# Meaning of "mono-N-demethylation"

I know what demethylation is.

I have no idea what mono- means, the N is nitrogen of course, I know that from the line structure image in front of me if I could not guess it - and after quite a bit of google searching I gave up and came here.

Chemistry is not my field but out of curiosity and for no practical purpose whatsoever I started learning a few things outside my field, and I came across this tiny little naming issue. I thought this is so simple I could easily find something, but apparently it is even MORE simple than I thought - meaning everybody uses the term but nobody bothers to explain it. :-(

• If the starting material were colloquially named "stuff," the product would be called N-desmethyl stuff. Apr 3 '14 at 18:58
• @UncleAl Thanks, but that wasn't the question. I already knew how structures are named. The question was the naming modifier of a process, the "mono" ("demethylation" was clear). Now I learned it means that ONE methyl group was removed (and not more). So, not a chemical structure naming question but a chemical process naming one. Apr 14 '14 at 14:02

Mono-N-demethylation means the removal of a single (mono) methyl group from a nitrogen(N)-containing functional group. For example, a reaction which transforms the alkylated amine group $\ce{-NHCH3}$ into $\ce{-NH2}$.
You might know the demethylation from removing a methyl group from an oxygen atom. A methoxy group $\ce{-OCH3}$ is converted to a hydroxy group $\ce{-OH}$.
This is correctly called a $\ce{O}$-demethylation.
The $\ce{N}$-demethylation is the same - for a nitrogen atom.