energy diagram on the axes below. Label your conformations A-F . The graph below shows potential energy as a function of bond rotation. Place the E min (lowest energy conformation) at 180 o and on the dashed line. Use the top dashed line for the highest energy conformation (wherever it ends up). Place the letter corresponding to each conformation at each relative minimum and relative maximum. Keep your graph close to scale. What is the barrier to rotation in KJ/mol? 18.0 KJ/mol For full credit, a smooth line should be drawn connecting each of the minima and maxima. E min E max E 0 60 120 180 240 300 360 Rotation (degrees) about C 1 -C 2 (KJ/mol) 6.0 24.0 A B C D E F F H Br Br H Et Br H Br Br Br H Et Br Br Br 1 2 Et H Br H Br Br H Br Et H Br Br H Br Et H Br Br Br Et H H Br Br 10.0 22.0 6.0 20.0 8.0 24.0 E max E min A B C D E F
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Interaction Energy (KJ/mol) eclipsing H - H 4.0 CH 3 - H 6.0 CH 3 CH 2 - H 7.0 Br - H 5.0 Br - Br 8.0 CH 3 CH 2 - Br 12.0 Gauche Br – Br 2.0 Br - CH 2 CH 3 4.0 2.(10) Give the products of the following two reactions based on the curved arrows: a) O O b) I C H H Br O O BrCH 2 I + 3.(25) Account for the following observations with good drawings and very few words: a) One of the compounds below has a pKa of 16 and the other has a pKa of 10. Match the pKa with the molecule and briefly explain the dramatic difference.
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Penn 241e1-06 ans - CHEM 241-601, U. Penn Hour Exam I...

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