[neobenzene]

Hi...I have a simple doubt. The common name of ethanal is acetalaldehyde, whereas the common name of propanone is acetone. Why is there a discrepancy for the prefix "acet" for a two-carbon chain (ethanal) and three-carbon chain (propanone)?

[discodermolide]

This is because the CH₃C=O group is an acetyl group, hence acetaldehyde and acetone.

[neobenzene]

Thank you! So that explains why it is acetic acid and so on..
So what would be the common name of butanone?

[discodermolide]

The name acetic is derived from Latin acetum meaning acid.
Butanone is also known as methyl ethyl ketone.

[neobenzene]

So are you saying that ethanal and propanone are acidic?

[discodermolide]

NO. I am saying that the word acetyl comes from the latin acetum which means vinegar, or acetic acid.

[neobenzene]

But the name "acetyl" would have been derived from "acetum", for a reason, right? Is the acetyl group acidic in nature? If not, why has it been derived from a word that means "acidic"?

[discodermolide]

Acetum means vinegar in latin. That's all there is to it.
The acetyl group is not acidic in nature.
For the derivation of the word ask a linguist.

[neobenzene]

Thanks.

[discodermolide]

No problem

[fledarmus]

But the name "acetyl" would have been derived from "acetum", for a reason, right? Is the acetyl group acidic in nature? If not, why has it been derived from a word that means "acidic"?

As Discodermolide notes, you viewed this back to front. Acetum was the name for vinegar - things were named "acidic" because they had properties similar to vinegar. Once it was determined what structure caused that acidity, it was named "acetic acid", because it was the acid found in acetum. Other compounds which also had that structure were giving names with the same "acet-" stem.

[neobenzene]

Thank you, Fledarmus...That sorted out my muddled thoughts