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I got the following 3 isomers of C5H9N correct:

enter image description here

I also got the following fourth isomer (ignore the blue dot, it was a slip of the pen!)

enter image description here

However, the given answers has the following 2 other isomers instead of my single one:

enter image description here

Could anyone advise me where I went wrong? What did I do incorrectly and more importantly, what could I note to avoid making the same mistake again? E.g. is there a particular method to follow when drawing all the isomers?

Many thanks!

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    $\begingroup$ Your red one has 2 optical isomers, drawn below that, being mutual non superimposable mirror images. for that you has to follow the above 3D drawing convention in a used software, or use Fischer projection, or draw it accordingly manually. $\endgroup$ – Poutnik Jan 11 at 12:01
  • $\begingroup$ You found all the structural isomers all right, but omitted stereoisomers. Also, what's the point of asking to ignore the blue dot when you can simply fix the drawing on your end? $\endgroup$ – andselisk Jan 11 at 12:06
  • $\begingroup$ Ah okay! Thanks @Poutnik and andselisk - so how would you suggest I find out, when I'm given a similar problem in the future, if stereoisomers do exist? $\endgroup$ – dubstep Jan 11 at 13:29
  • $\begingroup$ @Poutnik - why does only the red one have stereoisomers and not any of the others? $\endgroup$ – dubstep Jan 11 at 13:30
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    $\begingroup$ C5H9N has 2 degrees of unsaturation. Why limit yourself to nitriles? What about rings, double bonds or another type of triple bond? Alternatively, change your title. $\endgroup$ – user55119 Jan 11 at 15:12

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