Chemistry’s dividing lines: no matter how we split it, there is only one chemistry

A new chemistry undergraduate may be struck by their lecture timetable. After A-level timetables which allocated lessons simply to “chemistry,” they are now confronted by distinct divisions: organic chemistry, inorganic chemistry, physical chemistry, industrial chemistry, biochemistry. In my case – and I know of several other examples – the division was even in the university building: the organic, inorganic, physical, biochemical and industrial divisions were allocated their own floors. Like a department store, the guide on the wall of the lift listed its own divisions. Third floor for organic chemistry instead of haberdashery; fourth floor for inorganic chemistry instead of “gents’ ready-made suits.”

The students would go through the first year with these divisions appearing so strong as to be as unbreakable as a saturated carbon-fluorine bond. Lecturers would jest with each other about their respective groups: the inorganic professor – in jest! - applied for a pay rise of 110 times that of the organic professor on the basis that they were responsible for teaching the chemistry of 110 times more elements (at that time) than the organic professor (cue muted laughter). The organic and inorganic lecturers would gang up on the physical ones: “you glorified mathematicians, data loggers and machine operators!” Physical chemists would retort of the inability of organic and inorganic reactions to proceed without having established the thermodynamic drivers and reaction mechanisms. The biochemists would keep to themselves, protecting their endless supply of reaction sequences and unique dictionary of acronyms (“blah, blah, NADPH, blah ATP, blah RNA and DNA, blah, acetyl CoA, blah, blah…”).

This charade was maintained until a third of the way through the second year. The deadlock was broken with one molecule: ferrocene. The synthesis was in the organic lab – presumably on an atom count basis - but it really straddled the organic and inorganic divide. A simple gaze at the structure would provoke a shaking of the head. What was that iron atom doing there? What was the bonding? The structure looked like a sandwich of two slices of hydrocarbon bread with a single iron party egg between them, seemingly a product of a chemical reaction between an iron bar and a beaker of oil. This weird structure was intriguing and so came the introduction to organometallic chemistry. From there we went to Zeigler-Natta, the whole basis of polyolefin manufacture and a whole lecture course on transition metal mediated catalysis and orbital proof for the simple A-level statement that transition metals are often used as catalysts. There then followed the inevitable realisation that the divisions of chemistry were, in fact, made of tissue paper. We were back to studying chemistry: real chemistry with the whole periodic table as a toolbox. We would check the kinetics of the formation of such products, study possible mechanisms and try to isolate intermediates to subject them to spectroscopic techniques, the theory of which the physical chemists taught us, at the same time seeing the expansion of NMR from its first year organic chemistry 1-H and 13-C homeland into its multinuclear (i.e. inorganic) capability and thence to magnetic resonance imaging and biochemical studies for the diagnosis of disease. Some thirty years later, when I myself was the subject of an MRI scan I was advised to relax and try and think of something nice. I imagined being squeezed into an NMR tube and spun at 2500 rpm and sent into the magnetic field to give rise to a signal and thought of how the machine simulated this through the switching on and off of thousands of small magnets. The wonderful progress of scientific collaboration over three decades. Indeed a nice thought or, as my schoolfriends might say, once a geek, always a geek.

We also saw the paradoxes. Thermodynamics, the preserve of physical chemists, taught us about the two great drivers of reactions – enthalpy and entropy – and their combination in Gibbs’ free energy and that reactions were only spontaneous if there was a negative free energy change. We then learned of hundreds of biochemical reaction sequences in which the free energy change at every stage was not only positive but significantly so. Enthalpy increased significantly and entropy decreased significantly, yet the reactions occurred spontaneously in living systems and at great pace (if you have ever run marathons and received an electrolyte drink at twenty miles you will know how rapid some of these reactions can be). Why? Enzymes! The biochemists then took the ferrocene we had synthesised and moved seamlessly to haem, haemoglobin and thence to chlorophyll and vitamin B12. Having the thermodynamics lectures from the physical chemistry team made us appreciate the wonders of these amazing molecules more.

Although the divisions and humour still exist (an inorganic chemistry lecturer, for example, whose interest was the splitting of d-orbitals, describing a transition metal atom at the centre of a large organometallic complex, referred to the ligands as “a mass of organic shrubbery”), the overall result is to have a full, complete view of chemistry and a realisation that attempts to produce divisions are understandable and administrative but the walls can easily be knocked down. Perhaps it’s better to separate the classes simply in order to bring them back together.

Why is this important? In today’s world there is an increasingly used new division in chemistry: synthetic and natural. These divisions are put in not by just chemists and publishers (see, for example, the new “Journal of Natural Products (1): a “transformative” journal!”) but also by advertisers and campaigners. An increasing trend is to regard substances derived from nature as inherently safe and substances that are synthesised (by chemists) as inherently suspicious. The Royal Society of Chemistry bears the scars of trying to show that the term “chemical free” has no meaning (2). These hypotheses have many advocates. One well-known high-street chain claims to avoid the use of “obscure” chemicals and yet, when questioned, they struggle to name any that fall under that title. One other advocates the use of only naturally occurring preservatives and colourants. On further questioning, they maintain that they would not source synthesised versions of the naturally occurring preservatives and colourants they use. To do this meant subjecting plants to several solvent extractions to isolate the target molecule which probably constituted less than 0.01% by weight of the plant. After solvent extractions - with diethyl ether, methanol and ethanoic acid, say - there is little left of the plant that is useful other than for combustion with energy release. However, devising a synthetic route to the target molecule with waste minimisation in mind, using the principles of green chemistry, avoids this and has a potentially significant carbon footprint saving on the extraction process. The manager that oversaw the policy viewed the extracted and synthetic versions of the same molecule as inherently different; the natural version being somehow safer simply because it was a natural source, as if the molecule contained some form of molecular memory of its synthetic route. We should not deride the manager for their misunderstanding of chemistry: we should deride ourselves for not ensuring people have enough chemistry education to understand the reality and that pursuing this policy has no obvious sense from an environmental or sustainability standpoint.

Friedrich Wohler showed that the “vital force theory” – a theory, accepted in the 1840s, which stated that substances involved in living organisms were set apart from those associated with inanimate objects by some “vital force” – was not true. He did this by producing, essentially, urea from rocks. However, the vital force theory appears to be very much alive and well, having reappeared in a new guise which simply states that all natural substances have an inherent property that makes them safe; synthetic substances, by contrast, do not. Natural is the new adjective to the chemical noun and while this is better than the normal ones appearing in the media (toxic, deadly, hazardous, dangerous, unsafe) we need to convey better what this does and does not mean. We need to remember that many who comment on our industry came from different disciplines: I once made a presentation in which I referred to a phthalate plasticiser as being a “simple and straightforward organic ester.” I was asked afterwards by an interested journalist as to whether I was describing a product made from a plant-based feedstock grown without the aid of artificial pesticides. Out in the “real world,” our chemistry terms can have different meanings.

The truth, of course, is that just as the academic divisions are in fact walls made of tissue paper, so the walls between synthetic and natural are, at best, thin and easily dissolved. Ultimately all petrochemicals are derived from a natural source: decayed organic matter. The recent trend to manufacture bio-based products is indicative that numerous products can be grown from plant feedstocks. We can welcome this (it is, after all, one of the principles of green chemistry) from a sustainability viewpoint but we should not pretend that the products are in any way safer simply because they have come out of the ground as a plant rather than out of the ground as oil. Let the evidence and data inform us on safety. George Herbert, in the 1500s, spoke of the whole world, eventually, turning to coal (3), so let’s try and avoid the hubris of thinking all of this is really new and that a new branch of chemistry has been discovered. It’s more, I think, that chemistry is continuing to evolve for our benefit. It may be that in 2025 it seems that we are using chemistry to solve problems rather than making more new products, but all members of the chemistry community drive this, whichever atoms and whichever sources of the atoms they deal with.

References

1. Journal of Natural Products (acs.org)

2. Advertising Standards Authority must clean up its act, says chemistry chief (rsc.org)

3. George Herbert: Vertue (Virtue) (1633) (ccel.org)