Colour by Design Flashcards
what are the 3 bonds which can attach a dye to fambric?
intermolecular bonds
ionic bonds
covalent bonds
which 2 groups modify a chromocaphore?
OH and NH2 as they contain lone pairs in p orbitals which add to the delocalised system
what group does cotton have to make bonds to and hence what type of bond do dyes make to it?
OH groups which form hydrogen bonds with amine groups (to the nitrogen)
what groups do nylon, wool and silk fibres have?
amine groups
how can ion bonds form between a dye and a fabric?
between NH3+ (fabric in acid conditions) and sulponate group on the dye
what holds together dye wh=ith carboxylic acid groups to a dye with amine groups?
ionic interactions - becomes COO- NH2+
what is a chromophore?
delocalised electron systems in molecules that give them their colour
what happens when you change the chromophore?
the colour changes, the longer the delocalised system, the smaller the energy gap to lower frequency of light absorbed
what groups make dyes more soluble?
ionic groups such as sulphonium
what are arenes?
compounds that contain atleast 1 bezene ring
what properties does the delocalisation give aromatic compounds
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
what are the 2 common representations of benzene?
kekule and hexagon with circle in middle
what shape is benzene?
planar ring with bond angles of 120
what are the 3 bits of evidence against kekules structure?
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).
what are the 5 electrophillic substitution reactions that benzene undergoes?
halogenation
nitration
sulfonation
alkylation
acylation
what are the conditions and reagents for halogenation?
halogen
AlX3 -(e.g AlCl3)
anhydrous reflux
what are the conditions and reagents for nitration?
concentrated nitric acid (HNO3)
concentrated sulphuric acid
below 55 degree celcius
what are the conditions and reagents for sulfonation?
concentrated sulfuric acid
reflux
what are the reaction conditions and reagent for freidal crafts acylcation?
acyl chloride
AlCl3
anhydrous reflux
what are the reaction conditions and reagent for freidal crafts alkylation?
haloalkane
AlCl3
anhydrous reflux
what are the reagents and conditions for diazotisation ?
nitrous acid (HNO2) or NaNO2 +HCl(dilute)
<5 degrees celcius
what are the reagents and conditions for coupling reaction?
NaOH
<5 degrees celcius
what are the 2 steps needed to make an azo dye?
diazotization and coupling reaction
what is the mechanism of a coupling reaction?
electrophillic substitution
why cant ketone be oxidised?
no hydrogen to be removed
what mechanism occurs when carbonyls react with cyanide ions and what is formed?
nucleophillic addition
forms a cyanohydrin
what are the 3 tests for aldehydes?
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
why can organic molecules absorb ultraviolet or visible light?
as by absorbing the energy proportional to the energy gap you can excite electrons to higher energy levels (to higher empty molecular orbitals)
why are chromophores coloured?
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.
what is the mobile phase is gas liquid chromatography?
carrier gas - an inert gas such as Ar or N2
what is the stationary phase in gas liquid chromatography?
porous solid support soaked in a liquid with high boiling point
what are the 4 main stages of gas liquid chromatography?
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
what is the retention time?
time taken from injection to detection
if the retention time is very short what physical properties does this suggest?
insoluble in the stationary phase
volatile (stays as a gas)
what extra analysis can make glc results more accurate?
similar compounds have similar retention times so use mass spec to find Mr and fragmentation patterns
Compare the different reactivities of benzene and alkenes towards chlorine.
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)
describe the bonding in benzene?
p-orbitals overlap (1)
above and below the ring (1)
(to form) π-bonds / orbitals (1)
(π-bonds / electrons) are delocalised (1)
what does a curly arrow represent?
a pair of electrons
transferred
covalent bond breaks/ forms
what is an electrophile?
accepts a pair of electrons
how does an electron carrier allow halogenation to take place?
it induces a permanent dipole on chlorine, forming Cl+
describe the bonding and structure of benzene
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
describe how the bonding in bezene accounts for the fact that bond lengths are equal
one electron from each carbon is delocalised so all bonds are equal
explain in terms of delocalisation and energy levels why dye is coloured and benzene is yellow
- Electrons move to a higher energy level
- absorbing em radiation Δ E = hv
- Yellow dye has more delocalisation/ larger chromophore
AND energy levels are closer together/ Δ E is smaller - Energy absorbed is at lower visible frequencies
- complementary colour is transmitted
explain why compounds with an aromatic ring usually form substituted derivatives rather than adition compounds
(aromatic compounds have) delocalised electrons that
are lost on addition AND retained on substitution
(loss of delocalisation causes) less stability AW
what inorganic substance forms when fehilings solution is added to an aldehyde?
Cu2O
