Hydrolysis of 2-Bromo-3-methylbutane

Carbocation Rearrangement in the S l Hydrolysis of 2-Bromo-3-methylbutane THE OVERALL REACTION  

Step 1 The alkyl halide ionizes to give a carbocation and bromide ion. This is the rate-determining step. 

Step 2 The carbocation formed in step 1 is secondary it rearranges by a hydride shift to form a more stable tertiary carbocation. 

Step 3 The tertiary carbocation is attacked by water acting as a nucleophile. 

Step 4 Proton transfer from the alkyloxonium ion to water completes the process. 

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Why does the carbocation intermediate in the hydrolysis of 2 bromo 3 methylbutane rearrange by way of a hydride shift rather than a methyl shift ... 

Problem 7.27 How does the S l mechanism for the hydrolysis of 2-bromo-3-methylbutane, a 2° alkyl bromide, to give exclusively the 3° alcohol 2-methyl-2-butanol. establish a carbocation intermediate ... 

Additional evidence for carbocation intermediates in certain nucleophilic substitutions comes from observing rearrangements of the kind normally associated with such species For example hydrolysis of the secondary alkyl bromide 2 bromo 3 methylbutane yields the rearranged tertiary alcohol 2 methyl 2 butanol as the only substitution product... 

Reaction of 3-bromo-3-methylbutan-2-one with triphenylmethylhydrazine and potassium thiocyanate in acetic acid gives 7,7,7a-trimethyl-2,3,5,6,7,7a-hexahydro-li/-imidazo[l,5-Z>][l,2,4]-tri-azole-2,5-dithione (381b) due to the facile hydrolysis the triphenylmethyl group. <95FES379>. 

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