Arenes & benzene (unit 1 calculations also)

Question 1

Friedel crafts alkylation reaction produces….?

Answer 1

Alkylebenzenes

Question 2

Friedel crafts acylation reaction produces….?

Answer 2

Phenylketones

Question 3

In acylation…. How does acyl chlorides being polar molecules help the reaction???

Answer 3

Acyl chlorides are polar - so they can lose their chlorine atoms to form carbocations.

Question 4

What type of reaction are freidel crafts alkylation and acylation??

Answer 4

Electrophilic Substitution

Question 5

Why are the reactants of alkylation and acylation both heated under reflux with DRY ETHER???

Answer 5

Because AlCl3 is V. V. Sensitive to hydrolysis

Question 6

What conditions are the reactants of friedel crafts acylation and alkylation reacted at???

Answer 6

Reflexed in dry ether

Question 7

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??

Answer 7

It’s a halogen carrier!
It makes the electrophile/ carbocation
It forms AlCl4-

Question 8

Arenes will react with bromine using……

Answer 8

A halogen carrier!!

Question 9

Will benzene decolorise bromine water?? Why?

Answer 9

No!!! It takes too much energy to break up the delocalised ring of electrons

Question 10

Arenes will react with bromine using……?

Answer 10

A halogen carrier

Question 11

If you shake cyclohexane (any cycloalkene) with bromine water……

Answer 11

Bromine adds across the double bond to give dibromoalkane
This is an electrophilic addition reaction!
It decolourises the bromine water

Question 12

Why will Br2 not react with benzene on its own?? (Without a halogen carrier)

Answer 12

Bromine is not a strong enough electrophile to attack the benzene ring

Question 13

Benzene will undergo some addition reactions but you need v. _____ conditions!
E.g. ?

Answer 13

Very harsh conditions (in order to break the stable delocalised e- system)

H2 / Ni catalyst at 150•c

Question 14

Alternative molecule to using benzene ???

Answer 14

Methylbenzene
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Methoxybenzene

Question 15

Why do we use methlbenzene/ methoxybenzene in labs instead of benzene??

Answer 15

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

Question 16

Phenol + bromine water = ?

Answer 16

Bromine water decolourises
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Br substitutes Hydrogens 
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Forming 2,4,6-tribromophenol
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Which is insoluble in water - ppt. White solid - smells of antiseptic

Question 17

Phenol can be nitrated with ____ HNO3?

Answer 17

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!)

Question 18

The enthalpy of hydrogenation of benzene might be expected to be -360 KJmol-1 ✨✨✨ explain why it is not this value??

Answer 18

1. Delocalisation of electrons in benzene ring
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2. 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