30bFinal_Exam_2003_KEY

30bFinal_Exam_2003_KEY - CHEMISTRY 30B UCLA SUMMER SESSION...

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CHEMISTRY 30B UCLA SUMMER SESSION C 2003 FINAL EXAM KEY On my honor, I have neither given nor received any aid on this exam. KEY KEY ____________________________ __________________________ Signature I. D. Number KEY _____________________________ Name (Print) Question Points -------------------------------------------------- 1 (23) -------------------------------------------------- 2 (17) -------------------------------------------------- 3 (10) -------------------------------------------------- 4 (10) -------------------------------------------------- 5 (10) -------------------------------------------------- 6 (20) -------------------------------------------------- 7 (40) -------------------------------------------------- 8 (28) -------------------------------------------------- 9 (25) -------------------------------------------------- 10 (15) -------------------------------------------------- 11 (15) -------------------------------------------------- Total (213)
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Chemistry 30B FINAL, Summer 2003 Name: KEY Page 2 THEORY 1. A. (3) Explain why 3-hexene reacts with HBr faster than 3-hexyne. The first step of the reaction is addition of a proton. For the alkene this creates a secondary alkyl cation, but for the alkyne this creates a vinyl cation. The vinyl cation is much less stable and much higher in energy. Therefore, formation of the vinyl cation has a higher Activation Energy and thus a slower rate of formation. B. (10) What are the approximate pKa’s of the following compounds? Ammonia Acetic acid Acetone NH of Acetamide 36 5 20 16 Butane Ethanol Ethyl Acetate 50 16 24 2,4-pentanedione Propyne Triethylammonium 10 25 10 C. (3) Write a balanced equation for the hydrolysis reaction of a nitrile to a carboxylic acid. R C R O OH N NH 3 2 H 2 O + + D. (3) Consider the hydrogen bonding of ethanol and the hydrogen bonding of ethyl amine. Which is stronger and why? The hydrogen bonding of ethanol is stronger since oxygen is more electronegative than nitrogen. This makes the proton more electron deficient and ethanol a better Bronsted acid. E. (4) Normally, ethoxyethane (ether) or tetrahydrofuran are used for reactions involving Grignard reagents. Explain why ethanol or acetone cannot be used.
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