Chemistry 30A Spring 2004 Exam 2 Solutions: Organic Reactions and Mechanisms, Exams of Organic Chemistry

Download Chemistry 30A Spring 2004 Exam 2 Solutions: Organic Reactions and Mechanisms and more Exams Organic Chemistry in PDF only on Docsity! Chemistry 30A Spring 2004 Exam 2 Solutions Page 1 Statistics: High score = 97 Average = 65.0 Low score = 00 Standard deviation: Irrelevant - does not influence grades in this course. A note about exam keys: The answers presented here are usually significantly longer than expected from a student taking the exam. An exam key serves not only to reveal what was expected, but to instruct you as well. To see the grade curve, consult the Chem 30A Home Page. 1. CH3 Cl NaI DMF CH3 I 2. I Cl CH3 Cl δ-CH3 I δ- CH3 I 3. CH3 I NaI DMF CH3 I 4. I CH3OH OCH3 + OCH3 5. Ph I Ph Ph OCH3 H HOCH3 Ph OCH3 Ph Ph Ph OCH3 H CH3OH Ph OCH3CH3OH CH3OH rds 6. Cl CH3 CH3O CH3OH CH3 + major product CH2 Chemistry 30A Spring 2004 Exam 2 Solutions Page 2 7. CH3 Cl CH3O H CH3 Cl δ- HCH3O δ- CH3 Cl CH2 H OCH3 CH2 8. Rate = k [R-Cl] [CH3O-] 9. OSO2CF3 CH3 CH3OH CH3 + major product CH2 10. OSO2CF3 CH3 CH3 H HOCH3 CH3 CH2 H HOCH3 CH2 rds 11. Note that the base (CH3OH) is also the solvent for this reaction. Changing to a less polar solvent (tert-butanol) retards the carbon-leaving group bond ionization, but still allows the deprotonation to occur. OSO2CF3 CH3 (CH3)3COH CH3 + CH2 12. The most probable mechanism for this reaction is SN2. 13. When choosing between elimination and substitution mechanisms, we examine E2 first (except in the case of primary alkyl halides). E2 requires (among other things) a strong base (typically hydroxide or an alkoxide). Methanethiolate (CH3S-) is a weak base. This disfavors E2. We next consider SN2, which requires a moderate nucleophile, a moderate leaving group and the carbon bearing the leaving group cannot be tertiary. Methanethiolate is a good nucleophile (formal negative charge, low electronegativity of sulfur), chloride is a moderate leaving group, and the carbon bearing the chlorine is secondary. The SN2 conditions are reasonably met, so we predict the main reaction pathway is SN2.