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

Question

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.

Answer 1

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:

The terms constitutional isomers and stereoisomers make up two broad categories of isomers (molecules with the same chemical formula). Constitutional isomers typically have different connectivities and stereoisomers have the same connectivities but differ in spatial arrangements.

enantiomers are stereoisomers that are non-superimposeable mirror images of one another. Your hands are (roughly) enantiomers. both are optically active is true of enantiomers.

diastereomers also known as geometric isomers are also stereoisomers that are not mirror images of one another. cis- and trans-dichloroethene are diastereomers.

If you do a web image search of isomer flowchart you'll see a lot of informative information on isomers. Linked below is the public domain version from Wikipedia which is an example (although not the best in my opinion.)