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Fundamnetals of Chemistry for Biochemsists CHE00031C > Aromatics and Carbonyls > Flashcards

Aromatics and Carbonyls Flashcards

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1
Q

Huckels’s rule

A

Pi electrons = 4n + 2 for aromatic compounds

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2
Q

Halogenation of benzene

A

HX and FeX3 or AlX3
- X2 donates lp to halogen carrier
- Creates complex ion
- Benzene acts as nucleophile (attacks s+ X)
- HX and halogen carrier regenerate

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3
Q

Nitration of benzene

A

Sulfuric acid (H2SO4) and nitric acid (HNO2) -> nitronium ion
- Benzene reacts with nitronium ion
- Water picks up excess H+

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4
Q

Sulfonation of benzene

A

Sulfuric acid (H2SO4) and sulfer trioxide (SO3) create complex ion
- Benzene acts as a nucleophile and reacts with ion
- Regenerates sulfuric acid

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5
Q

Friedel-Crafts Alkylation of benzene

A

Lewis acid and complimentary lewis base (Haloalkane) form complex ion
- Benzene acts as nucleophile
- Regenerates Lewis acid and HX
- Forms polyalkylated benzenes
- Rarely used in synthesis

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6
Q

Friedel-Crafts acylation of benzene

A

Acyl choloride and lewis acid form coordiantion complex then acylium ion
- Benzene reacts with ion and regenerates lewis acid and HX
- Often used in synthesis

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7
Q
  • NH2, -NHR, -NR2
A

+M>-I strongly activating (1 reactive)

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8
Q

-OH, -OR

A

+M>-I strongly activating (2 reactive)

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9
Q

-NHCOR, -OCOR

A

+M>-I activating (3 reactive)

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10
Q

-Ph, -CH-CH2

A

+M, +I Activating (4 reactive)

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11
Q

-R

A

+I weakly activating (5 reactive)

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12
Q

-Cl, -Br, -I

A

-I>+M deactivating (6 reactive)

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13
Q

-CHO, -COR

A

-M, -I deactivating (7 reactive)

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14
Q

-CO2H, -CO2R

A

-M,-I deactivating (8 reactive)

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15
Q

-SO3H

A

-M,-I strongly deactivating (9 reactive)

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16
Q

-NO2

A

-M,-I strongly deactivating (10 reactive)

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17
Q

Regioselectivity of activating groups

A

Increased electron density at 2,4 positions

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18
Q

Where do halogens direct groups?

A

2,4 position

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19
Q

Regioselectivity of deactivating groups

A

Increase electron densitiy at 3 position

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20
Q

why is 2,4 more stable for +M groups?

A

Produces another resonance form (more disperse charge on intermediate)

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21
Q

Para

A

4

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22
Q

Ortho

A

2

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23
Q

Meta

A

3

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24
Q

NO2 -> NH2

A

Reduction - Sn/HCl

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25
Q

COR -> CH2R

A

Reduction - Zn/Hg/HCl

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26
Q

CH3 -> CO2H

A

Oxidation - KmNO4

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27
Q

Solution to Friedel-Crafts alkylation

A

Friedel-Crafts acyaltion and then Clemmensen reduction (Zn/HCl/Hg)

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28
Q

Amide -> amine

A

NaOH, H2O, heat

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29
Q

Sulfuric acid -> H

A

H2SO4, H2O, heat

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30
Q

Aldehyde

A

R-CO-H

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31
Q

Ketone

A

R-CO-R

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32
Q

Carboxylic acid

A

R-CO-OH

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33
Q

Acyl CHloride

A

R-CO-Cl

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34
Q

Acid anhydride

A

R-CO-OCOR

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35
Q

Ester

A

R-CO-OR

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36
Q

Amide

A

R-CO-NH2

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37
Q

Addition of strong nucleophile to carbonyl

A

Forms alcohol

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38
Q

Addition of weak nucleophile to carbonyl

A

Carbonyl is a weak base - protonate with H+ to form strong electrophile
- weak nucleophile reacts
- Forms alcohol

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39
Q

What groups can a negatively charged nucleophile substitute out of a carbonyl?

A

Cl, OCOR, OR, NR2

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40
Q

What groups can a neutral nucleophile substitute out of a carbonyl?

A

Cl, OCOR

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41
Q

What groups can a weak nucleophile substitute out of a carbonyl?

A

OH, OR, NR2

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42
Q

-ly charged nucleophile substitution of carbonyl

A

creates a substituted carbonyl and forms X-
- X- more unstable than Nu-
- But C-X (and C-O in intermediate) weaker than C=O

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43
Q

Neutral nucleophile substitution of carbonyl

A

Carbonyl must be strong electrophile
- Et3N/pyridine required to deprotonate weak nucleophile in intermediate
- creates a substituted carbonyl and forms X-

44
Q

Weak nucleophile substitution of carbonyl

A

Carbonyl initialy protonated (acid catalysis)
- Forms strong electrophile
Forms XH (seperates in solution) and substituted carbonyl

45
Q

Alpha-substituted reaction of a carbonyl

A
  • base removed H from alpha position
  • Forms enolate ion
  • More stable resonance forms has - on O (strong nucleophile)
  • Reacts with electrophile
46
Q

Why are aldehydes generally more reactive than ketones?

A
  • Nucleophile can approach aldehydes more readily and trans state is less crowded
  • Carbon in ketone less electrophilic
47
Q

Reduction of carbonyl

A

Sodium borohydride (NaBH4) (weaker) or lithium aluminium hydride (LiAlH4) (stronger)

48
Q

Reduction of carbonyl

A
  • Produced Alkoxide ion
  • Workup
49
Q

Why are tertiary alcohols not easily oxidised?

A

Because a C-C bond needs to be broken

50
Q

Oxidation of a 2’ alcohol forms….

A

Ketone

51
Q

Oxidation of a 1’ alcohol forms…

A

Aldehyde

52
Q

Further oxidation of a 1’ alcohol forms…

A

A carboxylic acid

53
Q

Oxidizing agent to form a ketone

A

CrO3 and H+ Jones reagent

54
Q

Oxidizing agent to form an aldehyde…

A

PCC

55
Q

Oxidizing agent to form carboxylic acid…

A

CrO3 and H+ Jones reagent/KMnO4

56
Q

What is an organometallic?

A

Organic group bonded to metal R-M

57
Q

organometallic acting as a nucleophile

A

forms primary alcohol and metal oxide

58
Q

Grignard reagent

A

R-MgX

59
Q

Formation of grignard reagent

A
  • Anhydrous
  • N2
  • Will ready react with O2 and water
60
Q

Grignard + aldehyde

A

2’ alcohol and HOMgX

61
Q

Grignard + ketone

A

tertiary alcohol + HOMgX

62
Q

Wittig reaction

A

Phosphonium Ylide and carbonyl

63
Q

Hydration of carbonyl

A

reversible forms hydrate
- Eq determined by stability of carbonyl relative to hydrate

64
Q

Addition of an alcohol to carbonyl

A

forms hemiacetals
acid catalyst

65
Q

Hemiacetal + 2nd eq of alcohol

A

Acetal

66
Q

why are acetals useful?

A

Act as protecting groups for aldehydes (do not react w bases, redox reagents and nucleophiles)

67
Q

How to reverse acetal formation

A

H+ catalyst and remove H2O

68
Q

Addition of primary amine to carbonyl

A

reversible, forms imine

69
Q

pH of formation of imine

A

4.5 - below and amine becomes protonated and above theres not enough H+ to protonate the -OH in hemiaminal

70
Q

Reduction of imine

A

NaBH4 to amine

71
Q

Ester + nucleophile

A

nucleophilic acyl substitution

72
Q

Carboxylic acid + Nucleophile

A

competitive deprotonation

73
Q

Best leaving groups

A
  • neutral
  • stable
  • for an anion - low pKa for conjugate acid indicates A- is relatively stable
74
Q

Why are ketones and aldehydes more reactive than etsers

A

C is more + in a/k
OR is +M

75
Q

Relative reactivity of carboxylic acid derivatives

A

acyl chloride, acid anhydride, ester, amide

76
Q

Why are acyl chlorides so reactive?

A

-I stronger than +M

77
Q

why are acid anhydrides so reactive?

A

-I>+M - lp on O is shared

78
Q

Why are esters less reactive?

A

+M>-I

79
Q

why are amides the least reactive?

A

+M»-I

80
Q

Esterification of carboxylic acid

A

Weak nucleophile with acid catalyst - produces ester
Reversible - alcohol and dehydrating agent to force equilibrium (like MgSO4)

81
Q

Carboxylic acid + ammonia

A

acid base reaction
room temp
RCO2- +NH4 salt formed

82
Q

Carboxylic avid Et3N/pyridine

A

forms salts

83
Q

Carboxylic + SOCl2

A

Acyl chloride + SO2 + HCl

84
Q

alternatives to SOCl2

A

Phosphorus trichloride/pentachloride

85
Q

Hydrolysis of acyl chloride

A

Cl- is the leaving group
carboxylic acid

86
Q

Alcoholysis of acid anhydride

A

ester + RCO2-

87
Q

What nucleophiles do esters react with?

A

Strong and weak (w catalyst)

88
Q

Why do amides undergo few nucleophilic substitutions?

A

carbonyl carbon not electrophillic

89
Q

Reduction of ester

A

LiAlH4 (NaBH4 not strong enough)
1’ alcohol

90
Q

Base hydrolysis of an ester

A

saponification carboxylic acid and ROH

91
Q

Ester + Grignard reagent

A

3’ alcohol

92
Q

Acyl chloride + ammonia (2 eq.)

A

Primary amide + Cl-

93
Q

Hydrolysis of amide

A
  • heating in conc. aq acid or hydroxide ion
  • carboxylic acid + NH4+
94
Q

What is an enol?

A

a C(OH)=R group
a structural isomer of a carbonyl

95
Q

What is keto-enol tautomerism?

A

The interconversion between keto and enol forms of a carbonyl

96
Q

Acid catalyst tautomerism

A
  • Protantates O of C=O
  • regenerates acid at end
97
Q

Base catalysed tautomerism

A
  • Forms enolate ion
  • -OH regenerated
98
Q

Why is the keto form more stable?

A
  • Combined enthalpy of bonds higher than enol
  • However enol stabilised if C=C is conjugated with a second pi bond and if -OH is involved in intramolecular H-bonding
99
Q

What molecules are prone to enolisation?

A

Aldehydes and ketones (not esters and carb acids)

100
Q

Are enols nucleophiles or electrophiles?

A

Nucleophiles

101
Q

Reaction of enols with bromine

A
  • Acid cat.
  • After acid cat. tautomerism Br- introduced at alpha pos. of ketone (extremely weak base, more likely that H2O acts as base in this step)
102
Q

Why will a brominated enol resist further bromination?

A

due to +I effect of Br

103
Q

Why are H atoms in the alpha positions of carbonyls acidic

A

the -I and -M effects of carbonyls stabilise the enolate ion

104
Q

Enolate ion + electrophile

A
  • 2 diff nucleophilic sites due to resonance
  • major product is substitution at C
105
Q

Aldol condensation

A
  • OH- catalyst
  • Rapid and reversible
  • product both aldehyde and alcohol
106
Q

What is the equilibrium of aldol condensation?

A
  • Aldehyde eq. lies to aldol
  • Ketone eq. lies to ketone
107
Q

What configurational isomer do enals favour?

A

E - more stable than Z

Fundamnetals of Chemistry for Biochemsists CHE00031C (5 decks)

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