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Enolate chemistry (condensation and conjugate addition) Flashcards

1
Q

Factors that effect the acidity of alpha carbons of various carbonyl compounds

A

Inductive effects
resonance localization
increasing electronegativity of the atom

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2
Q

Esters are ___ acidic than aldehydes or ketones

A

Less

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3
Q

ENolates are most nucleophilic at the

A

carbon

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4
Q

Nearly all of the negative charge on an enolate is on

A

the oxygen

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5
Q

overlap first then

A

deprotonation

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6
Q

enolate formation requires that the C-H bond

A

align parallel to the carbonyl bond

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7
Q

aligned enolates are

A

acidic

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8
Q

non aligned enolates are

A

not acidic

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9
Q

SN2 reactions are

A

MO controlled

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10
Q

MO controlled

A

for the reaciton ot proceed there should be good overlap oof the nucleophile and the sigma C-X bond of the electrophilek

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11
Q

keto-enol tautomerization via enolates mechanism

A
  • Break C-H
  • Form O-H
    -Break C-O
  • Form C-C
  • Form O-H
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12
Q

Deuterium

A

An isotope of hydrogen with one proton and one neutron in the nucleus having an atomic weight of 2.014

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13
Q

deuterium labelling does no occur on

A

the beta carbons

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14
Q

deuterium labelling

A

using deuterium to replace all hydrogens on a structure to label it

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15
Q

racemate

A

a mixture containing equal amounts of two enantiomers

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16
Q

racemization

A

the chemical reaction resulting in the conversion of L amino acids to D amino acids for amino acid dating

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17
Q

chiral center

A

carbon with four different substitutions and a lack a plane of symmetry

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18
Q

one conquesunce of enolates being flat

A

chiral centers on alpha carbon undergo reacemization

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19
Q

why does racemization occur

A

due to the ability of things to add to the top or bottom of an enolate

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20
Q

epimerization

A

the reversible the interconversion of epimers

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21
Q

epimer

A

diasteromers that differ at only one chiral center

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22
Q

diasteromer

A

stereoisomers that are NOT mirror images thus they have different physical properties and optical rotations

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23
Q

enolate

A

intermediate
stabilized by resonance
enol & base— enolate

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24
Q

unsymmetrical ketones can form

A

two different enolates

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25
kinetic enolate
less substituted enolate formed quickly removal of an acidic alpha hydrogen image
26
kinetic control
a reaction in which the product ration is determined by the rate at which the products are formed
27
thermodynamic control
a reaction in which the product ratio is determined by the relative stability of the products
28
thermodynamic enolate
more substituted double bond higher activation energy more thermodynamically stable image
29
lithium di-isopropyl amide
image
30
LDA is
strong bulky base
31
how to make a kinetic enolate
selectively using a strong bulky base at a low temperature
32
how to make a thermodynamic enolate
can make selectively by reading with RO-/ ROH and setting up an equilibrium mixture of enolates
33
less substituted alpha carbon will
be deprotonated faster
34
which could make deprotonation harder
steric interactions
35
kinetic vs thermodynamic energy diagram
Image
36
which enolate is less stable
kinetic enolate
37
which enolate is more stable
thermodynamic enolate
38
halogenation of enolates in thermodynamic conditions
substitution at the most substituted carbon
39
halogenation of enolates in kinetic conditions
additional the least substituted carbon
40
alkylation of enolates in thermodynamic conditions
addition to the most substituted carbon
41
alkylation of enolates in kinetic conditions
addition to the least substituted carbon
42
alkylation is restricted to
primary, allylic, and benzylic electrophiles
43
aldol
contains both aldehyde and alcohol functional groups image
44
thermodynamic aldol formation requires
two steps and heat for the aldol condensation product
45
what can occur between ketones
aldol condensations
46
aldol addition mechanism of thermodynamic aldol
1) protonation (annotate formation) 2) elimination
47
thermodynamic aldol conditions lead to what kind of reaction
E1, because it is a conjugate base mechanism that occurs in multiple parts
48
an intramolecular aldol reaction is the second step to the
Robinson annulation rection
49
in a mixture of two aldehydes
a mixture of enolates will form
50
each enolate will react
with itself and another aldehyde
51
nonenolizable aldehyde
image
52
nonenolizable aldehyde + symmetric ketone
makes a cross aldol product
53
kinetic aldol conditions are predictable
high selectivity at low temperature under non-aqueous conditons
54
reagents for thermodynamic aldol condensation
NaOH & H20, NaOH & H20 & heat
55
reagents for kinetic aldol condensation
LDA, low temp, aldehyde, acid workup
56
ester enolate reaction is called
clauses condensation
57
clasien condensation
enolate ion of one ester acts as nucleophile attacking another ester
58
clausien condensation product
image
59
transesterfication is competitive with
the claisen
60
always match he ester group with
the base used
61
clauses condensation mechanism
1) deprotonation of ester alpha carbon to give an ester enolate 2) attack of enolate on a second equivalent ester 3) elimination of RO(-) - Acid base reaction of beta-keto ester prodyct 4) mils acid quench image
62
beta-keto ester
image
63
acid base reaction of beta- keto ester
the enolate is not basic enough to deprotonate starting ester so all the RO- is consumed
64
quenching of the reaction
image
65
crossed claisen product
joins two different esters
66
Dieckmann condensation
intramolecular clauses condensation
67
thermal decarboxylation
image
68
beta-keto carboxylic acid
image
69
most carboxylic acids do not
spontaneously lose CO2
70
beta keto acid ____ CO2 upon heating
loses
71
acetic acid, butanoic acid, alpha keto acid, and gamma keto acid all boil without
losing CO2
72
mechanism of decarboxylation of beta-ketoacids
cyclic concerted transition start that results in the formation of an enol intermediate
73
aceoacetic ester synthesis
image
74
maolonic ester synthesis
the process by which to convert a Masonic ester to a carboxylic acid
75
Malonic ester synthesis mechanism
1) CH3O- acts as a base to remove acidic proton and create enolate 2) Enolate acts as a nucleophile to attack alkyl halide in the Sn2 reaction 3) addition of aqueous acids leads to hydrolysis of esters into carboxylic acids 4) decarboxylation occurs to form enol and carbon dioxide
76
strong acids can cause
racemization
77
ketones are
chiral
78
enrols are
achiral
79
halogenation of ketones are slow withou
acid
80
halogenation of ketone bond breaking and formation
break C-C, form C-X, Form C-O, break O-H
81
acid catalyzed aldol condensation bond breaking and formation
Form C-O, Break C-C (pi) & form C-C, break C-O pi, Break O-H
82
acid catalyzed aldol condensation mechanism
1) keto enol tautomerimsm 2) protonation, form O-H 3) elimination, form C-O 4) deprotonation, break O-H
83
H20 is a. ____ leaving group than OH-
better
84
Mannich reaction
compounds capable of forming an enol react with imines from formaldehyde and a primary or secondary amine to yield beta-aminoalkyl carbonyl compounds
85
mannich reaction mechanism
image
86
mannich reaction reagents
O=CH2, CH3CH2NH2, HCl
87
conjugation addition
is the addition of a nucleophile to a pi-bond conjugated with electron withdrawing groups such as C=O, CN, or NO2
88
conjugates addition can also be called a
1,4 addition
89
Michael reaction gives
1,5 diketones
90
1,5 diketone
image
91
Michael reaciton mechanism
1) enolate formation 2) conjugate addition
92
Michael reaction
1,4 nucleophilic addition of enolate anion or enamine to a,b-unsaturated carbonyl (done over EtO- and EtOH) image
93
Robinson annulation
A reaction that collectively constituted the following reactions: ---> Michael addition followed by Intramolecular Aldol Condensation followed by Dehydration
94
Michael reaction reactants
NaOH, Ketone
95
Robinson annulation reactants
KOH, CH3OH, heat
96
robinson annulation mechanism
1. Michael addition 2. aldol reaction 3. condensation, E1CB

Organic Chem 2 (4 decks)

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