Solutions_Manual_for_Organic_Chemistry_6th_Ed 162

Solutions_Manual_for_Organic_Chemistry_6th_Ed 162 - 7 -48...

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Unformatted text preview: 7 -48 CH3 CH3 C H 3-C-C- 3 CH HO :9 o I I I CH3 CH3 ---- I � H+ C- 3 CH CH 3-CHO I I "'9 H2 o I 1+ --I"� -H20 CH CH3 3 C- 3 CH C H3 -CHO I �I I C H3 CH 3-CC- 3 CH : 0 : CH3 II I I CH3 + I C-C-CH 3 CH 3 : OH CH3 l + m ethyl shift I I The dri ving force for thi s rearrangement i s the great stabil ity of the resonance-stabi lized, protonated c arbonyl group. 7 -49 NBS generates bromine w hich produces bromine radical. B romine radical abstracts an allylic hydrogen, resulting i n a resonance-stabi l ized aUylic radical. The allylic radical can bond to bromine a t either of the two carbons with radical character. See the soluti on to problem 6-63. NBS c::=> CC H \.-I B r2 hv 2 Br H2 + �� reCYCI Br �a B ro + 0 ____ 1a 0 CH 2 HBr <;:, H CH 2 + Br H Ph 7 -50 H , C H {" " Ph H X � Ph � CHCH3 \ H -----l.� N aOEt CH3 25,3R Br Ph '-r�---/ CH2CH3+ B Ph � Ph Ph Ph A = + , C H {" " Ph 25 5 ,3 E2 dehydrohalogenation requires anti-coplanar arrangement of H and Br, so specific ci s-trans I s ome rs (8 or C) are generated depending on the stereochemistry of the starting material . Removing a h ydrogen from C -4 (achiral) will give about t he s ame mixture o f c is a nd trans ( A) from e ither diastereomer. 155 X HCHCH 3 Ph ! A = E ,Z mixture + JYJ Ph Ph Br � E,Z mi xture ...
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This note was uploaded on 02/27/2010 for the course CHEM 140 taught by Professor Wade during the Spring '10 term at Whitman.

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