It is always rewarding when one comes across a problem in chemistry that can be solved using a continuous stream of rules and logical inferences from them. The example below[cite]10.1039/P19930000299[/cite] is one I have been using as a tutor in organic chemistry for a few years now, and I share it here. It takes around 50 minutes to unravel with students.

Although have dealt with the π-complex formed by protonation of PhNHOPh in several posts, there was one aspect that I had not really answered; what is the most appropriate description of its electronic nature?

With metrics in science publishing controversial to say the least, I pondered whether to write about the* impact*/ influence a science-based blog might have (never mind whether it constitutes any measure of esteem ). These are all terms that feature large when an (academic) organisation undertakes a survey of its researchers’ effectiveness. ^‡ WordPress (the organisation that provides the software used for this

The transient π-complex formed during the “[5,5]” sigmatropic rearrangement of protonated N,O-diphenyl hydroxylamine can be (formally) represented as below, namely the interaction of a six-π-electron aromatic ring (the phenoxide anion 2 ) with a four-π-electron phenyl dication-anion pair 1 . Can one analyse this interaction in terms of aromaticity?

Michael Dewar[cite]10.1016/S0040-4039(01)82765-9[/cite] famously implicated a so-called π-complex in the benzidine rearrangement, back in the days when quantum mechanical calculations could not yet provide a quantitatively accurate reality check. Because this π-complex actually remains a relatively unusual species to encounter in day-to-day chemistry, I thought I would try to show in a simple way how it forms.

If you search e.g. Scifinder for N,O-diphenyl hydroxylamine (RN 24928-98-1) there is just one literature citation, to a 1962 patent. Nothing else;

We tend to think of simple hydrocarbons as relatively inert and un-interesting molecules. However, a recent article[cite]10.1002/anie.201202894[/cite], which was in fact highlighted by Steve Bachrach on his blog , asks what “ The Last Globally Stable Extended Alkane ” might be. In other words, at what stage does a straight-chain hydrocarbon fold back upon itself, and no significant population of the linear form remain?

Kinetic isotope effects have become something of a lost art when it comes to exploring reaction mechanisms. But in their heyday they were absolutely critical for establishing the mechanism of the benzidine rearrangement[cite]10.1021/ja00373a028[/cite]. This classic mechanism proceeds via bis protonation of diphenyl hydrazine, but what happens next was the crux.

This is an interesting result I got when studying the [1,4] sigmatropic rearrangement of heptamethylbicyclo-[3.1.0]hexenyl cations. It fits into the last lecture of a series on pericyclic mechanisms, and just before the first lecture on conformational analysis. This is how they join.

In this post, I looked at some hydrogen bonds formed by interaction of a π-system with an acidic hydrogen. Unlike normal lone pair donors, π-systems can involve more than two electrons, most commonly four or six. Here I look at examples of both these higher-order donors. FIMNEU FIMNEU.

Eagle-eyed footnote readers might have spotted one at the bottom of the post on the benzidine rearrangement.