Module 6: Chapter 26 (Carbonyls & Carboxylic Acids) Flashcards Preview

A-Level OCR Chemistry > Module 6: Chapter 26 (Carbonyls & Carboxylic Acids) > Flashcards

Flashcards in Module 6: Chapter 26 (Carbonyls & Carboxylic Acids) Deck (79)
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1

Describe the oxidation reaction of a primary alcohol?

Distillation
H+/Cr2O7^2- (acidified dichromate)
primary alcohol + [O] -> aldehyde + water
orange to green

2

Describe the oxidation reaction of a secondary alcohol?

Reflux
H+/Cr2O7^2- (acidified dichromate)
secondary alcohol + [O] -> ketone + water
orange to green

3

Describe the oxidation reaction of a tertiary alcohol?

Reflux
H+/Cr2O7^2- (acidified dichromate)
NO REACTION TAKES PLACE
solution remains orange

4

Describe the colour change of acidified dichromate?

H+/Cr2O7^2- ORANGE -> [Cr(H2O)5SO4]+ "Cr3+" GREEN

5

What functional group do aldehydes and ketones both contain and where is it found on the carbon chain?

Both contain the carbonyl functional group C=O
- Aldehydes: C=O found at the end of the carbon chain
- Ketones: C=O is joined to 2 different carbon atoms in the chain

6

How do you name aldehydes?

Adding "-al" as a suffix
PentanAL, ethanAL etc

7

How do you name ketones?

Adding "-one" as a suffix
Propanone, pentan-2-one, hexan-2-one etc

8

What happens when aldehydes are further oxidised?

- Aldehydes can be further oxidised to carboxylic acid
Aldehyde + [O] -(reflux H+/Cr2O7^2-)-> carboxylic acid

9

How can scientists distinguish between ketones and aldehydes?

Further oxidation as ketones can't be further oxidised, meanwhile aldehydes will become carboxylic acids

10

What are aldehydes reduced into?

Primary alcohols
- warmed with aqueous tetrahydridoborate (III) NaBH4 (the reducing agent)
aldehydes + 2[H] -NaBH4-> primary alcohols

11

What are ketones reduced into?

ketones + 2[H] -NaBH4-> secondary alcohols
- warmed with aqueous tetrahydridoborate (III) NaBH4 (the reducing agent)

12

Describe the C=O bond

C=O bond is composed of a σ-bond and a π-bond
- the σ-bond is caused by direct overlap of orbitals between the C and O
- the π-bond is formed by sideway overlap of p-orbitals above and below the place of C and O atoms

13

Why is the C=O polar?

- Oxygen is more electronegative than carbon
- Electron density in the double bond lies closer to the oxygen atom than to the carbon atom
- This makes the carbon end partially positive and the oxygen end partially negative

14

What happens because of the polar C=O bond?

Due to partially positive bond on carbon, carbonyl compounds will react with nucleophiles in a nucleophilic addition reactions

15

What is a nucleophile?

An electron pair donor

16

Draw the mechanism of carbonyl compounds with HCN

Check in book

:CN- reacts first with carbon
H+ from HCN reacts with O

17

Describe the reaction of carbonyl compounds with HCN

- HCN adds across C=O bond
- HCN is extremely poisonous so NaCN/H2SO4 is used to provide HCN
- reaction increases carbon chain length
- organic product is a hydroxynitrile
- nucleophilic addition reaction

18

Draw the mechanism of an aldehyde being reduced

check in book

H- ion has 2 electrons that are from different atoms and comes from NaBH4
H from H2O makes hydroxyl group with oxygen

19

Draw the mechanism of a ketone being reduced

check in book

H- ion has 2 electrons that are from different atoms and comes from NaBH4
H from H2O makes hydroxyl group with oxygen

20

What type of reaction is ketone/aldehyde and HCN (H+/NaCN)?

Nucleophilic addition

21

What reagent can be used to detect presence of a carbonyl group in a ketone or aldehyde?

Brady's reagent (yellow/orange precipitate)

22

What is Brady's reagent?

- Solution of 2,4-DNP dissolved in methanol and sulfuric acid
- Detects presence of a carbonyl functional group in ketones or aldehydes only
- Positive test results in a yellow/orange precipitate forming

23

How can the identity of ketones and aldehydes be determined?

1. Separate precipitate by filtration from solution
2. Recrystallise to obtain a pure sample
3. Measure the melting point
4. Measured melting point can be compared to known values

24

What reagent can be used to distinguish between aldehydes and ketones?

Tollen's reagent

25

What is Tollen's reagent?

Solution of silver nitrate in aqueous solution

26

What is the positive test result of using Tollen's reagent?

In the presence of an aldehyde only a silver mirror is formed in an oxidation reaction

27

What reactions happen with Tollen's reagent with a positive test result?

Ag+ ions act as the oxidising agent, Ag+ ions are reduced to silver and aldehyde is oxidised to a carboxylic acid

28

What is the functional group of carboxylic acids?

-COOH (or -CO2H)

29

What are the partial charges on the carboxyl functional group?

partially positive = C and H
partially negative = O

30

How are carboxylic acids synthesised?

Oxidation of primary alcohols (heating with H+/K2Cr2O7 under reflux)