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19 Cards in this Set

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What is the reactivity in terms of methyl, primary, secondary, tertiary for SN2 reactions?
methyl > 1 > 2 > 3
What is the reactivity in terms of methyl, primary, secondary, tertiary for SN1 reactions?
3 > 2 > 1 > CH3
What is the RDS of an SN1 reaction?
Formation of the carbocation
What is the rate equation for an SN1 reaction? How can it be increased?
k*[haloalkanes]

Better leaving group-->quicker rate
Tertiary carbons are more stable Carbocations
Do SN1 reactions prefer a protic or an aprotic solvent? Why?
Protic

Stabilizes carbocation (less energy required to reach TS1)
Do SN2 reactions prefer a protic or an aprotic solvent? Why?
Aprotic

Protic solvents would stabilize charges on nucleophiles, thus requiring greater activation energy
Give examples of polar protic solvents.
ROH, H2O
Give examples of polar aprotic solvents.
DMSO, DMF, acetone
What kind of base does an E1 reaction require?
Weak base
What kind of base does an E2 reaction require?
Strong base
Describe the stereochemistry of SN1 reactions.
Since carbocation is sp2 (planar) then ROH can attack from either side and both enantiomers will be formed
Describe the reactivity in terms of methyl, primary, secondary, tertiary for E2 reactions.
3 > 2 > 1
What is the equation for rate in E2 reactions?
k*[haloalkanes]*[base]
What are the spatial requirements for bases and beta-hydrogens in E2 reactions?
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.
Describe how you would determine whether a reaction were SN1, SN2, E1 or E2.
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
What are some examples of weak bases that are good nucleophiles?
I-, Br-, Cl-, RS-, N3-, RC=O-, PR3
What are some examples of strong small bases?
-OH, RO-, NH2-, R2N-
What are some examples of strong bulky bases?
(CH3)3-CO-; Li+(CH3)3NC(CH3)3- (LDA)
What are some examples of weak nucleophiles?
H2O, ROH