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Organic chemistry year 2 > Fulton content > Flashcards

Fulton content Flashcards

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1
Q

Define heats of hydrogenation

A

Heat evolved when a mole of the compound is completely hydrogenated

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2
Q

What is the heat of hydrogenation usually for a double bond

A

Usually about 120kJ mol-1 for every double bond

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3
Q

Why is benzene so stable

A

All 6 carbon are sp2 hybridised - each carbon has a p-orbital perpendicular to the plane of the ring
Each of the p orbitals contains a single electron
Partial overlap of the p orbitals allows the electrons to delocalise around the entire ring

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4
Q

What must a molecule have to be aromatic

A

Must be cyclic
Must be planar
Must be cyclically conjugated
Must obey huckels rule
Must possess an induced ring current when placed in a magnetic field

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5
Q

What does cyclically conjugated mean

A

each atom of the ring(s) must have p-orbital perpendicular
to the plane of the ring to allow complete delocalization of the
π-electrons

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6
Q

What is huckels rule

A

Must possess (4n+2) pi electrons (n=0,1,2 etc)
2,6,10,14 electrons

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7
Q

Describe induced ring currents in benzene

A

Induced ring currents in benzene happen when its electrons move in response to an external magnetic field. This creates small currents in the ring structure, causing benzene to be repelled by h (a property called diamagnetism).

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8
Q

What effect does magnetic field have on the protons

A

The greater the magnetic field experienced, the further downfield those protons
appear in the 1H NMR spectrum

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9
Q

What is the best indication of whether a compound is aromatic

A

Detection of a ring current
All aromatic compounds possess a ring current

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10
Q

What reagents are needed to produce nitrobenzene from benzene

A

HNO3/H2SO4

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11
Q

What reagents are needed for sulfonation of benzene

A

SO3/H2SO4

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12
Q

What reagents are needed to add Cl to benzene

A

Cl2/FeCl3

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13
Q

What reagents are needed to add a C=O-R group to benzene

A

R-C=O-Cl
AlCl3

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14
Q

Describe the two step mechanism for electrophilic aromatic substitution of benzene

A

1) The p-electrons of the ring attack the electrophile to yield a resonance stabilized carbocation - wheland intermediate
2) Substitution is completed by loss of H+

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15
Q

What is the product and reagents when nitroaromatics are reduced

A

Nitroaromatics can be reduced to aromatic amines
Reagent - 1) SnCl2/HCl 2) OH-

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16
Q

What is the electrophilic in aromatic sulfonation

A

Electrophilic is SO3 or HSO3+

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17
Q

What reagents can be used to produce the reverse reaction of aromatic sulfonation

A

To make the reaction go in opposite direction use steam or dilute H2SO4

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18
Q

When does halogenating of aromatic rings occur and describe the reagents for chlorine, bromine and iodine

A

Halogenating occurs with either Cl2, Br2 or I2 in the presence of a Lewis acid catalyst
For bromination use Br2 and FeBr2
For chlorinations use Cl2 and FeCl2
For iodinations use I2 and CuCl2

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19
Q

What is Friedel crafts alkylation

A

Friedel crafts alkylation a H is substituted for an alkyl R group
Using R-X and AlCl3
Where R-X must be and alkyl halide

20
Q

Why is Friedel crafts alkylations not usually useful in synthesis

A

i) the alkyl group “activates” the ring towards further attack and the 2nd group substitutes on the ring more easily than the first
ii) When primary alkyl halides are used, the electrophile may rearrange to give unexpected products

21
Q

Reagents needed for Friedel crafts acylation

A

Acid chloride and AlCl3

22
Q

Why are Friedel crafts acylations synthetically much more useful

A

i) The acyl group has a deactivating
influence on the ring and further substitutions
are inhibited
ii) Ketones can be easily reduced

23
Q

If a substituent is already present on the benzene ring, what can it influence

A

The rate at which further substitution reactions occur
The location at which the next substituent is introduced

24
Q

What are activating substituents and give examples

A

Groups like -NH2 and -OH
They make the benzene ring more reactive towards electrophilic by donating a pair of electrons, the ring contains more electron density therefore increase the rate of reaction

25
Q

What are and give examples of deactivating substituents

A

Groups like -NO2 are deactivating substituents. It makes the benzene ring less reactive towards electrophilic by withdrawing electrons from the ring. The ring contains less electron density therefore decreased rate of reaction

26
Q

Describe inductive effects

A

These involve electron donation or electron withdrawal through σ bonds

27
Q

Do electronegative elements have a positive or negative inductive effect

A

Negative inductive effects

28
Q

Do electropositive elements have a positive or negative inductive effect

A

Positive inductive effects

29
Q

Describe resonance effects

A

Involves electron donation or withdrawal through pi bonds

30
Q

Do electron withdrawing groups have a positive or negative resonance effect

A

Negative resonance effect

31
Q

How do we classify substituents in terms of ortho, meta and para

A

Activating substituents afford ortho/para disubstituted benzene
Deactivating substituents afford meta disubstitued benzenes apart from halogens

32
Q

How do third substitutions occur

A

The more powerful activator exerts the predominant effect

33
Q

How do third substitutions not happen for meta disubstituted benzenes

A

Meta disubstituted benzenes do not usually undergo attack in the positions between the substituents due to steroids

34
Q

What reagents is needed to generate a benzenediazonium salt from phenylamine

A

HCl and HNO2

35
Q

Why are diazonium salts useful in synthesis

A

N2 is an excellent leaving group and is easily displaced by a variety of nucleophiles

36
Q

What reagents is needed to turn diazonium salt into a chlorobenzene

A

CuCl

37
Q

What reagents is needed to turn diazonium salt into a bromobenzene

A

CuBr

38
Q

What reagents is needed to turn diazonium salt into a cyanobenzene

A

CuCN

39
Q

What reagents is needed to turn diazonium salt into a iodobenzene

A

KI

40
Q

What reagents is needed to turn diazonium salt into a Flurobenzene

A

BF4-

41
Q

What reagents is needed to turn diazonium salt into a phenol

A

ArOH

42
Q

What reagents is needed to turn diazonium salt into a benzene ring

A

H3PO2
Hypophosphoric acid

43
Q

What reagent is used to oxidise alkylbenzene side chains

A

KMnO4 - potassium permanganate

44
Q

What do the alkylbenzene side chains get oxidised to

A

Carboxylate acids

45
Q

In order for the alkylbenzene side chain possess in order to be oxidised

A

Benzylic hydrogen

46
Q

What reagent is used to brominate of alkylbenzene side chain

A

N-bromosuccinimide (NBS)

Organic chemistry year 2 (1 decks)

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