# Are all molecular structures symmetric?

Are all molecular structure symmetric either in relation to a plane within itself or in relation to other molecules? Are there any completely asymmetrical structures when looking at molecular geometry? Are there any studies into the reason for symmetry?

• There is no 'reason' for symmetry as such. Unless you mean symmetric conformations rather than arrangements? – gilleain Jun 4 '15 at 10:58
• Different molecules have different levels of symmetry - we put in lots of effort into finding out exactly how symmetrical molecules are because symmetry is the basis of lots of other things, most notably molecular orbitals. You can find out more about symmetry elements here – orthocresol Jun 4 '15 at 11:40

## 2 Answers

There are a couple of notable types of structurally asymmetric molecules.

Firstly, those that are chiral due to different ligands attached to a central atom such as the improbable $\ce{CClFBrI}$ or 'bromo-chloro-fluoro-iodo-methane'. More generally, many molecules have chiral centers; sometimes multiple ones, like inositol which has 6 in a 6-carbon molecule.

Secondly, there are rarer structures where there are no chiral centers, but the whole thing is chiral. Usually this is because of steric restrictions that force it to be one shape or another. Helicene is a very nice example. Another might be a cage hydrocarbon in the shape of this graph but I don't know if any exist.

• are you saying there are no structures that match Helicane? I am not referring to the position of ligands but the 3d structure specifically. – Anoop Alex Jun 4 '15 at 12:53
• I'm saying that Helicane comes in two conformations that don't (readily?) interconvert and cannot be superimposed on each other. – gilleain Jun 4 '15 at 12:56
• Also, I apparently meant en.wikipedia.org/wiki/Helicene not "Helicane" which turns out to be a character from Shakespeare! – gilleain Jun 4 '15 at 12:57
• I guess I am basically asking if there exist any chiral molecules without a matching enantiomer or if some symmetry is always seen when looking at all levels instead of just the individual molecule? – Anoop Alex Jun 4 '15 at 13:55
• Ah, so theoretically every chiral molecule has a matching enantiomer - but we may not have observed them experimentally, or they might be unstable for some reason. I don't know of any chemically forbidden examples, although there are many reactions that force one enantiomer or another. – gilleain Jun 4 '15 at 14:18

It is not quite clear what do you mean by "in relation to a plane within itself or in relation to other molecules", but I think the answer is no, not all molecules are symmetric. Many of them belong to what is known as $\mathrm{C}_1$ point group, or, in other words they are are totally asymmetric. For more information on molecular symmetry and point groups read this Wiki article.