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A-level Chem > Carbonyl compounds > Flashcards

Carbonyl compounds Flashcards

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1
Q

What is the functional group for carbonyl compounds?

A

C=O

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2
Q

Describe the bonding of the C=O bond.

A

*Refer to carbonyl compounds notes.

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3
Q

Describe the difference between an aldehyde and a ketone (2 points).

A
  1. Aldehyde: the carbon atom of the carbonyl group is attached to one or two hydrogen atoms at the end of the chain.
  2. Ketone: the carbonyl functional group is attached to two carbon atoms in the carbon chain. C=O in the middle of the carbon chain.
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4
Q

What type of reaction forms aldehydes from primary alcohols?

A

Oxidation (partial).

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5
Q

What are the reagents and conditions to form aldehydes from primary alcohols?

A

Potassium dichromate; K2Cr2O7(aq).
Concentrated H2SO4(aq)
Distillation.

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6
Q

Explain why distillation is used when forming aldehydres from primary alcohols.

A
  1. Provides energy for the reaction.
  2. To remove the product from the oxidising mixture to prevent further oxidation.
  3. The aldehyde can be separated from the reaction mixture as it has a lower boiling point.
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7
Q

Write an equation for the formation of propanal using propan-1-ol and potassium dichromate as the reagents.

A

CH3CH2CH2OH + [O] …. CH3CH2CHO + H2O

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8
Q

What type of reaction forms carboxylic acids from aldehydes?

A

Oxidation.

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9
Q

What are the reagents and conditions used when forming a carboxylic acid from an aldehyde?

A

Potassium dichromate; K2Cr2O7(aq) and concentrated H2SO4(aq).
Reflux.

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10
Q

Write an equation, using structural formula, for the reaction between propanal and potassium dichromate. Name the product.

A

CH3CH2CHO + [O] …. CH3CH2COOH
Propanoic acid.

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11
Q

What type of reaction forms ketones from secondary alcohols?

A

Oxidation.

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12
Q

What are the reagents and conditions for the reaction that forms ketones from secondary alcohols?

A

Potassium dichromate; K2Cr2O7(aq)
Concentrated H2SO4(aq)
Reflux

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13
Q

Write an equation, using structural formula, for the reaction between propan-2-ol and potassium dichromate. Name the product formed.

A

CH3C(OH)HCH3 + [O] …. CH3COCH3 + H2O
Propanone

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14
Q

State and explain, including ionic half equations, the observations that would be made in oxidation reactions when using K2Cr2O7(aq) (5 points).

A
  1. Cr2O7^2- + 14H+ + 6e- …. 2Cr^3+ + 7H2O
  2. Orange –> green.
  3. Cr2O7^2- …. Cr^3+
  4. Dichromate (IV) ions into Chromium (III) ions.
  5. If the alcohol is oxidised, the orange solution containing the dichromate (IV) ions is reduced to green solution containing chromium (III) ions.
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15
Q

What type of reaction do alkenes undergo?

A

Electrophilic addition.

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16
Q

Describe how the double bond in a carbonyl compound differs from that of an alkene?

A
  1. The double bond in an alkene is non-polar, the double bond in a carbonyl compound is polar.
  2. This is because oxygen is more electronegative than carbon.
17
Q

Due to its dipole, what species does the C of the C=O bond attract?

A

Nucleophiles- electron pair donors.

18
Q

What type of reactions do carbonyls undergo?

A

Nucleophilic addition reactions.

19
Q

What kind of reaction changes aldehydes into primary alcohols and ketones into secondary alcohols?

A

Reduction reactions.

20
Q

What are the reagents and conditions for the reaction to change from a ketone to a secondary alcohol?

A

NaBH4- sodium borohydride (a source of H- ions). Warm in aqueous solution.

21
Q

*Write a general equation for the reaction of a general ketone with NaBH4.

A

*Refer to carbonyl compounds notes.
FOR EACH CARBONYL THAT’S REDUCED; 2[H]!!

22
Q

*Describe the mechanism for the reduction of methanal into methanol.

A

*Refer to carbonyl compounds notes.

23
Q

Why is HCN made in situ? (2 points)

A
  1. HCN is an extremely poisonous volatile liquid (bpt is 26 degrees).
  2. Making it in situ improves safety and increases reaction rate.
24
Q

What are the reagents used to make HCN in situ?

A

NaCN and H2SO4(aq).

25
Q

*Write a general equation for the reaction between a general ketone and HCN to produce a general hydroxynitrile.

A

*Refer to carbonyl compounds notes.

26
Q

*Describe the mechanism for the reaction between HCN and CH3CH2CH2COCH3.

A

*Refer to carbonyl compounds notes.

27
Q

What is the reagent used to identify the C=O bond in carbonyl compounds?

A

2,4-dinitriphenylhydrazine.

28
Q

What are the conditions for the reaction that identifies the C=O bond?

A

Room temperature and shake.

29
Q

What is the positive result for testing if C=O bond is present?

A

Orange precipitate (may be yellow or red).

30
Q

Describe the non-spectroscopic method of identifying the C=O bond in carbonyl compounds (4 points).

A
  1. Add 2,4-DNPH (if not already added).
  2. Re-crystallise the product (organe crystals) to purify it.
  3. Measure the elting point of the purified crystals.
  4. Compare the melting point to known values.
31
Q

What reagent is used to identify the presence of an aldehyde functional group?

A

Tollens’ reagent (silver nitrate in ammonia solution- AgNO3).

32
Q

What are the conditions for identifying the presence of an aldehydr functional group?

A

Warm in a water bath.

33
Q

What is the positive result for identifying an aldehyde functional group?

A

Silver mirror formed due to Ag(s).

34
Q

What happens during the reaction to test for an aldehyde functional group?

A

The silver ions (Ag+) are being reduced to silver atoms (Ag(s)) which is why the silver mirror forms. The aldehyde is being oxidised to a carboxylic acid.

35
Q

Write ionic half equations for the reaction of silver ions being reduced into silver atoms and CH3CHO (aldehyde) being oxidised to a carboxylic acid. Derive the overall equation.

A

Oxidation: CH3CHO + H2O …. CH3COOH + 2H+ + 2e-
Reduction: Ag+ + e- …. Ag(s)
Overall: 2Ag+ + CH3CHO + H2O …. CH3COOH + 2H+ + 2Ag

36
Q

Why do ketones not form a silver mirror?

A

A ketone cannot be oxidised any further, so the Ag+ will not be reduced so no mirror is formed.

A-level Chem (30 decks)

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