Posts Tagged ‘free energy barrier’
Tuesday, January 8th, 2013
Eagle-eyed footnote readers might have spotted one at the bottom of the post on the benzidine rearrangement
. I was comparing the N-N bond lengths in crystal structures of known diprotonated hydrazines (~1.45Å) with the computed N-N bond length at the start point of the intrinsic reaction coordinate for the [5,5] sigmatropic rearrangement of di-N-protonated diphenylhydrazine (the active species in the benzidine rearrangement itself), which was some 1Å longer. This post explores the implications of this oddity.
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Tags: free energy barrier
Posted in Reaction Mechanism | 2 Comments »
Monday, December 3rd, 2012
I promised that the follow-up to on the topic of Birch reduction would focus on the proton transfer reaction between the radical anion of anisole and a proton source, as part of analysing whether the mechanistic pathway proceeds O or M.
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Tags: Birch reduction, dielectric, energy, free energy, free energy barrier, Hammonds postulate, proton transfer
Posted in Reaction Mechanism, Tutorial material | 2 Comments »
Friday, November 4th, 2011
An attosecond is 10-18s. The chemistry that takes place on this timescale is called electron dynamics. For example, it is the time taken for an electron to traverse the 1s orbit in a hydrogen atom. And chemists are starting to manipulate electrons (and hence chemistry) on this timescale; for example a recent article (DOI: 10.1021/ja206193t) describes how to control the electrons in benzene using attosecond laser pulses.
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Tags: attosecond, chemical processes, exasecond, free energy barrier, G/RT, Inga Ulusoy, laser, Mathias Nest
Posted in General, Interesting chemistry, Tutorial material | 1 Comment »
Monday, May 9th, 2011
Introductory organic chemistry invariably features the mechanism of haloalkane solvolysis, and introduces both the Sn1 two-step mechanism, and the Sn2 one step mechanism to students. They are taught to balance electronic effects (the stabilization of carbocations) against steric effects in order to predict which mechanism prevails. It was whilst preparing a tutorial on this topic that I came across what was described as the special case of neopentyl bromide, the bimolecular solvolysis of which has been identified (DOI: 10.1021/ja01182a117) as being as much as 3 million times slower than methyl bromide. This is attributed to a very strong steric effect on the reaction, greater even than that which might be experienced by t-butyl bromide! Time I thought, to take a look at what might make neopentyl bromide so special, and what those supposed electronic and steric effects were really up to.
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Tags: free energy, free energy barrier, potential energy surface
Posted in Historical, Tutorial material | 1 Comment »
Friday, January 7th, 2011
This story starts with a calixarene, a molecule (suitably adorned with substituents) frequently used as a host to entrap a guest and perchance make the guest do something interesting. Such a calixarene was at the heart of a recent story where an attempt was made to induce it to capture cyclobutadiene in its cavity.
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Tags: animation, calixarene, chiral, dielectric, free energy barrier, gas phase, gas phase model, pericyclic, proton transfer, watoc11, zwitterionic
Posted in Interesting chemistry | 1 Comment »
Sunday, December 19th, 2010
Chemistry gets complex very rapidly. Consider the formula CH3NO as the topic for a tutorial in introductory chemistry. I challenge my group (of about 8 students) to draw as many different molecules as they can using exactly those atoms. I imply that perhaps each of them might find a different structure; this normally brings disbelieving expressions to their faces.
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Tags: /RT, anomeric effects, arrow pushing, configurational isomer, conformational somer, double bond equivalent, electron octet, entwined systems, free energy barrier, Jan Jensen, optical isomerism, pericyclic reaction, resonance isomer, stereochemical, stereoelectronic, tautomers
Posted in Interesting chemistry | No Comments »
Sunday, August 8th, 2010
Tags: author, Barboiu, cavity, crystalline calixarene network, cyclobutadiene, Diels Alder, free energy, free energy barrier, gas phase calculation, host/guest, Interesting chemistry, Legrand, pericyclic, Prins, supramolecular, van der Lee, watoc11, X-ray
Posted in Interesting chemistry | 8 Comments »
Saturday, March 13th, 2010
One future vision for chemistry over the next 20 years or so is the concept of having machines into which one dials a molecule, and as if by magic, the required specimen is ejected some time later. This is in some ways an extrapolation of the existing peptide and nucleotide synthesizer technologies and sciences. A pretty significant extrapolation, suitable no doubt for a grand future challenge in chemistry (although the concept of tumbling a defined collection of atoms in a computer model and seeing what interesting molecules emerge, dubbed with some sense of humour as mindless chemistry, is already being done; see DOI: 10.1021/jp057107z).
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Tags: free energy, free energy barrier, Interesting chemistry, metal catalysts, nucleotide synthesizer technologies, similar energy
Posted in Interesting chemistry | No Comments »
