Quick questions on Aromaticity - WJEC A-Level Chemistry

Because addition would destroy the stable ring, benzene undergoes electrophilic substitution: a strong electrophile attacks the $\pi$ system, then $\text{H}^+$ is lost to restore aromaticity.

Phenol ($\text{C}_6\text{H}_5\text{OH}$) is more reactive than benzene because the oxygen lone pair feeds electron density into the ring, so it reacts with bromine water at room temperature (no catalyst) to give 2,4,6-tribromophenol (white precipitate). Phenol is also weakly acidic, dissolving in sodium hydroxide.

The Kekule structure drew benzene as cyclohexatriene with three localised double bonds. Three pieces of evidence overturn it: all the carbon-carbon bond lengths are equal (between single and double), benzene is far less reactive than an alkene (it does not decolourise bromine water), and its enthalpy of hydrogenation is about $208$ kJ mol$^{-1}$ less exothermic than three times that of cyclohexene. Together these show the $\pi$ electrons are delocalised over the whole ring, giving the extra stability that defines aromaticity.

Nitration of aromatics produces nitro compounds used in explosives (such as TNT) and as intermediates for azo dyes, central to the chemical industry. Antiseptics from phenol. Phenol's reactivity and mild acidity made it the first surgical antiseptic, and substituted phenols remain in disinfectants today.

Name the electrophile in the nitration of benzene. [1 mark]

State the observation when bromine water is added to phenol. [1 mark]

State why benzene is more stable than the Kekule (cyclohexatriene) model predicts. [1 mark]

State one piece of evidence that benzene does not contain localised double bonds. [1 mark]

Name the catalyst used in the bromination of benzene. [1 mark]