[minimal]

They seem to be the same, or at least a carbonyl is an acyl but an acyl is not necessarily a carbonyl?

[agrobert]

Just terminology, the hydroxyl removed from a carboxylic acid can have any substituent R

ex. COOH --(SOCl₂)--> COCl (Acyl halide)

http://en.wikipedia.org/wiki/Acyl

http://en.wikipedia.org/wiki/Carbonyl

[minimal]

For that matter, what is the difference between using the -R or a -A or -B.  Is a -A or -B a single group, whereas the -R could be anything, including continuing carbon chains?

[agrobert]

A or B can be anything and they can be different, it is the same as say R and R'

[minimal]

A or B can be anything and they can be different, it is the same as say R and R'

Then why is the distinction made on something like wikipedia between the acyl and the carbonyl groups, where the carbonyl is listed with A & B, while the acyl has an -R group.

And secondly, does the acyl group imply that there is a negative charge? I notice that it does not list two R groups.  And since an acyl is the removal of the hydroxyl group on a carboxylic acid, does that mean that it must end with the negative charge?

[agrobert]

Just different terminology but yes they can mean the same thing formally.

An acyl group is derived from a carboxylic acid.  Anytime you add a RC=O to a heteroatom you are acylating that group.  If any charge is present it is positive.  The acyl carbocation is a common synthon.

http://en.wikipedia.org/wiki/Synthon

[minimal]

Just different terminology but yes they can mean the same thing formally.

An acyl group is derived from a carboxylic acid.  Anytime you add a RC=O to a heteroatom you are acylating that group.  If any charge is present it is positive.  The acyl carbocation is a common synthon.

http://en.wikipedia.org/wiki/Synthon

Great, thanks for the reference.  However, I have another question after checking out that wiki page about Synthons.  How do they determine that CN- is a synthetic equivalent for COOH-?  Just because there is a similar carbanion? I understand that they get there in two steps (first the NaCN and then adding H20), but that really doesn't make CN- a synthetic equivalent unless you add the part about adding H20 correct? Unless I'm missing something.  Wouldn't a synthetic equivalent be more like NaCOOH? instead of CN- and then H20?