bilirubin3 Posted July 29, 2011 Report Share Posted July 29, 2011 Hey so the princeton review books don't really elaborate on this but what makes a good nucleophile (Other than a negative charge or a lone pair). Which halogen is the best nucleophile (flourine?). Link to comment Share on other sites More sharing options...
Cerena Posted July 29, 2011 Report Share Posted July 29, 2011 Hey so the princeton review books don't really elaborate on this but what makes a good nucleophile (Other than a negative charge or a lone pair). Which halogen is the best nucleophile (flourine?). Sorry, I- is the strongest halogen nucelophile. (I am guessing you said fluroine because of its strong electronegativity. But, the more electronegative an atom is, the less nucleophilic it will be.) Link to comment Share on other sites More sharing options...
bilirubin3 Posted July 29, 2011 Author Report Share Posted July 29, 2011 Isn't iodine the best leaving group though? Link to comment Share on other sites More sharing options...
Cerena Posted July 29, 2011 Report Share Posted July 29, 2011 Ah, okay. Forgot about this. The difference is in the solvent. Protic solvent - iodine is best Aprotic solvent - fluoride is best Link to comment Share on other sites More sharing options...
ameltingbanana Posted July 29, 2011 Report Share Posted July 29, 2011 Aside from solvent effects, steric hindrance is a biggie too. If the potential nucleophile is very steric and bulky, it likely won't act as a nucleophile, because nucleophilic attack generally requires a free path to the atom being attacked. In that case, it'll probably act as a base instead and set off a beta-elimination through a deprotonation. Bear in mind this all refers to Sn2/E2, as the nucleophile strength isn't nearly as important in Sn1/E1 reactions. Link to comment Share on other sites More sharing options...
bored Posted July 30, 2011 Report Share Posted July 30, 2011 anything that is unstable on its own and has polarity of charges./. Link to comment Share on other sites More sharing options...
ElPenguino Posted July 31, 2011 Report Share Posted July 31, 2011 I'm having some similar (?) issues. I was doing some practice questions on substitution rxns and came across a question where I was deemed wrong for stating that the nucleophile/leaving group pairing of Cl-/I- in an SN2 rxn would not be work b/c I- is too strong of a nucleophile. HOWEVER, as we are discussing here, I- is NOT a strong nucleophile in aprotic solutions and, as I understand it, SN2 rxns occur in aprotic sol'ns. Is this an error in the book? They deemed tosylate/CN- more appropriate. I know CN- is a strong nucleophile in protic sol'n, but does it not follow the same rules as iodide whereby it is weaker in aprotic sol'ns? And, do SN2 rxns always occur in aprotic sol'ns? Is it possible that they can proceed in protic sol'ns (I thought not)? Link to comment Share on other sites More sharing options...
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