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Henry Rzepa's Blog

Henry Rzepa's Blog
Chemistry with a twist
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Crystal_structure_miningBondBond Valence MethodChemical BondChemical BondingChimieAnglais
Publié

An N-B single bond is iso-electronic to a C-C single bond, as per below. So here is a simple question: what form does the distribution of the lengths of these two bonds take, as obtained from crystal structures?  The Conquest search query is very simple (no disorder, no errors). When applied to the Cambridge structure database (CSD) the following two distributions are obtained.

Chemical ITGeneralAcademic PublishingArticle Processing ChargeAuthorChimieAnglais
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We have heard a lot about OA or Open Access (of journal articles) in the last five years, often in association with the APC (Article Processing Charge) model of funding such OA availability. Rather less discussed is how the model of the peer review of these articles might also evolve into an Open environment. Here I muse about two experiences I had recently.

PericyclicReaction MechanismAnimationBicyclic Ring ProductEnergy Derivative Gradient NormChimieAnglais
Publié

I noted in my WATOC conference report a presentation describing the use of calculated reaction barriers (and derived rate constants) as mechanistic reality checks. Computations, it was claimed, have now reached a level of accuracy whereby a barrier calculated as being 6 kcal/mol too high can start ringing mechanistic alarm bells.

Reaction MechanismAmmonia BoraneAnimationBoranesChemistryChimieAnglais
Publié

A recent article reports, amongst other topics, a computationally modelled reaction involving the capture of molecular hydrogen using a substituted borane (X=N, Y=C).[cite]10.1073/pnas.1709586114[/cite] The mechanism involves an initial equilibrium between React and Int1 , followed by capture of the hydrogen by Int1 to form a 5-coordinate borane intermediate ( Int2 below, as per

Bond SlamInteresting ChemistryBondChemical BondChemical Bond ZooChimieAnglais
Publié

The chemical bond zoo is relatively small (the bond being a somewhat fuzzy concept, I am not sure there is an actual count of occupants). So when two new candidates come along, it is worth taking notice. I have previously noted the Chemical Bonds at the 21st Century-2017: CB2017 Aachen conference, where both were discussed.

Interesting ChemistryWATOC ReportsGas PhaseJournalistMagnetismChimieAnglais
Publié

Conferences can be intense, and this one is no exception. After five days, saturation is in danger of setting in. But before it does, I include two more (very) brief things I have learnt. Sason Shaik introduced a theme he first investigated years ago, but for which no experiment had been devised for verification. He revived his theme when a journalist contacted him last year to report exactly such an observation, which I now recount.

Interesting ChemistryWATOC ReportsChemical ShiftsChemistryCity: MunichChimieAnglais
Publié

Another selection (based on my interests, I have to repeat) from WATOC 2017 in Munich. Odile Eisenstein gave a talk about predicted^ 13^C chemical shifts in transition metal (and often transient) complexes, with the focus on metallacyclobutanes. These calculations include full spin-orbit/relativistic corrections, essential when the carbon is attached to an even slightly relativistic element.

Interesting ChemistryWATOC ReportsBond Dissociation EnergyCity: AachenCity: MunichChimieAnglais
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The triennial conference is this year located in Munich. With 1500 participants and six parallel sessions, this report can give only a flavour of proceedings. Edward Valeev talked about the scaling problem in coupled cluster theories, the so-called gold standard for computing the energy and properties of small molecules.

Bond SlamInteresting ChemistryChimieAnglais
Publié

It is always interesting to observe conference experiments taking place. The traditional model involves travelling to a remote venue, staying in a hotel, selecting sessions to attend from a palette of parallel streams and then interweaving chatting to colleagues both old and new over coffee, lunch, dinner or excursions.