module 6

Question 1

give the characteristics of benzene

Answer 1

colourless, sweet smelling and highly flammable

Question 2

describe kekule’s benzene model

Answer 2

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

Question 3

what was the first reason debunking kekule’s model

Answer 3

lack of reactivity of benzene

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

Question 4

give a second reason debunking kekule’s model

Answer 4

lengths of the C-C in benzene

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

(kekule claimed otherwise)

Question 5

give a third reason debunking kekule’s model

Answer 5

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

Question 6

describe the delocalised model of benzene

Answer 6

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)

Question 7

when is benzene a substituent in a compound

Answer 7

when the alkyl chain has 7+ carbons

prefix is phenyl

Question 8

describe nitration of benzene

Answer 8

benzene reacts with nitric acid => nitrobenzene

catalysed by sulfuric acid
heated by water bath

Question 9

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

Answer 9

higher temperature (>50)

Question 10

what is the electrophile in nitration of benzene

Answer 10

NO2 +

Question 11

how is the electrophile generated in nitration

Answer 11

HNO3 + H2SO4 –>
NO2+ + HSO4 - + H2O

Question 12

describe the halogenation of benzene

Answer 12

benzene reacts with halogen in substitution

AlX3 (X is halogen)

Question 13

how does the halogen react with benzene?

Answer 13

benzene is too stable to react with bromine as is

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

Question 14

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

Answer 14

dative covalent bond

Question 15

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

Answer 15

reacts with halogen carrier ion to regenerate the catalyst

H+ + FeBr4- – > FeBr3 + HBr

Question 16

describe an alkylation reaction

Answer 16

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

Question 17

describe an acylation reaction

Answer 17

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

forms aromatic ketone

Question 18

what is an acyl

Answer 18

alkyl attached to C=O

> ethanoyl chloride

C - C = O
- Cl

Question 19

describe the delocalisation of phenol

Answer 19

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

Question 20

explain how phenol is more acidic than benzene

Answer 20

the H+ ion in OH dissociates

very weak acid

Question 21

describe the reaction of phenol with sodium hydroxide

Answer 21

forms sodium phenoxide and water

Question 22

how can we demonstrate how phenol is a weak acid

Answer 22

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

Question 23

outline directing groups

Answer 23

different electrophiles attack benzene in different directions

Question 24

what’s an activating group

Answer 24

electron donating

Question 25

what's a deactivating group

Answer 25

electron withdrawing

Question 26

what is the placement of 'ortho' in the benzene ring give examples

Answer 26

position 2 -- activating group (except halogens) NH2 -- para and ortho director

Question 27

what is the placement of 'meta' in the benzene ring give examples

Answer 27

position 3 -- deactivating group NO2 -- meta director

Question 28

what is the placement of 'para' in the benzene ring

Answer 28

position 4 -- activating group (except halogens)

Question 29

describe the effect of NH2 on the benzene ring

Answer 29

NH2 activates the benzene ring as the aromatic ring reacts more readily with electrophiles it has a 2,4-directing effect

Question 30

describe the effect of NO2 on the benzene ring

Answer 30

NO2 deactivates the ring as the aromatic ring reacts less readily with electrophiles it has a 3-directing effect

Question 31

how does bromine react with phenol compared to benzene

Answer 31

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

Question 32

describe the reaction between phenol and nitric acid

Answer 32

phenol forms a mixture of 2-nitrophenol and 4-nitrophenol under RTP and dil. nitric acid (no catalyst)

Question 33

what is the functional group of an ester/ester link

Answer 33

= O R - C - O - R

Question 34

give the conditions for making esters by carboxylic acid

Answer 34

method of forming esters using c.acids is too slow at RTP reflux, with catalyst c. H2SO4

Question 35

give the equation for the formation of esters by carboxylic acid

Answer 35

carboxylic acid + alcohol -> ester + water

Question 36

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

Answer 36

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

Question 37

describe alkylation what is the catalyst for this reaction

Answer 37

substitution of an R group onto the benzene ring AlX3

Question 38

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

Answer 38

CH3Cl + AlCl3 -> AlCl4- + CH3+

Question 39

what does an acylation reaction produce

Answer 39

aromatic ketone and hydrogen halide

Question 40

what is the reactivity of aldehydes and ketones influenced by

Answer 40

carbonyl group (C=O)

Question 41

describe the polarity of the carbonyl

Answer 41

polar electron density lies closer to oxygen allows reaction with nucleophiles

Question 42

describe the reduction of propanal with NaBH4

Answer 42

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

Question 43

describe the reduction of propanone with NaBH4

Answer 43

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

Question 44

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

Answer 44

reducing agent remember it is warmed in reduction

Question 45

describe hydrogen cyanide (HCN)

Answer 45

colourless very poisonous boils slightly above RTP

Question 46

describe the reaction of HCN with propanal

Answer 46

propanal + HCN -> hydroxynitrile

Question 47

give the mechanism for the reaction with NaBH4 and propanone give the name for this mechanism

Answer 47

nucleophilic addition

Question 48

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

Question 49

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

Answer 49

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)

Question 50

what is a hazard of 2,4-DNPH

Answer 50

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

Question 51

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

Answer 51

-- solution of AgNO3 in aq. ammonia contains Ag+ which acts as the oxidising agent forms a silver mirror when aldehyde is present

Question 52

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

Answer 52

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

Question 53

what is the properties of carboxylic acids

Answer 53

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

Question 54

compare the melting points of alkanes to carboxyls

Answer 54

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

Question 55

compare the solubility of alkanes to carboxyls

Answer 55

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

Question 56

describe the test of carboxylic acids

Answer 56

reacts with carbonate produce fizzing (and the solid dissolves) pass gas through limewater to ensure the gas is CO2

Question 57

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

Answer 57

redox with metals neutralisation with water

Question 58

define a carboxylic acid derivative

Answer 58

compound that is hydrolysed to form the parent carboxylic acid

Question 59

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

Answer 59

carboxylic acid

Question 60

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

Answer 60

carboxylic acid + alcohol -> ester + water

Question 61

in (1), how is the product water formed

Answer 61

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

Question 62

define hydrolysis

Answer 62

breakdown of a molecule using water molecule

Question 63

give the general equation for acid hydrolysis of esters

Answer 63

ester + water <-> c.acid + alcohol

Question 64

give the general equation for alkaline hydrolysis

Answer 64

ester + hydroxide ion -> carboxylate + alcohol

Question 65

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

Answer 65

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

Question 66

the products of forming acyl chlorides from their parent c. acid are harmful how to deal with this?

Answer 66

use a fume cupboard

Question 67

describe the 2nd method of forming esters using acyl chlorides

Answer 67

acyl chloride + alcohol -> ester + hydrochloric acid

Question 68

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

Answer 68

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

Question 69

are acid anhydrides more or less reactive than acyl chlorides

Answer 69

less

Question 70

give the third method of forming esters through acid anhydrides

Answer 70

acid anhydride + alcohol -> ester + carboxylic acid

Question 71

give the mechanism for the reaction between acyl chlorides and nucleophiles give the name of the mechanism

Answer 71

nucleophilic addition-elimination

Question 72

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

Answer 72

heat under reflux c. H2SO4

Question 73

what are the conditions required for acid hydrolysis of esters

Answer 73

HCl (warmed) heat under reflux

Question 74

give the general equation for alkaline hydrolysis of esters

Answer 74

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

Question 75

after alkaline hydrolysis, how can a carboxylic acid be formed

Answer 75

carboxylate + HCL -> carboxylic acid + NaCl (the carboxylate contains Na in this example)

Question 76

give the amide link

Answer 76

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

Question 77

what does an amide and an ammonia contain

Answer 77

lone pair at N so nucleophile

Question 78

give the reaction forming a primary amide

Answer 78

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

Question 79

give the reaction forming a secondary amide

Answer 79

acyl chloride + primary amine -> secondary amide + salt