Posts Tagged ‘potential energy surface’

Cyclopropenium cyclopentadienide: a strangely neutral ion-pair?

Sunday, April 9th, 2017
No Gravatar

Both the cyclopropenium cation and the cyclopentadienide anion are well-known 4n+2-type aromatic ions, but could the two together form an ion-pair?

(more…)

What is the (calculated) structure of a norbornyl cation anion-pair in water?

Saturday, April 1st, 2017
No Gravatar

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. The latter would have been required if the species equilibrated between two classical carbocations. I then pondered what might happen to both the magnitude and the sign of this force constant if various layers of solvation and eventually a counter-ion were to be applied to the molecule, so that a bridge of sorts between the different states of solid crystals, superacid and aqueous solutions might be built.

(more…)

The smallest C-C-C angle?

Monday, October 31st, 2016
No Gravatar

Is asking a question such as “what is the smallest angle subtended at a chain of three connected 4-coordinate carbon atoms” just seeking another chemical record, or could it unearth interesting chemistry?

(more…)

A better model for the mechanism of Lithal (LAH) reduction of cinnamaldehyde?

Friday, April 10th, 2015
No Gravatar

Previously on this blog: modelling the reduction of cinnamaldehyde using one molecule of lithal shows easy reduction of the carbonyl but a high barrier at the next stage, the reduction of the double bond. Here is a quantum energetic exploration of what might happen when a second LAH is added to the brew (the usual ωB97XD/6-311+G(d,p)/SCRF=diethyl ether).

(more…)

WATOC2014 Conference report. Emergent themes.

Thursday, October 9th, 2014
No Gravatar

This second report highlights two “themes”, or common ideas that seem to emerge spontaneously from diversely different talks. Most conferences do have them.

(more…)

Intersecting paths in molecular energy surfaces.

Sunday, February 16th, 2014
No Gravatar

The potential energy surface for a molecule tells us about how it might react. These surfaces have been charted for thousands of reactions using quantum mechanics, and their basic features are thought to be well understood. Coming across an entirely new feature is rare. So what do you make of the following?

(more…)

Caesium trifluoride: could it be made?

Saturday, November 23rd, 2013
No Gravatar

Mercury (IV) tetrafluoride attracted much interest when it was reported in 2007[1] as the first instance of the metal being induced to act as a proper transition element (utilising d-electrons for bonding) rather than a post-transition main group metal (utilising just s-electrons) for which the HgF2 dihalide would be more normal (“Is mercury now a transition element?”[2]). Perhaps this is the modern equivalent of transmutation! Well, now we have new speculation about how to induce the same sort of behaviour for caesium; might it form CsF3 (at high pressures) rather than the CsF we would be more familiar with.[3] Here I report some further calculations inspired by this report.

(more…)

References

  1. X. Wang, L. Andrews, S. Riedel, and M. Kaupp, "Mercury Is a Transition Metal: The First Experimental Evidence for HgF4", Angewandte Chemie International Edition, vol. 46, pp. 8371-8375, 2007. http://dx.doi.org/10.1002/anie.200703710
  2. W.B. Jensen, "Is Mercury Now a Transition Element?", Journal of Chemical Education, vol. 85, pp. 1182, 2008. http://dx.doi.org/10.1021/ed085p1182
  3. M. Miao, "Caesium in high oxidation states and as a p-block element", Nature Chemistry, vol. 5, pp. 846-852, 2013. http://dx.doi.org/10.1038/nchem.1754

The Sn2 reaction and the anomaly of carbon.

Thursday, September 6th, 2012
No Gravatar

It was three years ago that I first blogged on the topic of the Sn2 reaction. Matthias Bickelhaupt had suggested that the Sn2 reaction involving displacement at a carbon atom was an anomaly; the true behaviour was in fact exhibited by the next element down in the series, silicon. The pentacoordinate species shown below (X=Si) is naturally a minimum, and the fact that for carbon (X=C) one gets instead a transition state resulting in a significant thermal barrier (~ 20 kcal/mol) was a manifestation of abnormal behaviour.

(more…)

Cyclopentadiene: a hydrocarbon at the crossroads of …

Sunday, July 29th, 2012
No Gravatar

organic chemistry. It does not look like much, but this small little molecule brought us ferrocene, fluxional NMR, aromatic anions and valley-ridge inflexion points. You might not have heard of this last one, but in fact I mentioned the phenomenon in my post on nitrosobenzene. As for being at a crossroads, more like a Y-junction. Let me explain why.

(more…)

Dynamic effects in nucleophilic substitution at trigonal carbon.

Monday, July 16th, 2012
No Gravatar

Singleton and co-workers have produced some wonderful work showing how dynamic effects and not just transition states can control the outcome of reactions. Steve Bachrach’s blog contains many examples, including this recent one.

(more…)