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Henry Rzepa's Blog

Henry Rzepa's Blog
Chemistry with a twist
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The quote of the post title comes from R. B. Woodward explaining the genesis of the discovery of what are now known as the Woodward-Hoffmann rules for pericyclic reactions.[cite]10.1021/ja01080a054[/cite] I first wrote about this in 2012, noting that “*for (that) blog, I do not want to investigate the transition states”.* Here I take a closer look at this aspect. I will start by explaining my then reluctance to discuss transition states.

Published

I occasionally spot an old blog that emerges, if only briefly, as “trending”. In this instance, only the second blog I ever wrote here, way back in 2009 as a follow up to this article.[cite]10.1021/ed084p1535[/cite] With something of that age, its always worth revisiting to see if any aspect needs updating or expanding, given the uptick in interest.

Published

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.

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In the previous posts, I explored reactions which can be flipped between two potential (stereochemical) outcomes. This triggered a memory from Alex, who pointed out this article from 1999[cite]10.1070/MC1999v009n02ABEH000995[/cite] in which the nitrosonium cation as an electrophile can have two outcomes A or B when interacting with the electron-rich 2,3-dimethyl-2-butene.

Published

This post, the fifth in the series, comes full circle. I started off by speculating how to invert the stereochemical outcome of an electrocyclic reaction by inverting a bond polarity. This led to finding transition states for BOTH outcomes with suitable substitution, and then seeking other examples.