Portmess Homework Q&S 112

Portmess Homework Q&S 112 - 106 STRUCTURE AND...

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( d ) Acid-catalyzed dehydration of 2,3-dimethyl-2-butanol can proceed in either of two directions. The major alkene is the one with the more highly substituted double bond, 2,3-dimethyl-2- butene. Its formation corresponds to Zaitsev s rule in that a proton is lost from the b carbon that has the fewest hydrogens. ( e ) Only a single alkene is capable of being formed on E2 elimination from this alkyl iodide. Stereoisomeric alkenes are not possible, and because all the b hydrogens are equivalent, regioisomers cannot be formed either. ( f ) Despite the structural similarity of this alcohol to the alkyl halide in the preceding part of this problem, its dehydration is more complicated. The initially formed carbocation is secondary and can rearrange to a more stable tertiary carbocation by a hydride shift. The tertiary carbocation, once formed, can give either 2,4-dimethyl-1-pentene or 2,4-dimethyl-2-pentene by loss of a proton. The proton is lost from the methylene group in preference to the methyl group. The major
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This note was uploaded on 09/20/2011 for the course CHM 2210 taught by Professor Reynolds during the Fall '01 term at University of Florida.

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