tert-butylamine is primary or tertiary? And how do I pick the parent chain for N-substituted amines
Nisha Verma12th Sample
15 Sept 2026 · 1 min read
Boards are around the corner and I am still losing marks on amine classification, which is honestly embarrassing for a "toppers' list" student 🙃
Today's confusion: . The carbon attached to N has three other carbons, so my brain says "tertiary". But the book says classification is by number of alkyl/aryl groups on nitrogen. If that's the rule it should be primary. Which is it? Why does it feel opposite to the alcohol rule where tert-butyl alcohol is tertiary?
Second doubt is naming. I wrote as N-ethylbutan-2-amine. I picked butan-2-amine as the parent because the bigger group sits on the "amine carbon". Is that the correct way, or should the parent be the ethyl group? And for I wrote N-methyl-N-ethylethanamine, which looked wrong in alphabetical order but I wasn't sure.
Last one, the shape. Trimethylamine is pyramidal, but what is the C–N–C angle? I've seen both 109.5° and 108° in different places.
7 answers & replies
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[+][–]Aman YadavDropperSample· 1mo ago
Tertiary. The carbon is tertiary so the amine is tertiary. Same as alcohol.
[+][–]Zoya Khan12thSample· 1mo ago
Aman, I'd gently disagree here, because this is exactly the trap examiners use. For alcohols and alkyl halides we classify by the carbon that holds the functional group. For amines we classify by the nitrogen: how many hydrogens of have been replaced by alkyl or aryl groups. has only one group on nitrogen, so it is a primary amine, even though that carbon is a tertiary carbon. Its IUPAC name is 2-methylpropan-2-amine.
Compare with : three groups on N, so tertiary, even though each carbon attached is just a methyl group.
[+][–]Nisha Verma12thSample· 1mo agoAuthor
this is the clearest version so far, thank you zoya. "Classify by N, not by the carbon" - writing it on my first page.
[+][–]Kavya NaikDropperSample· 1mo ago
Naming: yes, you did it right for the first one. The parent chain is the larger alkyl group on nitrogen, with the amine locant, and the smaller group(s) become N-substituents. So N-ethylbutan-2-amine is correct.
For the second one the parent is ethanamine, and the two other groups on N (one methyl and one ethyl) are alphabetical: ethyl before methyl, so N-ethyl-N-methylethanamine. Alphabetical order beats the order they appear in your drawing. If both substituents were the same you would write N,N-dimethyl... with the locant repeated.
[+][–]Siddharth RaoDropperSample· 1mo ago
108° is the one for trimethylamine, that's the number NCERT gives. Nitrogen is sp3 hybridised but one of the four sp3 orbitals holds a lone pair and the lone pair repels the three bond pairs more than they repel each other. So the C–N–C angle is squeezed slightly below 109.5°, and the molecule is pyramidal. Same logic as ammonia (H–N–H about 107°), just the bulky methyl groups open it up a little.
If a question says "tetrahedral angle" in the options, it's a trap. Pick the one below 109.5°.
[+][–]Meera Patel11thSample· 1mo ago
Maybe a silly follow-up, but is aniline's IUPAC name benzenamine, and do I have to write that in the exam? NCERT writes both, I'm confused which is "official".
[+][–]Nisha Verma12thSample· 1mo agoAuthor
Meera, as far as I understand IUPAC accepts "aniline" as a retained name, and NCERT writes benzenamine as the systematic one with aniline in brackets. For MCQs either will be recognised; in boards I write benzenamine (aniline) and that's it.
