organic 3

• What are arenes?


  Arenes are aromatic compounds that contain a benzene ring as part of their structure.
• Why do arenes have high melting points?

  They have high melting points due to the high stability of the delocalised benzene ring.
• Why do arenes have low boiling points?

  Arenes have low boiling points because they are non-polar molecules and generally cannot be dissolved in water.
• What is the molecular formula of benzene?

  The molecular formula of benzene is C₆H₆.
• What type of electrons are present in the benzene ring structure?

  Benzene has a ring of delocalised electrons.
• How does the p-orbital of each carbon atom contribute to benzene's structure?

  The outer electron from the p-orbital of each carbon atom is delocalised into the centre to form the central ring.
• What results from the overlap of electrons in benzene?

  The overlap of electrons results in the formation of π-bonds.
• Why is benzene considered very stable compared to other molecules of a similar size?

  The delocalised ring structure makes benzene very stable compared to other molecules of a similar size.
• What was the initial predicted structure of benzene based on empirical measurements?

  The initial predicted structure of benzene was similar to that of cyclohexatriene, with three double bonds and three single bonds.

  
• What did chemical evidence and experiments suggest about benzene's structure?

  Chemical evidence and experiments suggested that benzene actually had a different structure than cyclohexatriene.

  
• What was the predicted enthalpy change of hydrogenation for benzene?

  The predicted enthalpy change of hydrogenation for benzene was -360 kJmol^-1.
• What was the actual enthalpy change of hydrogenation of benzene?

  The actual enthalpy change of hydrogenation of benzene was -208 kJmol^-1.
• What does a less negative enthalpy change of hydrogenation indicate about benzene's stability?

  A less negative enthalpy change of hydrogenation indicates that benzene is more stable than the suggested cyclohexatriene structure predicts.

  
• What did X-ray diffraction experiments reveal about benzene's bond lengths?

  1. ray diffraction experiments showed that all the bond lengths between carbon atoms in benzene are the same.
• How does the bond length in benzene compare to that of cyclohexatriene?

  Each bond in the benzene ring has an intermediate length in between that of a double and single bond.
• What does the cyclohexatriene structure fail to explain regarding benzene?

  The cyclohexatriene structure does not explain the infrared data collected from benzene molecules.
• What type of reactions is benzene resistant to?

  Benzene is resistant to electrophilic addition reactions.
• Why does benzene not undergo electrophilic addition reactions?

  Benzene does not undergo electrophilic addition because it would involve breaking up the stable delocalised ring of electrons.
• What type of reactions does benzene undergo instead of electrophilic addition?

  Benzene undergoes electrophilic substitution reactions.
• What makes the delocalised ring in benzene susceptible to attack from electrophiles?

  The delocalised ring in benzene is an area of high electron density.
• What happens during an electrophilic substitution mechanism in benzene?

  Electrophiles attack the electron ring, partially destroying it, before it is then restored to form the aromatic product.

  
• What is halogenation in the context of benzene reactions?

  Halogenation is a type of electrophilic substitution reaction in which benzene reacts with halogens in the presence of a catalyst.
• What role does the catalyst play in halogenation reactions of benzene?

  The catalyst is required to generate the electrophile, which then reacts with benzene.
• How does iron(III) bromide function in the halogenation of benzene?

  Iron(III) bromide polarises the bromine molecule, making it easier for the bromine bond to break so that the bromine atom can act as an electrophile.
• What is nitration in the context of benzene reactions?

  Nitration is a form of electrophilic substitution where the electrophile is a NO₂⁺ ion.
• How is the NO₂⁺ electrophile produced in nitration reactions?

  The NO₂⁺ electrophile is produced in the reaction of concentrated sulfuric acid with concentrated nitric acid.
• What role does sulfuric acid play in the nitration of benzene?

  Sulfuric acid behaves as a catalyst since it is not used up in the reaction.
• What occurs when benzene is heated with the reagents used in nitration?

  These reagents lead to the substitution of the NO₂⁺ electrophile onto the benzene ring, replacing a hydrogen atom.
• What happens to the hydrogen ion released during the nitration of benzene?

  The hydrogen ion released reacts with the HSO₄^- to reproduce the sulfuric acid catalyst.
• What is the significance of the reaction temperature during nitration?

  The reaction temperature must be 55°C for mono-substitution; at higher temperatures, multiple substitutions can occur.
• Why is it vital that only one substitution occurs during the production of aromatic amines?

  It is vital that only one substitution occurs for the production of aromatic amines.
• What is Friedel-Crafts acylation in relation to benzene?

  Friedel-Crafts acylation is a reaction where the delocalised electron ring in benzene acts as a nucleophile, attacking acyl chlorides.
• What must occur for Friedel-Crafts acylation to take place?

  A reactive intermediate must be produced from a reaction between the acyl chloride and an aluminium chloride catalyst.
• What happens at the end of the Friedel-Crafts acylation reaction?

  The H⁺ ion removed from the ring reacts with the AlCl₄^- ion to reform the aluminium chloride, indicating it to be a catalyst.
• What is produced as a result of Friedel-Crafts acylation?

  The product of Friedel-Crafts acylation is a phenylketone.
• What is the significance of the benzene group in the context of Friedel-Crafts acylation?

  The benzene group is called a phenyl group in the context of Friedel-Crafts acylation.
• What are some common applications of phenylketones produced from Friedel-Crafts acylation?

  Phenylketones are commonly used in the industrial production of dyes, pharmaceuticals, and explosives.
• What is phenol and how is it produced?

  Phenol is an aromatic compound with the formula C₆H₅OH, produced in electrophilic substitution reactions with benzene.
• How does phenol react with bromine water?

  Phenol can react with bromine water via multiple substitutions to produce 2,4,6-tribromophenol, which forms as a white precipitate.
• What is the result of the reaction between phenol and bromine water?

  This reaction decolourises bromine water.