[Teddy]

How do I determine if a reaction proceeds by nucleophilic substitution or elimination? With that in mind, how do I know what is a strong nucleophile vs. a weak nucleophile?

[nate]

Sn1 = Unimolecular (one molecule reacting in the rate determining step), prefer polar protic solvents, form carbocation transition states, work with weak bases, requires a good leaving group, occurs with inversion and retention of configuration, usually get some racemization in the products, prefers tertiary substrates.

Sn2 = Bimolecular (two molecules reacting in the rate determining step), prefer polar aprotic solvents, do not form carbocation transition states, require strong bases, requires a good leaving group, always occurs with inversion of the stereogenic center's configuration due to steric hinderance in a frontside attack of the substrate, prefers primary substrates, likes strong Nu:.

E1 = Similar to Sn1, Unimolecular (one molecule reacting in the rate determining step), usually forms the most stable alkene as a product, also works well with weak bases, prefer high temperatures so look for heat in the equation, requires a good leaving group, prefers tertiary and secondary substrates, needs a good ionizing solvent (polar protic or aprotic).

E2 = Requires a strong base, works in variety of solvents, can work with primary, secondary, or tertiary substrates, requires a good leaving group, Bimolecular (two molecules reacting in the rate determining step), also likes heat, will usually form the most stable alkene unless the base and substrate are bulky - then it will favor forming the more unstable alkene as product (Hoffman Elimination), likes strong Nu:, the proton being taken and the L: must be arranged anti- to each other.

Weak bases are good Nu: and L:, OH groups make poor L: and must be converted to H2O - which is a good leaving group.

Anyone else??  Is there anything that I mispoke on or am just wrong??

[movies]

There are a couple of other threads that have discussed this topic as well.  Try using the search feature at the top right corner of the page.

[Teddy]

Thank you so much for the reply. That is just what I was looking for!
I did use the search feature, but that did not help me with what I was looking for.

[movies]

Hmmm...you must have used different search words.  Anyway, here is another thread.  The explaination is a little different:

http://www.chemicalforums.com/index.php?board=3;action=display;threadid=5667