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EDEXCEL A2 Chemistry > carbonyl compounds > Flashcards

carbonyl compounds Flashcards

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1
Q

Carbonyl compounds are organic compounds containing a - - - - - - - - group (?)

A

carbonyl
(C=O)

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2
Q

why can aldehydes and ketones hydrogen bond with water?

A

The functional group (-CO) allows these molecules to form hydrogen bonds with water.

  • A hydrogen bond forms between a lone electron pair on the oxygen atom and a + region on a hydrogen atom.
  • Aldehydes and ketones are, therefore, soluble in water since they can form hydrogen bonds with water molecules.
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3
Q

what type of intermolecular bonds exist between aldehydes and ketones?

A

van der Waals forces

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4
Q

do aldehydes and ketones from hydrogen bonds between themselves?

A

no, because aldehydes and ketones themselves do not have a §+ hydrogen atom, they do not form hydrogen bonds between molecules

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5
Q

how are aldehydes produced?

A

Aldehydes are produced from the initial oxidation and distillation of primary alcohols

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6
Q

distillation of primary alcohols
- PRODUCT
- CONDITIONS

A
  • product= aldehydes
  • conditions= Primary alcohols can be heated in the presence of acidified potassium dichromate(VI) and distilled to produce aldehydes
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7
Q

where is the carbonyl group of the aldehyde?

A

Aldehydes have a carbonyl group on a carbon atom at the END OF THE CARBON CHAIN (only attached to one other carbon atom)

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8
Q

how are carboxylic acids produced from aldehydes?

A

Aldehydes can be oxidised further and heated under reflux, in the presence of acidified potassium dichromate(VI), to produce carboxylic acids

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9
Q

how are ketones produced?

A

They are produced from the oxidation of secondary alcohols with acidified potassium dichromate(VI)

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10
Q

where is the carbonyl group on a ketone?

A

Ketones have a carbonyl group on a carbon atom that is attached to two other carbon atoms

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11
Q

potassium dichromate(VI) formula

A

K2Cr2O7

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12
Q

Potassium dichromate(VI) is used as…

A

an oxidising agent in the oxidation of alcohols

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13
Q

As the alcohol is oxidised, potassium dichromate(VI) is…

A

reduced

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14
Q

what indicates that the alcohol has undergone oxidation?

A

a colour change from orange to green

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15
Q

can a tertiary alcohol undergo oxidation?

A

NO

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16
Q

2 ways to test for aldehydes?

A
  • tollens reagent (silver mirror test)
  • fehlings solution
17
Q

1 way to test for a ketone?

A
  • fehlings solution
18
Q

how to test for a ketone using fehlings solution?

A

A few drops of Fehling’s solution are added and the test tube is gently warmed. If a ketone is present the solution will remain blue

19
Q

how to test for a ketone using fehlings solution?

A

A few drops of Fehling’s solution are added and the test tube is gently warmed. If a ketone is present the solution will remain blue.

20
Q

how to test for an aldehyde using tollens reagent?

A

add a few drops of tollens reagent to a test tube and is gently warmed. If an aldehyde is present a layer of silver will form on the walls of the test tube.

21
Q

how to test for a ketone using tollens reagent?

A

add a few drops of tollens reagent to a test tube and is gently warmed. If a ketone is present the solution will remain colourless.

22
Q

All of the oxidation reactions involved in the production of carbonyl compounds from alcohols can be reversed via…

A

reduction reactions

23
Q

what’s the reducing agent involved in the reduction of aldehydes (into primary alcohols) and ketones (into secondary alcohols)

A

a reducing agent of lithium tetrahydridoaluminate(III) (lithium aluminium hydride) (LiAIH4) is used

24
Q

what type of reaction is the reduction of aldehydes (into primary alcohols) and ketones (into secondary alcohols)

A

nucleophillic addition

25
Q
  • conditions for tthe reduction of aldehydes and ketones
  • products
A
  • LiAlH4 in dry ether
  • products = primary and secondary alcohols
26
Q

why is the reduction of aldehydes and ketones carried out in a solvent of dry ether?

A

LiAH, is a very reactive compound and will react violently with water and alcohols, so the reaction is carried out in a solvent of dry ether.

27
Q

how is the reducing agent represented in the chemical equation?

A

The reducing agent can be represented by 2[H] in the chemical equation

28
Q

Nucleophilic addition reactions can also take place with the :CN- nucleophile, this produces…

A

a hydroxynitrile

29
Q

Hydroxynitriles commonly contain a chiral carbon centre meaning…

A

optical isomers of the product are produced

30
Q

The triiodomethane test (iodoform test) is used to identify…

A

CH3CO- groups
- This means it can be used to identify aldehydes and ketones.

31
Q

the iodoform test process + positive result…

A
  • lodine solution is added to the unknown sample, followed by enough sodium hydroxide solution to remove the colour in the solution created by the iodine.
  • A positive result is indicated by the formation of a pale yellow precipitate, known as triiodomethane (CHI,).
  • Aldehydes and ketones will both give a positive result
32
Q

what is the 2,4-dinitrophenylhydrazine (2,4-DNPH) Test used for?
- what does a positive result look like?

A

IDENTIFYING CARBONYL COMPOUNDS…
2,4-DNPH can be used as a qualitative test for the carbonyl functional group.

  • When aldehydes and ketones are reacted with
    2,4-DNPH a yellow, orange or reddish-orange precipitate will form; the exact colour depends on the identity of the compound.
  • Alcohols and other molecules which don’t contain carbonyl groups do not produce a precipitate.
33
Q

IDENTIFYING CARBONYL COMPOUNDS using melting points…

A
  • Carbonyl compounds and their derivatives have sharp melting points, meaning they melt over a narrow range of temperatures.
  • These compounds can have their melting points determined experimentally and their values compared to a databook to identify them.
34
Q

how can 2,4-DNPH be used to identify specific aldehydes/ketones?

A

by use of melting point data.

  • The 2,4-DNPH is added to the compound so that a precipitate forms.
  • The solid is then purified by recrystallisation.
  • The melting point of the pure crystals formed can then be compared with the melting points of 2,4-dinitrophenylhydrazones of all the common aldehydes and ketones.

EDEXCEL A2 Chemistry (13 decks)

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