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Henry Rzepa's Blog

Henry Rzepa's Blog
Chemistry with a twist
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Ken Houk’s group has recently published this study of cycloaddition reactions, using a combination of classical transition state location followed by molecular dynamics trajectory calculations,[cite]10.1021/jacs.8b12674[/cite] and to which Steve Bachrach’s blog alerted me. The reaction struck me as being quite polar (with cyano groups) and so I took a look at the article to see what both the original[cite]10.1021/jo00042a039[/cite] experimental

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Previously, I explored the Graham reaction to form a diazirine. The second phase of the reaction involved an Sn2′ displacement of N-Cl forming C-Cl. Here I ask how facile the simpler displacement of C-Cl by another chlorine might be and whether the mechanism is Sn2 or the alternative Sn1.

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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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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

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In a comment appended to an earlier post, I mused about the magnitude of the force constant relating to the interconversion between a classical and a non-classical structure for the norbornyl cation. Most calculations indicate the force constant for an “isolated” symmetrical cation is +ve, which means it is a true minimum and not a transition state for a [1,2] shift.

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The example a few posts back of how methane might invert its configuration by transposing two hydrogen atoms illustrated the reaction mechanism by locating a transition state and following it down in energy using an intrinsic reaction coordinate (IRC). Here I explore an alternative method based instead on computing a molecular dynamics trajectory (MD). I have used ethane instead of methane, since it is now possible to

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A pyrophoric metal is one that burns spontaneously in oxygen; I came across this phenomenon as a teenager doing experiments at home. Pyrophoric iron for example is prepared by heating anhydrous iron (II) oxalate in a sealed test tube ( i.e. to 600° or higher). When the tube is broken open and the contents released, a shower of sparks forms. Not all metals do this;

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In the previous post, I found intriguing the mechanism by which methane (CH 4 ) inverts by transposing two of its hydrogens. Here I take a look at silane, SiH 4 . It appears it is a three-stage process! Firstly, silane eliminates molecular hydrogen to form a molecular complex between H 2 and SiH 2 (DOI: 10.14469/hpc/2290). The barrier (~60 kcal/mol) is very much lower than with methane.