[Fatma Adel]

are these compounds with molecular formula C3H9N metamers :

propylamine (CH3CH2CH2NH2),
isopropylamine ((CH3)2CHNH2)
ethylmethylamine (CH3CH2NHCH3)
and trimethylamine ((CH3)3N).

my teacher said that but i think :

propylamine (CH3CH2CH2NH2) and
isopropylamine ((CH3)2CHNH2) are only metamers.
 and propylamine (CH3CH2CH2NH2), ethylmethylamine (CH3CH2NHCH3) and trimethylamine ((CH3)3N) are functional group isomer.
Any of them more correct ?

[mikasaur]

I believe isomer and metamer are synonyms. So yes those are all isomers/metamers of C₃H₉N.

Anyone else?

[mjc123]

Never heard of metamers before, they didn't have them in my day (Fetch my pipe and slippers!) However, a quick look on the internet gives definitions like this:

"The metamerism arises when different alkyl groups are attached to same functional group. E.g.

1) The following metamers contain the ether functional group. However they differ by the nature of alkyl groups attached to the oxygen atom.

metamerism: diethyl ether, methyl propyl ether and isopropyl methyl ether

 2) The metamerism is also possible in amines as shown below.

 metamerism: diethyl amine, methyl propyl amine and isopropyl methyl amine" (http://www.adichemistry.com/organic/basics/isomerism/structural/structural-isomerism.html)

But someone else says (http://padakshep.org/otp/subjects/chemistry/organic-chemistry/structural-isomerism/)

"Metamerism This form of isomerism is rare and is limited to molecules having a divalent atom like O or S and alkyl groups around it. The main examples come from ethers and thioethers."

But I think most people disagree with that limitation.

Here (https://www.youtube.com/watch?v=EIctIshOR_8) it says that metamers "have the same structure of the carbon chain", but elsewhere says that e.g. methyl n-propyl ether and methyl isopropyl ether are metamers.
Also says that metamers must have a polyvalent functional group and at least four C atoms (which would rule out all your amines).

It is implied (rather than stated) that they have the same functional group, so that e.g. ethanol and dimethyl ether are not metamers. I would apply that to amines: primary, secondary and tertiary amines are different functional groups, and cannot be metamers of each other (video only admits secondary amines). (But he allows butanamide and N-ethylacetamide, which may be a mistake).

I think propylamine, ethylmethylamine and trimethylamine are functional group isomers, and n- and isopropylamine are chain isomers, None of them are metamers.

In the light of the ambiguities and disagreements, I think metamerism is a pointless and unnecessary concept.

[Fatma Adel]

thank you about your reply 
first , i had seen this page: http://www.adichemistry.com/organic/basics/isomerism/structural/structural-isomerism.html before i wrote my post and saw that diethyl amine, methyl propyl amine and isopropyl all have same functional group ( secondary amine ) and i thought that they consider primary , secondary and tertiary amine are difference functional group and not all consider amines whatever they are primary , secondary or tertiary (as my teacher thought !! )
 but finally , i understand

please , Through your words , you said  "that metamers must have a polyvalent functional group and at least four C atoms"
 i understand what polyvalent means but i don't understand why metamers must have at least four C atoms like this CH3CH2CH2NHCH3 you mean !

   

[mjc123]

Four is the minimum you need to have metamers. With three, the only secondary amine you can have is ethyl methyl amine (assuming, as above, that propylamine is not a metamer). With four, you can have diethylamine or methyl propylamine.

[Fatma Adel]

Ok  thanks alot ^^