Topic 18 Flashcards by Shayan Rafique

Describe bonding and structure of a benzene molecule

3 sigma bonds between each carbon and 2 adjacent carbon and 2 hydrogen
The lone electron in the p orbitals combine to form a delocalised ring
overlaps sideways to form pi bonds
C-C bonds are all the same length
Trigonal planar Arrangement of atoms around each carbon

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Explain why there is resonance in a benzene ring

The lone electrons in the p orbital combine and overlap and the pi bonds overlap causing resonance.
Due to this all the C-C bonds are the same length

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What are the evidence for the delocalised model of bonding in benzene instead of kekule

Data from enthalpy of hydrogenation
Carbon carbon bond lengths

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Explain evidence for benzene being delocalised via enthalpy of hydrogenation

The enthalpy of hydrogenation of benzene(-208KJ) is higher than the expected which was -360KJ
This means more energy is needed to break bonds in benzene suggesting more stable due to resonance

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What is an arene

Aromatic compound and are a class of organic compounds characterised by having the benzene ring

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Why is benzene resistant to bromination and what reactions do arenes undergo

Arenes undergo electrophillic substitution

Benzene has a high electron density due to delocalised ring this attracts electrophiles

They cannot be brominayed as they are stable as this disrupts the ring of electrons

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What are halogen carriers and why are they used in electrophillic substitution reactions of benzene

Benzene is very stable so reactions require a VERY STRONG electrophile.
These can be generated via halogen carriers such as AlCl3

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Explain alkylation reaction

React an acyl chloride or haloalkane with AlCl3 to create a strong electrophile

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Nitration of benzene: generating the electrophile
What two acids are used

Equation for Formation of electrophile: (Learn!)
HNO3 + 2H2SO4 →NO2+ + 2HSO4+ H3O+

Acid base reaction

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Nitration of benzene conditions

NO2+ electrophile by forming it from 2 reactions
H2SO4 catalyst
Temperature below 55

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Why are electrophiles attracted to react with benzene

Benzene has a high electron density as it has a delocalised ring of electrons
This is attractive to electrophiles

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Does benzene go through electrophillic addition or electrophillic substiution

Electrophillic substitution

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What type of reaction is Fields Craft Acylation and Fields Craft Acylation

Electrophillic aromatic substitution

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Fields Craft Alkylation reaction conditions,reagents
And give an example:
Benzene → alkylbenzene

Reagents: Chloroalkane in AlCl3 catalyst
Conditions: Heat under reflux
Mechanism: Electrophillic substitution

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Formation of CH3CH2+ electrophile which will react with benzene to form alkylbenzene

Formation of the electrophile.
AlCl3 + CH3CH2Cl → CH3CH2
+ AlCl4-

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What is the purpose of Fields Craft ALKYLATION

To form an alkyl Arene(alkylbenzene)

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What reaction will help form Phenyl Ketone from a benzene

Fields Craft ACYLATION

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Conditions reagents of going from benzene to Phenyl Ketone

Acyl Chloride in presence of AlCl3 catalyst
Heat under reflux
Electrophillic substitution

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Formation of electrophile for Fields Craft Acylation

Equation for formation of the electrophile.
AlCl3 + CH3COCl → CH3CO+ AlCl4

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Explain the reactivity of phenols

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In a phenol the lone pair of electrons on the
oxygen is delocalised with the electron
charge cloud of the arene ring.
The delocalised bonding changes the
reactivity of the OH group and the arene ring.

Uses of nitrating benzene

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Dyes for clothing and explosives

Describe how orbitals overlap to form pi and sigma bonds in a benzene ring

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Sigma bond:
The s orbitals directly overlap from neighbouring carbon atoms

Pi bonds:
Perpendicular p orbitals overlap sideways
So p orbitals form a delocalised pi system

How to make aspirin
Is aspirin an ester

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Ethanoic anhydride + salicylic acid —> aspirin + ethanoic acid

Why is ethanoic anhydride used instead of ethanoyl chloride

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Less corrosive
Cheaper
Does not produce HCl gas
Does not react vigorously with water

Phenols are weak acids so they disassociate weakly to form...

Phenoxide ion and H+ ion

Phenols react with 3 moles of bromine to form...

2,4,6 tribromophenol

Why can phenols react with dilute nitric acid but Benzene requires concentrated nitric acid and concentrated H2SO4

Phenols are more reactive than benzene

What are the 2 isomers formed when phenol reacts with dilute nitric acid

2-nitrophenol 4-nitrophenol

What is an aliphatic amine

An amine without an aromatic ring(benzene ring)

How to make an aliphatic amine Method 1

React Halogenoalkane with excess ammonia

What is the downside of making aliphatic amines with Halogenoalkane and excess ammonia

Produces an impure product as it produces secondary, tertiary quarternary salts

How to make aliphatic amine by Reducing Nitrile method What's the name and conditions

Catalytic hydrogenation Nickel catalyst, high temp and pressure

Benefits of making aliphatic amines using nickel catalyst and high temp and pressure (Reducing Nitrile method)

Pure product is made Cheapest method in industry

What is the 2nd method of making aliphatic amines

Using LiAlH4 in dry ether solvent Dilute acid More expensive than nickel catalyst

What is the reaction name of making aromatic amines from nitro compounds

Reduction

What is the use of aromatic amines

Dye stuffs and pharmaceutical

Name ALL conditions of making aromatic amines by reducing nitrocompounds

Reducing agents [H] which reacts with nitro compound Heat nitro compound with concentrated HCl and tin catalyst to produce a salt Heating requires reflux React salt with NaOH to produce an aromatic amine

Why can amines act as a base

They have a lone pair which can be used to accept a proton(H+)

If amines act as a base, what is the strength of the base dependant on

Dependant on the availability of the lone pair of electrons on the nitrogen

Why are aromatic amines weak bases Explain using terms such as electron density and lone pair availability

The aromatic ring( benzene ring) is an electron with drawing group so it pulls electrons away from the Nitrogen This means there is reduced electron density at the Nitrogen so lone pair availablility is reduced

Why is aliphatic amines a strong base

The alkyl groups are electron pushing groups so they push electrons towards nitrogen Electron density at Nitrogen increases so lone pair availability is reduced

Why are only small amines soluble in water

They can form hydrogen bonds with water The Lone pair on nitrogen forms H bond with H

Why can large amines not dissolve in water

As the longer hydrocarbon components are non-polar so the London forces between polar hydrocarbon chain will be stronger than hydrogen bond So will not dissolve

How to make amides

React acyl chloride with ammonia

What does the reaction ethanoyl chloride with ammonia produce

Ethanamide and HCl This is a vigorous reaction and white misty fumes of HCl are produced

How are polyamides made

Formed by reacting diamines with carboxylic acid

How is a polyester made

By reacting dicarboxylic acids and diols together Water is eliminated as it's a condensation reaction

Compare and contrast reactions between bromination of benzene and bromination of phenol

Both electrophillic addition Tri sub for phenol compared to mono sub for benzene Bromination of phenol requires room temp but bromination of phenol requires heating under reflux Bromination of phenol is more likely to occur due to oxygens lone pair interacting with ring Bromination of phenol does not require a halogen carrier

Topic 18 Flashcards

(48 cards)