Colour by Design

Question 1

what are the 3 bonds which can attach a dye to fambric?

Answer 1

intermolecular bonds

ionic bonds

covalent bonds

Question 2

which 2 groups modify a chromocaphore?

Answer 2

OH and NH2 as they contain lone pairs in p orbitals which add to the delocalised system

Question 3

what group does cotton have to make bonds to and hence what type of bond do dyes make to it?

Answer 3

OH groups which form hydrogen bonds with amine groups (to the nitrogen)

Question 4

what groups do nylon, wool and silk fibres have?

Answer 4

amine groups

Question 5

how can ion bonds form between a dye and a fabric?

Answer 5

between NH3+ (fabric in acid conditions) and sulponate group on the dye

Question 6

what holds together dye wh=ith carboxylic acid groups to a dye with amine groups?

Answer 6

ionic interactions - becomes COO- NH2+

Question 7

what is a chromophore?

Answer 7

delocalised electron systems in molecules that give them their colour

Question 8

what happens when you change the chromophore?

Answer 8

the colour changes, the longer the delocalised system, the smaller the energy gap to lower frequency of light absorbed

Question 9

what groups make dyes more soluble?

Answer 9

ionic groups such as sulphonium

Question 10

what are arenes?

Answer 10

compounds that contain atleast 1 bezene ring

Question 11

what properties does the delocalisation give aromatic compounds

Answer 11

they are more stable (as negative charge is more spread than if it were in localised double bonds)

so addition reactions would need to take out electrons from the stablised ring to form new bonds

so substitution more likely to happen as the stability of the delocalised electrons is preserved - this is often slow however

Question 12

what are the 2 common representations of benzene?

Answer 12

kekule and hexagon with circle in middle

Question 13

what shape is benzene?

Answer 13

planar ring with bond angles of 120

Question 14

what are the 3 bits of evidence against kekules structure?

Answer 14

doesn’t react with bromine water to go colourless

bond lengths are actually identical

the enthalpy change of hydrogenation of benzene is less than 3 times the hydrogenation of cyclohexene (as more energy needed to break bonds as the delocalised pi system makes it more stable so more positive enthalpy change).

Question 15

what are the 5 electrophillic substitution reactions that benzene undergoes?

Answer 15

halogenation

nitration

sulfonation

alkylation

acylation

Question 16

what are the conditions and reagents for halogenation?

Answer 16

halogen

AlX3 -(e.g AlCl3)

anhydrous reflux

Question 17

what are the conditions and reagents for nitration?

Answer 17

concentrated nitric acid (HNO3)

concentrated sulphuric acid

below 55 degree celcius

Question 18

what are the conditions and reagents for sulfonation?

Answer 18

concentrated sulfuric acid

reflux

Question 19

what are the reaction conditions and reagent for freidal crafts acylcation?

Answer 19

acyl chloride

AlCl3

anhydrous reflux

Question 20

what are the reaction conditions and reagent for freidal crafts alkylation?

Answer 20

haloalkane

AlCl3

anhydrous reflux

Question 21

what are the reagents and conditions for diazotisation ?

Answer 21

nitrous acid (HNO2) or NaNO2 +HCl(dilute)

<5 degrees celcius

Question 22

what are the reagents and conditions for coupling reaction?

Answer 22

NaOH

<5 degrees celcius

Question 23

what are the 2 steps needed to make an azo dye?

Answer 23

diazotization and coupling reaction

Question 24

what is the mechanism of a coupling reaction?

Answer 24

electrophillic substitution

Question 25

why cant ketone be oxidised?

Answer 25

no hydrogen to be removed

Question 26

what mechanism occurs when carbonyls react with cyanide ions and what is formed?

Answer 26

nucleophillic addition

forms a cyanohydrin

Question 27

what are the 3 tests for aldehydes?

Answer 27

fehlings solution
positive test goes from blue solution to red precipitate

tollens reagent
forms a silver mirror when warmed gently from colourless

add acidified sodium dichromate
goes orange to green

Question 28

why can organic molecules absorb ultraviolet or visible light?

Answer 28

as by absorbing the energy proportional to the energy gap you can excite electrons to higher energy levels (to higher empty molecular orbitals)

Question 29

why are chromophores coloured?

Answer 29

the delocalised pi systems make the energy gap smaller so they need to absorb lower frequency to be excited as deltaH= hv.

as delocalisation increases , enrgy gap decreases and the frequency of light absorbed drops.

Question 30

what is the mobile phase is gas liquid chromatography?

Answer 30

carrier gas - an inert gas such as Ar or N2

Question 31

what is the stationary phase in gas liquid chromatography?

Answer 31

porous solid support soaked in a liquid with high boiling point

Question 32

what are the 4 main stages of gas liquid chromatography?

Answer 32

sample is vaporised and injected into the carrier gas

sample moves through the column

samplr is detected and retention time is measured

retention time is compared to known data base

Question 33

what is the retention time?

Answer 33

time taken from injection to detection

Question 34

if the retention time is very short what physical properties does this suggest?

Answer 34

insoluble in the stationary phase

volatile (stays as a gas)

Question 35

what extra analysis can make glc results more accurate?

Answer 35

similar compounds have similar retention times so use mass spec to find Mr and fragmentation patterns

Question 36

Compare the different reactivities of benzene and alkenes towards chlorine.

Answer 36

In benzene, π electrons are delocalised/spread out (1)
In alkenes, π electrons are concentrated between 2 carbons (1)
Electrophiles attracted more to greater electron density in alkenes (1)

Question 37

describe the bonding in benzene?

Answer 37

p-orbitals overlap (1)
above and below the ring (1)
(to form) π-bonds / orbitals (1)
(π-bonds / electrons) are delocalised (1)

Question 38

what does a curly arrow represent?

Answer 38

a pair of electrons

transferred

covalent bond breaks/ forms

Question 39

what is an electrophile?

Answer 39

accepts a pair of electrons

Question 40

how does an electron carrier allow halogenation to take place?

Answer 40

it induces a permanent dipole on chlorine, forming Cl+

Question 41

describe the bonding and structure of benzene

Answer 41

p-orbitals overlap (1)
 above and below the ring (1)
 (to form) π-bonds / orbitals (1)
any of the first three marks are available from a labelled
diagram
eg
bonds
 (π-bonds / electrons) are delocalised (1)
4 marks

Question 42

describe how the bonding in bezene accounts for the fact that bond lengths are equal

Answer 42

one electron from each carbon is delocalised so all bonds are equal

Question 43

explain in terms of delocalisation and energy levels why dye is coloured and benzene is yellow

Answer 43

1. Electrons move to a higher energy level 
2. absorbing em radiation Δ E = hv
3. Yellow dye has more delocalisation/ larger chromophore
   AND energy levels are closer together/ Δ E is smaller 
4. Energy absorbed is at lower visible frequencies 
5. complementary colour is transmitted

Question 44

explain why compounds with an aromatic ring usually form substituted derivatives rather than adition compounds

Answer 44

(aromatic compounds have) delocalised electrons that
are lost on addition AND retained on substitution 
(loss of delocalisation causes) less stability AW 

Question 45

what inorganic substance forms when fehilings solution is added to an aldehyde?

Answer 45

Cu2O