[Big-Daddy]

What is the general method for finding symmetry in molecules which would allow you to find which nuclei are equivalent and thus how many sets of nuclei with different chemical environments there will be?

I know it sounds vague but it seems inevitable. Any good guides on the Internet would be great. My main issue is with larger molecules whose structures are drawn in 2D, and virtually any 3D structure (e.g. adamantane).

[Corribus]

Sorry, sounds very vague.  I'm not sure there's a very easy way to answer this in a general way.

[Big-Daddy]

How am I meant to find the planes of symmetry in adamantane? And an answer which is completely specific to adamantane wouldn't help me much, but one which uses principles that apply to all compounds with structures that must be drawn in 3D would be very helpful.

[Corribus]

Generally speaking I'd look for symmetry planes and rotational axes.  This isn't a full proof method because internal rotation at nonzero temperature can create equivalences that a simple molecular symmetry analysis would miss.  As with your previous question about structure and polarity, it's really mostly based on intuition and a feel for symmetry.

Adamantane only has two nonequivalent positions because of it's high molecular symmetry point group.

[Big-Daddy]

Generally speaking I'd look for symmetry planes and rotational axes.  This isn't a full proof method because internal rotation at nonzero temperature can create equivalences that a simple molecular symmetry analysis would miss.  As with your previous question about structure and polarity, it's really mostly based on intuition and a feel for symmetry.

Could you point out the lines of symmetry in the various conformations of cyclohexane? I want to be able to tell which atoms are equivalent.

Adamantane only has two nonequivalent positions because of it's high molecular symmetry point group.

OK, what about a ³¹P spectrum of P₄O₆ or P₄O₁₀? Would each molecule have just 1 peak?

[curiouscat]

Formal group theory might offer a general, algorithmic way.

Though, that's probably more trouble than it's worth.

[Big-Daddy]

As far as the example problems I have are concerned, I now understand most of them with the exception of cyclohexane derivatives.

I've heard of group theory applications to find molecular symmetry before. Do you know if the general algorithm you speak of is documented and I can find it somewhere?

It might teach me a bit more about how to look for symmetry in my problems.

[Big-Daddy]

I found a good one here: http://asadchev.googlecode.com/svn-history/r354/trunk/articles/ci990322q.pdf Seems fine to understand so far.