The story so far. Imines react with a peracid to form either a nitrone (σ-nucleophile) or an oxaziridine (π-nucleophile).[cite]10.1016/S0040-4039(00)98582-4[/cite] The balance between the two is on an experimental knife-edge, being strongly influenced by substituents on the imine. Modelling these reactions using the “normal” mechanism for peracid oxidation did not reproduce this knife-edge, with ΔΔG (π-σ) 16.2 kcal/mol being rather too far from a fine balance.
σ or π nucleophilic reactivity of imines? A mechanistic twist emerges.
September 28th, 2016More stereoelectronics galore: hexamethylene triperoxide diamine.
September 22nd, 2016Compounds with O-O bonds often have weird properties. For example, artemisinin, which has some fascinating stereoelectronics. Here is another such, recently in the news and known as HMTD (hexamethylene triperoxide diamine). The crystal structure was reported some time ago[cite]10.1021/jp0123841[/cite] and the article included an inspection of the computed wavefunction. However this did not look at the potential stereoelectronics in this species, which I now address here.
σ or π? The ambident nucleophilic reactivity of imines: crystallographic and computational reality checks.
September 21st, 2016Nucleophiles are species that seek to react with an electron deficient centre by donating a lone or a π-bond pair of electrons. The ambident variety has two or more such possible sources in the same molecule, an example of which might be hydroxylamine or H2NOH. I previously discussed how for this example, the energetics allow the nitrogen lone pair (Lp) to win out over the O Lp. Here, I play a similar game, but this time setting an NLp up against a π-pair.
What’s in a name? Stabilised “nitrenes”.
September 19th, 2016I previously explored stabilized “carbenes” with the formal structures (R2N)2C:, concluding that perhaps the alternative ionic representation R2N+=C–NR2 might reflect their structures better. Here I take a broader look at the “carbene” landscape before asking the question “what about nitrenes?”
Molecule orbitals as indicators of reactivity: bromoallene.
September 1st, 2016Bromoallene is a pretty simple molecule, with two non-equivalent double bonds. How might it react with an electrophile, say dimethyldioxirane (DMDO) to form an epoxide?[cite]10.1039/C6CC06395K[/cite] Here I explore the difference between two different and very simple approaches to predicting its reactivity. 
Journal innovations – the next step is augmented reality?
August 17th, 2016In the previous post, I noted that a chemistry publisher is about to repeat an earlier experiment in serving pre-prints of journal articles. It would be fair to suggest that following the first great period of journal innovation, the boom in rapid publication “camera-ready” articles in the 1960s, the next period of rapid innovation started around 1994 driven by the uptake of the World-Wide-Web. The CLIC project[cite]10.1080/13614579509516846[/cite] aimed to embed additional data-based components into the online presentation of the journal Chem Communications, taking the form of pop-up interactive 3D molecular models and spectra. The Internet Journal of Chemistry was designed from scratch to take advantage of this new medium.[cite]10.1080/00987913.2000.10764578[/cite] Here I take a look at one recent experiment in innovation which incorporates “augmented reality”.[cite]10.1055/s-0035-1562579[/cite]
A periodic table for anomeric centres, this time with quantified interactions.
August 8th, 2016The previous post contained an exploration of the anomeric effect as it occurs at an atom centre X for which the effect is manifest in crystal structures. Here I quantify the effect, by selecting the test molecule MeO-X-OMe, where X is of two types:
A periodic table for anomeric centres.
August 6th, 2016In the last few posts, I have explored the anomeric effect as it occurs at an atom centre X. Here I try to summarise the atoms for which the effect is manifest in crystal structures.