47 Cards in this Set
| Front | Back |
|---|---|
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What happens in SN2 mechanism?
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Nucleophile joins α carbon and leaving group leaves α carbon all in one step
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What happens in SN1 mechanism?
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Step 1: Leaving group leaves α carbon
Step 2: Nucleophile joins α carbon
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What happens in E2 mechanism?
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Base takes β hydrogen, π bond forms between α and β carbons, leaving group leaves carbon all in one step
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What happens in E1 mechanism?
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Step 1: leaving group leaves α carbon
Step 2: base takes β hydrogen, π bond forms between α and β carbons
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N
|
good nucleophile
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P
|
good nucleophile
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O
|
poor nucleophile
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S
|
good nucleophile
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Se
|
good nucleophile
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F
|
not a nucleophile
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Cl
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not a nucleophile
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Br
|
not a nucleophile
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I
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not a nucleophile
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N-
|
good nucleophile
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P-
|
good nucleophile
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O-
|
good nucleophile
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S-
|
good nucleophile
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Se-
|
good nucleophile
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F-
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not a nucleophile
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Cl-
|
good nucleophile
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Br-
|
good nucleophile
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I-
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good nucleophile
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CN-
|
good nucleophile (charge is on carbon and not nitrogen NC-)
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N3-
|
good nucleophile (azide)
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less electronegative (in terms of nucleophilicity)
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better nucleophile (willing to donate electrons)
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less electronegative (in terms of basicity)
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stronger base (willing to donate electrons)
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more electronegative (in terms of leaving group ability)
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better leaving group (willing to accept electrons)
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bigger atom (in terms of nucleophilicity)
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better nucleophile (big nucleophiles are less hindered by solvent, more polarizable)
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bigger atom (in terms of basicity)
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weaker base (large base can spread out and stabilize electron density)
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bigger atom (in terms of leaving group ability)
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better leaving group (big LG can spread out and stabilize electron density)
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1o Carbon/Strong Nucleophile
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SN2 Mechanism
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1o Carbon/Strong nucleophile & bulky base
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E2 mechanism
bulkybase: (CH3)3O-, R2N-
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2o Carbon/ Weak base/ protic solvent
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SN1/E1 mechanism; racemization of Sn1 products
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2o Carbon/ Weak base/ Strong nucleophile/ aprotic solvent
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SN2 mechanism (inversion of stereochemistry)
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2o Carbon/ Strong base
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E2 mechanism (most stable alkene preferred)
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3o Carbon/ Weak base-nucleophile
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SN1/E1 mechanisms (racemization)
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3o Carbon/ Strong base
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E2 mechanism (most stable preferred)
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Rate law: k[R-X]
Stereochemistry: racemization
Nucleophile: weak
Substrate: 3o>2o
Solvent: protic
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SN1 mechanism
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Rate law: k[R-X][Nuc]
Stereochemistry: inversion
Nucleophile: strong
Substrate: 1o>2o
Solvent: aprotic
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SN2
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What makes a good (strong) nucleophile?
|
-negative charge
-nucleophilicity decreases from left to right on pt
-nucleophilicity increases down pt
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I-, HS-, RS-, are all examples of
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very good nucleophiles
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Br-, HO-, RO-, CN-, N3-, are examples of
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good nucleophiles
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NH3, Cl-, F-, RCO2-, are examples of
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fair nucleophiles
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H2O & ROH are
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weak nucleophiles
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RCO2H is an
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very weak nucleophile
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CH3CN, DMF, DMSO, acetone are all examples of
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polar aprotic solvents preferred by SN2 mechanisms
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Acid catalyzed (H2SO4, H2PO4) resembles
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E1 mechanism
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CH 221: TEST 2