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The compound in question, and the name generated by ChemSketch:

enter image description here

I have looked at relevant (outdated) documentation for naming of substituted amines. I understand tertiary amines are named as: $\text{N-alkyl}_1\text{N-alkyl}_2\text{alkyl}_3\text{amine}$.

Now, I am confused at the first point: when we have to select the parent carbon chain. For this compound, I would have selected "benzylamine" as the parent chain, as it obviously has more number of carbon atoms and more unsaturation than both methyl and propyl. Thus, my preferred IUPAC name would have been "N-methyl-N-propylbenzylamine".

But, for some reason "propane" is the main carbon chain here instead. So, what is the logical reasoning for the naming these tertiary amines?

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  • $\begingroup$ Notice propane not -yl here? Can you make such change in benzyl? $\endgroup$
    – Mithoron
    Commented Feb 3, 2018 at 16:18
  • $\begingroup$ @Mithoron No, I can't... But still, that small detail shouldn't stop benzyl from being the main chain. There must be another way to name benzyl as the main chain I hope? $\endgroup$ Commented Feb 3, 2018 at 16:22

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The longest carbon chain is the base name. Benzyl has a "one carbon chain". Compare the two structures below. In the top example, the butane chain, even though it bears a phenyl group, is the main chain. On the bottom example (yours), the phenyl is attached to a "one carbon" chain. therefore, propane is the main chain.

enter image description here

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  • $\begingroup$ "Benzyl has a "one carbon chain"" That's interesting, but then, what about all the unsaturation it has? Is it just being ignored? $\endgroup$ Commented Feb 5, 2018 at 1:25
  • $\begingroup$ You look for the longest chain, just like acyclic alkanes. The aromatic ring in the top example is just a substituent. In your example, aromatic ring is part of the benzyl group. $\endgroup$
    – user55119
    Commented Feb 5, 2018 at 1:43
  • $\begingroup$ After checking out phenylacetic acid and 1-phenylbutan-2-ol, I think I get your point. Apparently benzyl can't be the part of the main chain as long as it doesn't have the functional groups directly attached to it (like phenol or aniline) $\endgroup$ Commented Feb 5, 2018 at 1:59

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