# Difference between conformational, constitutional, and structural isomers and the same and different molecules

Consider the following sets of problems:

I was hoping someone could clarify what each checkbox means exactly. All of these answers are incorrect (except the first one with the check marks signifies the correct answers).

For example, why are the first pair different molecules? What makes something a conformation/constitution/structural isomer?

What does it mean to say something is an "identical conformation of the same molecule" vs "different conformation of the same molecule?"

When can I definitiviely tell if something is an enantiomer or just a diastereomer? It seems like (for an enantiomer) you can't just do the check of "switch all dashes to wedges and all wedges to dashes" because, as in the third pair of newman projections, they are enantiomers of each other but I don't understand why that is.

• This isn't an answer as I can't summarize it, but this site is really useful for that: Isomers explained via metaphor with cats. masterorganicchemistry.com/2010/11/11/… – Canageek Nov 29 '13 at 3:31
• Which book is this ?? – Chloritone_360 Feb 19 '16 at 18:45
• Can you mention the right answers to the questions in the picture? – user28867 Apr 13 '16 at 4:53

I'm going to assume that you don't need an explanation for the checkboxes the same molecule and difference molecules, so that leaves the following: