# Definition of an amide

If I asked you to draw me an amide, we'd likely end up with something in the form of:

The exact definition of this is given fairly clearly in the IUPAC gold book.

Derivatives of oxoacids [...] in which an acidic hydroxy group has been replaced by an amino or substituted amino group. Chalcogen replacement analogues are called thio-, seleno- and telluro-amides. Compounds having one, two or three acyl groups on a given nitrogen are generically included and may be designated as primary, secondary and tertiary amides, respectively Source: IUPAC Gold Book, 1995 recommendations

There is however another class of compounds which we call 'amides', for instance LDA (lithium diisopropylamide). Again, the IUPAC gold book has this covered.

The term applies also to metal derivatives of ammonia and amines, in which a cation replaces a hydrogen atom on nitrogen.

I fully accept this, my question is, why we decided to re-use the word 'amide' to describe these compounds. Is the reason historical (i.e. before we knew better), or is there a logical basis for the grouping of the two classes of compounds.

• Without being sure about it, but amide derives from amine much like chloride does from chlorine — and both are used for the negatively charged, dehydrogenated version of their parent. If the formal $\ce{OH-}$ group of an acid is replaced by $\ce{Cl-}$ we arrive at a carboxylic chloride, so it seems only natural to arrive at an amide if we substitute with (formal) $\ce{R2N-}$. – Jan Feb 2 '16 at 21:51
• In addition to what Jan said, the carboxylic acid derivative "amide" can, more specifically, be referred to as a carboxylic amide. So, really, we didn't reuse the term, we simply shortened the one in a potentially confusing way. Along the same lines, hexamethyldisiliazane can be deprotonated to form hexamethyldisilazide, so I would bet that an amide formed from HMDS would be a silazide or, more specifically, a carboxylic silazide. – SendersReagent Feb 2 '16 at 22:19
• en.wikipedia.org/wiki/Sodium_amide – K_P Feb 2 '16 at 22:45
• @Jan: I hadn't thought about it like that (come to think of it, I had never really considered what we call N-). I think you're probably right. – NotEvans. Feb 2 '16 at 22:48