3.10 Aromatic chemistry

• The specification for AQA includes topics on bonding with benzene and delocalized electrons, and reactions of benzene, specifically electrophilic substitution reactions.
• Benzene is a cyclic compound that is planar, has the formula C6H6, and each carbon is bonded to two other carbons and one hydrogen atom.
• The final lone electron in benzene is in a p orbital that sticks out above and below the plane of rings.
• Delocalized electrons and lone orbitals combine together to form a ring, which looks like a doughnut, and they share electrons and distribute it equally around the benzene ring.
• The halogen carrier in the Friedel-Crafts reaction is a compound that has an extra chlorine atom attached to it, which is used to form HCl when it reacts with a hydrogen atom.
• Water is a byproduct of the nitration of benzene.
• In the nitration of benzene, the first step is to form a powerful electrophile by reacting nitric acid with sulfuric acid, which forms nitrobenzene.
• The intermediate formed in the Friedel-Crafts reaction is a phenyl group attached to a benzene ring with a hydrogen atom shortened due to its importance in forming a bond with the halogen carrier.
• The second step in the nitration of benzene is to use the nitronium ion formed in the previous step to react with benzene, producing nitrobenzene.
• All bonds in benzene, including the CC bonds, are the same length, which is 139 picometers.
• The length of the bonds in benzene sits between a single bond (154 picometers) and a double bond (134 picometers), giving it a unique property.
• The delocalized electrons in the benzene ring are attracted to the carbo cation, forming a bond and breaking the ring structure.
• The semi-circular electron ring structure should not extend beyond the adjacent carbons to the one that's been attacked.
• Alcl3 is a halogen carrier used in Friedel-Crafts isolations.
• The carbo cation is primed and ready to be introduced to benzene where it can attack and add on to the benzene ring.
• The halogen carrier accepts a pair of electrons away from the acyl group, forming a carbo cation.
• A preparatory step is necessary to create a strong positive charge, such as reacting an acyl chloride with a halogen carrier.
• Benzene ring breaking is difficult due to the delta positive charge of chlorides or acyl chlorides.
• The lower negative values from -208 suggest that benzene is more stable than the theoretical value due to its delocalized electron structure.
• Benzene is more stable because the bond length is equal in all bonds and the bond density is improved by bond enthalpy.
• The predicted energy for three double bonds in benzene is -360 kilojoules per mole, but the experimental value is -208 kilojoules per mole, suggesting that more energy is required to break the bonds in benzene than in cyclohexylene.
• Benzene can also be used in reactions such as Friedel-Crafts and nitration.
• The enthalpy change of hydrogenation for benzene is -208 kilojoules per mole, which is lower than expected if it had three separate double bonds.
• Benzene can be used to name other aromatic compounds, such as aniline, by adding benzene to the end of the name.
• Benzene has a unique property known as delocalized electron shell or delocalized electron ring.
• Friedel-Crafts isolation is a reaction mechanism developed by Charles Friedel and James Kraft to help solve the problem of benzene's stability being a barrier to reaction.
• The stability of benzene comes from the delocalized ring structure.
• Benzene does not undergo addition reactions, instead it undergoes electrophilic substitution.
• In Friedel-Crafts isolation, an acyl group, which is RC or, is added to a benzene molecule, making the benzene structure weaker and easier to modify.
• Addition reactions do not happen in benzene because they disrupt the harmony of the delocalized structure.
• Benzene undergoes electrophilic substitution instead of addition reactions.
• The hydrogen functional group on the benzene ring is substituted for the electrophile that is reacting with it.
• There are two types of reactions that benzene undergoes: Friedel-Crafts isolation and nitration reaction.
• Benzene is more than happy being a stable molecule and anything which disrupts that stability puts up a bit of resistance.
• Atoms, molecules, protons, neutrons, electrons, and anything else want to be in the lowest energy state possible.
• Calculated structure is sometimes easier to draw for reactions.
• Benzene is more stable than the theoretical alternative, cyclohexene, according to the Coqille a model.
• If the structure of benzene had three double bonds, the enthalpy change of hydrogenation would be minus 360 kilojoules per mole.
• The stability of benzene is due to bond enthalpies.
• Benzene can be represented using a skeletal formula, which is used to draw benzene and is used throughout organic chemistry.