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    I dont understand why ipso substitution occurs at the t-butyl group ?

    The markscheme says all other positions are blocked and hence ipso sub. must occur.

    Is this really true ? Is this position para to the t-butyl group really that sterically hindered by the methyl group such that it cant be accessed by the NO2+ ion ?

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    (Original post by Ari Ben Canaan)
    I dont understand why ipso substitution occurs at the t-butyl group ?

    The markscheme says all other positions are blocked and hence ipso sub. must occur.

    Is this really true ? Is this position para to the t-butyl group really that sterically hindered by the methyl group such that it cant be accessed by the NO2+ ion ?

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    Yes it is! Also, the [CMe3]+ leaving group is far better than Me+ or H+
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    (Original post by JMaydom)
    Yes it is! Also, the [CMe3]+ leaving group is far better than Me+ or H+
    Hmmm, that bit about the [CMe3]+ being a better leaving group does make sense... Actually, I can sort of see that the Me groups provide steric hindrance.

    Thanks !
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    (Original post by Ari Ben Canaan)
    Hmmm, that bit about the [CMe3]+ being a better leaving group does make sense... Actually, I can sort of see that the Me groups provide steric hindrance.

    Thanks !
    Given it some extra thought.... Also the t-butyl group give extra stabilisation to the transition state
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    Also, there is steric hinderance of the t-Bu group being forced to be in the plane of the ring as it is bonded to an sp2 carbon. In the first stage of attack this becomes sp3 and hence the t-Bu group is out of the plane, reducing steric hinderance.
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    (Original post by illusionz)
    Also, there is steric hinderance of the t-Bu group being forced to be in the plane of the ring as it is bonded to an sp2 carbon. In the first stage of attack this becomes sp3 and hence the t-Bu group is out of the plane, reducing steric hinderance.

    (Original post by JMaydom)
    Given it some extra thought.... Also the t-butyl group give extra stabilisation to the transition state
    Please have a look at the last post. Thanks !

    http://www.thestudentroom.co.uk/show....php?t=2213607
 
 
 
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