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Unformatted text preview: 7 -4 1 continued (c) � + � ( d) � )l U+U
major rrunor (e) �� U +U
maj or rrunor The E2 m echanis m requires anti-coplanar orientation of R and B r. 7-42 The bromides are shown here . Chlorides or iodides would also work. (a) Br � (b) Br 7-43 ( a) There are two reasons w h y alcohols do not dehydrate with strong base. The potential leaving group, hydroxide, i s i tself a strong base and therefore a terrible leaving group . Second, the strong base deprotonates the -OR faster than any other reaction can occur, consuming the base and making the leaving group anionic and therefore even worse. Y ( c) �
Br (d) cSf
Br (b) A halide i s already a decent leaving group. S i nce halides are extremely weak bases , the halogen atom is not easily protonated, and even if it were , the leaving group abi l i ty is not significantly enhanced. The hard step is to remove the adj acent R, something only a strong base can do-and strong bases will not be present under strong acid condi tions. 7-44 (a) � ( b) (c) ( d) )==I rearrangement without rearrangement �H
153 maJor Zaitsev ...
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- Spring '10