Topic 18 Flashcards
What are the properties of Benzene?
What is the Kekulé model for benzene?
What is the evidence against the Kekulé model using bromination
According to Kekulé model:
- Bromine should be decolourised but doesn’t
- Where it should undergo an addition reaction but doesnt
What is the thermochemical evidence for disproving the kekulé model?
- Hydrogenation (adding a Hydrogen) of cyclohexane = -120 kJ/mol
- Logically because of the addition of three more bonds it should be
-120 x 3 = -360 kJ/mol - ****But its only -208 kJ/Mol****
How does the enthalpy change of formation disprove kekulé model?
- ΔHf of kekule model suggests it should be +252 kJ/mol
- But is actually +44 kJ/mol
- Meaning less energy to make
- Structure is more stable where connections between C and H are attracted and made more easily
- **Disproving kekules model**
What is the Linus Pauling model and why does the evidence support it?
- Because of the ring of stability its more stable meaning its harder to undergo addition reactions without a catalyst
- The connections of C and H attract H so it takes more energy to hydrogenate it
How do you name benzene compounds
- Determine which is the main group
- If its benzene then you use - benzene as the ending
- If its not benzene then you use phen- for benzene as the side group
What is the names of different compounds of benzene?
What is the combustion equation for benzene?
What are the conditions for addition reactions to work?
Addition of hydrogen to a normal C=C would require
- Nickle Catalyst
- 150 degrees celcius
- 1 atmosphere of pressure
What are the conditions for a benzene addition reaction?
- Ring of delocalised electrons
- Requires a N**ickel Raney Catalyst**
- Nickel with holes to increase SA
- Made by using acid to make holes
What are the different types of benzene reactions with halogens?
- Different reactions occur in the light and dark
- Since light disrupts the e- ring
- Which means a halogen carrier is required for reactions in the dark
- Dark reactions = mono substitution - control easily
- Light reactions = multi substitution - cant control
What are halogen carriers?
- Compounds that accept a lone pair of electrons
- From one of the halogen atoms
- Inducing a positive charge
What is the mechanism for a benzene halogen reaction in the dark?
What is the mechanism for a benzene halogen reaction in the light?
What is the titration of Benzene reaction?
- Benzene doesn’t mix with concentrated HNO3 alone
- Nitrating mixture is required made form concentrated nitric acid and concentrated sulfuric acid
- Which creates Nitrogen Dioxide Ion which is attracted to benzene
- Forming Nitrobenzene (toxic)
- If the temp is higher than 55 then you get multiple substitutions
What is the mechanism for benzene in a titration?
What is the alkylation of benzene and the mechanism?
What is the Acylation of benzene and the mechanism?
What are amines?
- Nitrogen-containing compounds
- With similarities to ammonia
- Where the three bonding pairs of electrons around the nitrogen
- The amount of alkyl groups dictates if the amine is primary, secondary or tertiary
How do you form amines?
- Reduction of a halogen alkane with excess ammonia
- Reducing a nitrile
What is the reaction of aliphatic amines with haloalkanes?
-
******Will increase the number of alkyl groups******
- **Primary amine → Secondary Amine (etc)**
How can nitrile be turned into an amine?
- Nitriles are reduced
- Using reducing agent lithium tetrahydridoaluminate
- Reactants mixed in dry ether (so water cannot effect the reaction)
What are aliphatic amines?
- Non-aromatic amines (don’t have the benzene ring)
- Below is an aromatic amine
