Elimination vs. Substitution...

[pineappletree]

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How do I know which reaction will be favored when both are possible?

I heard a very strong base and high temperatures favor elimination reactions. Is there anything else??

 

[PiBond]

How do I know which reaction will be favored when both are possible?

I heard a very strong base and high temperatures favor elimination reactions. Is there anything else??

high temps and strong bases do favor elimination over substitution. i've noticed that the mcat is not too interested in testing the subtle differences on this topic. for example they'll give you a rate table which will signifies that they want you to consider kinetics...this should translate to nucleophilicity (a kinetic term) in your head. or they'll raise reaction temps to around 50 degrees celsius or something higher, indicating elimination.

bottom line, SN2 doesn't proceed for tertiary carbons, elimination is favored at higher temps and strong bases, primary/methyl carbons always substitute (at least, for mcat purposes), if you get a potentially on-the-fence reaction (a secondary carbon, for example) look at the solvent and you'll find your answer.