Interlocked cyclic compounds

Question

Being new to chemistry, there may ought to be some properties I couldn't understand fully. One of them being cyclic compounds.

One particular question about this is, whether these cyclic compounds, say benzene rings 'link' in-between one another like a chain. Having one molecule chain of one benzene molecule, go through the center of another, before closing back up as a ring.

Unfortunately, I couldn't seem to find any term describing it for further research.

This may be a stupid question or have been asked before, but since I couldn't find my answer anywhere, hopefully someone may either point out why wouldn't this exist in any case or redirect me to an answer.

Answer 1

The compounds you are referring to are called catenanes (see also rotaxanes, as they are a close relative).

(image source)

one molecule chain of one benzene molecule, go through the center of another, before closing back up as a ring

While catenanes involving larger rings can be prepared, having one benzene ring threaded through a second benzene ring is not likely. If you build a model you can see that there would be severe steric interactions, I've tried to depict this in the following drawing.

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The carbon-carbon bond length in benzene is 139 pm. Therefore, the approximate side to side distance in benzene is $\mathrm{2 \cdot 139~ pm \cdot cos(30°)= 241~pm}$. The van der Waals radius is defined as "half of the internuclear separation of two non-bonded atoms of the same element on their closest possible approach" (source). The van der Waals radius for carbon is 170 pm, meaning that the closest approach for two non-bonded carbon atoms is around 340 pm. This value is significantly larger than the 241 pm side-to-side distance we calculated above for benzene. This means that a carbon atom cannot pass through the interior of a benzene ring, at least not for carbon atoms with energies typically found in an organic laboratory.