Isomers of Water

A week or so ago I stumbled across an article on the BBC website talking about isomers of water. At first, I thought a mistake had been made and that the article should have used the word ‘isotopes’. I was thinking it was something to do with ‘heavy water’, water that contains the heavier isotope of hydrogen, deuterium.

How wrong I was. (There is a lesson here: don’t make assumptions!)

The article was talking about the nuclei of the hydrogen atoms. We know, from our work on NMR that the nuclei of atom spin. It turns out that it is possible for the nuclei of both hydrogen atoms in water to be found spinning together (or in the same direction) and spinning oppositely (or in different directions).

Source: Kim Hansen (CC BY-SA 3.0), via Wikimedia Commons

Water that has both nuclei spinning in the same direction is called ortho-water and if the nuclei are spinning in opposite directions it is para-water. It’s a shame we don’t have to teach about ortho, meta and para isomers as I found this quite interesting in university (correct me if I am wrong but these terms have been replaced by the UPAC numbering system, so ortho-methyl benzene is now 1, 2 dimethy benzene – it has been a while since I studies this so please do correct me below if I have got this wrong!)

OK, the fact that we could get the two isomers of waters did make sense but so what? Would it really make a difference? In the everyday sense, this does not make a difference to the water we consume or use in the lab. It looks the same, tastes the same and for all intents and purposes it reacts the same…or does it?

It turns out that when water reacts with diazenylium ions (N₂H⁺) in ‘ultra’ cold conditions (the article didn’t define what it meant by ultra cold) para water reacted around 25% faster.

Chemists think the reason for this is that the spin of the hydrogen nuclei effects how the water molecules rotate, which affects how fast they react with the diazenylium ions.

It all sounds very much like something out of Star Trek but we shouldn’t joke (how many things in Star Trek are now reality? (https://screenrant.com/star-trek-real-life-gadgets/) but what I want to know is how did somebody come up with this idea?!

The article can be found here: https://www.bbc.co.uk/news/science-environment-44305663

What are the implications of this phenomena and can you think of any other molecules that may be affected by this property? Ammonia? Methane? The list is almost endless.

Please feel free to post your ideas below – I would love to hear them.