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Year 1 Organic Chemistry > Topic 14: Aromaticity and Electrophilic Aromatic Substiution > Flashcards

Topic 14: Aromaticity and Electrophilic Aromatic Substiution Flashcards

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1
Q

Kekule structure of benzene year

A

Correct structure (C6H6)
1865

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2
Q

Incorrect structure of benzene

A

Triprimane (C6H12)
1825

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3
Q

Faraday

A

Discovered benzene in 1825

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4
Q

Aryl group (Ar)
Benzyl (Bn)
Benzoyl group

A

C6H5R
R is alkane in benzyl
R is C=O R in benzoyl

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5
Q

Benzene’s reactivity is … to a typical alkene. It is … and …

A

different
less reactive (e.g. doesn’t react with X2 (halogenation)
more stable

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6
Q

Hydrogenation of Benzene: Benzene can be … and is … due to ..

A

reduced
more stable than expected
resonance stabilisation energy

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7
Q

Origin of name for aromatic compounds
They were … than expected

A

Smell
more stable

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8
Q

Aromaticity comes from …

A

complete delocalisation of pi electron density around the ring

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9
Q

C-C bonds in Benzne are ..

A

1.4 angstroms

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10
Q

Benzene has … resonase forms
The resonance hybrid is … for drawing mechanisms

A

reduced
more inconvenient

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11
Q

Hybridisation of C in benzene

A

Sp2
unhybridised pz orbitals -orthogonal to the plane
strong overlap of pz orbitals
6 electrons in 6 pz orbitals evenly distributed around the ring

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12
Q

nodal planes

A

regions where the probability of finding an electron is 0

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13
Q

The chemical shift of a H in benzene is … than a H in cyclohexene because …

A

higher
the pi cloud electron density sets up a ring current when placed in a magnetic field. The ring current seats up its own magnetic field. The H atoms at the edge of benzene experience a greater field than the applied field alone so a greater frequency is required to bring protons into resonance. Can induce a field to oppose applied field and lower chemical shift.

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14
Q

4 rules of aromaticity

A

Cyclic ring
Cyclic ring must be planar
Cyclic ring must be fully conjugated (must have sp2 hybridised atoms with unhybridised p orbitals in ring atoms)
Cycic ring must have 4n + 2 pi electrons (Huckel rule) (all pi electrons form p orbitals are in bonding MOs)

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15
Q

In benzene, electrophilic addition is … as it … . … is favoured as it … . The … is attracted to … and the … such as … because … activates the …

A

unfavourable
loses aromaticity
substitution
doesn’t lose aromaticity
electrophile
electron in aromatic ring
catalyst
Lewis acids like AlCl3
it is electron deficient so attracts electron density from lewis base
electrophile to generate E+

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16
Q

Wheland intermediate is …
It is a … and it’s not …
It has … resonance forms

A

Positively charged intermediate in the electrophilic aromatic substitution
reactive intermediate
aromatic
3

17
Q

Describe the reaction coordinate diagram of electrophilic aromatic substitution

A

2 peaks
TS1 at top of first higher peak
Wheland intermediate between peaks (lower in energy than TS1 + TS2, higher than reactants and products)
TS2 at top of second, lower peak
loses aromaticity slowly, gains quickly

18
Q

Freidel Crafts Acylation is the reaction between … where a curly arrow goes from … to … .This forms the intermediate … where the curly arrow goes from … into to … which forms … and … .The … is stabilised by … and the 2nd is formed when a curly arrow goes from … to the … which forms … and moves the positive charge to the … .The … resonance form reacts with … . A curly arrow comes from … to the … and from the … to the … .This forms a … intermediate which reacts with a … . A curly arrow comes from … to the … and the … to the … and a … is formed.

A

acid chloride (R-(C=O)-Cl) and a lewis acid catalyst such as AlCl3
Cl lone pair on acid chloride
Al on AlCl3
[R-(C=O)-Cl]^+[AlCl3]^-
The C-Cl^+ bond
Cl^+
R-C^+=O (acylium cation)
AlCl4^-
R-C^+=O (acylium cation)
2 resonance forms
lone pair on oxygen
C=O bond
a triple C-o bond
O
2nd
benzene
double bond in benzene
C in electrophile
triple bond in the electrophile
O^+ on the electrophile
positively charged
base
base lone pair
H on the same C as C=O-R
The C-H bond (same H as above)
C-C^+ bond
phenyl ketone (C6H5-C(=O)-R)

19
Q

Freidel Crafts Alkylation is the reaction between … where a curly arrow goes from … to … .This forms the intermediate … where the curly arrow goes from … into to … which forms … and … .The … is stabilised by … .The … reacts with … . A curly arrow comes from … to the … .This forms a … intermediate which reacts with a … . A curly arrow comes from … to the … and the … to the … and … is formed.

A

an alkyl halide reagent such as tertiary butyl chloride and AlCl3
Cl lone pair on acid chloride
Al on AlCl3
[(CH3)3C-Cl]^+[AlCl3]^-
C-Cl^+
Cl^+
(CH3)3C^+
[AlCl4]^-
(CH3)3C^+
+I inductive effect
(CH3)3C^+
benzene
double bond in benzene
C^+ in (CH3)3C^+
positively charged
base
base lone pair
H on the same C as C(CH3)3
The C-H bond (same H as above)
C-C^+ bond
C6H5C(CH3)3

20
Q

2 problems of alkylation

A

scrambling with primary and secondary alkyl halides e.g. formation of secondary or tertiary carbocations
polyalkylation can occur

21
Q

How to avoid scrambling/polyalkylation

A

Make phenyl ketone by Fredel Crafts Acylation and reduce carbonyl
Make desired product using Gringard reagent

22
Q

Halogenation is the reaction between … where a curly arrow goes from … to … .This forms … .This also works with … .

A

Cl2 and AlCl3
Cl lone pair on Cl2
Al on AlCl3
Cl-Cl^+-Al^–Cl3
Br2 or FeBr2

23
Q

Nitration forms … from … and continues to form products such as … . … reacts with … .A curly arrow goes from … to the … to form … and … and then … which reacts with … .A curly arrow comes from … to the … .This forms a … intermediate which reacts with a … . A curly arrow comes from … to the … and the … to the … and … is formed.

A

amine
nitrobenzene
diammonium cation
conc HNO3
conc H2SO4
the lone pair on the O attached to H and N^+ on O^–N^+(=O)-O-H
H on H2SO4
O^–N^+(=O)-O(-H)-H
HSO4^-
O=N^+=O
benzene
double bond in benzene
N^+ in O=N^+=O
positively charged
base
base lone pair
H on the same C as NO2
The C-H bond (same H as above)
C-C^+ bond
C6H5CNO2

24
Q

Sulphonation is the reaction between … and … to form the electrophile … which reacts with … . A curly arrow comes from … to the … .This forms a … intermediate which reacts with a … . A curly arrow comes from … to the … and the … to the … and … is formed. It can react with … and … under … to reform benzene

A

H2SO4
SO3
S(=O)2=O^+-H
benzene
double bond in benzene
N^+ in O=N^+=O
positively charged
base
base lone pair
H on the same C as SO3H
The C-H bond (same H as above)
C-C^+ bond
C6H5SO3 (benzene sulphonic acid)
steam
H^+
steam distillation

25
Q

Formulation is the introduction of … . The … reacts with … under … to form … which reacts with … to form … so can act as a … . The final product when reacting with benzene is …

A

an aldehyde group
C^-=O^+
HCl
equilibrium
H-C(-Cl)=O (formy chloride)
AlCl3 and CuCl
H-C(triple bond)O^+
benzylaldehyde

26
Q

Halogenation:
reagents
active species
product

A

X2, Lewis acid (AlCl3 for Cl2/ FeBr3 for Br2)
Cl-CL^+-[AlCl3]^-
C6H5Cl/Br (chloro/bromobenzene)

27
Q

Nitration
reagents
active species
product

A

Conc HNO3 and conc H2SO4 (or Ac2O)
Nitronium (O=N^+=O)
C6H5NO2 (nitrobenzene)

28
Q

Sulfonation
reagents
active species
product
notes

A

Oleum (H2SO4 +SO3)
O=S(=O)=O^+-H
C6H5SO3H (benzene sulphonic acid)
Reversible using H^+, H2O under heat

29
Q

Freidel-Crafts Alkylation
reagents
active species
product
notes

A

R-Cl, Lewis acid
Alkyl carbocation
Alkyl benzene
(1,2 H-shift polyalkylation, scrambling)

30
Q

Freidel-Crafts Acylation
reagents
active species
product
notes

A

ROCl, Lewis acid
Acylation (R-C triple bond O^+)
C6H5C(-R)=O
Benzene ketone
Solution to alkylation problems- reduce carbonyl alkyl

31
Q

Formylation
reagents
active species
product

A

CO, HCl, AlCl3, CuCl
Formyl (H-C triple bond O^+)
Benzaldehyde

Year 1 Organic Chemistry (15 decks)

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