[opti384]

57. Which molecules can exist as stereoisomers?
(a) CHF=CHF (b) F₂C=CCl₂ (c) CH₂F-CHF₂ (d)CF₃-CH₃

Okay, I understand that stereoisomers are isomers that are chiral. But I don't quite understand how you determine whether a molecule is a stereoisomer or not. For this question the answer is (A).

Is there a specific axis that you refer to? Or do I have to spin the molecule and check out?

[Schrödinger]

Stereoisomers are isomers with different spatial arrangement... The molecule doesn't have to be chiral...

For more info, try wikipedia http://en.wikipedia.org/wiki/Stereoisomers

[opti384]

Now I see. The term stereoisomer contains isomers that show chiral. Then is the answer (a) because it can show cis trans isomers?

[Abstractineum]

Yes, (a) has stereoisomers.

[nigel433]

Videos available on YouTube (See "Yale Videos") of lectures on
Organic Chemistry by a Professor McBride go into great detail about
this fiendish subject.

The presentation is interesting, but a bit too discursive to actually
"nail" the ideas for examination purposes.

Incidentally, this is the only place where I have seen the paradox
about a mirror reversing left-to-right, but not top-to-bottom, properly
answered. It is blindingly simple. Mirrors do not do either! They reverse
in the third dimension, in-to-out. It is a trick of the brain - a "trompe l'oeil'
which makes us think that they reverse left-to-right.

McBride shows an illustration from "Alice Through The Looking Glass" where
she is coming back into the drawing room and gets his class to say "No that's
wrong" and then shows that it IS correct. He then says dryly that Lewis
Carroll, alias Charles Dodgson, was a renowned geometer and an EXTREMELY
smart man.