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Chemistry OCR A > Module 6: Organic Chemistry and Analysis > Flashcards

Module 6: Organic Chemistry and Analysis Flashcards

1
Q

What was Kekulé’s model of benzene?

A

Alternating single and double bonds.

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2
Q

What was the evidence against Kekulé’s model of benzene?

A
  1. Benzene isn’t as reactive as other alkenes. It doesn’t decolourise bromine water and can’t undergo electrophilic addition.
  2. All the carbon-carbon bond have a length of 0.139 nm, which is between the length of carbon-carbon single and double bonds.
  3. It’s enthalpy of hydrogenation is only -208 kJ mol⁻¹, and it should be -360 kJ mol⁻¹ (3x the enthalpy of hydrogenation of cyclohexene) if Kekulé’s model is correct.
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3
Q

Describe the delocalised model of benzene?

A
  • Benzene is a planar cyclic hydrocarbon.
  • Three out of four of the valence electrons of the carbons are bonded to two other carbons. This leaves one electron.
  • The 6 p-orbitals overlap sideways in both directions above and below the plane.
    This forms a ring of delocalised electrons.
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4
Q

When naming aromatic compounds, when is benzene not the prefix?

A

When the benzene ring is attached to alkyl groups with a carbon chain of less than 7, halogens and nitro groups.

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5
Q

When naming aromatic compounds, when is benzene the prefix?

A

The prefix used is phenyl.

When benzene is bonded to an alkyl chain with a functional group or an alkyl chain with 7 or more carbons.

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6
Q

What are the three exceptions when naming aromatic compound?

A
  1. Benzoic acid
  2. Phenylamine
  3. Benzaldehyde
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7
Q

How are aromatic compounds named when benzene has more than one substituent group?

A

In alphabetical order using the smallest numbers possible.

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8
Q

What are the conditions for nitration of benzene?

A

Catalysed using concentrated sulfuric acid at 50℃ and refluxed

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9
Q

What is the difference between how alkenes and benzene react?

A

Alkenes react by electrophilic addition and benzene reacts by electrophilic substitution.

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10
Q

If a group is electron-withdrawing…

A

It deactivates the ring, as it pulls the electron ring towards it. This makes it 3,5 (meta)-directing.

An example of this is nitro groups, halogens and carbonyls.

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11
Q

If a group is electron-donating…

A

It activates the ring, as it adds to the electron density of the ring. This makes it 2,4,6 (ortho-para)-directing.

An example of this is amine groups, hydroxyl groups and alkyl groups.

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12
Q

Is a nitro group electron-withdrawing or electron-donating?

A

Electron-withdrawing.

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13
Q

Is an amine group electron-withdrawing or electron-donating?

A

Electron-donating.

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14
Q

What is a phenol?

A

A compound where a hydroxyl group is directly bonded to an aromatic ring. If the hydroxyl is primary, phenol forms the root of the name.

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15
Q

Phenol + Bromine → …

A

… 2,4,6 - tribromophenol + hydrogen bromide

Observations: Bromine decolourises and a white precipitate is formed.

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16
Q

What type of acid is phenol?

A

A weak acid. It partially dissociates to form a phenoxide ion and a proton. It’s stronger than other alcohols but weaker than carboxylic acids.

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17
Q

What atoms is NMR relevant for?

A

Hydrogen-1 and carbon-13

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18
Q

What is resonance?

A

When the nucleus absorbs energy and rapidly flips between spin states.

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19
Q

What is TMS?

A

TMS stands for tetramethylsilane, it is the reference chemical and all chemical shifts are measured against it.

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20
Q

Why is TMS used as a standard in NMR spectra?

A
  • Doesn’t interfere with other peaks
  • Single peak
  • Non-toxic and inert
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21
Q

What do the signals on a carbon NMR spectrum correspond to?

A
  • The position of the signal corresponds to the type of carbon environments, which are the individual situations each carbon is in. If two carbons are positioned symmetrically, they are equivalent
  • The intensity of each signal correspond to the number of carbons in that environment
22
Q

What do the signals on a proton NMR spectrum correspond to?

A
  • The position of the signal corresponds to the type of hydrogen environments
  • The splitting pattern corresponds to the number of adjacent hydrogens
  • The integration of each signal correspond to the number of carbons in that environment
23
Q

What type of ion do carboxylic acids form when the react with metals?

A

Carboxylate ions.

24
Q

How are carboxylic acids different to other organic acids?

A

It is acidic enough to react with carbonates.

25
Q

What type of intermolecular forces are formed between carboxylic acids and water?

A

Hydrogen bonds.

26
Q

What happens to solubility as the carbon chain length of carboxylic acids increases?

A
  • Solubility in polar solvents decreases
  • Solubility in non-polar solvents increases
27
Q

What are carboxylic acid derivatives?

A

Functional groups that can be hydrolysed to form carboxylic acid, for example, esters, acyl chlorides, amides, acid anhydrides

They all have acyl groups.

28
Q

What is esterification?

A

When carboxylic acids and alcohols are warmed with a small amount of concentrated sulfuric acid, the acid loses the -OH, and an ester is formed.

29
Q

What type of reaction do carbonyl compounds take part?

A

Nucleophilic addition.

30
Q

How are carbonyl compounds reduced?

A

Using NaBH₄, or hydrogen and a nickel catalyst under high pressure.

31
Q

How can carbonyl compounds be identified?

A

Using 2,4 DNP, yellow/orange precipitate is formed.

32
Q

How can different crystals formed after adding 2,4 DNP be distinguished?

A

Compare its melting point to a database.

33
Q

How can aldehydes and ketones be distinguished?

A

Use Tollen’s reagent, aldehyde will result in a silver/mirror-like substance.

34
Q

What type of reactions do amines undergo?

A

Nucleophilic substitution.

35
Q

How are acyl chlorides formed?

A

Carboxylic acid + SOCl₂ → acyl chloride + SO₂ + HCl

Harmful products

36
Q

What are the reactions of acyl chlorides

A

Acyl chloride + alcohol → ester + HCl
Acyl chloride + phenol → ester + HCl
Acyl chloride + H₂O → carboxylic acid + HCl
Acyl chloride + 2NH₃ → 1° amide + NH₄Cl
Acyl chloride + 1° amine → 2° amide + 1° ammonium + chloride

37
Q

What is an acid anhydride?

A

A compound formed when two carboxylic acid molecules react, removing H₂O

38
Q

What are the reactions of acid anhydrides?

A

Acid anhydride + alcohol → ester + carboxylic acid
Acid anhydride + phenol → ester + carboxylic acid

39
Q

How can hydroxynitriles be formed?

A

Carbonyls are reacted with NaCN and dilute sulfuric acid at RTP.

This is nucleophilic addition.

40
Q

What happens as the number of R-groups attached to a nitrogen in amine increases?

A

The basicity of the amine increases.

41
Q

How can ammonium salts be converted back to an amine?

A

Add NaOH.

42
Q

What are the different types of amines?

A

Primary - One R group attached to the nitrogen
Secondary - Two R groups attached to the nitrogen
Tertiary - Three R groups attached to the nitrogen
Quaternary - Four R groups attached to the nitrogen (positively charged)

43
Q

How can primary amines be formed?

A
  1. Nucleophilic substitution reaction between haloalkanes and ammonia dissolved in ethanol, and this reaction can carry on until a quaternary amine is formed. To prevent this, a large excess of ammonia should be used.
  2. Forming a nitrile by reacting a haloalkane with a cyanide ion, then reducing nitriles in a mixture of tin and concentrated HCl heated to reflux.
44
Q

What is an 𝛂 amino acid

A

Both the NH₂ and COOH groups are joined to the same carbon.

45
Q

What are zwitterions?

A

A molecule that has an equal number of positively and negatively charged functional groups, resulting in a net formal charge of zero.

Amino acids exist as zwitterions at a pH value called the isolelectric point.

46
Q

How do amino acids react?

A

The carboxylic acid groups and amine groups react as they usually do.

Amino acids react with each other, forming dipeptides with amide groups.

47
Q

How are polyamides and polyesters formed?

A

By condensation polymerisation.

48
Q

Define condensation polymerisation?

A

The joining of monomers with the elimination of a small molecule e.g. water.

49
Q

What is formed when polyamides are hydrolysed with acids and alkalis?

A

Acid: Carboxylic acids and ammonium ions
Alkali: Carboxylate ions and amines

50
Q

What is formed when polyesters are hydrolysed with acids and alkalis?

A

Acid: Carboxylic acid and alcohols
Alkali: Carboxylate ions and alcohols

Chemistry OCR A (6 decks)

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