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Henry Rzepa's Blog

Henry Rzepa's Blog
Chemistry with a twist
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In a previous post, I set out how to show how one can reduce a 1 H NMR spectrum to the structure [A] below. I speculated how a further test could be applied to this structure; back predicting its spectrum using just quantum mechanics. Overkill I know, but how well might the two match? The process must start by considering the conformational possibilities of [A]. Each will have a different predicted spectrum.

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The electronic interaction between a single bond and an adjacent double bond is often called σ-π-conjugation (an older term for this is hyperconjugation), and the effect is often used to e.g. explain why more highly substituted carbocations are more stable than less substituted ones.

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This is a recently published[cite]10.5560/ZNB.2012-0189[/cite] (hypothetical) molecule which has such unusual properties that I cannot resist sharing it with you. It is an annulene with 144 all-cis CH groups, being a (very) much larger cousin of (also hypothetical) systems mooted in 2009[cite]10.1021/ja710438j[/cite],[cite]10.1021/jp902176a[/cite]. A 144-carbon annulene.

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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.

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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

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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?

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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.

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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?