Arenes & benzene (unit 1 calculations also) Flashcards
Friedel crafts alkylation reaction produces….?
Alkylebenzenes
Friedel crafts acylation reaction produces….?
Phenylketones
In acylation…. How does acyl chlorides being polar molecules help the reaction???
Acyl chlorides are polar - so they can lose their chlorine atoms to form carbocations.
What type of reaction are freidel crafts alkylation and acylation??
Electrophilic Substitution
Why are the reactants of alkylation and acylation both heated under reflux with DRY ETHER???
Because AlCl3 is V. V. Sensitive to hydrolysis
What conditions are the reactants of friedel crafts acylation and alkylation reacted at???
Reflexed in dry ether
What is the purpose of AlCl3 in friedel crafts reactions and what do we call that type of chemical compound, and what species does it form??
It’s a halogen carrier!
It makes the electrophile/ carbocation
It forms AlCl4-
Arenes will react with bromine using……
A halogen carrier!!
Will benzene decolorise bromine water?? Why?
No!!! It takes too much energy to break up the delocalised ring of electrons
Arenes will react with bromine using……?
A halogen carrier
If you shake cyclohexane (any cycloalkene) with bromine water……
Bromine adds across the double bond to give dibromoalkane
This is an electrophilic addition reaction!
It decolourises the bromine water
Why will Br2 not react with benzene on its own?? (Without a halogen carrier)
Bromine is not a strong enough electrophile to attack the benzene ring
Benzene will undergo some addition reactions but you need v. _____ conditions!
E.g. ?
Very harsh conditions (in order to break the stable delocalised e- system)
H2 / Ni catalyst at 150•c
Alternative molecule to using benzene ???
Methylbenzene
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Methoxybenzene
Why do we use methlbenzene/ methoxybenzene in labs instead of benzene??
Reaction is faster (the group donates e-s to the delocalised ring ^ e- density of the ring)
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They’re non toxic - safer
Phenol + bromine water = ?
Bromine water decolourises ⭐️⭐️ Br substitutes Hydrogens ⭐️⭐️ Forming 2,4,6-tribromophenol ⭐️⭐️ Which is insoluble in water - ppt. White solid - smells of antiseptic
Phenol can be nitrated with ____ HNO3?
Dilute!!!!
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Easier than nitration of benzene B/C of the activating effect of -OH (also why substitutions more likely on 2,4,6!)
The enthalpy of hydrogenation of benzene might be expected to be -360 KJmol-1 ✨✨✨ explain why it is not this value??
- Delocalisation of electrons in benzene ring
⭐️⭐️⭐️ - Results in more energy needed to break the bonds know benzene (compared with 3 separate C=C bonds)
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ALLOW : makes benzene more stable than expected
