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A-Level Chemistry > Topic 18 Organic 3 > Flashcards

Topic 18 Organic 3 Flashcards

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1
Q

What process occurs when benzene reacts with a halogen?

A

Conditions:

  • Warmed when catalyst added
  • FeBr₃

Formation of Br⁺ ion:
Br₂ + FeBr₃ –> Br⁺ + FeBr₄⁻

Reaction:
Delocalised electrons bond to the Br⁺ ion. This is shown by breaking the circle of delocalised electrons and adding a plus at the centre of the benzene ring. The H atom then breaks off giving a full ring of delocalised electrons. (Shown on One Note pg Revision - Electrophilic reactions of benzene)

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2
Q

What process occurs when benzene reacts with HNO₃?

A

Conditions:

  • 55ᵒC
  • Concentrated H₂SO₄

Formation of NO₂⁺ ion:
HNO₃ + H₂SO₄ –> NO₂⁺ + HSO₄⁻ + H₂O

Reaction:
Delocalised electrons bond to the NO₂⁺ ion. This is shown by breaking the circle of delocalised electrons and adding a plus at the centre of the benzene ring. The H atom then breaks off giving a full ring of delocalised electrons. (Shown on One Note pg Revision - Electrophilic reactions of benzene)

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3
Q

What is electrophilic substitution in arenes?

A

A reaction which involves the replacement of a hydrogen atom following the attack by an electrophile.

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4
Q

What is a halogen carrier?

A

A term used to describe substances such as FeBr₃ and AlCl₃ which catalyse the reaction of benzene with Cl₂ or Br₂.

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5
Q

What is nitration of an arene?

A

An electrophilic substitution where a hydrogen atom is replaced by a nitro group, -NO₂

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6
Q

What are Friedel-Crafts reactions?

A

An electrophilic substitution reaction in which a hydrogen atom in an arene is replaced by an alkyl or acyl group following an attack by a carbocation or an acylium ion electrophile.

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7
Q

What are the conditions used during Friedel-Crafts reactions?

A
  • Heated

- AlCl₃ catalyst

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8
Q

How are carbocations and acylium ions formed during Friedel-Crafts reactions?

A

CH₃Cl + AlCl₃ –> CH₃⁺ + AlCl₄⁻

or CH₃COCl + AlCl₃ –> CH₃CO⁺ + AlCl₄⁻

Both (so catalyst is unchanged):
H⁺ + AlCl₄⁻ –> HCl + AlCl₃

(On One Note pg Revision - Electrophilic reactions of benzene)

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9
Q

What is an arene?

A

A hydrocarbon with a ring or rings of carbon atoms of which there are delocalised electrons.

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10
Q

What are delocalised electrons?

A

Non bonding electrons that are fixed between 2 atoms in a bond but shared between 3 or more atoms.

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11
Q

What is Kekule’s model of benzene?

A

A ring of carbons with alternating single and double bonds.

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12
Q

What is hydrogenation?

A

The reaction of hydrogen gas with a molecule containing a double bond.
Hydrogen adds across the double bond making it saturated.

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13
Q

Why is Kekule’s model of benzene incorrect?

A
  • Bond lengths –> as C-C = 0.154nm and C=C = 0.134nm but the bond lengths in benzene are 0.139nm.
  • Hydrogenation enthalpies –> as Kekule’s benzene gives an estimate of ΔH = -360 KJ mol⁻¹, where as benzene actually gives ΔH = -208 KJ mol⁻¹.

This displays that benzene does not have typical C-C and C=C bonds and therefore has a ring of delocalised electrons.

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14
Q

How does the ring of delocalised electrons in benzene form?

A

This ring forms as a result of P orbitals of neighbouring C atoms overlapping and forming π bonds.

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15
Q

What occurs when arenes burns in air?

A

Due to the high ratio of C to H atoms in arenes, it burns with a very smoky flame and forms 6CO₂ + 3H₂O.

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16
Q

What process occurs when benzene reacts with hydrogen?

A

The delocalised ring of electrons is broken as the hydrogen is added and all bonds between 2 C atoms become saturated.

Conditions = Raney Nickel + 200ᵒc

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17
Q

What process occurs when phenol reacts with Bromine Water (Br₂)?

A

3Br₂ is added to the phenol at room temperature.
2,4,6-tribromophenol is formed rapidly.
There is no need for a catalyst.

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18
Q

What process occurs when phenol reacts with Nitric Acid?

A

The reaction between 2 C₆H₅OH & 2 HNO₃ forms 2-nitrophenol, 4-nitrophenol and water.
This occurs at room temperature with no catalyst.

19
Q

Why does phenol react much quicker with milder conditions than benzene?

A

A lone pair of electrons on the -OH functional group of phenol interacts with the delocalised ring of electrons in the benzene ring and releases electrons which increases the electron density. This makes an electrophilic attack easier and therefore phenol is more reactive.

20
Q

What are primary, secondary, tertiary and quaternary amines?

A

Primary - Nitrogen atom has 2 hydrogen atoms attached
Secondary - Nitrogen atom has 1 hydrogen atom attached
Tertiary - Nitrogen atom has 0 hydrogen atoms attached
Quaternary - Same as tertiary but has another hydrocarbon chain attached to the nitrogen lone pair

21
Q

How do you name amines?

A
  • Change the name of the hydrocarbon to be alkyl (methyl, ethyl, propyl etc) (e.g. ethane –> ethyl)
  • Use amine as the suffix after the alkyl
  • If it is secondary, tertiary or quaternary use N-alkyl (N-alkyl-N-alkyl) as a prefix to the alkyl
  • The alkyl groups in the prefix are in alphabetical order
  • If the same alkyl group is used in the prefix multiple times use di/tri/tetra etc
  • if there is more than one functional group attached, use the prefix amino instead (e.g. NH₂-CH₂CH₂COOH is (1-)aminopropanoic acid)

E.g. CH₃CH₂CH₂N(CH₂CH₃)CH₃ is
N-ethyl-N-methylpropyl(-1-)amine

22
Q

What are amines and amides?

A

Amine - An organic substance with the functional group -NH₂

Amide - An organic substance with the functional group CONH (with C=O)

23
Q

How do you change the NO₂ functional group on a benzene ring to NH₂?

A

Concentrated HCl (6[H]) is added to nitrobenzene (C₆H₅NO₂) with a Tin (Sn) catalyst and heat. This forms phenylamine (C₆H₅NH₂) + 2H₂O.

24
Q

How do amines act as nucleophiles?

A

The nitrogen atom in the amine functional group has a lone pair of electrons which allows the amine to act as a nucleophile.

In a reaction, the lone pair on the N atom attacks the C centre of a Halogenoalkane molecule (e.g. CH₃Br). The C bond between the C atom and the halogen atom (Br) is broken.

E.g. CH₃Br + C₄H₉NH₂ –> C₄H₉NH₂CH₃⁺ + Br⁻
C₄H₉NH₂CH₃⁺ – > C₄H₉NHCH₃ + H⁺

25
Q

What occurs when an amine reacts with an acyl chloride?

A

An amide is formed. This is because the lone pair on the N atom attacks the C atom in the acyl chloride and the Cl atom is removed.

E.g. CH₃COCl + C₄H₉NH₂ –> CH₃CONHC₄H₉ + HCl

26
Q

What occurs when ammonia reacts with a halogenoalkane?

A

An amine is formed. This is because the lone pair on the N atom attacks the C atom in the halogenoalkane and the halogen atom is removed.

E.g. C₄H₉Br + NH₃ –> C₄H₉NH₃⁺ + Br⁻
C₄H₉NH₃⁺ + NH₃ –> C₄H₉NH₂ + NH₄⁺
(NH₄⁺ + Br⁻ –> NH₄Br)

27
Q

How can an amine be formed from a nitrile?

A

There are two different methods.
The first is hydrogenation of the nitrile because the N atom in the C≡N reacts with the H₂ forming a C-NH₂ bond.

E.g. C₄H₉C≡N + 2H₂ –> C₄H₉NH₂

The second method is the reduction of the nitrile followed by a dilute acid because the H⁺ ions in the acid react with the nitrile.

E.g. C₄H₉C≡N + 4[H] –> C₄H₉NH₂

28
Q

How are secondary, tertiary and quaternary amines formed from primary amines?

A

They form when a primary amine reacts with a halogenoalkane. The formations are (primary –> secondary), (secondary –> tertiary), (tertiary –> quaternary salt).

E.g. C₄H₉NH₂ + CH₃Br –> C₄H₉NH₂⁺CH₃ + Br⁻ –> C₄H₉NHCH₃ + HBr (Primary –> Secondary)

C₄H₉NHCH₃ + CH₃Br –> C₄H₉NH⁺(CH₃)₂ + Br⁻ –> C₄H₉N(CH₃)₂ + HBr (Secondary –> Tertiary)

C₄H₉N(CH₃)₂ + CH₃Br –> C₄H₉N⁺(CH₃)₃ + Br⁻

29
Q

What is an amino acid? and what is a 2-amino acid?

A

Amino Acid –> Compounds which contain both the amino group and a carboxylic acid group.

2-Amino Acid –> Amino acids that have the formula RCH(NH₂)COOH. The amino group is attached to the carbon next to the carboxylic group.

30
Q

What is a zwitterion?

A

An ion that has both a positive and negative charge.

31
Q

What is a amino acid zwitterion?

A

An amino acid that contains both NH₃⁺ & COO⁻ ions.

32
Q

What is the isoelectric point of an amino acid?

A

The pH value at which the amino acid exists as a zwitterion. This can vary between different amino acids due to the different characters of the attached R groups. (Some may have more COOH and others more NH₂)

33
Q

What amino acid ions form at different pH values?

A

Low pH –> NH₃⁺CH(R)COOH

Isoelectric Point –> NH₃⁺CH(R)COO⁻

High pH –> NH₂CH(R)COO⁻

34
Q

What are peptides and peptide bonds?

A

Peptide –> Chains of amino acids that are linked by peptide bonds.

Peptide bond –> An amide link (CONH) formed when the -NH₂ group of one amino acid reacts with the -COOH group of another

35
Q

What is a condensation reaction?

A

A reaction in which molecules join together by splitting off a small molecule such as water.

In amino acids this is when a H⁺ in the -NH₂ group of one amino acid and the OH⁻ in the -COOH group in another split off to form H₂O and the remaining NH⁺ and CO⁻ react to form a peptide bond.

36
Q

What is condensation polymerisation?

A

When a polymer is formed by a series of condensation reactions.

37
Q

What are polyesters and polyamides?

A

Polyester –> Polymers that have ester links between monomer units.

Polyamide –> Polymers with amide links between monomer units.

38
Q

What is a Grignard reagent?

A

An organometallic compound with the general formula RMgX formed from a halogenoalkane RX and magnesium.

39
Q

How are Grignard reagents formed?

A

They are formed during the reaction of a halogenoalkane (RX) and magnesium in dry ether.

Dry ether is important as it does not react with the product (RMgX). Other substances e.g. H₂O do react with the product.

40
Q

Why are Grignard reagents used?

A

They are used because they turn the 𝛿⁺ C atom (attached to the halogen) to 𝛿⁻. This allows for the product (RMgX) to act as a nucleophile and attack other ) 𝛿⁺ centres in other molecules.

R(𝛿⁺) - X(𝛿⁻) + Mg –> R(𝛿⁻) - Mg(𝛿⁺) - X(𝛿⁻)

41
Q

What is steam distillation?

A

A synthetic technique used to distil a liquid which decomposes when heated at its boiling temperature and does not mix with water.

The distillate consists of a layer of water with separate layer of immiscible liquid.

42
Q

What is a desicator?

A

A container that is used to dry a solid and also to store materials in a dry atmosphere.

43
Q

What is a vapour?

A

A gas which is formed by the evaporation of a substance that is usually a liquid or solid at room temperature.

They are not called gases as they are easily condensed due to their relatively strong intermolecular forces.

44
Q

What does volatile mean?

A

This means a substance is evaporated easily.

A-Level Chemistry (20 decks)

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