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Strong base vs. strong nucleophile

Discussion in 'MCAT: Medical College Admissions Test' 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!
     
  2. 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.
     
  3. 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.
     
  4. wannabadr10

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    I get it now. Thanks for the help!
     

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