One of the most fascinating and important articles dealing with curly arrows I have seen is that by Klein and Knizia on the topic of C-H bond activations using an iron catalyst.[cite]10.1002/anie.201805511[/cite] These are so-called high spin systems with unpaired electrons and the mechanism of C-H activation involves both double headed (two electron) and fish-hook (single electron) movement. Here I focus on a specific type of reaction, the concerted proton-coupled-electron transfer or cPCET, as illustrated below. These sorts of reactions happen also to be of considerable biological importance, including e.g. the mechanism of photosynthesis and many other important transformations.
Fascinating stereoelectronic control in Metaldehyde and Chloral.
June 9th, 2020Metaldehyde is an insecticide used to control slugs. When we unsuccessfully tried to get some recently, I discovered it is now deprecated in the UK. So my immediate reaction was to look up its structure to see if that cast any light (below, R=CH3, shown as one stereoisomer).
The first ever curly arrows. Revisited with some crystal structure mining.
May 27th, 2020With the current global lockdown, and students along with everyone else staying at home, I have noticed some old posts of mine are getting more attention than normal. One of these is an analysis I did in 2012 of Robinson’s original curly arrow illustration.[cite]10.1002/jctb.5000435208[/cite] That and the fact that I am about to give a lecture on what I call my autobiographical journey discovering them, to our own students here (remotely of course), has prompted me to revisit my original discussion.
The strongest bond in the universe: A crystallographic reality check?
May 25th, 2020My previous two posts on the topic of strongest bonds have involved mono and diprotonating N2 and using quantum mechanics to predict the effect this has on the N-N bond via its length and vibrational stetching mode. Such species are very unlikely to be easily observed for verification. But how about a metal M+ instead of H+? It turns out that structures containing the fragment Ru-N≡N-Ru are a small but well studied class of organometallic. Here is a search of the CSD crystal database for this motif.
The strongest bond in the universe: revisited ten years on.
May 23rd, 2020I occasionally notice that posts that first appeared here many years ago suddenly attract attention. Thus this post, entitled The strongest bond in the universe, from ten years back, has suddently become the most popular, going from an average of 0-2 hits per day to 92 in a single day on May 22nd (most views appear to originate from India). I can only presume that a university there has set some course work on this topic and Google has helped some of the students identify my post. Well, re-reading something you wrote ten years ago can be unsettling. Are the conclusions still sound? Would I establish my claim the same way now? After all, one picks up a little more experience in ten years. So here is my revisitation.
Choreographing a chemical ballet: what happens if you change one of the actors?
May 8th, 2020Earlier, I explored the choreography or “timing”, of what might be described as the curly arrows for a typical taught reaction mechanism, the 1,4-addition of a nucleophile to an unsaturated carbonyl compound (scheme 1). I am now going to explore the consequences of changing one of the actors by adding the nucleophile to an unsaturated imine rather than carbonyl compound (scheme 2).
Discussion of (the) Room-temperature chemical synthesis of dicarbon – open and transparent science.
May 6th, 2020A little more than a year ago, a ChemRxiv pre-print appeared bearing the title referenced in this post,[cite]10.26434/chemrxiv.8009633.v1[/cite] which immediately piqued my curiosity. The report presented persuasive evidence, in the form of trapping experiments, that dicarbon or C2 had been formed by the following chemical synthesis. Here I describe some of what happened next, since it perhaps gives some insight into the processes of bringing a scientific result into the open.
A databank of molecular dynamics reaction trajectories (DDT) focused on undergraduate teaching.
April 22nd, 2020In a previous post, I talked about a library of reaction pathway intrinsic reaction coordinates (IRCs) containing 115 examples of organic and organometallic reactions. Now (thanks Dean!) I have been alerted to a brand new databank of dynamics trajectories (DDT), with the focus on those reactions taught in undergraduate organic chemistry courses, some of which are shown below.
A molecular sponge for hydrogen storage- the future for road transport?
April 19th, 2020In the news this week is a report of a molecule whose crystal lattice is capable of both storing and releasing large amounts of hydrogen gas at modest pressures and temperatures. Thus “NU-1501-Al” can absorb 14 weight% of hydrogen. To power a low-polluting car with a 500 km range, about 4-5 kg of hydrogen gas would be need to be stored and released safely. The molecule is of interest since it opens a systematic strategy of synthetically driven optimisation towards a viable ultra-porous storage material,[cite]10.1126/science.aaz8881[/cite] much like a lead drug compound can be optimised.
Choreographing a chemical ballet: a story of the mechanism of 1,4-Michael addition.
April 13th, 2020A reaction can be thought of as molecular dancers performing moves. A choreographer is needed to organise the performance into the ballet that is a reaction mechanism. Here I explore another facet of the Michael addition of a nucleophile to a conjugated carbonyl compound. The performers this time are p-toluene thiol playing the role of nucleophile, adding to but-2-enal (green) acting as the electrophile and with either water or ammonia serving the role of a catalytic base to help things along.†
