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Organic Chemistry > Organic Chemistry > Flashcards

Organic Chemistry Flashcards

1
Q

What is a synthetic equivalent?

A

Reagent that behaves like a synthon- valid synthon (fragments, usually anions and cations that result from a disconnection- might not be possible)

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2
Q

FGA?

A

Functional Group Addition- addition of a functional group to facilitate a disconnection

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3
Q

RSA

A

Retrosynthetic analysis- process of breaking down the TM by disconnections and FGIs

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4
Q

Retrosynthetic arrow?

A

3D arrow

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5
Q

Good leaving groups and what do they stem from?

A

Halides, OTs (tosylate), OMs (mesylate)

all stem from alcohols

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6
Q

What do you need to react with alcohol FG to get good leaving group- OTs, OMs

A

TsCl, py

MsCl, py

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7
Q

What do you need to react with an alcohol FG to get good leaving group I and Br and which is more reactive?

A

HI or Ph3, I2
PBr3
I is more reactive

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8
Q

Why do you not need to generate an alkoxides with acid chlorides?
Draw acid chloride

A

They are such reactive electrophiles- don’t need to generate alkoxide
py added to react with HCL produced

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9
Q

pKa of py and what used for

A

5.23

mop up HCL

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10
Q

How do you make acid chlorides and anhydrides?

A

Carboxylic acids

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11
Q

What are usually made from acid chlorides and anhydrides

A

Esters and Amides

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12
Q

Why is alkylation of amines difficult to control?

What will oppose this

A

Each alkyl group added makes the nitrogen more nucleophilic as alkyl groups are inductively electron releasing. Therefore, the product is more reactive than the SM and will compete with the unreactive SM for the remaining alkyl halide.

steric effects- but clean alkylation is difficult and a mixture of products can result

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13
Q

Solution to overalkylation of primary amines?

A

do not alkylate ammonia
use two step method
e.g. NaN3 then H2, Pd-C to get from R-I to R-NH2

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14
Q

Good way to make primary, secondary or tertiary amines?

A

Reduction of amides

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15
Q

What is reductive animation?

A

Conversion of Aldehydes and ketones into amines
2 FGIs
Retrosynthetically: Amine –> Immine –> Aldehyde

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16
Q

How do you make an acetal

2 group C-X disconnection, 1,1- Difunctional compounds

A

Aldehyde and alcohol with H+ and heat

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17
Q

How do you make Cyanohydrins
draw Cyanohydrin
2 group C-X disconnection, 1,1- Difunctional compounds

A

Aldehydes OR Ketones and HCN

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18
Q

Describe 1,2-Difunctional Compound

A

heteroatoms on adjacent carbon atoms

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19
Q

Why are epoxides reactive electrophiles

draw one

A

Ring strain on three membered ring means that they readily ring-open when attacked by a nucleophile

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20
Q

how to synthesis an epoxide?

A

treatment of alkene with mCPBA- stereospecific

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21
Q

1,2 disconnections- what do carbonyls facilitate

A

disconnections elsewhere in the molecule- heteroatoms on the 2-carbon are readily disconnected
presence of carbonyl groups increases reactivity

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22
Q

how to achieve clean alpha-halogenation of esters and ketones

A

acidic conditions

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23
Q

1,3 Difunctional compounds

A

1,3- relationship with a carbonyl- readily disconnected - to unsaturated bond

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24
Q

why is the Grignard reagent not compatible with the free OH group?

A

The reactive, highly basic organometallic would simply protonate to give the alkene- need to mask the alcohol with a protecting group

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25
Q

what do you need for 1,4-addition

A

soft organometallic

inclusion of Cu(1) salt generates the soft organocopper species from the Grignard

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26
Q

how to identify the best RSA?

A

Max simplification
disconnect somewhere around the middle
disconnect at a branch point

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27
Q

Why is it better to disconnect at a branch point?

A

Will give straight chain fragments and these are more likely to be readily available than branched fragments

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28
Q

pKa aliphatic nitro compound?

what does this tell you?

A

CH3NO2 around 10

readily deprotonated- more so than acidic aldehydes and ketones

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29
Q

What is the Henry reaction

A

the nitro aldol reaction

nitroalkanes undergo condensation with aldehydes and ketones

nitro compound is much more acidic than the carbonyl compound so is deprotonated preferentially- there isn’t a competing self condensation to worry about

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30
Q

What is the Nef reaction and why is it important

A

reaction of nitroalkane with TiCl3 (aq)–> converts nitroalkane into a carbonyl

means that nitroalkanes can function as acyl anion equivalents

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31
Q

Problem with disconnecting the bond alpha, beta to a carbonyl— want to go to enolate but

A

must be carried out at low temperatures (-78C) + strong base (LDA), excess base so no unreacted ketone to condense with enolate in an ALDOL reaction

Regioselectivity of deprotonation- if have acidic protons on either side of the carbonyl group then will be difficult to control which enolate forms

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32
Q

How to get around the problems of Regioselectivity and Aldol with enolates

A

Use beta-keto ester activating group- achieve unambiguous enolisation
can then be removed by hydrolysis and decarboxylation

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33
Q

How to solve problems of carbonyl condensations

A

choice of conditions
use of an activating group to control site of enolisation
use an enamine rather than an enolate

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34
Q

Michael Addition

A

1,5-Dicarbonyl

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35
Q

Robinson Annelation

A

intermolecular condensation of 1,5-dicarbonyls

good strategy for 6 membered ring synthesis

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36
Q

how do you make a 1,2-diol

A

alkene dihydroxylation

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37
Q

Reaction conditions for Dieckmann cyclisation

A

base, NaOET, EtOH

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38
Q

What is the pinacol rearrangement

A

Rearrangement of substituted 1,2-diols to form ketones. The diol is a pinacol
H+ catalyst

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39
Q

Stages of the Pinacol Rearrangement

A

1) Treatment with acid- protonation
2) Loss of water generates carbocation which undergoes 1,2-alkyl shift
3) resulting CC stab. by delocalisation of the lone pair on the O- mesomeric stabilisation- sufficient to drive reaction forward
4) elimination of a proton (regenerates acid)
5) formation of ketone

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40
Q

which step in the pinacol rearrangement is ireversible

A

1,2-alkyl shift

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41
Q

Why, in the Pinacol rearrangement, is an At migration with sub X that is ED, more favourable than a Ph

A

The intermediate bridged transition state is lowered in energy by the electron donating unit
most stable cation formed
draw diagram

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42
Q

why do allyl anions adopt sp2 hybridisation

A

stabilization achieved from effective overlap of adjacent p-orbitals

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43
Q

conditions and steps for enolate alkylation

A

LDA, THF, -78C

Addition material with LG, warming

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44
Q

electrophile for clasien reaction

product

A

ester

1,3-dicarbonyls

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45
Q

electrophile for robinson annulation

A

alpha beta- saturated ketone

46
Q

How to promote O Alkylation

A

Oxygen is a hard nucleophile- use of sulphates

47
Q

How to promote C Alkylation

A

Carbon is a soft nuclephile- larger coefficient of the HOMO

48
Q

When is the enol the preferred tautomeric form?

A

Intramolecular H-bond- gains stab.

Conjugation

Aromatic

49
Q

Difference between enol and enolate

A

enol formed by acid- not charges

enolate formed by base- negative charge on oxygen

50
Q

pKa of a dicarbonyl

A

5

51
Q

why are carb. acids an exception to pkas

A

most acidic proton is on the OH, not the alpha proton

52
Q

If a base has a large pKa then…

A

it’s conjugate acid is poor and wants it’s proton back

53
Q

Strategy 1 for forming enolates

A

Use a very strong base to perform rapid and complete deprotonation of carbonyl then add desired electrophile

54
Q

Why is LDA good

A

non- nucleophilic
Li+ counter ions can be useful
very strong base

55
Q

Forming enolates - strategy 2

A

weak base
electrophile much more electrophilic than the canbonyl starting material

Alhehydes are ridiculously strong electrophiles

56
Q

Kinetic enolate

A 
Lower Eact
Faster to Form
Higher energy enolate
least hindered position of ketone
irreversible 
LDA
-78C
57
Q

TDY enolate

A 
Higher Eact
slower to form
more stable
Weak base NaOEt
room temp- access to TDY enolate
reversible
58
Q

How do beta ketoesters fors selective enolates

A

Extra ester group dramatically decreases pKa at desired carbon
ester can be removed by decarboxylation

59
Q

Nef Reaction

why important

A

treatment of nitroalkane with TiCl3 (aq) forms carbonyl

means nitroalkanes can function os acyl anion equivalents

Umplong

60
Q

Conditions for Diekmann

A

NaOEt

EtOH

61
Q

k=
K=
p=
other one x=

A

Rate constant
Equib. constant
reaction constant
sub. constant

62
Q

Condition for formation of carbocations

A

AgSbF6

addition of silver salt or Lewis acid (SbF6)

63
Q

How can we provide evidence about the mechanism of a reaction

A 
measuring reaction kinetics
isotopic labelling
isolating or detecting intermediates
crossover experiments
stereochemical studies
64
Q

The Steady State Approximation

A

method used to derive the rate law, based on the assumption that one intermediate in a reaction mechanism is consumed as quickly as it is generated- conc. stays the same for the duration of the reaction

65
Q

a successful reaction

A

energy of collision
specific orientation
prob. entropy. limitation on collision being successful

66
Q

Diels-Alder reactions

A

traps benzynes

67
Q

Crossiver experiments

A

indicate wether the reaction proceeds in an intermolecular or intramolecular fashion

68
Q

The HP

A

a transition state will most closely resemble the species nearest to it in energy

69
Q

HP Assumes for exothermic reaction

A

TS resembles the SM- early TS

70
Q

HP assumes for an endothermic reaction

A

TS resembles the product- TS is late

71
Q

+ve value of sigma x

A

x is acid strengthening, lower pKa than benzoic acid, X is electron withdrawing

72
Q

-ve value of sigma x

A

x is acid weakening, higher pKa than benzoic acid, X is electron donating

73
Q

If plot log Ka against sigma x get…

A

straight line

get one form of Hammett eq.

74
Q

diff in Hammett eq for squib and non equip reactions

A

equip uses equip constant- K

Non equip uses rate constant- k

75
Q

PKIE

A

CH/D bond is broken in the reaction

replacing H/D does not alter the mechanism of the reaction

76
Q

v=o vibrational energy level

A

ZPEL

different for H and D due to differences in masses

77
Q

How can we work out ZPVE?

A

Treat bonds as springs with masses at each end- SHO and apply Hooke’s Law

78
Q

kh/kd = 1 if

A

bond isn’t actually broken in the RDS

79
Q

Pharmokinetics of a drug

A

Rate at which absorbed by the body, metabolised and excreted- important in determining the effectiveness of a drug- if metabolic pathway known and involves CH/D cleavage may be possible to slow down the rate at which the drug is being broken down- extending lifetime in body and increasing effectiveness

80
Q

If the TS is moving to be ,ore symmetrical

A

The PKIE gets bigger- better LG

81
Q

Poorer LG for PKIE

A

TS will be later

CH bond starts to break before the poor LG begins to leave

82
Q

Kinetic Isotope effects arise from

A

Difference in CH/D ZPELs

83
Q

SKIES

A

Vib frequency depends on hydribisation state of the carbon- at reaction centre
wagging shows biggest dependence of hybridisation

84
Q

If the reaction is endothermic

A

HP tells us that the TS will resemble the product

85
Q

reaction exothermic

A

HP tells us that the TS will resemble the SM

86
Q

SN1

A

Sp3-Sp2 (cation)
Cation formation is endothermic, therefore the HP states that the transition state for the formation of a cation will resemble the cation
around 1.2

87
Q

SN2

A

Not as much crowding around reacting centre as go from SM to TS, therefore not much change in wagging Vib.
0.95-1.04

88
Q

How can relatively remote isotopic effects affect ror

A

hypenconjugation

89
Q

Hooke’s Law for SHO

A

v=(1/2*pi)(sqrtk/u)

90
Q

Stability of a cC is affected by if it can be

A

Sp2

91
Q

Formation of CCs

A

Ionisation- silver salt AgBF4
Addition of a proton to neutral species- proton to alkene, carbonyl group, alcohol
Electrohpilic additions- NO2- +ve charge stab. mesomerically
Formation from other cations (NH2- –> N2+–> C+)
Intermolecular reaction between CC and neutral species- takes off H+

92
Q

driving force for cc undergoing intramolecular rearrangements

A

additional stability

93
Q

Cation MOs

A

LUMO is empty p orbital of the cation

HOMO CC sigma bond which is breaking

94
Q

Neopently rearrangement

A

2 CC to 3 CC

1,2-alkyl shift

95
Q

Pinacol RA

A

2 OH groups to one carbonyl +H2O

more electron rich unit migrates stab. CC

96
Q

Stability of Carbocations is indicated by the

A

pKa of conjugate acid

97
Q

Framework for inductive and mesomeric

A

sigma and pi

98
Q

Allyl anion has

A

2 resonance forms

99
Q

Why are phenols acidic compared to aliphatic alcohols

A

4 rf

100
Q

Carbons with adjacent 2nd row elements undergo deprotonation more readily than would be expected if only consider inductive effects

A

3d orbitals stab adjacent CAs

hyperconjugation of lp on c into antibonding sigma* of CS

101
Q

Arynes are

A

neutral reactive intermediates- aromatic compounds which formally contain a triple bond- remain sp2 hb
more reactive than standard triple bond

102
Q

How to make 1/3 dicarbonyl

A

Ester + Enolate
with Claisen
Dieckmann

103
Q

How to make 1,5-dicarbonyls

A

Enolate + alpha beta unsat canbonyls

Michael

104
Q

How to Make cyclic enone

A

enone + Enolate

Robinson

105
Q

The larger the pKa of the base

A

Poor conjugate acid- wants proton back- base is strong

high pKa = strong base

106
Q

2 methods of forming enolates

A

1) Rapid complete deprotonation of carbonly- stong base, electrophilic carbonly removed before can react with enolate
2) W|eak base in presence of desired electrophile which is more electronegitve than carbonly in SM

107
Q

R-MgBr

A

1,2- addition

108
Q

R-Cu

A

1,4- addition

organocuprates formed in situ from organolithium species

109
Q

How to achieve clean alkylations

A

reactive alkylating agents
dilute enolate+ excess R-X
Keep reaction as cold as possible
Enhance reactivity of enolate add HMPA

110
Q

Ambident nuc

A

react at O (HMPA) or C (RX)

111
Q

Mukaiyama Aldol addition

A

convery aldehyde and silyl enol ether to 1,3- ketol using lewis acid cat. TiCl4 + aq WU

Organic Chemistry (1 decks)

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