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A2 Chemistry > Rings, acids and amines > Flashcards

Rings, acids and amines Flashcards

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1
Q

Describe the structure of Benzene.

A
  • Planar hexagonal hydrocarbon
  • 3 valance electrons to bind to 2 carbon atoms and 1 hydrogen atom.
  • The fourth electron is found on the p-orbital at a right angle to the plane (120).
  • Adjacent p-orbitals overlap sideways on each side to form a ring of electron density above and below the plane.
  • Delocalised p-electron system)
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2
Q

What are the types of evidence for the structure of benzene?

A

Bond lengths
Enthalpy change of hydrogenation
Resistance to reaction

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3
Q

What is the evidence for bond length?

A

All six C-C bonds are the same length 0.139nm. Which shows there aren’t any alternative C=C bonds and single bonds (0.134nm).

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4
Q

What is the evidence for enthalpy change of hydrogenation?

A

Expected to have three times the energy as cyclohexene. (-360kjmol^-1).
However benzene has an enthalpy change of -208.
Therefore shows that benzene is 152 more stable than Kekule structure and why it doesn’t react like alkenes.

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5
Q

What is the evidence for resistance to reactions?

A

If contained C=C bonds, it would similarly to alkenes.

However does not decolourise in bromine water or takes part in electrophilic addition reactions.

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6
Q

Why is a halogen carrier needed in the process of bromination of benzene?

A

The delocalised pi electrons make benzene more stable. The electron density is higher in alkenes because of the localised electrons, therefore electrophiles are more attracted.

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7
Q

Why there is more of a relative ease of bromination of phenol compared with benzene?

A
  • A lone pair of electrons on the oxygen atom in the phenol group is drawn into the benzene ring.
  • This creates a higher electron density in the ring structure and the ring is activated.
  • This increased electron density polarises bromine molecules, which are then attracted more strongly towards the ring structure in benzene.
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8
Q

What are the uses of Phenols?

A

In the production of plastics, antiseptics, disinfectants and resins for paints.

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9
Q

What type of mechanism involves conc.HNO3?

A

Electrophilic substitution

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10
Q

What are examples of halogen carriers?

A

Iron, iron halides and aluminium halides.

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11
Q

What are the uses of phenol?

A

plastics, antiseptics, disinfectants and resin for paints.

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12
Q

What is the reducing agent?

A

NaBH4

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13
Q

What mechanism is used to reduce aldehydes and ketones?

A

Nucleophilic addition

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14
Q

What is Brady’s solution?

A

2,4- dinitrophenylhydrazine

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15
Q

What does Brady’s solution do?

A

Detects the presence of a carbonyl group in an organic compound.

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16
Q

How does Brady’s solution detect carbonyl compounds?

A

By producing a red-brick precipitate which can be used tot measure the melting point of the derivative.

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17
Q

What is the chemical name of Tollen’s reagent?

A

ammoniacal silver nitrate

18
Q

What effect does Tollen’s reaction have on ketones and aldehydes?

A

Ketones- nothing

Aldehydes- acts as a oxidising agent and silver ions are reduced to silver.
Produces silver mirror effect

19
Q

What is an alternative method to reducing carbonyl compounds?

A

React with hydrogen under a nickel catalyst

20
Q

Explain the solubility of carboxylic acids.

A

Very soluble in organic solvents.
More hydrogen bonds are made with the water and more dipole-dipole interactions.
As the carbon chain increases the solubility decreases.

21
Q

What is the acidity of carboxylic acids?

A

Weak monobasic acids

22
Q

What happens when a CA reacts with a metal?

A

Produces a salt and hydrogen

23
Q

What happens when a CA reacts with a carbonate?

A

Produces a salt, carbon dioxide and water

24
Q

What happens when a CA reacts with a base?

A

Salt and water

25
Q

What is needed in esterification?

A

An acid catalyst under reflux.

26
Q

What are the uses of esters?

A

perfumes and flavourings

27
Q

What are facts about saturated fats?

A
  • Solids at room temperature
  • found in meat and dairy products
  • are bad for your health
  • known to increase cholesterol levels which could lead to heart disease.
28
Q

What are facts about monounsaturated fats?

A
  • Contain just one C=C bond.
  • Thought to be neutral to your health.
  • Found in oils, avocados and nuts.
29
Q

What are facts about polyunsaturated fats?

A
  • are considered to be ‘good fats’
  • contain more than one C=C bond
  • Tend to be liquids at room temperature
30
Q

What is biodiesel?

A

Fuel made from waste vegetable oil or oil produced from seeds.
- Non-toxic and biodegradable

31
Q

What are the advantages of biodiesel?

A 
Renewable
Dramatically reduces emissions
Carbon neutral
High flashpoint
Simple to make
32
Q

What are the disadvantages of biodiesel?

A

Poor availability- very few outlets & manufacturers
More expensive to produce
Poorly made biodiesel can cause engine problems

33
Q

Explain the basicity of amines.

A

The lone pair on nitrogen makes amines a base.

The greater the electron density on the nitrogen, the better ability to pick up protons.

34
Q

How do you prepare aliphatic amines?

A

By substitution of halogenoalkanes with excess ethanol ammonia.
Nucleophilic substitution.

35
Q

How do you prepare aromatic amines?

A

By the reduction of nitroarenes using tin and concentrated HCl.

36
Q

What can aromatic amines become?

A

azo dyes

37
Q

What are the 2 steps of preparing an azo dye from an amine?

A

Diazotisation and coupling

38
Q

What happens in diazotisation?

A

Conditions: NaNO2/ HCl

39
Q

What happens in coupling?

A

The diazonium ion reacts with a phenol under alkaline conditions.
NaOH.

40
Q

What is a common oxidising agent?

A

(Cr2O7)^2-/H+

A2 Chemistry (7 decks)

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