# Why is 2-(3-aminomethyl-2-hydroxypropyl) cyclohexan-1-one named so and not 2-(2-hydroxy-4-aminobutyl) cyclohexan-1-one?

What is wrong with naming it as 2-(2-hydroxy-4-aminobutyl) cyclohexan-1-one and taking the side chain to be having 4 carbon atoms with NH as substituent on the last? Would someone please explain this? This is the exact picture given in my book labelled 2-(3-aminomethyl-2-hydroxypropyl) cyclohexan-1-one.

• Because -NHCH3 means a different thing from -CH2NH2 which is what you seem to be thinking of. – orthocresol Jul 8 '18 at 8:58

## 1 Answer

As drawn the compound does not contain a butyl side chain with four carbon atoms; the side chain is only a propyl chain with three carbon atoms.

The propyl side chain has two substituents: a hydroxyl ($\ce{-OH}$) group and an methylamino ($\ce{-NH-CH3}$) group. Since these groups are not the principal characteristic group in this case, they have to be expressed as prefixes. Note that the correct prefix for the secondary amine is “methylamino” and not “aminomethyl” as proposed in the question.

Therefore, the correct name is 2-[2-hydroxy-3-(methylamino)propyl]cyclohexan-1-one.

• I have a doubt, why isn't the -OH group a principal characteristic group of the propyl side chain? – Hema Jul 8 '18 at 10:17
• @Hema The entire compound can only have one principal characteristic group that is expressed as a suffix, which in this case is the ketone. – user7951 Jul 9 '18 at 16:18