Colour By Design
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Describe beta-carotene.
Orange colour given to vegetables. Present in leaves, absorbs energy from sunlight.
Define a conjugated system.
Alternating double and single bonds.
What factors affect colour?
More delocalised electrons, smaller energy gap. Absorption of longer wavelengths.
What is the bond angle in benzene?
120.
How is cyclohexane formed?
Benzene reacts with hydrogen in an addition reaction.
Describe chlorination.
Aluminium chloride catalyst, anhydrous conditions.
Describe bromination.
Iron bromide catalyst, heat.
Describe alkylation.
Aluminium chloride catalyst, heated under reflux.
Describe acylation.
Aluminium chloride catalyst, anhydrous conditions.
Describe nitration.
Nitric acid and sulfuric acid, concentrated, less than 55C.
Describe sulfonation.
Sulfuric acid, heated under reflux. Produces benzenesulfonic acid, forms salts in alkaline conditions.
How are azo functional groups formed?
Diazonium salt + coupling agent.
Describe azo groups.
Unstable, diazonium group easily lost forming nitrogen gas. If attached to benzene ring, stabilised. Prepared in ice-cold solutions. Dissolved in HCl and sodium nitrite, below 5C, diazotisation.
Define a chromophore.
Energy levels of delocalised electron system.
Describe cationic dyes.
N+ forms ionic bonds with COO-. Applied in alkaline conditions. Relies on hydrogen bonding, easily washed out.
Describe colourfast dyes.
Azo modified with trichlorotriazine, attacked by nucleophilic groups reacted with hydroxyl groups, strong covalent bonds.
Describe wool and silk.
Protein fibres. Able to be ionised. Strong electrostatic forces, under acidic conditions. Ionic bonding.
Describe fibre reactive dyes.
Fast forming, more covalent bonds, trichlorotriazine.
Describe disperse dyes.
Insoluble in water, instantaneous induced dipoles.
Describe mordanting.
Metal ion joined to dye through dative covalent bonds. Chelate complex ions Al3+ or Cr3+.
Describe a triglyceride.
Propane-1,2,3,-triol. Forms 3x H2O. Saturated, cis. Unsaturated, trans.Produces sodium salts with sodium hydroxide.
What catalyst is used with hydrogenation?
Nickel.
Describe the mobile phase of gas-liquid chromatography.
Inert gas, helium or nitrogen.
Describe the stationary phase of gas-liquid chromatography.
A liquid with a high boiling point on an inert porous solid.