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OCR Chemistry > F324 > Flashcards

F324 Flashcards

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1
Q

State the mechanism and conditions for benzene nitration.

A

Mechanism: electrophilic substitution.

Conditions: concentrated HNO3, concentrated H2SO4 and 50 degrees.

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2
Q

State the conditions for reduction of nitrobenzene.

A

Tin and concentrated HCl in reflux.

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3
Q

State the conditions to form a diazonium ion from phenylamine.

A

Sodium nitrite (NaNO2) and HCl, below 10 degrees.

This will cause a chloride diazonium salt.

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4
Q

What are the conditions to form an azo dye from a diazonium ion? State the mechanism.

A

Mechanism: electrophilic substitution.

Conditions: phenol in alkaline conditions, below 10 degrees.

This is a coupling reaction.

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5
Q

Why should a diazonium ion be kept below 10 degrees?

A

At temperatures above 10 degrees, it decomposes to make phenol.

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6
Q

What is formed in the acid hydrolysis of a polyamide?

A

Amine and a carboxylic acid. All amine groups are protonated.

HCl would form NH3Cl.

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7
Q

What is formed in the base hydrolysis of a polyamide?

A

Amine and salts of all carboxylic acid groups.

NaOH would form sodium salts.

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8
Q

What colour precipitate does phenol and bromine make?

A

White precipitate.

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9
Q

How does TLC separate compounds?

A

Adsorption onto solid stationary phase.

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10
Q

How does a liquid stationary phase separate compounds?

A

Relative solubility.

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11
Q

Paper chromatography and TLC analysis involves Rf values. How are Rf values calculated?

A

Distance travelled by component/distance travelled by solvent.

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12
Q

What are limitations of GC?

A

Unknown compounds have no reference retention times for comparison. Similar compounds have similar retention times.

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13
Q

Review the evidence for the delocalised benzene structure.

A

All C-C bonds are the same length. If the structure had double bonds, you would expect them to be longer than single bonds.

Benzene only reacts with bromine when a halogen carrier is used.

The enthalpy change of hydration for benzene is much less than expected when compared with cyclohexene. Benzene is much more stable.

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14
Q

List the things that should be mentioned when describing the bonding of benzene.

A
  • sideways p orbital overlap above and below the ring.
  • overlapping p orbitals form delocalised pi bonds.
  • sigma C-C bonds.
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15
Q

What is the reaction between a halogen carrier and a halogen?

A

AlBr3 + Br2 —> AlBr4- + Br+

Note: benzene has a low electron density, so multiple substitution does not occur.

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16
Q

Name four uses of phenol.

A

Production of plastics, antiseptics. disinfectants and resins for paints.

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17
Q

What should be mentioned when comparing resistance to bromination?

A
  • delocalised pi bonds.
  • lone pair from O or N is delocalised into the ring.
  • pi bonds in alkenes are localised (between two carbon atoms).
  • benzene cannot polarise bromine.
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18
Q

Describe the solubility of carboxylic acids.

A

Molecules that have not dissociated for hydrogen bonds with water due to OH groups.
Dissociated molecules form strong dipole-dipole attractions between COO- and the partially positive H in water.
As formula mass increases, solubility decreases because van dear waal’s forces start to dominate its properties.

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19
Q

Name two uses of esters.

A

Perfumes and flavourings.

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20
Q

What are optical isomers?

A

Non-superimposable mirror images about a chiral centre.

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21
Q

Which two monomers form the polyester Terylene?

A

Benzene-1,4-dicarboxylic acid and ethane-1,2-diol.

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22
Q

Which single monomer is used to make the ester poly(lactic acid).

A

2-hydroxypropanoic acid.

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23
Q

Name a use of polyesters and polyamides.

A

Fibres in clothing. The polymers have strong intermolecular forces due to having a high surface area of contact.

24
Q

State two ways in which a condensation polymer can biodegrade.

A

They can be photodegradable since the C–O bond absorbs UV radiation and breaks.
The ester or amide (peptide) bond can be hydrolysed.

25
Q

State the mechanism and conditions for monohalogenation of benzene.

A

Mechanism: electrophilic substitution.

Conditions: halogen, halogen carrier.

26
Q

What is formed when phenol reacts with NaOH or Na.

A

NaOH: sodium phenoxide and water.

Na: sodium phenoxide and hydrogen.

-O-Na+

27
Q

Phenol reacts with bromine to form…

A

…2,4,6-tribromophenol.

28
Q

Name two test tube tests to identify types of carbonyls.

A
  1. Add tollens reagent, an aldehyde will be oxidised to a carboxylic acid (silver mirror as Ag+ is reduced).
  2. Add acidified potassium dichromate VI. Carbonyls that have a tertiary alcohol group will show no colour change.
29
Q

What is the difference between a polyamide and a polypeptide?

A

A polypeptide is formed from alpha amino acids only. A polyamide is a condensation polymer with the amide functional group.

30
Q

Why doesn’t 2,4-DNPH react with carboxylic acids?

A

Carboxylic acids are not carbonyls.

31
Q

How is an aliphatic amine prepared? Include reactions.

A

Mechanism: nucleophilic substitution.

Conditions: excess hot ethanolic ammonia.

CH3CH2Br + NH3 —> CH3CH2NH2 + HBr

NH3 + HBr —> NH4Br

The product is also a nucleophile which can react with halogenoalkanes to form secondary and tertiary amines. Excess ammonia decreases the chance of this happening.

32
Q

Show two reactions which show ammonia and an amine acting as a base.

A

NH3 + HCl NH4+ + Cl-

C2H5NH2 + HCl —> C2H5NH3+ + Cl-

The nitrogen electron lone pair accepts a proton.

33
Q

What two monomers are used to make the polyamide Kevlar?

A

Benzene-1,4-dicarboxylic acid and 1,4-diaminobenzene.

34
Q

Which two monomers are used to make the polyamide nylon-6,6.

A

Hexanedioic acid and 1,6-diaminohexane. Both monomers have 6 carbon atoms, hence the name nylon-6,6.

35
Q

What is formed in the acid and base hydrolysis of an ester?

A

Acid: carboxylic acid and an alcohol.

Base: carboxylate salt and an alcohol.

36
Q

What is triglyceride?

A

A triester of glycerol (propane-1,2,3-triol) and fatty acids.

37
Q

What is meant by isoelectric point?

A

The pH where the zwitterion exists (at maximum concentration).

38
Q

What is a zwitterion?

A

An internal salt of an alpha amino acid. It has a net charge of zero.

39
Q

What effect do basic and acidic R groups have on the isoelectric point?

A

Acidic R - lowers isoelectric point.

Basic R - increases isoelectric point.

40
Q

What is formed in acid and base hydrolysis of peptides?

A

Acid - protonated amine groups/ammonium salts and carboxylic acids.
Base - carboxylate salts and amine groups.

Peptide hydrolysis forms alpha amino acids.

41
Q

Name three disadvantages to producing drugs with mixtures of optical isomers.

A
  1. One stereoisomer may cause adverse side effects.
  2. It may be difficult to separate the stereoisomers, increasing the cost.
  3. Reduces pharmaceutical activity.
42
Q

Name three methods of synthesising a single optical isomer.

A
  1. Use enzyme catalysts that promote stereo selectivity.
  2. Use chiral synthesis/chiral catalysts.
  3. Use natural chiral starting compounds.
43
Q

What is retention time?

A

The time between injection into the column and detection.

44
Q

Chromatography separates components in a mixture between a mobile and stationary phase. The stationary phase may be…

A

…solid (TLC) or liquid on a solid support (GC).

45
Q

Name three uses of GC-MS.

A
  1. Forensics.
  2. Airport security.
  3. Space probes.
46
Q

Name two solvents used in NMR spectroscopy.

A

CCl4 and CDCl3. They are used because they don’t contain hydrogen and so don’t cause peaks.

47
Q

Which groups can undergo proton exchange?

A

NH and OH.

48
Q

What is the problem with trans fatty acids?

A

They increase bad cholesterol and increase the risk of coronary heart disease and strokes.

49
Q

What is used to make biodiesel?

A

Esters of fatty acids can be used as biodiesel.

50
Q

What does tollens reagent distinguish between?

A

Ketones and aldehydes. Tollens is not a strong enough oxidising agent to oxidise a ketone.

51
Q

How is tollens reagent made?

A

NaOH is added to AgNO3. Ammonia is then added. This forms the diammine silver ion, (Ag(NH3)2)+.

52
Q

What can be used to reduce carbonyl compounds?

A

NaBH4.

53
Q

What is the reaction to form a diazonium ion?

A

Phenylamine + HNO2+ + HCl —-> Diazonium ion+Cl- + 2H2O.

54
Q

What is the formation of nitrous acid from sodium nitrite and HCl?

A

Phenylamine + NaNO2 + 2HCl —> Diazonium ion+Cl- + NaCl +2H2O.

55
Q

Why is sodium nitrite used?

A

Nitrous acid is very unstable and decomposes very rapidly, so it is made in situ when HCl and NaNO2 are reacted.

56
Q

What is the reaction between HCl and NO2?

A

H+ + NO2- —> HNO2.

Nitrous acid is a weak acid, so this equilibrium is well over to the right.

OCR Chemistry (3 decks)

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