Chem II: 6-10 Flashcards
(184 cards)
1
Q
lewis acid
A
electron acceptor
tend to be electrophiles
vacant p orbitals that can accept electron pair
2
Q
lewis base
A
electron donor
tend to be nucleophiles
have lone pair of electrons that can be donated
3
Q
coordinate covalent bonds
A
covalent bonds in which both electrons in the bond came from the same starting atom (lewis base)
when lewis acid and bases interact
4
Q
amphoteric
A
molecules that can act as either bronsted lowry acids or bases
ex: water
5
Q
acid dissociatio constant
A
Ka
measures strength of an acid in solution
6
Q
dissociation of acid HA
A
HA = H+ + A-
7
Q
pKa of more acid molecules
A
smaller or negative pKa
8
Q
pKa of more basic molecules
A
larger pKa
9
Q
main functional groups that act as acids
A
alcohols, aldehydes and ketones (at alpha carbon), carboxylic acids and most derivatives
10
Q
main functional groups that act as bases
A
amines and amides
11
Q
nucleophiles
A
have either lone pairs or pi bonds that can form new bonds to electrophiles
tend to be good bases
strength based on rate of rxn - kinetic property
12
Q
the more basic the nucleophile, the more ___ it is
A
reactive
13
Q
factors that contribute to nucleophilicity
A
- charge: inc with inc electron density (more neg charge)
- electronegativity: dec as electroneg inc (bc less likely to share electron density)
- steric hindrance: dec as molecule is bulkier
- solvent: protoic solvents hinder
14
Q
electrophile
A
- electron loving species with a positive charge or positively polarized atom
- accepts an electron pair when forming new bonds with a nucleophile
- usually act as lewis acids
- better leaving groups make it more likely that a rxn will happen
15
Q
electrophilicity of carboxilic acid derivatives
A
most reactive to least: anhydrides, carboxilic acids, esters, amides
16
Q
leaving groups
A
- retain the electrons after heterolysis
- stabilize extra electrons
- weak bases and conjugate bases of strong acids are GLGs
17
Q
heterolytic rxns
A
- opposite of coordinate covalent bond formation
- a bond is broken and both electrons are given to one of the 2 products
18
Q
nucleophilic subsitution reactions
A
SN1 and SN2
nucleophile forms a bond with a substrate carbon and LG leaves
19
Q
SN1 steps
A
- LG leaves, making a carbocation: rate limiting step
- nucleophile attacks carbocation
20
Q
SN1
A
- first order reaction
- loss of leaving group to make carbocation intermediate then nucl attack
- produce usually racemic mixture
- varied sterochemsitry bc nucl can attack C+ from either side
- most likely to occur on tertiary carbons (C+ easily stabilized)
21
Q
SN2
A
- one step -> concerted rxn
- backside attack
- inversion
- stereospecific reaction
- 1° and 2° NOT 3° carbons
22
Q
stereospecific reaction
A
configuration of reactant determines the configuration of the product due to the reaction mechanism
23
Q
SN2 steps
A
24
Q
how must the nucleophile and LG be related in order for a substitution reaction to proceed?
A
a substitution reaction will proceed when the nucleophile is a stronger base (more reactive) than the LG
25
what trends increase electrophilicity
greater positive charge snd better LGs --\> make reaction more likely to proceed
26
features of GLGs
stabilize electra electrons
weak bases, resonance stabilization, electron withdrawing groups
27
chemoselectivity
preferential reaction of one function group in the presence of other functional groups
28
steric hindrance
prevention of reactions at a particular location within a molecule due to the size of substituent groups
29
SN1 vs SN2
mechanism
* SN2: single step, no intermediate, one transition state,
* lvg group departs **as** nucl adds (concerted)
* SN1: not single step, C+ intermediate (**rate determining step**)
* lvg grp leaves first --\> C+ --\> then nucl adds
30
SN1 vs SN2
kinetics
* SN2: bimolecular
* rate = k [nucl][RX]
* SN1: unimolecular
* rate = k [RX]
31
SN1 vs SN2
sterochemistry
* SN2: every substitution goes with **inversion** at carbon undergoing substitution
* SN1: **mix** of inversion and retention
* loss of configuration
32
SN1 vs SN2
electrophile scope
SN2:
* Best: Me-X
* Good: 1° R-X
* Possible: 2° R-X
* **NO**: 3° R-X
SN1:
* Best: 3° R-X
* Possible: 2° R-X
* Unlikely: 1° R-X
* **NO:** Me-X
33
SN1 vs SN2
solvent effect
* SN2: more polar solvent = rate inc or dec
* SN1: more polar solvent = inc rate
34
protection o fLGs
can temporarily maks a LG with sterically bulky group during synthesis
35
what are the 2 reactive centers of carbonyl containing compounds
carbonyl carbon -\> electrophilic
alpha hydrogens -\> acidic
36
what to consider for sterospecificity
consider whether configuration of reactant necessarily leads to specific configuration
37
what to consider for stereoselectivity
* if more than one product, major product will be determined by differences in strain or stability
* more striained molecules (with significant angle, torsional, or nonbonded strain) are less likely to form
* products with conjugation (alternating single and multiple bonds) are significant more stable
38
steps to problem solving
1. nomenclature
2. identify functional groups
1. good nucleophiles, electrophiles, LGs, acid/bases
3. identify other reagents
1. same qs ^
4. identify most reactive functional groups
1. more oxidized arbons tend to be more reactive to both nucleo-electro rxns and redox rxns
5. identify first step of rxn
6. consider stereospecificity/stereoselectivity
39
alpha hydrogen
connected to alpha carbon
easily lost hydrogens --\> acidic --\> resonance stabilized conjugate base
40
alpha carbon
adjacent to carbonyl carbon
41
carbanion
molecule with negatively charged atom
42
alpha hydrogens of ketones vs aldehydes
alpha hydrogens slightly less acidic than aldehydes because of electron donating property of additional alkyl group in ketone --\> destabilizes carbanion
43
aldehyde vs ketone reactivity
aldehydes slightly more reactive to nucleophiles than ketones because of steric hindrance in ketone --\> makes higher energy, crowded intermediate
44
why are the alpha hydrogens of aldehydes and ketones acidic?
* inductive effects
* electronegative oxygen pulls electron density from C-H bond, weakening it
* resonance effects
* once deprotonated, resonance stabilization of neg charge between alpha carbon, carbonyl carbon, and electron withdrawing carbonyl oxygen increases stability
45
tautomers
constitutional isomers that differ from each other in the placement of a proton and the position of a double bond
46
enol
C-C double bond and alcohol
acidity at alpha carbon
47
enolate
conjugate base of enol
acidity at alpha carbon
48
enolization/tautomerization
process of interconverting from keto to enol tautomer
49
solutions to form enolate carbanion
common strong bases: OH, LDA, KH
50
michael addition
enolate attacks alpha beta unsaturated carbonyl
formation of new C-C bond
51
michael addition
electrophile
alpha beta unsat carbonyl
52
michael addition
nucleophile/michael acceptor
enol/enolate
53
michael addition
mechanism
54
kinetically controlled product
* formed more rapidly
* less stable
* favored with:
* rapid irreversible reactions
* lower temperatures
* strong, sterically hindered base
55
kinetic enolate
double bond on less substituted alpha carbon
56
thermodynamically controlled product
* formed more slowly
* more stable
* favored with:
* higher temperatures
* slow reversible reactions
* weaker, smaller bases
57
thermodynamic enolate
double bond with more substituted alpha carbon
58
enamination
59
imine
60
enamine
tautomers of imines
61
which tautomer of aldehydes and ketones is thermodynamically favored: keto or enol?
keto
62
aldol condensation
adding aldehyde/ketone to carbonyl of another
aldehyde or ketone acts as both electrophile and nucleophile
end result: C-C bond
63
aldol condensation
mechanism
64
aldol
molecule that condanes an aldhehyde and alcohol functional groups
65
condensation reaction
two molecules are joined with tthe loss of a small molecule
66
dehydration raction
water is lost
67
retro aldol reaction
aqueous base added and heat is applied
break bond between alpha and beta carbon of carbonyl
68
If you started with a chiral α-carbon, could tautomerization affect its chirality?
(A) Yes, because interconverting between the keto and enol forms can completely change the chirality to the opposite orientation (S-\>R).
(B) Yes, because interconverting between the keto and enol forms can create a racemic mixture of the α-carbon's chirality center.
(C) No, because tautomerization is focused on the carbonyl carbon and cannot effect the α-carbon.
(D) No, because after any number of tautomerizations, the α-carbon will still retain its chirality.
(B) Yes, because interconverting between the keto and enol forms can create a racemic mixture of the α-carbon's chirality center.
This effect is actually called α-racemization.
69
In an enolate formation reaction, the pKa of the α-hydrogen is 16.42 and the pKa of the resulting alcohol is 19.89. What is the Keq for this reaction? Will this reaction favor products or reactants?
(A) 29,512
(B) 2,951.2
(C) 295.12
(D) 29.512
(B) 2,951.2
```
pKeq = pKa(r) - pKa(p)
pKeq = 16.42 - 19.89
pKeq = -3.47
```
```
Keq = 10^-pKeq
Keq = 10^3.47
Keq = approx. 4700 (actual: 2,951.2) Thus, products are HIGHLY favored.
```
70
Why is the pKa of a ketone higher than an aldehyde?
The Methyl group donates electron density toward the carbonyl group, making it less willing to accept electrons from the α-hydrogen.
71
Draw the energy diagram a reaction as it goes to the thermodynamic product and as it goes to the kinetic product.
72
Why is the thermodynamic enolate more stable?
The thermodynamic enolate is more stable because it is more substituted.
73
The kinetic product is favored by a ________ base at _______ temperatures. Why is this the case?
(A) Bulky, High
(B) Bulky, Low
(C) Small, High
(D) Small, Low
(B) Bulky, Low
The kinetic product is favored by a bulky base at low temperatures. This is because the kinetic product is not sterically hindered, which results in a low activation energy; thus you only need a low temperature.
74
The thermodynamic product is favored by a ________ base at ________ temperatures. Why is this the case?
(A) Bulky, High
(B) Bulky, Low
(C) Small, High
(D) Small, Low
(C) Small, High
## Footnote
The thermodynamic product is favored by a small base at high temperatures. This is because the thermodynamic product is sterically hindered, which results in a high activation energy; thus you need a high temperature to overcome this.
75
Draw the Aldol Addition Reaction Mechanism in the presence of base.
76
Draw the Retro-Aldol Reaction Mechanism.
77
a
78
b
79
d
80
d
81
d
82
c
83
d
84
c
85
d
86
nomenclature
when aldehyde is attached to a ring
-carbaldehyde
87
dipole moment of carbonyl carbon of aldehydes and ketones
oxygen pulls electrons away from carbon --\> makes carbon electrophilic and good target for nucleophiles
88
pyridinium chlorochromate (PCC)
used to make aldehydes thourgh partial oxidation of primary alcohol
89
name the compounds
butanone, propanal
90
given an alkane, an aldehyde, and an alcohol with equal length carbon chains, which will have the highest BP? why?
lowest to highest BP: alkane, aldehyde, alcohol
BP of aldehyde is elevated by its dipole, but the BP of alcohol is further elevated by hydrogen bonding
91
method for forming aldehyde
oxidation of primary alcohols
using weaker and anhydrous oxidizing agents like PCC (otherwise will fully oxidize to carboxylic acid)
92
method for forming ketones
oxidation of secondary alcohols
using reagents suchas sodium, potassium dichromate salts, CrO3, PCC
93
carbonyl carbon during reactions
electrophile -\> ripe for nucleophilic attack
* when nucleophile attacks, forms covalent bond to carbon -\> breaks pi bond in carbonyl
* electrons from pi bond pushed onto oxygen
* broken pi bond forms tetrahedral intermediate
* if no GLG
* carbonyl does not reform
* O- accepts proton from solvent to form hydroxyl group -\> alcohol
* if GLG present
* carbonyl double bond can reform
94
nucleophilic addition reaction mechanism
95
hydration reaction
with aldehydes and ketone
mechanism
form geminal diols
nucleophilic oxygen in water attacks electrophilic carbonyl carbon
96
hemiacetal structure
97
acetal structure
98
hemiacetal formation
mechanism
one equiv of alc is added to aldehyde or ketone
99
acetal and ketal formation
mechanism
two equiv of alcohol added
100
imine formation
mechanism
101
HCN
hydrogen cyanide
classic nucleophile
102
cyanohydrin
structure
103
cyanohydrin formation
mechanism
104
when HCN reacts with an aldehyde or ketone, what functional group is produced? is the product stable?
cyanohydrin is produced, which is a stable product
105
Draw 4-bromopentanal.
106
Draw Cyclohexane Carbaldehyde
107
Draw 1,5-pentanedial
108
Draw (E)-4-hexen-2-one.
109
Draw 2-methylcyclohexanone.
110
Which of the following oxidizing agents would be able to convert an aldehyde to an alcohol?
(A) PCC
(B) PDC
(C) HIO4 (Periodic acid)
(D) None of the above
(D) None of the above
For the reaction in the question to occur, there must be a reducing agent! PCC, PDC and HIO4 are all weak oxidizing agents that can turn an alcohol into an aldehyde/ketone.
111
Order the following functional groups in order of increasing boiling point:
I. Isopropyl Alcohol
II. Acetone
III. Propane
IV. Propanal
(A) I \< II \< III \< IV
(B) IV \< III \< II \< I
(C) IV \< II \< III \< I
(D) III \< IV \< II \< I
(D) III \< IV \< II \< I
In order of increasing boiling point: Propane (London Dispersion Forces only) \< Propanal (Dipole-dipole Interactions) \< Acetone (Dipole-dipole Interactions) \< Isopropyl Alcohol (Hydrogen Bonding)
112
Why do Aldehydes have lower boiling points than Ketones?
The alkyl groups are electron-donating, which will make the carbons have a greater partial-positive charge and the oxgen have a greater partial-negative charge.
113
Functional groups with Nitrogen can be very good nucleophiles, and when added to carbonyls, can form either imines or enamines. Draw the general structure of both imines and enamines.
114
Draw the Hemiacetal Formation Reaction Mechanism in water.
115
Draw the Hemiacetal Formation Reaction Mechanisms in base.
116
Which of the following will shift the acetal mechanism to the right toward more product?
I. Add water
II. Increase amount of Aldehyde
III. Increase amount of Alcohol
(A) I Only
(B) I and II Only
(C) II and III Only
(D) I and III Only
(C) II and III Only
The following will shift the acetal mechanism to the right toward more product: REMOVING water (a product), increasing amount of aldehyde (a reactant), increasing amount of alcohol (also a reactant).
117
One final key nucleophilic additions to carbonyls is with Cyanide. Draw out the mechanism for creating a cyanohydrin with acid.
118
b
119
a
120
c
121
b
122
d
123
c
124
b
125
how oxidized are aldehydes in comparison to carboxylic acids and alcohols?
more oxidized than alcohols and less oxidized than carboxylic acids
126
oxidation of aldehydes with something stronger than PCC forms...
form carboxylic acids
127
oxidation reagents for making aldehydes to carboxylic acids
potassium permanganate (KMnO4), chromium trioxide (CrO3), silver (I) oxide (Ag2O), hydrogen peroxide (H2O2)
128
reduction of aldehydes and ketones forms...
alcohols
129
reduction reagents from making aldehydes and ketones into alcohol
hydride reagents
LiAlH4, NaBH4
130
what functional group is formed when an aldehyde is oxidized? what are some common oxidizing agents that assist this reaction?
functional group: carboxylic acid
common oxidizing agents: KMnO4, CrO3, Ag2O, H2O2
131
what functional group is formed when aldehydes and ketones are reduced? what are some common oxidizing agents that assist this reaction?
functional group: alcohol
common reducing agents: LiAlH4, NaBH4
132
A chemistry student reacts butanone with PCC and KMnO4. What are the expected products of each reaction?
Butanone reacts with neither because ketones cannot be oxidized with common oxidizing reagent.
133
A chemistry student reacts butanal with PCC and KMnO4. What are the expected products of each reaction?
Butanal is oxidized by KMnO4 to form butanoic acid, but does not react with PCC, which is not a strong enough oxidant.
134
Your lab instructor asks you to reduce the carboxylic acid of a compound that contains both a carboxylic acid and a ketone. You run the reaction, but end up with two alcohol groups instead of an alcohol group and a ketone. What important step did you forget?
You forgot to protect your ketone group by turning it into an ketal. A ketal would have been resistant to the reducing agent.
135
An Enamine is composed of what two functional groups?
(A) Amide, Alkane
(B) Amide, Alkene
(C) Amine, Alkane
(D) Amine, Alkene
(D) Amine, Alkene
An Enamine is composed of an amine and an alkene functional group.
136
Draw the reaction mechanism for Sodium Borohydride (NaBH4) reacting with an aldehyde.
Why would this reaction not work as well with NaH?
NOTE: A similar mechanism is seen with LiAlH4.
The previous reaction would not work well with H- because H- is a good base, but not a good Nucleophile.
137
True or false? The strong reducing agents often work by adding a proton (H+) to a carbonyl.
False. the strong reducing agents often work by adding a HYDRIDE (H-) to the carbonyl.
138
Why does Lithium Aluminum Hydride (LiAlH4) need to be used in dry conditions whereas Sodium Borohydride (NaBH4) does not?
LiAlH4 will react with water to form H2 gas, which could be dangerous. NaBH4 is not as reactive, so it isn't an issue.
139
Why is Sodium Borohydride (NaBH4) less reactive than Lithium Aluminum Hydride (LiAlH4)?
Aluminum is less electronegative than Boron, resulting in greater electron density on the hydrogen for LiAlH4 (larger dipole moment).
140
LiAlH4 is strong enough to reduce all of the following functional groups, however, NaBH4 is only strong enough to reduce:
I. Aldehydes
II. Ketones
III. Carboxylic Acids
IV. Esters
(A) I Only
(B) II Only
(C) I and II Only
(D) I, II, III, and IV
(C) I and II Only
NaBH4 is strong enough to reduce Aldehydes and Ketones but not Carboxylic Acids and Esters.
141
a
142
c
143
d
144
d
145
d
146
phenol
aromatic ring
147
phenol nomenclature
two groups on adjacent carbons: ortho-, o-
two groups separated by a carbon: meta-, m-
two groups on opposite sides of the ring: para-, p-
148
alcohol physical properties
capable of intermolecular hydrogen bonding --\> higher MP and BP, increased solubility in water
149
phenol physical properties
* aromatic ring --\> resonance stabilized -\> more acidic than other alcohols
* hydrogen bonding -\> higher MP and BP
* slightly soluble in water
150
electron withdrawing groups ____ acidity
increase
151
electron donating groups ____ acidity
decrease
152
presence of more alkyl groups in nonaromatic alcohols produces ____ acidic molecules bc
less
alkyl groups donate electron density -\> destabilize negative charge, stabilize positive charge
153
\_\_\_\_\_ alcohols can be oxidized to aldehydes using PCC
primary
154
jones oxidation
oxidizes primary alcohols to carboxyilic acids and secondary alcohols to ketons
reagent: CrO3, H2SO4
155
mesylate
compounds containing SO3CH3
156
tosylates
contain functional group -SO3C6H4CH3
157
mesylates and tosylates as protecting groups
protect when we do not want alcohols to react
will not react with other agents that would attack alcohols, especially oxidizing reagents
158
acetal
primary carbons with two -OR groups and a hydrogen atom
159
ketal
secondary carbons with two -OR groups
160
acetals and ketals as protecting groups
protect carbonyls from reacting with strong reducing agents like LiAlH4
161
what will happen to primary alcohols in the presence of strong oxidizing agents?
completely oxidized to carboxylic acids
162
what will happen to secondary alcohols in the presence of strong oxidizing agents?
can only be oxidized to ketones
163
what is the product when 1-butanol is treated with PCC?
aldehyde 1-butanal
164
what is the product when 1-butanol is treated with chromium trioxide?
carboxylic acid butanoic acid
165
how can aldehydes or ketones be protected using alcohols
can be reacted with 2 equiv of alc oh a diol to form an acetal or ketal
can be reverted back to carbonyl by catalytic acid
166
quinone
resonance stabilized electrophiles
used in ETC
167
treatment of phenols with oxidizing agents produces...
quinones
168
examples of biochemically relevant quinones
vitamin K1 (phylloquinone) and vitamin K2 (menaquinone
169
hydroxyquinone
ring with 2 carbonyls and variable number of hydroxyl groups
behave like quinones with EDGs
slightly less electrophilic than quinones (still quite reactive)
170
hydroquinone
benzene ring with 2 hydroxyl groups
171
ubiquinone
aka coenzyme Q
* vital electron carrie associated with Complexes I, II, and II of the ETC
* can be reduced to ubiquinol upon acceptance of electrons
* lipid soluble bc of long alkyl chain
172
how are quinones generally produced?
oxidation of phenols
173
how are hydroxyquinones produced?
oxidation of quinones
174
what chemical properties of ubiquinone allow it to carry out its biological functions?
* conjugated rings -\> stabilize molecule when accepting electrons
* long alkyl chain -\> lipid solubility -\> allows molecule to function in phospholipid bilayer
175
Draw 1,4-Benzenediol (hydroquinone).
176
Draw 2-Bromophenol.
177
The Jones Reagent consists of Na2Cr2O7, H2SO4, and H2O. When these compounds are mixed they result in the formation of Chromic Acid. Draw the structure of Chromic Acid.
178
True or False? CrO3, H3O+, and Acetone may also be mixed to form Chromic Acid.
True. CrO3, H3O+, and Acetone may also be mixed to form Chromic Acid.
179
Draw the structure of Pyridinium Chlorochromate (PCC).
180
Draw the SN2 reaction of HBr reacting with an alcohol.
181
Draw the SN1 reaction of HBr reacting with an alcohol.
182
Draw the reduction of Benzoquinone to Hydroquinone.
183
b
184
b
