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19 Cards in this Set
- Front
- Back
What is the reactivity in terms of methyl, primary, secondary, tertiary for SN2 reactions?
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methyl > 1 > 2 > 3
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What is the reactivity in terms of methyl, primary, secondary, tertiary for SN1 reactions?
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3 > 2 > 1 > CH3
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What is the RDS of an SN1 reaction?
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Formation of the carbocation
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What is the rate equation for an SN1 reaction? How can it be increased?
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k*[haloalkanes]
Better leaving group-->quicker rate Tertiary carbons are more stable Carbocations |
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Do SN1 reactions prefer a protic or an aprotic solvent? Why?
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Protic
Stabilizes carbocation (less energy required to reach TS1) |
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Do SN2 reactions prefer a protic or an aprotic solvent? Why?
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Aprotic
Protic solvents would stabilize charges on nucleophiles, thus requiring greater activation energy |
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Give examples of polar protic solvents.
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ROH, H2O
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Give examples of polar aprotic solvents.
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DMSO, DMF, acetone
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What kind of base does an E1 reaction require?
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Weak base
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What kind of base does an E2 reaction require?
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Strong base
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Describe the stereochemistry of SN1 reactions.
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Since carbocation is sp2 (planar) then ROH can attack from either side and both enantiomers will be formed
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Describe the reactivity in terms of methyl, primary, secondary, tertiary for E2 reactions.
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3 > 2 > 1
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What is the equation for rate in E2 reactions?
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k*[haloalkanes]*[base]
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What are the spatial requirements for bases and beta-hydrogens in E2 reactions?
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Beta-H pulled off by base must be anti to LG in Newman projection
In cyclohaloalkanes, X & beta-C must be trans-diaxial (If disubstituted and have bulky equitorial: E2 really slow or won't happen) In cyclopentanes (for example), H must be TRANS to halogen. |
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Describe how you would determine whether a reaction were SN1, SN2, E1 or E2.
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1) Look at haloalkane-C
If primary: SN2/E2 Look at nucleophile/base: If weak base, good nucleophile: SN2 If strong, small base: Primary UNbranched: SN2 Primary Branched: E2 Major If bulky, strong (hindered) base: E2 If secondary: Look at nuc/base Wk base, good nuc: SN2 Strong, small base: E2 (major) Strong bulky base: E2 Weak nuc: SN1, E1 Tertiary: E2, SN1, E1 Weak nuc: SN1/E1 Weak base, good nuc: SN1 (major) Strong base: E2 |
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What are some examples of weak bases that are good nucleophiles?
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I-, Br-, Cl-, RS-, N3-, RC=O-, PR3
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What are some examples of strong small bases?
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-OH, RO-, NH2-, R2N-
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What are some examples of strong bulky bases?
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(CH3)3-CO-; Li+(CH3)3NC(CH3)3- (LDA)
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What are some examples of weak nucleophiles?
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H2O, ROH
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