Carbonyls- Aldehydes And Ketones Flashcards

1
Q

What is an aldehyde?

A

Molecules with a carbonyl group (C=O) at the end of the carbon chain

Functional group CHO

Eg ethanal CH3CHO

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2
Q

What is a ketone?

A

A molecule with a C=O carbonyl group in the middle of the molecule

Eg propanone CH3COCH3

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3
Q

How are aldehydes formed?

A

Via the oxidation of primary alcohols (but not refluxed)

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4
Q

How are ketones formed?

A

Via the oxidation of secondary alcohols

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5
Q

What happens when you oxidise an aldehyde?

A

Aldehydes can be oxidised to form a carboxylic acid

Heat with acidified potassium dichromate and refluxed

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6
Q

What are some physical properties of carbonyls?

A

Cannot form intermolecular hydrogen bonds as all the hydrogen atoms are bonded to a carbon atom

Can form hydrogen bonds with water molecules making aldehydes and ketones soluble in polar solvents (short chain)

There are permanent dipole dipole interactions due to the bond polarity of the C=O bond

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7
Q

What addition reactions do carbonyls under go?

What other kind of reaction is it?

A

Due to carbonyls having a dipole they are susceptible to attack from nucleophiles (nucleophilic addition)

Also a reduction reaction

Aldehydes form a primary alcohol

Ketones form a secondary alcohol

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8
Q

What nucleophile is used to reduce aldehydes and ketones? And what is the source of these nucleophiles?

A

Reduced via hydride ions

Source from sodium tetrahydridoborate (III)
NaBH4

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9
Q

What is the purpose of using cyanide nucleophiles?

A

Enables us to increase carbon chain length

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10
Q

What is formed when we mix a carbonyl with a cyanide nucleophile?

A

Forms a hydroxynitrile

This uses NaCN or KCN as the source of cyanide ions and mixed with dilute acid as a source of H+ ions

Hydroxy nitriles have stereoisomers for all asymmetric ketones and all aldehydes other than methanal

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11
Q

Why is hydrogen cyanide not used?

A

This is a highly toxic gas and is not easily contained in a lab

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12
Q

What is the test for a carboxylic acid?

A

Add sodium carbonate and look for effervescent

If CO2 is produced then carboxylic acid is present

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13
Q

What tests are used to distinguish between aldehydes and ketones?

A

Fehlings

Tollens

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14
Q

What is the fehlings test?

A

Fehlings solution

produces a colour change from blue to brick red with aldehydes

Not result with tollens

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15
Q

What is the tollens test

A

When warmed with aldehyde they produce a silver mirror as the aldehydes become oxidised and silver ions a reduced to metallic silver

Ketones give no reaction to this test

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