This is a draft cheat sheet. It is a work in progress and is not finished yet.
Step 1: The Solvent
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Is it Protic? Hydrogen-donating (H bonded to electronegative molecule) will add lots of H+ to the solution. Would stablilize strong base/nucleophile.
SN2 and E2 unlikely.
Necessary for SN1 or E1.
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Is it Aprotic? No Hydrogens attached to electronegative molecules. Would not react with strong base or strong nucleophile.
SN1 or E1 unlikely.
Necessary for SN2 or E2.
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Step 2: The Leaving Group
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Is it a good leaving group? Favors all reactions, but is necessary for SN1 or E1 because the LG must leave on its own first.
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Some Examples: I, Br, Cl
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Step 3: The Reactant
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Is it a strong Nucleophile? Small (not "bulky") nucleophilic.
Able to perform backside attack in SN2 reaction.
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Is it a strong base? If there is no protic solvent, will attack Beta-carbon-hydrogens to form carbocations in E2 reaction.
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Step 4: The Substrate
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Is the alpha carbon Primary (1o)? Can only go through an SN2 reaction.
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Is the alpha carbon Secondary (2o)? Favors either SN2 or E2 reaction.
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Is the alpha carbon Tertiary (3o)? Favors an E1 or E2 reaction through alkene stability.
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