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Strong base vs. strong nucleophile

Discussion in 'MCAT Discussions' started by wannabadr10, Jan 2, 2009.

  1. wannabadr10

    2+ Year Member

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    I never understood the difference between the two. I've looked up the definitions for both and it seems that a strong base would be a strong nucleophile and a strong nucleophile would always be a strong base. My prep book states that Sn2 rxns are favored by strong nucleophiles and E2 rxns are favored by strong bases. What is the difference and why?

    Thanks!
     
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  3. futuredoctor10

    Classifieds Approved 10+ Year Member

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    A strong nucleophiles can better attack electrophiles.
    A strong bases can better donate electrons.

    There are some strong nucleophiles which are also strong bases.
     
  4. Yope

    Yope New Member
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    Like you said, a strong base is often a strong nucleophile, which complicates matters. However, determining SN2 vs. E2 requires considering more factors. Let's assume that the nucleophile is a strong base.

    The substrate, for instance, plays a big role. Bulky substrates that hinder access of the nucleophile/base to the carbon will favor elimination, since the nucleophile/base can more easily get to the hydrogens than the carbon. Furthermore, for an E2 reaction to happen, a hydrogen has to be antiperiplanar to the one the nucleophile/base pulls off. If that antiperiplanar hydrogen is not there, an SN2 reaction will dominate.
     
  5. wannabadr10

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    I get it now. Thanks for the help!
     

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