Dolbier HW Solutions 208

Dolbier HW Solutions 208 - have their origin in the...

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8.37 ( a ) Tertiary alkyl halides undergo nucleophilic substitution only by way of carbocations: S N 1 is the most likely mechanism for solvolysis of the 2-halo-2-methylbutanes. ( b ) Tertiary alkyl halides can undergo either E1 or E2 elimination. Since no alkoxide base is present, solvolytic elimination most likely occurs by an E1 mechanism. ( c , d ) Iodides react faster than bromides in substitution and elimination reactions irrespective of whether the mechanism is E1, E2, S N 1, or S N 2. ( e ) Solvolysis in aqueous ethanol can give rise to an alcohol or an ether as product, depending on whether the carbocation is captured by water or ethanol. ( f ) Elimination can yield either of two isomeric alkenes. Zaitsev s rule predicts that 2-methyl-2-butene should be the major alkene. ( g ) The product distribution is determined by what happens to the carbocation intermediate. If the carbocation is free of its leaving group, its fate will be the same no matter whether the leaving group is bromide or iodide. 8.38 Both aspects of this reaction its slow rate and the formation of a rearranged product
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Unformatted text preview: have their origin in the positive character developed at a primary carbon. The alcohol is protonated and the carbon oxygen bond of the resulting alkyloxonium ion begins to break: As positive character develops at the primary carbon, a methyl group migrates. Rearrangement gives a tertiary carbocation, which is captured by bromide to give the product. 2 H 2 O CH 3 C CH 2 O H H d1 d1 CH 3 CH 3 CH 3 C CH 2 CH 3 1 CH 3 CH 3 C CH 2 CH 3 Br Br 2 CH 3 2-Bromo-2-methylbutane CH 3 CCH 2 OH CH 3 CH 3 CH 3 CCH 2 O H H 1 CH 3 CH 3 CH 3 C CH 2 O H H d1 d1 CH 3 CH 3 HBr 2,2-Dimethyl-1-propanol (CH 3 ) 2 CCH 2 CH 3 X 1 2-Methyl-1-butene CCH 2 CH 3 CH 3 CH 2 2-Methyl-2-butene CHCH 3 (CH 3 ) 2 C (CH 3 ) 2 CCH 2 CH 3 X 1 (CH 3 ) 2 CCH 2 CH 3 OH 2-Methyl-2-butanol (CH 3 ) 2 CCH 2 CH 3 OCH 2 CH 3 Ethyl 1,1-dimethylpropyl ether CH 3 CH 2 OH H 2 O CH 3 CCH 2 CH 3 X CH 3 2-Halo-2-methylbutanes are tertiary alkyl halides. 202 NUCLEOPHILIC SUBSTITUTION...
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This note was uploaded on 09/26/2011 for the course CHM 2210 taught by Professor Reynolds during the Fall '01 term at University of Florida.

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