Y13 Aromatics Flashcards
Aromatic compound definition
Contains at least one benzene ring
Arene definition
Aromatic hydrocarbon which contains at least one benzene ring
What are the 3 problems with Kekule’s benzene model?
- Reactivity
- Bond length
- Enthalpy change of hydrogenation
Explain why reactivity is a problem with Kekule’s benzene model?
Benzene doesn’t undergo electrophilic addition reactions, doesn’t react with Br2, and usually undergoes substitution reactions
Explain why bond length is a problem with Kekule’s benzene model?
Carbon to carbon bond lengths in benzene are all equal and a C-C single bond is longer than a C=C double bond
Explain why enthalpy change of hydrogenation is a problem with Kekule’s benzene model?
Enthalpy change of hydrogenation is less exothermic than expected which tell us benzene is a more stable molecule than Kekule’s model suggests
When is benzene the suffix?
When small alkyl groups, NO2, and halogens are attached
What is the prefix when NO2 is a substituent to benzene?
Nitro-
When is benzene the prefix?
When the benzene ring is attached to an alkyl chain with a functional group or with 7+ carbons
What is the prefix of benzene?
Phenyl-
Describe the delocalised model of benzene (4 bullet points)
Each carbon has a spare electron in a p-orbital
P-orbitals overlap sideways
Form an electron pi cloud above and below the ring
Pi electrons are delocalised and electron density is more spread out
What 3 things must be remembered when drawing out the electrophilic substitution of benzene mechanism?
- How many e- are spread over how many carbons e.g. 4e- spread over 5C in step 2
- Benzene ring is broken in step 2
- on the carbon where the benzene ring is broken
What is the conversion, reagents, and conditions of the halogenation of benzene?
Conversion: Benzene –> chloro/bromobenzene
Reagents: Cl2/Br2
Conditions: Halogen carrier catalyst (Fex3/Alx3)
What 3 equations must be included with the halogenation of benzene?
- Forming electrophile
- Curly arrows (mechanism)
- Reforming catalyst
What is the standard equation for forming an electrophile in the halogenation of benzene?
Alx3 + x2 –> Alx4- + x+
(Same with Fex3)
What is the curly arrow equation for the halogenation of benzene the same as?
Electrophilic substitution of benzene mechanism (broken ring, +)
What is the standard equation for reforming the catalyst in the halogenation of benzene?
Alx4- + H+ –> Alx3 + Hx
What is the conversion, reagents, conditions, and type of reaction for the alkylation of benzene?
Conversion: Benzene –> alkylbenzene
Reagents: Haloalkane
Conditions: Alx3/Fex3
Type: Electrophilic substitution
What is the conversion, reagents, conditions, and type of reaction for the acylation of benzene?
Conversion: Benzene –> aromatic ketone
Reagents: Acyl chloride
Conditions: Alx3/Fex3
Type: Electrophilic substitution
What is the method for purifying an organic solid (4 steps)?
- Dissolve impure solid in MINIMUM volume of HOT solvent
- COOL
- FILTER under REDUCED PRESSURE
- Wash with cold solvent and leave to DRY
Why does the minimum volume of solvent have to be used when purifying an organic solid?
If too much solvent is used, more of the organic compound will remain in solution on cooling
Why does hot water have to be used when purifying an organic solid?
Ensures maximum recrystallisation
Why must the sample be cooled in ice when purifying an organic solid?
Organic compound insoluble in cold solvent so will recrystallise and impurities stay dissolved in solution
Why must the sample be washed with cold water when purifying an organic solid?
Any remaining impurities are washed off and removed
