Previously, a mechanistic twist to the oxidation of imines using peracid had emerged. Time to see how substituents respond to this mechanism.
σ or π nucleophilic reactivity of imines? A mechanistic reality check using substituents.
October 9th, 2016σ or π nucleophilic reactivity of imines? A mechanistic twist emerges.
September 28th, 2016The story so far. Imines react with a peracid to form either a nitrone (σ-nucleophile) or an oxaziridine (π-nucleophile).[1] 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.
References
- D.R. Boyd, P.B. Coulter, N.D. Sharma, W. Jennings, and V.E. Wilson, "Normal, abnormal and pseudo-abnormal reaction pathways for the imine-peroxyacid reaction", Tetrahedron Letters, vol. 26, pp. 1673-1676, 1985. https://doi.org/10.1016/s0040-4039(00)98582-4
More 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[1] 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.
References
- A. Wierzbicki, E.A. Salter, E.A. Cioffi, and E.D. Stevens, "Density Functional Theory and X-ray Investigations of P- and M-Hexamethylene Triperoxide Diamine and Its Dialdehyde Derivative", The Journal of Physical Chemistry A, vol. 105, pp. 8763-8768, 2001. https://doi.org/10.1021/jp0123841
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?[1] Here I explore the difference between two different and very simple approaches to predicting its reactivity. 
References
- D. Christopher Braddock, A. Mahtey, H.S. Rzepa, and A.J.P. White, "Stable bromoallene oxides", Chemical Communications, vol. 52, pp. 11219-11222, 2016. https://doi.org/10.1039/c6cc06395k
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[1] 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.[2] Here I take a look at one recent experiment in innovation which incorporates “augmented reality”.[3]
References
- D. James, B.J. Whitaker, C. Hildyard, H.S. Rzepa, O. Casher, J.M. Goodman, D. Riddick, and P. Murray‐Rust, "The case for content integrity in electronic chemistry journals: The CLIC project", New Review of Information Networking, vol. 1, pp. 61-69, 1995. https://doi.org/10.1080/13614579509516846
- S.M. Bachrach, and S.R. Heller, "The<i>Internet Journal of Chemistry:</i>A Case Study of an Electronic Chemistry Journal", Serials Review, vol. 26, pp. 3-14, 2000. https://doi.org/10.1080/00987913.2000.10764578
- S. Ley, B. Musio, F. Mariani, E. Śliwiński, M. Kabeshov, and H. Odajima, "Combination of Enabling Technologies to Improve and Describe the Stereoselectivity of Wolff–Staudinger Cascade Reaction", Synthesis, vol. 48, pp. 3515-3526, 2016. https://doi.org/10.1055/s-0035-1562579