Colour by Design Flashcards
What is a conjugated system?
across the alternate double and single carbon bonds electrons are delocalised through the overlap of p orbitals.
Why are organic molecules coloured?
Coloured due to the prescence of a conjugated system in a molecule which decreases the energy gap (ΔE) between the ground state and the excited state. So the more e- that are delocalised in the conjugated system, the smaller the energy gap and this results in the absorption of longer wavelenths of light.
Which molecules will absorb visible light?
Delocalised systems with 5 π bonds in the conjugated system are likely to absorb light in the visible range of the spectrum and be coloured.
What happens in molecules with localised covalent bonds with regard to light.
They have a large ΔE so absorb UV light - single bonds absorb UV
Why does benzene not undergo addition reactions?
What is hydrogenation?
A reaction where H2 is added to an alkene to remove its double bonds
Define Dye
A soluble, organic molecule that is able to bind to a substrate such as a fibre, and impact colour to it.
Define arene
unsaturated hydrocarbons that contain rings stabilised by electron delocalisation. Contain only hydrogen and carbon (aromatic hydrocarbons) e.g. benzene
What is the -NO2 group known as?
Nitro group
What is the -SO3H group know as?
Sulfonic acid group
What does aromatic mean?
A compound which contains a beneze ring
Define feedstock.
The reactants that go into a chemical process
Why can arenes/ benzene able to undergo electrohphilic substitution reactions?
The benzene ring in arenes is an aera of high electron density so can react with electrohiles. A catalyst is used to create an electrophile reactive enough to attack the benzene ring.
First step disrupts the delocalised electrons so has a high activation energy.
What is R-N=N-R’ functional group known as?
Azo group
What is a chromophore?
A group of atoms and electrons forming part of an organic molecule that causes it to be coloured, that is, the groups that contribute to the delocalisation.
Describe recrystallisation.
- Dissolve solid in minimum amount of hot solvent
- Filter the mixture to remove insoluble impurities
- Cool the mixture - crystals appear
- Filter the mixture to remove soluble impurities
- Allow crystals to dry
What is diazotisation?
An amine group in converted into a diazonium salt.
What is coupling?
the reaction between a diazonium salt and a phenol or aromatic amine.
What are colourfast dyes?
Retain its colour - doesn’t wash out or fade easily. Due to very strong bonds between the dye and fabric (ususally covalent or ionic bonding).
What is a fibre-reactive dye?
Contains a reactive group of atoms that can bond covalently to molecules of the fibre. (triazine derivatives)
What is mordanting?
Uses a metal ion to join the dye to the fabric.
Groups on the fabric and the dye form dative covalent bonds to the metal, forming chelate complex ions. Metal ions used as mordants include Al3+ and Cr3+
What is a chelate?
A complex ion in which the metal ion is bonded to two or more atoms in the same molecule.
Describe acid dyes.
Have a negative charge when dissolved in water due to presence of sulfonate groups (SO3-). They are applied in acid conditions to fibres, and under these conditions, polyamide and protein fibres will have positively charged NH3+ groups present at the end of polyamide chains or on side groups in proteins. IONIC BONDING
Describe direct dyes.
Long, linear dye chains with NH2 and OH groups that can hydrogen bond. e.g. cotton and cellulose can hydrogen bond to the fibre.
