Final - Fall 200606

Final - Fall 200606 - 14. (4 pts) When A and B react in...

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6 13 . (4 pts) Which structure shows a major intermediate formed in the electrophilic nitration of chlorobenzene? a) b) c) d) Cl O 2 N H N O O H NO 2 Cl Cl H O 2 N Cl Answer: a Comments: This question tests the understanding of the electrophilic aromatic substitution. Chlorine is o- and p- directing. Thus, the nitro group (just added) and H (about to be removed) must be on the same carbon o- or p- to Cl. Only (a) qualifies. The rest is simple drawing of an alternative resonance structure. Check the book on p. 547. This question has no direct precedent in the practice set, but it addresses the basic question of the electrophilic substitution mechanism and directing effect of groups.
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Unformatted text preview: 14. (4 pts) When A and B react in t-BuOH, the following rate expression is observed: -d[ A ]/dt = k[ A ][ B ] Ph A : B : OK OTos What is the most likely mechanism of this reaction? a) E2 b) S N 2 c) E1 d) S N 1 e) it cannot be determined Comments: The rate expression indicated a bimolecular reaction (S N 2 or E2). Elimination cannot take place because there are no hydrogens on carbons directly adjacent to the carbon with the leaving group. Compare: TS4: 65, or PE4A: 10-11, PE4C: 26....
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