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chemistry > module 6 > Flashcards

module 6 Flashcards

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1
Q

give the characteristics of benzene

A

colourless, sweet smelling and highly flammable

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2
Q

describe kekule’s benzene model

A

six-membered ring of carbons joined by alternate single and double bonds

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3
Q

what was the first reason debunking kekule’s model

A

lack of reactivity of benzene

benzene doesn’t readily undergo electrophilic addition reactions
(> doesn’t decolourise bromine)

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4
Q

give a second reason debunking kekule’s model

A

lengths of the C-C in benzene

found that bond length of a double bond and single bond was the same

(kekule claimed otherwise)

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5
Q

give a third reason debunking kekule’s model

A

hydrogenation enthalpies

if kekule’s model is essentially a cyclohexene, it would be expected to have enthalpy change of hydrogenation three times of cyclohexene (it has 3 double bonds)

actual enthalpy change of benzene is lower

therefore actual structure of benzene is more stable

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6
Q

describe the delocalised model of benzene

A

planar, cyclic hexagonal hydrocarbon

each carbon has one electron in a p-orbital perpendicular to the plane

these orbitals overlap sideways (above and below plane)

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7
Q

when is benzene a substituent in a compound

A

when the alkyl chain has 7+ carbons

prefix is phenyl

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8
Q

describe nitration of benzene

A

benzene reacts with nitric acid => nitrobenzene

catalysed by sulfuric acid
heated by water bath

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9
Q

how can more nitro groups be substituted onto the benzene in nitration

A

higher temperature (>50)

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10
Q

what is the electrophile in nitration of benzene

A

NO2 +

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11
Q

how is the electrophile generated in nitration

A

HNO3 + H2SO4 –>
NO2+ + HSO4 - + H2O

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12
Q

describe the halogenation of benzene

A

benzene reacts with halogen in substitution

AlX3 (X is halogen)

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13
Q

how does the halogen react with benzene?

A

benzene is too stable to react with bromine as is

halogen carrier (AlX3) reacts with X to form X+

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14
Q

what bond forms between the halogen and the benzene in the intermediate phase

A

dative covalent bond

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15
Q

what happens to the H+ ion that is substituted off the bezene

A

reacts with halogen carrier ion to regenerate the catalyst

H+ + FeBr4- – > FeBr3 + HBr

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16
Q

describe an alkylation reaction

A

substitution of a H atom in the benzene ring by alkyl group

> reaction of benzene with a haloalkane in the prescence of a halogen carrier

electrophilic substitution

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17
Q

describe an acylation reaction

A

benzene reacts w/ acyl chloride (in prescence of halogen carrier)

forms aromatic ketone

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18
Q

what is an acyl

A

alkyl attached to C=O

> ethanoyl chloride

C - C = O
- Cl

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19
Q

describe the delocalisation of phenol

A

lone pair of e- occupies a p-orbital on O delocalised into the benzene ring

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20
Q

explain how phenol is more acidic than benzene

A

the H+ ion in OH dissociates

very weak acid

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21
Q

describe the reaction of phenol with sodium hydroxide

A

forms sodium phenoxide and water

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22
Q

how can we demonstrate how phenol is a weak acid

A

no reaction takes place with a metal carbonate because phenol is a weak acid

shows that phenol can react with alkalis but not wiht a carbonate

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23
Q

outline directing groups

A

different electrophiles attack benzene in different directions

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24
Q

what’s an activating group

A

electron donating

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25
Q

what’s a deactivating group

A

electron withdrawing

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26
Q

what is the placement of ‘ortho’ in the benzene ring

give examples

A

position 2 – activating group (except halogens)

NH2 – para and ortho director

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27
Q

what is the placement of ‘meta’ in the benzene ring

give examples

A

position 3 – deactivating group

NO2 – meta director

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28
Q

what is the placement of ‘para’ in the benzene ring

A

position 4 – activating group (except halogens)

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29
Q

describe the effect of NH2 on the benzene ring

A

NH2 activates the benzene ring as the aromatic ring reacts more readily with electrophiles

it has a 2,4-directing effect

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30
Q

describe the effect of NO2 on the benzene ring

A

NO2 deactivates the ring as the aromatic ring reacts less readily with electrophiles

it has a 3-directing effect

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31
Q

how does bromine react with phenol compared to benzene

A

bromine reacts more readily with phenol

due to the lone pair of electrons occupied in the p-orbital on O-H, delocalised into the benzene ring

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32
Q

describe the reaction between phenol and nitric acid

A

phenol forms a mixture of 2-nitrophenol and 4-nitrophenol

under RTP and dil. nitric acid
(no catalyst)

33
Q

what is the functional group of an ester/ester link

A

= O
R - C - O - R

34
Q

give the conditions for making esters by carboxylic acid

A

method of forming esters using c.acids is too slow at RTP

reflux, with catalyst c. H2SO4

35
Q

give the equation for the formation of esters by carboxylic acid

A

carboxylic acid + alcohol -> ester + water

36
Q

where does the water come from in the reaction of carboxylic acid with alcohol

A

the OH from alcohol and the H from the COOH of the c.acid

37
Q

describe alkylation

what is the catalyst for this reaction

A

substitution of an R group onto the benzene ring

AlX3

38
Q

how is the electrophile generated in the alkylation reaction between CH3Cl and AlCl3

A

CH3Cl + AlCl3 -> AlCl4- + CH3+

39
Q

what does an acylation reaction produce

A

aromatic ketone and hydrogen halide

40
Q

what is the reactivity of aldehydes and ketones influenced by

A

carbonyl group (C=O)

41
Q

describe the polarity of the carbonyl

A

polar

electron density lies closer to oxygen

allows reaction with nucleophiles

42
Q

describe the reduction of propanal with NaBH4

A

propanal + 2[H] -> propan-1-ol

43
Q

describe the reduction of propanone with NaBH4

A

propanone + 2[H] -> propan-2-ol

44
Q

what does NaBH4 act as in the reduction of aldehyde and ketone

A

reducing agent

remember it is warmed in reduction

45
Q

describe hydrogen cyanide (HCN)

A

colourless

very poisonous

boils slightly above RTP

46
Q

describe the reaction of HCN with propanal

A

propanal + HCN -> hydroxynitrile

47
Q

give the mechanism for the reaction with NaBH4 and propanone

give the name for this mechanism

A

nucleophilic addition

48
Q

give the mechanism for the reaction with NaCN/H+ and propanal

give the name for this mechanism

A
49
Q

how can we detect the prescence of a carbonyl in a compound

A

2,4-dinitrophenylhydrazine (2,4-DNPH)

dissolved in methanol and sulfuric acid as a pale orange ppt. (brady’s reagant)

when 2,4-DNPH reacts with carbonyl, the NH2 group adds to the C=O followed by removal of water molecule

forming a yellow/orange ppt. (positive result)

50
Q

what is a hazard of 2,4-DNPH

A

when solid, any friction or sudden blow can cause an explosion

51
Q

describe the use of tollen’s reagent in detecting an aldehyde between a ketone

A

– solution of AgNO3 in aq. ammonia

contains Ag+ which acts as the oxidising agent

forms a silver mirror when aldehyde is present

52
Q

describe the process of measuring the melting point of the aldehydes and ketones

A

impure yellow/orange solid (by 2,4-DNPH) filtered to separate the ppt from solution

solid recrystalises

melting point of the purified 2,4-DNPH measured and recorded

compare the melting point to database to identify the compound

53
Q

what is the properties of carboxylic acids

A

contains a carbonyl and a hydroxyl group, forming a carboxyl group

54
Q

compare the melting points of alkanes to carboxyls

A

carboxyls have a higher melting point due to hydrogen bond forming and permanent dip-dip interactions

alkanes form LDF

hydrogen bonds are stronger than LDF

so carboxyls have a higher melting point

55
Q

compare the solubility of alkanes to carboxyls

A

carboxyls form hydrogen bonds with water molecules

alkanes are insoluble

the longer the chain, the lower the solubility (lower influence of -OH)
after 4C, the carboxyl is insoluble

56
Q

describe the test of carboxylic acids

A

reacts with carbonate

produce fizzing (and the solid dissolves)

pass gas through limewater to ensure the gas is CO2

57
Q

give a few ways to how carboxylates can be formed by carboxylic acids

A

redox with metals

neutralisation with water

58
Q

define a carboxylic acid derivative

A

compound that is hydrolysed to form the parent carboxylic acid

59
Q

what is the only organic compound to react with sodium carbonate or sodium hydrogen carbonate

A

carboxylic acid

60
Q

give the method of formation of esters using carboxylic acids and one other organic compound (reaction 1)

A

carboxylic acid + alcohol -> ester + water

61
Q

in (1), how is the product water formed

A

H from the carboxylic acid and OH from the alcohol forms water

62
Q

define hydrolysis

A

breakdown of a molecule using water molecule

63
Q

give the general equation for acid hydrolysis of esters

A

ester + water <-> c.acid + alcohol

64
Q

give the general equation for alkaline hydrolysis

A

ester + hydroxide ion -> carboxylate + alcohol

65
Q

how can acyl chlorides be formed from their parent carboxylic acid?

A

carboxylic acid + thionyl chloride (SOCl2) -> acyl chloride + HCl + SO2

66
Q

the products of forming acyl chlorides from their parent c. acid are harmful

how to deal with this?

A

use a fume cupboard

67
Q

describe the 2nd method of forming esters using acyl chlorides

A

acyl chloride + alcohol -> ester + hydrochloric acid

68
Q

what organic compounds can and can’t react with phenol to form esters

A

can - acid anhydrides and acyl chlorides
can’t - carboxylic acids

69
Q

are acid anhydrides more or less reactive than acyl chlorides

A

less

70
Q

give the third method of forming esters through acid anhydrides

A

acid anhydride + alcohol -> ester + carboxylic acid

71
Q

give the mechanism for the reaction between acyl chlorides and nucleophiles

give the name of the mechanism

A

nucleophilic addition-elimination

72
Q

for reaction (1) of forming esters, what are the conditions and catalyst required

A

heat under reflux
c. H2SO4

73
Q

what are the conditions required for acid hydrolysis of esters

A

HCl (warmed)
heat under reflux

74
Q

give the general equation for alkaline hydrolysis of esters

A

ester + NaOH (OH-) -> carboxylate + alchol

75
Q

after alkaline hydrolysis, how can a carboxylic acid be formed

A

carboxylate + HCL -> carboxylic acid + NaCl

(the carboxylate contains Na in this example)

76
Q

give the amide link

A

R - C = O
- NH (number of H depends on how many C attached)

77
Q

what does an amide and an ammonia contain

A

lone pair at N so nucleophile

78
Q

give the reaction forming a primary amide

A

acyl chloride + NH2 -> primary amide + NH4Cl (ammonium chloride)

79
Q

give the reaction forming a secondary amide

A

acyl chloride + primary amine -> secondary amide + salt

chemistry (5 decks)

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