Ciencias QuímicasInglésWordPress

Henry Rzepa's Blog

Henry Rzepa's Blog
Chemistry with a twist
Página de inicioFeed Atom
language
PericyclicReaction MechanismPotential Energy SurfaceCiencias QuímicasInglés
Publicado

The potential energy surface for a molecule tells us about how it might react. These surfaces have been charted for thousands of reactions using quantum mechanics, and their basic features are thought to be well understood. Coming across an entirely new feature is rare. So what do you make of the following? The reaction is shown above[cite]10.1039/P19920001709 [/cite], and on the face of it, it looks like a normal pericyclic cascade.

GeneralInteresting ChemistryCiencias QuímicasInglés
Publicado

This is the time of year when I deliver two back-2-back lecture courses, and yes I do update and revise the content! I am always on the look-out for nice new examples that illustrate how concepts and patterns in chemistry can be joined up to tell a good story. My attention is currently on conformational analysis;

Interesting ChemistryPericyclicReaction MechanismCiencias QuímicasInglés
Publicado

A game one can play with pericyclic reactions is to ask students to identify what type a given example is. So take for example the reaction below. The alternatives are: A cyclo-elimination reaction (red arrows). Two concurrent electrocyclic ring openings (blue and magenta arrows) Two consecutive electrocyclic ring openings Or could it be a hybrid with characteristics of both the first two?

PericyclicReaction MechanismCiencias QuímicasInglés
Publicado

As my previous post hints, I am performing my annual spring-clean of lecture notes on pericyclic reactions. Such reactions, and their stereochemistry, are described by a set of selection rules . I am always on the lookout for a simple example which can most concisely summarise these rules. The (hypothetical) one shown below I think nicely achieves this, and raises some interesting issues in the process.

Curly ArrowsGeneralReaction MechanismCiencias QuímicasInglés
Publicado

I have several times used arrow pushing on these blogs. But since the rules for this convention appear to be largely informal, and there appears to be no definitive statement of them, I thought I would try to produce this for our students. This effort is here shared on my blog. It is what I refer to as the standard version; an advanced version is in preparation. Such formality might come as a surprise to some;

Chemical ITChemical DataChemical SemanticsChemical Structure DiagramsChemical StructuresCiencias QuímicasInglés
Publicado

This is one of those topics that seems to crop up every three years or so. Since then, new versions of operating systems, new versions of programs, mobile devices and perhaps some progress?  Right, I will briefly recapitulate. Chemical structure diagrams are special; they contain chemical semantics (what an atom is, what a bond is, stereochemistry, charges, etc). One needs special programs to represent this. Take two well-known ones.

HypervalencyInteresting ChemistryAnimationEnergyFree Energy BarrierCiencias QuímicasInglés
Publicado

Mercury (IV) tetrafluoride attracted much interest when it was reported in 2007[cite]10.1002%2Fanie.200703710[/cite] as the first instance of the metal being induced to act as a proper transition element (utilising d-electrons for bonding) rather than a post-transition main group metal (utilising just s-electrons) for which the HgF 2 dihalide would be more normal (“Is mercury now a transition

PericyclicReaction MechanismSteve BachrachCiencias QuímicasInglés
Publicado

Not long ago, I described a cyclic carbene in which elevating the carbene lone pair into a π-system transformed it from a formally 4n-antiaromatic π-cycle into a 4n+2 aromatic π-cycle. From an entirely different area of chemistry, another example of this behaviour emerges; Schreiner’s[cite]10.1039/C2SC21555A[/cite] trapping and reactions of t-butyl-hydroxycarbene, as described on Steve Bachrach’s blog.