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SN1 Rxn: is hyrdride shift major product or the LG position?

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  1. May 6, 2017 #1
    1. The problem statement, all variables and given/known data
    So LG is on 2° position, and you have a hydride shift. So you form one product on 2° and one product on 3°.

    Which product will be major which will be minor?

    XwrrTZ5.jpg

    2. Relevant equations
    none.

    3. The attempt at a solution
    I know hydride shift will be more major than a methide shift, because it's not as energetically costly. But for hydride shift vs original LG position (2°), i'm not really sure. I know it does take extra energy to have the hydride shift, so thats making me think original LG position (2°) will be more major than the hydride shift. But i also know that 3° is better than 2°, so i'm really not sure
     
    Last edited: May 7, 2017
  2. jcsd
  3. May 7, 2017 #2

    Ygggdrasil

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    Science Advisor

    The extra energy required for the hydride shift to occur is merely the activation energy for the hydride shift, which does not change the fact that the tertiary carbocation will be more thermodynamically stable than the secondary carbocation. As long as enough activation energy is available for the hydride shift to occur, the more thermodynamically stable intermediate will be favored (under these conditions the reaction is said to occur under thermodynamic control). Sometimes, chemists will set up reactions to minimize the thermal energy available to promote rearrangements of intermediates to more stable intermediates such that the reaction to form product occurs much more quickly than the rearragement (not sure if that is possible in this case, howerver). Under those conditions, the reaction is said to occur under kinetic control as the major product will be dictated by the relative kinetics or rearrangement or reaction of the intermediate and not the thermodynamic stability of the two intermediates.
     
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