Colour by Design

Question 1

What is a conjugated system

Answer 1

A conjugated system has alternating single and double bonds, allowing the overlap of p-orbitals

Question 2

Colourless and coloured objects

Answer 2

Colourless objects reflect all visible light and do not absorb any

Coloured objects absorb the wavelength of the colour they appear

Question 3

What are complimentary colours

Answer 3

Two colours which combined together produce white light

Question 4

Factors affecting colour

Answer 4

• The more electrons that are delocalised in the conjugated system, the smaller the energy gap
• Smaller energy gaps result in the absorption of longer wavelengths of light absorbed

It usually takes 5 pi bonds in a conjugated system for the system to start absorbing visible light

Question 5

The geometry of benzene

Answer 5

• The benzene ring is a regular, planar hexagon
• All the bond angles are 120 degrees
• All the carbon-carbon bonds are the same length

Question 6

Stability of delocalised structures

Answer 6

The more delocalised a system is, the more stable it is

Question 7

Benzene reaction with bromine

Answer 7

Electrophilic substitution with an iron catalyst to form bromobenzene and HBr