Reactions at sp Carbon: Leaving Groups Other Than...
Transcript of Reactions at sp Carbon: Leaving Groups Other Than...
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Reactions at sp3 Carbon: Leaving Groups Other Than Halogen
In this lesson we will reason by analogy to predict the outcome of new reactions (e.g., predictions of leaving group ability)
Breaking C–O bonds: –OH is a poor leaving group and does NOT directly participate in [SN1], [SN2], [E1] or [E2] reactions.
Why is –OH a poor leaving group?
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Why –OH is a Poor LG
-10.0
-9.0
15.7
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Protonation of an Alcohol Improves the Leaving Group Ability
___ _____________ ____________ LG Conjugate Acid pKa of
Conjugate Acid
H2O H3O+ -1.7
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Protonated Alcohol as a Leaving Group
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Reactions of Protonated Ethers [SN2] or [SN1] pathway depending on: • steric accessibility of nucleophile • stability of carbocation
If a stable carbocation can form, the reaction will follow the [SN1] pathway (otherwise [SN2])
[SN2]
[SN1]
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Examples - Nucleophilic Substitution
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Examples - Water Elimination (dehydration)