Let's say we have a pentane with an oxygen double bonded to carbon 2. Is that an acetyl functional group or a ketone? My organic chemistry book by McMurry doesn't list acetyl in the table of functional groups which orders them in the priority they have in the name. How do I prioritize an acetyl functional group when naming a compound?

Edited June 29, 201411 yr by DariushS

It's both. An acetyl group is a specific type of carbonyl in the form of CH₃COR. It's not listed in McMurry because anything you can call an acetyl is also under the banner of some other functional group.

I see. So do I prioritize it as if it were a ketone? What if the compound was CH₃CHO, would that be a acetyl or an aldehyde?

If it is a ketone then yes. It being an acetyl doesn't really tell you what the real functionality of the carbonyl actually is, just that the carbonyl has a CH3 attached to it. In naming them, you still need to indicate the functional group. For instance, propanone could also be called (and more often is called) acetone.

 

As for your other compound, again, it's both. The systematic name is ethanal, but you would more commonly see it called acetaldehyde.

Interesting, so basically all aldehydes and acetyls are ketones and naming the compound as a ketone or an aldehyde/acetyl would be correct?

Edited July 2, 201411 yr by DariushS

No. An aldehyde is an aldehyde and a ketone is a ketone. Acetyl groups can sometimes be aldehydes or sometimes ketones. Have a look again at the general formlae for these groups.