Substitution and Elimination Reactions Flashcards
What is a furan? A tetrahydrofuran (THF)?
What is a diethyl ether?
An ethyl methyl sulfide?
What is a vinyl alcohol?
An allyl alcohol?
What is chloroform?
Vinyl or allyl chloride?
What are primary, secondary, and tertiary alcohols?
What does SN2 mean?
What are the charactestics (and examples) of good leaving groups?
Good leaving groups are weak bases
(meaning, they make strong acids)
What are the characteristics (and examples) of poor leaving groups?
Poor leaving groups are strong bases (weak acids)
What are the characterstics (and some examples) of good nucleophiles?
- high energy donor
- (-) negative formal charge
- electropositive
What makes for a rapid SN2 reaction?
Steric Effects (most important)
- Good if the halide is methyl or 1o
- Fair if the halide is 2o
- Poor if the halide is 3o, β-branch. Or if the nucleophile is very bulky.
Leaving-Group ability
- Good leaving groups are weak bases.
Nucleophilicity
- Good: High energy lone pairs (C, P, S, I)
- Fair: OH-, Br-, N, Cl-
- Poor: F-, ROH, H2O
Each of the following carbocations is significantly more stable than the methyl cation. Explain why each of these species is especially stable. You should use both molecular orbital and resonance arguments in your explanations.
What are the primary requirements for…
- SN2 reactions
- E2 reactions
- SN1 and E1 reactions
- SN2 reactions: need good steric interactions
- (Me, 1° is good, 2° less good, 3° bad)
- E2 reactions: need strong attacking base
- at least as strong as OH–
- SN1 and E1 reactions: need stable carbocation
- 3° is good, 2° is OK, 1° is bad, protic conditions
Predict the major product, and indicate the type of mechanism.
Predict the major product, and indicate the type of mechanism.
Saytzeff’s rule
Saytzeff’s rule: more substituted alkene is more thermodynamically stable (that is, the one with more carbon-carbon bonds).
What are the alkene isomers formed by this reaction?
Note: 20% are SN2
SN2 vs E2: The “GFP” Reaction Hierarchy
What is the rate law of an SN1 or E1 reaction?
What would the reaction energy profile look like?
Rate = K[R-X]
first order reaction (unimolecular)
K depends on the stability of carbocation
Here are two other examples of “carbocations.” Can you make any statement about their stability, relative to each other?
In an SN1 reaction, the racemic product is not exactly 50/50.
Why not?
SN1, E1 and SN2, E2
The “GFP” Hierarchy Revisted
- SN2 reactions: Require minimal steric interactions (and a good nucleophile)
- Good if the halide is methyl or 1o
- Fair if the halide is 2o
- Poor if the halide is 3o or if the nucleophile is bulky (e.g. tBuO– ) or poor
- E2 reactions: Require a strong base
- Good if the base is at least as strong as OH
- Fair if the base is between H2O and OH– in strength
- Poor if the base is weaker than H2O
- SN1 and E1: Require a stable carbocation
- Good if the halide is 3o
- Fair if the halide is 2o
- Poor if the halide is methyl or 1o
(Note that S N 1 and E1 reactions almost always occur together, although you can ensure elimination by treating an alcohol with concentrated mineral acid.)
Each of the following products can be synthesized in one step from an alkyl halide or alkyl sulfonate. Be sure to consider stereochemistry where relevant.
Each of the following products can be synthesized in one step from an alkyl halide or alkyl sulfonate. Be sure to consider stereochemistry where relevant.
Each of the following products can be synthesized in one step from an alkyl halide or alkyl sulfonate. Be sure to consider stereochemistry where relevant.
