How do you identify an aldehyde vs a ketone?

An aldehyde has a carbonyl group (C=O) at the end of the carbon chain, while a ketone has it in the middle.

In more detail, aldehydes and ketones are both types of carbonyl compounds, which means they contain a carbon-oxygen double bond (C=O). This carbonyl group is the defining feature of both aldehydes and ketones. However, the location of this carbonyl group within the molecule is what distinguishes an aldehyde from a ketone.

In an aldehyde, the carbonyl group is always at the end of the carbon chain. This means that the carbon atom in the carbonyl group is always bonded to at least one hydrogen atom. The general formula for an aldehyde is RCHO, where R represents any alkyl group and CHO represents the carbonyl group and the hydrogen atom. An example of an aldehyde is ethanal (CH3CHO), where the carbonyl group is at the end of the molecule.

On the other hand, in a ketone, the carbonyl group is located in the middle of the carbon chain, meaning it is bonded to two carbon atoms. The general formula for a ketone is RCOR', where R and R' represent any alkyl groups and CO represents the carbonyl group. An example of a ketone is propanone (CH3COCH3), where the carbonyl group is in the middle of the molecule.

In terms of physical properties, aldehydes and ketones are often colourless and have strong, sometimes pleasant, odours. They are polar due to the presence of the carbonyl group, which means they have higher boiling points than similar-sized hydrocarbons or ethers.

In terms of chemical reactions, aldehydes are generally more reactive than ketones. This is because the carbonyl carbon in aldehydes is more readily available for attack by nucleophiles, due to it being bonded to a hydrogen atom, which is less electron-donating than a carbon atom. This makes aldehydes more susceptible to oxidation reactions, whereas ketones are resistant to oxidation.