Organic Chemistry 2 - Carbonyl Compounds to Carboxylic acids and Their Derivatives Flashcards Preview

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Flashcards in Organic Chemistry 2 - Carbonyl Compounds to Carboxylic acids and Their Derivatives Deck (68)
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1

What is the general formula of an aldehyde?

RCHO, where R is a hydrogen atom or alkyl group
..........O
........//
R - C
.........\
..........H

2

What is the boiling point of aldehydes in relation to other organic homologous series?

Boiling point lies between alkanes and alcohols and methanal is the only gas. This is because aldehydes have a permanent dipole which means there are stronger intermolecular forces than in alkanes, but weaker than the hydrogen bonds that exist between alcohol molecules

3

Solubility of aldehydes

Soluble in organic solvents and low Mr aldehydes (methanal and ethanal) are soluble in water

4

Explain the pattern of boiling points in aldehydes and ketones

Boiling point increases as number of carbons increases because the strength of London forces increases while the dipole forces stay constant

5

Explain why methylpropanal has a lower boiling point than butanal

Methylpropanal is branched when butanal is straight chain, and the branched methylpropanal has lower surface area of contact so a lower boiling point

6

What is the general formula of a ketone?

RCOR', where R and R' are alkyl groups
...........O
.........//
R - C
.........\
...........R'

7

What is the geometry of an aldehyde?

Trigonal planar carbonyl group with a bond angle of 120°

8

Which aldehydes and ketones are soluble and why?

Lower members (up to 3 carbons) are soluble in water because of hydrogen bonding between the lone pair of electrons in the 𝛿- oxygen in the carbonyl compound and the 𝛿+ hydrogen in the water molecule

9

Why are most carbonyl compounds insoluble in water?

Larger molecules have large R groups which are in no way attracted to the water molecules, outweighing the slight attraction of the C = O group

10

Why is propanone a very good solvent for organic molecules?

C = O part can have dipole attractions to polar molecules
Two CH3 groups have London forces

11

Oxidation of a primary alcohol

Primary alcohol -> aldehyde -> carboxylic acid

12

Oxidation of a secondary alcohol

Secondary alcohol -> ketone

13

Oxidation of a tertiary alcohol

No oxidation

14

What is the general preparation of an aldehyde?

Partial oxidation of primary alcohols using a saturated solution of sodium or potassium dichromate (VI), acidified with sulfuric acid. Temperature must be below the boiling point of the alcohol and above that of the alcohol and a distillation apparatus should be used **FIX**

15

Method for the preparation of ethanal

Heat ethanol in a flask in a distillation apparatus to 60°C using an electric heater. Add a solution of potassium dichromate in dilute sulfuric acid slowly from a tap funnel. As it distils off, collect the ethanal in a flask surrounded by iced water.

16

Why is iced water used when collecting ethanal?

The boiling point of ethanal is 21°C, so this prevents it from evaporating

17

What are the reagents, conditions and observations of the preparation of ethanal?

Reagents: Excess alcohol and potassium dichromate (VI) dissolved in dilute sulfuric acid
Conditions: Heat in a distillation apparatus at 60°C. Collect the aldehyde as it distils off
Observations: Orange potassium dichromate changes to green as chromium ions are formed

18

How can the ethanal produced through distillation be purified?

Ethanal can be purified by re-distillation. A water bath is used as the heat source and the fraction collected boils between 20 - 23°C

19

Equations in the preparation of ethanal

CH3CH2OH + [O] -> CH3CHO + H2O

20

Method for the preparation of propanone

Heat propan-2-ol and excess potassium dichromate (VI) dissolved in dilute sulfuric acid. Heat under reflux for about 15 minutes. Change to a distillation apparatus to distil off the propanone

21

What are the reagents, conditions and observations of the preparation of propanone?

Reagents: Secondary alcohol and excess potassium dichromate dissolved in dilute sulfuric acid
Conditions: Heat under reflux and distil off the ketone
Observations: Orange potassium dichromate changes to green as chromium ions are formed

22

Equations in the preparation of propanone

.......................................................O
........................................................||
CH3CH(OH)CH3 + [O] -> CH3CCH3 + H2O

23

Carbonyl compounds undergo oxidation reactions with which solutions/compounds?

Potassium dichromate (VI)
Fehling's or Benedict's solution
Ammoniacal silver nitrate (Tollens' reagent)
Iodine in the presence of alkali (iodoform)

24

Carbonyl compounds undergo reduction reactions with solutions/compounds?

Lithium tetrahydridoaluminate (III) (lithium aluminium hydride)

25

Carbonyl compounds undergo heterolytic nucleophilic addition reactions with which solutions/compounds?

Hydrogen cyanide/potassium cyanide

26

Carbonyl compounds undergo addition-elimination (condensation) reactions with which solutions/compounds?

Ammonia
Primary amines
Hydrazine
2,4 - dinitrophenylhydrazine

27

What is the general equation for oxidation of aldehydes in acidic conditions?

RCHO + [O] -> RCOOH
Produces a carboxylic acid

28

What is the general equation for oxidation of aldehydes in alkaline solution?

...............................................O
..............................................//
RCHO + OH^- + [O] -> RC + H2O
...............................................\
.................................................O^-

29

What is Fehling's solution and what is its test result with an aldehyde?

A mixture of copper (II) sulfate (which makes it blue) and sodium potassium tartrate in alkali. It is reduced from a deep-blue solution to a red precipitate of copper (I) oxide, Cu2O when warmed with an aldehyde

30

What is Tollens' reagent and what is its test result with an aldehyde?

Tollens' reagent is made by adding a few drops of sodium hydroxide to silver nitrate solution and then dissolving the precipitate in dilute ammonia. The silver (I) is reduced to silver metal on warming with the aldehyde to give a silver mirror on the inside of the test tube