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    During the nitration of phenyltrimethylammonium, which has an electron withdrawing group, there's still a significant amount of para product (10%).

    I understand why its meta directing (positive charge not delocalized to the electron withdrawing group), but why does para products result? Wouldn't the positive charge be delocalized to the electron withdrawing group?
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    Regioselectivity is often not 100%. It reflects a tendency rather an absolute rule, though in the case of SEAr regioselectivity tends to be very high.

    Para is favoured for steric reasons as it's furthest from the other substituent. Selectivity can be increased in several ways, most obviously by reducing the reaction temperature.
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    could it be just thermodynamic or kinetic controlled product, like kaeroll mentioned?
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    I looked this up and it doesn't look particularly simple: http://books.google.co.uk/books?id=N...monium&f=false
 
 
 

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