3.8 Aldehydes and Ketones Flashcards

1
Q

What is the carbonyl group?

A

C=O

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2
Q

What kind of intermolecular forces do molecules with the carbonyl group have? Why?

A

Permanent dipole-dipole due to the polar C=O bond (O is delta -)

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3
Q

How soluble are they in water? What influences solubility?

A

Yes - form hydrogen bonds between water molecules and oxygen of C=O. As C chain length increases, solubility decreases.

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4
Q

Which bond in carbonyl compounds is usually involved in reactions? Why?

A

C=O, due to the polarity of the bond (large difference in electronegativity between C and O)

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5
Q

What is the strongest bond in carbonyl compounds?

A

C=O

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6
Q

Why is the addition of HCN important?

A

Increases the length of the carbon chain by one carbon atom - very useful

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7
Q

Will the product of HCN added to a carbonyl compound have optical isomers? Why?

A

Yes they will. In the aldehyde/ketone, the carbonyl carbon is planar, so the :CN- can attack from either above or below, forming two enantiomers.

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8
Q

What is the name of the product when HCN is added to a carbonyl compound?

A

Hydroxynitriles (have OH and CN groups)

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9
Q

What is Fehling’s solution? What colour is it?

A

Copper complex ions, blue

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10
Q

What happens when an aldehyde is added to Fehling’s solution?

A

Reduced to Cu+ ions → colour change to brick red ppt

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11
Q

What happens when a ketone is added to Fehling’s solution?

A

No visible change → stays blue

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12
Q

What is in Tollens’ reagent?

A

Silver complex ions, colourless solution

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13
Q

What happens when an aldehyde is added to Tollen’s reagent?

A

Silver mirror forms as Ag+ reduced to Ag (s)

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14
Q

What happens when a ketone is added to Tollen’s reagent?

A

No visible change

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15
Q

What is another oxidising agent for alcohols and aldehydes? What change in colour does this undergo?

A

Acidified potassium dichromate (VI) - H2SO4 and K2Cr2O7. Colour change from orange to green.

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16
Q

What is a reducing agent for aldehydes and ketones? What ions does this release in solution?

A

NaBH4 (sodium tetrahydridoborate (III)), releases an H- ion