structural isomer questions :( (1 Viewer)

[quarkkkk]

for questions along the lines of "how many structural isomers does [insert organic compound here] have?" is there a way to ensure you don't miss any? like how are we supposed to think of the more difficult ones (e.g. methylcyclopropane for C4H8)

 

[wizzkids]

for questions along the lines of "how many structural isomers does [insert organic compound here] have?" is there a way to ensure you don't miss any? like how are we supposed to think of the more difficult ones (e.g. methylcyclopropane for C4H8)

Yeah, I agree these sorts of questions are a bit daunting. You won't be asked about really large molecules with dozens of potential structural isomers, but in the example you gave C₄H₈ it is pretty obvious that it is not a straight-chain alkane or a straight-chain alkene. Therefore you can dispense with straight chain, then go straight to branched chain then maybe consider cyclo-compounds. The most difficult example you can expect to be asked is an oxy-compound like an alcohol, aldehyde or ketone.
Can you write out all the structural isomers of n-butanol?

 

[quarkkkk]

or a straight-chain alkene

Wait i'm slightly confused aren't but-1-ene and but-2-ene structural isomers of C4H8?

Can you write out all the structural isomers of n-butanol?

The ones I got were:
2-butanol, 2-methyl-2-propanol, 2-methyl-1-propanol
Idk if there are any more though...

 

[Eagle Mum]

Wait i'm slightly confused aren't but-1-ene and but-2-ene structural isomers of C4H8?



The ones I got were:
2-butanol, 2-methyl-2-propanol, 2-methyl-1-propanol
Idk if there are any more though...

Yes, 1-butene and 2-butene are both isomers of C4H8.
Technically, cis-2-butene and trans-2-butene are different structural isomers, so there are six structural isomers of C4H8.

I otherwise agree with wizzkids about first considering straight chains with possible combinations of multiple bonds, then branched chains with multiple bonds, then cyclic molecules, then possible cis/trans different structures for each 2D chemical formula.