Aldehydes and Ketones

aldehydes always……

ketones always……

"How do we name aldehydes in organic chemistry?"

For aldehydes, we use the suffix - anal . We never need to add a position number.

"How do we name ketones in organic chemistry?"

For ketones, we use the suffix anone . And we add a position number if the carbonyl group could go in more than 1 position.

"What are the oxidation products of primary and secondary alcohols?"

Primary alcohols are oxidised to aldehydes

And secondary alcohols are oxidised to ketones

When we write equation for these reaction we represent the oxidisng agent with an O in square brackets. Water is always produced

"How can Tollens' reagent be used to test for aldehydes and ketones?"

To test whether an unknown sample contains an aldehyde or ketone we can use Tollens reagent. We can tell if the sample is an aldehyde because an oxidation reaction will occur and a silver mirror will form. We can tell if the sample is a ketone because no reaction will take place.

"What are the oxidation and reduction reactions for alcohols, aldehydes, and ketones?"

Alcohols react to produce aldehydes/ketones = oxidation

Aldehydes/Ketones react to produce alcohols = reduction

"How are aldehydes and ketones reduced to alcohols?"

Aldehydes can be reduced to primary alcohols. Ketones can be reduced to seocndary alcohols.

"What happens in a reduction reaction?"

A reduction reaction takes place whenever a carbon atom forms a bond with a less electronegative element. So if a new C-H bod is formed/ H increases we can say a reduction reaction has taken place

How can aldehydes and ketones be reduced, and what role does sodium borohydride (NaBH₄) play in the reaction?

Aldehydes and ketones are reduced to alcohols using sodium borohydride (NaBH₄), which provides hydride (H⁻) ions as nucleophiles. Solid NaBH₄ is dissolved in water, dissociating into Na⁺ and BH₄⁻ ions. A hydride ion from BH₄⁻ reacts with the aldehyde or ketone, forming the alcohol.

representing the reduction of aldehydes and ketones

This is how we represent the reaction

Mechanism for the reduction of any aldehydes

The first step in the reaction mechanism for the reduction of aldehydes looks like:

• An arrow points from a separate hydrogen ion to a carbon on the aldehyde group. This arrow shows the C-H bond forming

• A second arrow from the C on the aldehyde group to the oxygen is it double bonded to. This arrow shows the pi bond between carbon and oxygen breaking

what the next step:

In the intermediate molecule we add a negative sign to the O and a lone pair of electrons. Everything is a single bond and an extra hydrogen is added

The second step of an aldehyde reaction

We draw curly arrow from the O to a H+ to show an OH bond forming on intermediate molecule

We draw the Hydorgen now bonded to the carbon in the intermediate molecule

We then draw the alcohol. With an OH bond instead of the O atom in the final product .

Full example of the reduction of aldehydes

the reduction of a ketone

The reduction of ketones is almost identical to the reduction of aldehydes (except its ketone molecule rather than an aldehyde molecule)

An arrow points from a separate hydrogen ion to a carbon on the ketone group. This arrow shows the C-H bond forming

A second arrow from the C on the ketone group to the oxygen is double bonded to. This arrow shows the pi bond between carbon and oxygen breaking 

We add a negative sign to the O and a lone pair of electron in the intermediate molecule. Everything is a single bond and an extra hydrogen is added 

The second step of an ketone reaction 

We draw curly arrow from the O to a H+ to show an OH bond forming 

We then draw the alcohol. With an OH bond instead of the O atom.

reduction of aldehyde vs ketone

Why do aldehydes and ketones have almost identical reaction mechanisms

Aldehydes and ketones contain a(n) C=O double bond that is polar.

And so, hydride ions can bond to the partially positive carbon

How to write equations for the reduction of aldehydes and alchohols

Each time we write an equation for the reaction of aldehydes and ketones, we write the structural formula for the aldehyde or ketone.

Next, we add two atoms of hydrogen, keeping it in brackets.

Finally, we write the structural formula for the alcohol.

"When is a ketone asymmetrical?"

Ketones are asymmetrical/unsymmetrical when the groups either side of the C=O bond are different

how are optical isomers are produced

Optical isomers are produced when asymmetrical ketones are produced 

"Why doesn’t plane polarised light rotate when an unsymmetrical ketone is reduced?"

If we carried out the reduction of an unsymmetrical ketone in the lab, and then shone plane polarised light through the product, the plane polarised light wouldn’t rotate.

Why does the reduction of aldehydes and ketones with NaBH₄ produce a racemic mixture?

Within carbonyl groups in aldehydes and ketones, the carbon’s bonds form an arrangement called trigonal planar. When reacting with a reducing agent, a bond between the carbon and the hydride ion can form from either side. The chances of this are 50/50. So, when this reaction takes place, the final product is a 50/50 mix of enantiomers , which we call a racemic/racemate mixture.

"What is the structure and reactivity of the cyanide ion (-CN)?"

Cyanide is made up of a carbon triple bonded to a nitrogen atom and we write cyanide like :-CN. Cyanide reacts as if the negative charge is around the carbon atom. And we include two dots in front of the cyanide ion to represent its lone pair

"Why is cyanide (-CN) considered an inorganic molecule?"

Even though cyanide contains a carbon atom, we say that it is an inorganic molecule

what does a cyanide ion contain

If a molecule contains a cyanide ion then we say it contains a nitrile group.

RECAP: When we name nitriles:

Write the name of the lkane chain including the carbon in the nitrile

Write nitrile after it

"What is the bond angle of a cyanide (-C≡N) group, and how do we represent it?"

The bond angle for a cyanide group is 180. So when we draw the skeletal formula of this molecule we draw the bond angle of the cyanide group at 180 degrees

"How do aldehydes and ketones react with cyanide ions (-CN)?"

Aldehydes and ketones react with cyanide ions to produce hydroxynitriles. These are molecules which contain both a(n) CN/nitrile group and a(n) OH/alchohol group.

How to produce a hydroxy nitrile

To produce a hydroxy nitrile, we take an aldehyde or ketone, and react it with potassium cyanide (KCN that is in aqueous solution, alongside some dilute sulfuric acid (H2SO4) .

IF asked in the exam why people dont carry out this reaction state that:

You won’t carry out a reaction to produce hydroxynitriles in a lab since potassium cyanide is toxic when ingested.

In addition, potassium cyanide could react to produce the deadly gas HCN/Hydrogen cyanide

1. An arrow from the cyanide ion to the carbon in the aldehyde gorup

2. A second arrow from the carbon in the adlehyde group to the oxygen it is doublebonded to 

3. We add lone pair and a negative charge to the oxygen in the intermediate molecule 

4. We draw a curly arrow from the oxygen in the intermediate molecule to a H+

5. Draw the CN bonded to the C in the intermediate molecule 

6. Draw the hydroxynnitrile which should have a OH and a CN

Ketones react to form hydroxynitriles in an almost identical manner aldehydes (except its ketone molecule rather than an aldehyde molecule)

1. An arrow from the cyanide ion to the carbon in the ketone group

2. A second arrow from the carbon in the ketone group to the oxygen it is double bonded to

3. We add lone pair and a negative charge to the oxygen in the intermediate molecule

4. We draw a curly arrow from the oxygen in the intermediate molecule to a H+

5. Draw the CN bonded to the C in the intermediate molecule

6. Draw the hydroxynitrile which should have a OH and a CN

What is an example of a nucleophilic addition reaction, and why is the production of hydroxynitriles classified as one?

The production of hydroxynitriles is an example of a nucleophilic addition. It is an addition reaction because a CN is added to an aldehyde/ketone where the CN is a nucleophile. Another example of a nucleophilic addition reaction that we’ve already seen is the reduction of aldehydes and ketones.

Naming hydroxylnitriles

When naming hydroxynitriles we always count the cabron in the nitrile group as position number 1 in the carbon chain.Then we follow the naming steps as normal

"How do you write the equation for the nucleophilic addition of cyanide to an aldehyde or ketone?"

We give the structural formula of the organic compounds.

We also include the reactants KCN (potassium cyanide) and H2SO4 (sulfuric acid).

Finally, we must remember to include the product KHSO4 (potassium bisulfate)

Structural formula of adelyhyde/ketone + KCN + H2SO4 -------------- structural formula of hydroxnitirle formed + KHSO4

"What happens when aldehydes or unsymmetrical ketones react with potassium cyanide and dilute sulfuric acid?"

When reacted with potassium cyanide and dilute sulfuric acid, then aldehydes and unsymmetrical ketones will produce optical isomers.

do symmetrical ketones produce optical isomers when reacted with potassium cyanide and dilute sulfuric acid?"

But, symmetrical ketones won’t produce optical isomers when reacted with potassium cyanide and dilute sulfuric acid?"

"What happens when an aldehyde is reduced in the lab,

If we reduced an aldehyde in the lab and shone plane polarised light through the product, then the light wouldn’t rotate. That’s because the final product would be a racemic mixture.