[Year 2] CD

Cyclic planar.

• Each carbon has 4 valent electrons. • 3 of these are used to bong with 2 carbons and a hydrogen. • The lone electron exists in the p-orbital above and below the planar ring. • This creates a delocalised ring of electrons.

• Hexagonal ring. - Alternating double bonds.

• By measuring and comparing their enthalpy changer of hydrogenation. • Benzene has a larger enthalpy of hydrogenation. • Therefore it is more stable.

• X-ray diffraction shows benzene has the same bond lengths, in Kekule’s structure, they would be different. • Enthalpy change of hydrogenation, is not what it is theoretically for Kekule’s structure. • Benzene doesn’t react with bromine water (electrophilic addition of bromine), as no colour change is observed.

• Benzene is stable due to its stable ring of delocalised electrons. • So if an addition reaction were to take place it would make benzene less stable.

• Benzene has a high electron density due to its delocalised ring. • This is attractive to an electrophile. • So a substitution can take place kicking off hydrogen for the attracted electrophile.

• ‘-benzene’ (e.g. bromobenzene) - ‘phenyl-‘ (e.g. phenylamine)

• Delocalised electrons on benzene are attracted to the positive charge on the electrophile. • This breaks the ring and forming an unstable intermediate with the electrophile bonded with carbon on benzene. • The area of positive charge (where the initial electrons left) attracts electrons from the C-H of the same carbon. • This causes H⁺ to act as a leaving group (which is substituted for) and restores the delocalised ring. (Diagram: https://bit.ly/3mNH9Zb )

A very strong electrophile as benzene is stable. • This can be done by a halogen carrier catalyst like Aluminium chloride or, Iron and iron chloride

• An acylchloride is not reactive enough by its self to react with benzene. • So it is reacted with AlCl₃ first to give… R-C⁺=O and AlCl₄⁻ … as the halogen carrier pulls electrons from the chlorine on the acylchloride. • Under reflux and using a dry ether solvent electrophilic substitution takes place with the carbonation. • The hydrogen on the intermediate is attacked by electrons from a Cl-Al bond reforming the catalyst and forming HCl. ( Diagram: https://bit.ly/3dmnigq )

• A halogenoalkane is not reactive enough by its self to react with benzene. • So it is reacted with AlCl₃ first to give… R⁺ and AlCl₄⁻ … as the electrons in the R-Cl bond is attracted to the delta negative chlorine. Which then breaks the bond and is attracted to the delta positive aluminium halogen carrier. • Under reflux and using a dry ether solvent electrophilic substitution takes place with the carbocation. • The hydrogen on the intermediate is attacked by electrons from a Cl-Al bond reforming the catalyst and forming HCl. (Diagram https://bit.ly/2RGGbT7 )

• A halogen is not reactive enough by its self to react with benzene. • AlCl₃ polarises Cl₂ • Delacalised electron in benzene attack the delta positive end and the electrons from the Cl-Cl bond is attack the delta positive AlCl₃ • (is an electrophilic substitution.) • The hydrogen on the intermediate is attacked by electrons from a Cl-Al bond reforming the catalyst and forming HCl. ([1] Diagram: https://bit.ly/3mQgBq1 ) ([2] Diagram: https://bit.ly/2Q8Pbj8 )

• Nitric acid is not reactive enough by its self to react with benzene. • So it is reacted with a sulphuric acid cataylst… HNO₃ + H₂SO₄ → H₂NO₃⁺ + HSO₄⁻ (nitric acid acts as a base) • H₂NO₃⁺ decomposes to form a nitronium ion… H₂NO₃⁺ → NO₂⁺ + H₂O • electrophilic substitution of NO₂⁺ to form nitrobenzene. • The H⁺ leaving group reacts with HSO₄⁻ to reform H₂SO₄. (Diagram: https://bit.ly/3ge6VEK )

• below 55ᵒC - Sulphuric acid catalyst.

• Sulphuric acid is not reactive enough by its self to react with benzene. • So it is turned into sulfur trioxide first… H₂SO₄ → H₂O + SO₃ • SO₃ can then act as the electrophile in electrophilic substitution. • in the electrophilic substitution a lone pair of lectron from the R-SO₃⁻ attacks the H on the benzene forming R-SO₂OH as the substituted group ([1] Diagram: https://bit.ly/32dXZqC ) ([2] Diagram: https://bit.ly/3gaElDV )

• Conc sulfuric • under reflux OR • 40ᵒC with fuming sulfuric acid • fro 30 mins.

Fuming sulfuric acid results in a higher concretion of sulfur trioxide which is the electrophile in the sulfonation of benzene.

Due to their delocalised electron ring systems. • These are able to extend over molecules that have lone pairs of electrons. • Like the azo group.

• Nitrous acid is made first by reacting hydrochloric acid with sodium nitrate… NaNO₂ + HCl → HNO₂ + NaCl • In situ, the nitrous acid, hydrochloric acid and phenylamine react to form diazonium salt and water. • a phenol is reacted with the diazonium salt and sodium hydroxide in a coupling reaction. • This forms the azo link and produces water and sodium chloride. • the azo dye then precipitates out.

• Below 5ᵒC. - In situ with the production of nitrous acid as nitrous acid is unstable.

• amine groups form hydrogen bonds with -OH on cellulose fibres (like cotton). • Ionic slats form ionic bonds in acidified conditions as the fibre is protonated. • Some groups can covalently bond with groups on the fibre.

The chromophore.

• Soluble in water. • Able to bond with fibres. • Have a chromophore.