Chapter 9: Substitution and Elimination Flashcards
1
Q
Which reactions have a carbocation intermediate?
A
E1 and SN1
2
Q
H2O can be the base in the E1 mechanism. This is because the E1 mechanism creates a carbocation, which can allow beta H’s to be deprotonated even with ___ bases.
A
weak
3
Q
The E2 Energy Diagram has only one hill (and no intermediates), because the base comes in at the ___ ___ as the LG leaves.
A
same time
4
Q
Rank the following nucleophiles from best to worst if the solvent is H2O or ROH:
I-, Br-, Cl-, F-
A
I- > Br- > Cl- > F-
5
Q
___ Mechanism:
primary LG needs a large base, i.e. KOtBu or LDA
secondary LG needs a strong base, i.e. OH- or OR-
tertiary LG needs a strong base, i.e. OH- or OR-
A
E2
6
Q
Anions going DOWN the periodic table are better nucleophiles if the solvent is ___ or ___.
A
H2O or ROH
7
Q
Rank the following nucleophiles from best to worst if the solvent is polar (No OH):
I-, Br-, Cl-, F-
A
F- > Cl- > Br- > I-
8
Q
SN2 needs a ___ nucleophile and a ___ base.
A
good nucleophile, poor base
9
Q
___ ___ is the opposite of Zaitsev’s Rule.
A
Hoffman’s Rule
10
Q
In substitution reactions, the LG leaves for a ___ to take its place.
A
nucleophile
11
Q
E2 Elimination needs the LG and H to be antiperiplanar. This means on the same ___ but opposite ___ of each other.
A
plane, sides
12
Q
Anions going UP the periodic table are better nucleophiles if the solvent is ___.
A
polar (No OH)
13
Q
poor base = Its conjugate acid has a pKa < ___ - ___.
A
pKa < 10 - 12
14
Q
SN1/E1 need a ___ nucleophile and a ___ base.
A
bad nucleophile, poor base
15
Q
E alkenes are favored over Z alkenes. Less steric ___.
A
clash
16
Q
The more ___ (lower pKa) the LG’s conjugate acid is, the better the LG.
A
acidic
17
Q
E2 needs a ___ nucleophile and a ___ base.
A
good nucleophile, good base
18
Q
Examples of a poor base:
A
RS-, RCO2-, X-, CN-, N3-
19
Q
E2 is a bimolecular reaction. rate = ___ ___ ___.
A
rate = k[Base][Elec]
20
Q
Perform ___ at lower temperatures with weak nucleophiles around.
A
SN1
21
Q
Polar aprotic solvents are good at stabilizing ___, not anions. This means the nucleophile will NOT H-bond, and will be free to react.
A
cations
22
Q
___ works with hindered, uncharged, N bases.
Example: DBu.
A
E2
23
Q
OH- is a ___ LG.
A
horrible
24
Q
___ ___: The more substituted alkene is favored as a product of elimination. This is because the transition states leading up to the product are lower in energy (hill is lower).
A
Zaitsev’s Rule
25
The more ___ the LG, the better the LG.
stable
26
\_\_\_ \_\_\_: The less substituted alkene of elimination is favored. This is due to the steric clash between the bulky base and the more substituted C.
Hoffman's Rule
27
\_\_\_ are better nucleophiles than neutral species.
i.e. HS- \> H2S
Anions
28
In ___ reactions, the LG leaves for a nucleophile to take its place.
substitution
29
SN1 and E1 usually produce a ___ of products.
mixture of products
30
The E2 Energy Diagram has ___ hill (transition state) and ___ intermediates.
one, no
31
The ___ the base, the more favorited the less substituted alkene is.
larger (bulkier)
32
Resonance stabilized primary LG's tend to be \_\_\_, as there are rarely beta H's present for \_\_\_.
SN1, E1
33
\_\_\_ has the same LG preferences as SN1.
E1
34
\_\_\_ - Loss of H and LG.
elimination
35
\_\_\_ works for primary and secondary LG's, but never for tertiary LG's.
SN2
36
Examples of bad nucleophiles which will NOT do SN2. Will probably do SN1 or E1 instead (need a carbocation to react):
H2O, ROH, Carboxylic Acid
37
SN1 is an unimolecular reaction. rate = ___ \_\_\_.
rate = k[Elec]
38
E1 is an unimolecular reaction. rate = ___ \_\_\_.
rate = k[Elec]
39
Examples of good nucleophiles (which are also good bases which will prefer to do E2 instead):
OH-, OR-, H2N-
40
SN1 loses ___ from SM -\> product.
stereochemistry
41
SN2/E2 are faster in polar aprotic solvents, because the nucleophile does not \_\_\_, so it can \_\_\_. The transtition states of ___ SN2 and E2 are stabilized.
H-bond, react, only
42
In elimination, both of the Cs next to the H and LG must be ___ hybridized.
sp3
43
E1 has the same LG preferences as \_\_\_.
SN1
44
SN2 doesn't work for tertiary LG's because it is too hard for the nucleophile to attack ___ of the LG. It is blocked by steric \_\_\_.
backside, clash
45
\_\_\_/\_\_\_ are faster in polar protic solvents.
SN1/E1
46
A ___ hydrogen is a hydrogen on a C next to the LG.
beta hydrogen
47
H2O, ROH, Carboxylic Acid are bad nucleophiles which will not do SN2. Will probably do SN1 or E1 instead (need a ___ to react):
carbocation
48
\_\_\_ needs a good nucleophile and a poor base.
SN2
49
SN2/E2 are faster in ___ \_\_\_ solvents.
polar aprotic solvents (polar but without OH)
50
The E2 Energy Diagram has one ___ (transition state), and no \_\_\_.
hill, intermediates
51
Zaitsev's Rule: The ___ substituted alkene is favored as a product of elimination. This is because the ___ \_\_\_ leading up to the product are ___ in energy (hill is lower).
more, transition states, lower
52
The more acidic (\_\_\_ pKa) the LG's conjugate acid is, the better the LG.
lower
53
\_\_\_ works for primary, secondary, and tertiary LG's.
E2
54
\_\_\_ needs a good nucleophile and a poor base.
SN2
55
\_\_\_ needs a bad nucleophile and a poor base.
SN1/E1
56
Some examples of a leaving group:
A Halide (I, Br, Cl), An Electrophile
57
A(n) ___ hydrogen is a hydrogen on the same C as the leaving group.
alpha hydrogen
58
SN2 needs a ___ nucleophile and a ___ base.
good, poor
59
H2O can be the base in the ___ mechanism.
E1
60
Elimination has 2 mechanisms:
E2, E1
61
Perform E1 at ___ temperatures with ___ around. Also ___ nucleophiles around.
higher, H2SO4 around, NO nucleophiles around
62
Perform SN1 usually at ___ temperatures with ___ nucleophiles around.
lower, weak nucleophiles around
63
Anions going DOWN the periodic table are ___ nucleophiles if the solvent is H2O or ROH.
better
64
H2O, ROH, Carboxylic Acid are bad nucleophiles which will NOT do SN2. Will probably do ___ or ___ instead (need a carbocation to react):
SN1, E1
65
Syn elimination CAN happen in E2 elimination.
Anti elimination is just much \_\_\_.
faster
66
H2O, ROH, Carboxylic Acid are bad nucleophiles which will NOT do \_\_\_. Will probably do SN1 or E1 instead (need a carbocation to react):
SN2
67
\_\_\_ alkenes are favored over ___ alkenes. Less steric clash.
E, Z
68
\_\_\_ ___ = Its conjugate acid has a pKa \< 10 - 12.
poor base
69
SN1/E1 are faster in polar protic solvents, because the ___ are stabilized.
carbocations
70
Substitution has two mechanisms:
SN2, SN1
71
SN1 ___ stereochemistry from SM -\> product.
loses
72
\_\_\_ works for tertiary and secondary LG's, but not for primary LG's, unless they are resonance stabilized.
E1
73
E2 works for \_\_\_, \_\_\_, and ___ LG's.
primary, secondary, and tertiary
74
\_\_\_ ___ - Reaction rate is dependent on the concentration of 2 molecules.
bimolecular reaction
75
You can make OH- a better LG by either adding ___ or \_\_\_.
H+, tosylate
76
When drawing Newman Projections to illustrate E2 Eliminations, ___ the LG and opposite H, and draw a ___ \_\_\_ down their plane to visually split up the resulting alkene.
erase, dotted line
77
SN1 works for tertiary and secondary LG's, but not for primary LG's, unless they are ___ \_\_\_.
resonance stabilized
78
When the nucleophile is adding during the SN2 mechanism, ___ occurs to the nucleophile being added.
inversion
79
Hoffman's Rule: The ___ substituted alkene of elimination is favored. This is due to the steric ___ between the bulky base and the more substituted C.
less, clash
80
E1 works for ___ and ___ LG's, but not for ___ LG's, unless they are resonance stabilized.
tertiary, secondary, primary
81
E2 Mechanism:
\_\_\_ LG needs a large base, i.e. KOtBu or LDA
\_\_\_ LG needs a strong base, i.e. OH- or OR-
\_\_\_ LG needs a strong base, i.e. OH- or OR-
primary, secondary, tertiary
82
\*IMPORTANT: The most stable conformation may not always be the most ___ conformation. This is true for both Newman Projections and Chair Conformations.
reactive
83
Which reactions produce an alkene?
E2 and E1
84
For E2 Elimination to happen to cyclohexane, the H and LG need to be \_\_\_.
anti-axial (one up, one down)
85
LG = ___ \_\_\_.
Leaving Group
86
SN1/E1 need bad nucleophiles and bad bases.
Examples:
H2O, ROH, Carboxylic Acid
87
Examples of good nucleophiles/good bases:
OH-, OR-, tert-butyl O-
88
E2 Mechanism:
primary LG needs a ___ base, i.e. KOtBu or LDA
secondary LG needs a ___ base, i.e. OH- or OR-
tertiary LG needs a ___ base, i.e. OH- or OR-
large, strong, strong
89
Anions going UP the periodic table are ___ nucleophiles if the solvent is polar (No OH).
better
90
Polar protic solvent means the solvent is ___ AND has a ___ group.
polar (delta negative somewhere), OH
91
\_\_\_ is a good LG (as a result of changing OH-). It has a pKa of 0.6.
tosylate
92
Rank the following nucleophiles from best to worst:
NH3, H2O, HF
NH3 \> H2O \> HF
93
The E2 Energy Diagram is similar to the ___ Energy Diagram.
SN2
94
\_\_\_ can be the base in the E1 mechanism.
H2O
95
\_\_\_ needs a strong base, ___ does NOT.
E2, E1
96
In elimination reactions, the LG leaves for a ___ to steal a \_\_\_, and for an ___ to form.
base, proton, alkene
97
Rank the following LG's from best to worst:
I-, Br-, Cl-, F-
I- \> Br- \> Cl- \> F-
98
E2 also works with \_\_\_, \_\_\_, ___ bases.
Example:
hindered, uncharged N bases
Example: DBu
99
Examples of good nucleophiles (which are actually good bases as well, so they will instead prefer to do E2).
OH-, OR-, H2N-
100
Leaving Group = \_\_\_.
LG
101
\_\_\_ ___ - Functional group/atom that makes off with the electrons from its old sigma bond.
Leaving Group
102
E2 needs a strong \_\_\_, E1 does NOT.
base
103
SN1 works for ___ and ___ LG's, but not for ___ LG's, unless they are resonance stabilized.
tertiary, secondary, primary
104
E alkenes are ___ over Z alkenes. Less steric clash.
favored
105
Perform ___ at higher temperatures with H2SO4 around. Also NO nucleophiles around.
E1
106
\_\_\_/\_\_\_ are faster in polar aprotic solvents.
SN2/E2
107
\_\_\_ isn't usually a LG (compared to other halides).
F-
108
Examples of a "bulky" base:
KOtBu (KO-tert-butyl), LDA (Li-N-2-iso-propyl)
109
Across the periodic table, the ___ of a nucleophile the molecule is.
worse
110
SN2 works for ___ and ___ LG's, but never for ___ LG's.
primary, secondary, tertiary
111
Examples of good nucleophile/good base are anions with pka \> ___ - \_\_\_.
pka \> 13 - 15
112
SN2 is a bimolecular reaction. rate = ___ \_\_\_ \_\_\_.
rate = k[Nuc][Elec]
113
E2 Elimination needs the LG and H to be antiperiplanar. This means on the ___ plane but ___ sides of each other.
same, opposite
114
In ___ reactions, the LG leaves for a base to steal a proton, and for an alkene to form.
elimination
115
Polar aprotic solvent means the solvent is ___ but DOES NOT have a ___ group.
polar (delta negative somewhere), OH
116
\_\_\_ ___ solvents are good at stabilizing cations, not anions. This means the nucleophile will NOT H-bond, and will be free to react.
polar aprotic
117
\_\_\_ works for tertiary and secondary LG's, but not for primary LG's, unless they are resonance stabilized.
SN1
118
\_\_\_ is a horrible LG, because its conjugate acid of H2O has a high pKa of 15.
OH-
119
In substitution reactions, the C next to the LG has to be ___ hybridized.
sp3
120
E2 Elimination needs the LG and H to be \_\_\_. This means on the same plane but opposite sides of each other.
antiperiplanar
121
SN1/E1 are faster in ___ \_\_\_ solvents.
polar protic solvents (polar solvents with OH)
122
OH-, OR-, H2N are good nucleophiles and good bases too which will prefer \_\_\_.
E2
123
\_\_\_ ___ - Reaction rate is dependent on the concentration of a single molecule.
unimolecular reaction
124
\_\_\_ needs a good nucleophile and a good base.
E2
125
Anions are ___ nucleophiles than neutral species.
i.e. HS- \> H2S
better
126
E1 works for tertiary and secondary LG's, but not for primary LG's, unless they are ___ \_\_\_.
resonance stabilized
