Letters: August 2019

Do you know about C–H…O?

In the feature article on June Sutor (p22), Andy Extance lays out the history of a 50-year-old controversy surrounding C–H…O hydrogen bonds.

Despite the time that has passed and the mountain of evidence supporting Sutor’s hypothesis, we have found that many chemists still do not know that carbon can be a hydrogen bond donor. In part, this deficiency could be due to the long shadow cast by Jerry Donohue as described in the article, but possibly a more telling reason could be the way that hydrogen bonding is taught to students in general chemistry courses.

Our recent experience with general chemistry exams in the US suggests that instructors will incorrectly use carbon as an example of an atom that does not form hydrogen bonds. Typically, the hydrogen-bond definition used in general chemistry education relies on electronegativity values of the bond’s donor and acceptor atoms. Including carbon as a hydrogen bond donor requires expanding the electronegativity definition to include effects that can polarise the carbon through its chemical environment.

However, in our experience, this logic is not typically taught in general chemistry courses. As a result, the knowledge that carbon forms hydrogen bonds remains hidden to large swaths of the chemist population.

The story of Sutor and her work is complicated. Whether the underlying root of her work’s suppression is due to institutional sexism, the nature of scientific advancement, or some combination of both remains a difficult historical question. In a time when the chemistry community is attempting to create a more open, inclusive and diverse atmosphere, stories such as Sutor’s should be highlighted in early chemistry courses.

As a chemistry community, it is important to examine where our knowledge comes from, and how bias affects what we often pretend is a completely rational and logical process of scientific advancement. It can be instructive to view chemistry through a historical lens.

Scott Horowitz
University of Denver, US

Ray Trievel
University of Michigan, US

Steve Scheiner
Utah State University, US

Carl Schwalbe MRSC
University of Aston, UK

Toxic waste

With reference to David Bradley’s letter on plastic pollution (Chemistry World, July 2019, p4) I would say that there are significant differences between the issues of climate change and plastics waste.

Essentially, the emission of CO2 from the combustion of fossil fuels is supposed to happen. There is no reason in chemistry to send plastics into the environment. This surely means that part of the answer lies in ceasing this emission, whether from homes, supermarkets or plastics factories, and diverting plastics to recycling streams. Simultaneously, schemes such as Operation Clean Sweep, already doing the work for which Bradley calls, can intensify.

For his suggestion of the use of the recovered plastics, there have long been plans within government to recover landfilled plastics once the date of ‘peak oil’ has been passed, since, as a rich source of hydrocarbons, they can be used for energy production. It’s just that the date of ‘peak oil’ appears to be, like Alice’s jam in Through the Looking Glass, sometime in the future.

I suggest that part of the solution should be to encourage the unrecyclable waste that is produced today to go to safe energy recovery now. I agree that eventually chemical recycling should be included in the mix of solutions.

Chris Howick FRSC
Chester, UK

Regarding David Bradley’s points about plastic and plutonium waste, gamma irradiation breaks and crosslinks polymer chains.

I hold the view that the random conversion of waste plastics into short oligomers or a highly crosslinked polymer will impede recycling into new plastic objects. If we choose to recover energy by incinerating plastic then crosslinking will make it harder to burn them; crosslinking of polyethene can be used as a means of making this combustible polymer into a flame retardant solid.

The plutonium needed for the thermoelectric powerpacks of space probes is 238Pu. This is a special isotope of plutonium that is made by neutron activation of neptunium. This plutonium has a far higher radioactivity per gram and heating effect than the main plutonium isotopes normally found in used fuel.

Additionally, the plutonium in PCM (plutonium contaminated material) includes contaminated plastic and I expect will have been stabilised by mixing with cement.

If the large-scale separation of plutonium from this waste was to be attempted, I suspect that this process would produce more waste than the existing volume of PCM and the cost would be high. I think it is best to ‘let sleeping dogs lie’ and to not attempt to recover the small amount of plutonium from this waste.

Mark Foreman MRSC
Gothenburg, Sweden

Door handled

In his recent letter, Anselm Kuhn writes about aluminium framed doors comprising a thermal break (Chemistry World, June 2019, p4). According to Kuhn, a thermal break comprising a homogenous layer is less beneficial than one consisting of a resin foam. He states that such a porous structure would have advantages such as improved insulation, reduced cost and weight and pleads for a resourceful chemist to redeem the situation.

I can tell him that such a construction has already been described and it can be found in patent application GB2427428 ‘Composite door’, available to download from the European Patent Office’s free-to-use Espacenet database.

The relevant passage is as follows: ‘the means for resisting the transfer of heat may include … a material having a low thermal conductivity compared with aluminium. Preferably … an expanded foam material such as polyurethane’.

In this case, according to Kuhn, the inventors Christopher Brook and Adam Penson should be welcomed with open arms.

Nigel Clarke MRSC CChem
Vienna, Austria

Correction

The letter from E J Behrman published in the July issue (Chemistry World, July 2019, p4) contained an incorrect reference. This should read: J. Chem. Health Safety, 2018, 25, 41.