Posts Tagged ‘Cambridge’

The butterfly effect in chemistry: Bimodal M~S bonds?

Sunday, July 14th, 2013

I noted previously that some 8-ring cyclic compounds could exist in either a planar-aromatic or a non-planar-non-aromatic mode, the mode being determined by apparently quite small changes in a ring substituent. Hunting for other examples of such chemistry on the edge, I did a search of the Cambridge crystal database for metal sulfides. 


Computers 1967-2013: a personal perspective. Part 5. Network bandwidth.

Wednesday, June 5th, 2013

In a time of change, we often do not notice that Δ = ∫δ. Here I am thinking of network bandwidth, and my personal experience of it over a 46 year period.


The mysterious (aromatic) structure of n-Butyl lithium.

Sunday, March 17th, 2013

n-Butyl lithium is hexameric in the solid state and in cyclohexane solutions. Why? Here I try to find out some of its secrets.


The conformation of acetaldehyde: a simple molecule, a complex explanation?

Friday, February 8th, 2013

Consider acetaldehyde (ethanal for progressive nomenclaturists). What conformation does it adopt, and why? This question was posed of me by a student at the end of a recent lecture of mine. Surely, an easy answer to give? Read on …


σ-π-Conjugation: seeking evidence by a survey of crystal structures.

Sunday, February 3rd, 2013

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. This conjugation is more subtle in neutral molecules, but following my use of crystal structures to explore the so-called gauche effect (which originates from σ-σ-conjugation), I thought I would have a go here at seeing what the crystallographic evidence actually is for the σ-π-type.


The gauche effect: seeking evidence by a survey of crystal structures.

Friday, January 4th, 2013

I previously blogged about anomeric effects involving π electrons as donors, and my post on the conformation of 1,2-difluorethane turned out one of the most popular. Here I thought I would present the results of searching the Cambridge crystal database for examples of the gauche effect. The basic search is defined belowCCDC-search


Hydrogen bond strength as a function of ring size.

Thursday, January 3rd, 2013

One frequently has to confront the question: will a hydrogen bond form between a suitable donor (lone pair or π) and an acceptor? One of the factors to be taken into consideration for hydrogen bonds which are part of a cycle is the ring size. Here I explore one way of quantifying the effect for the series below, n=1-5 (4-8 membered rings).h-bond


What is the range of values for a (sp3)C-C(sp3) single bond length?

Wednesday, September 12th, 2012

Here is a challenge: what is the longest C-C bond actually determined (in which both carbon termini are sp3 hybridised)? I pose this question since Steve Bachrach has posted on how to stabilize long bonds by attractive dispersive interactions, and more recently commenting on what the longest straight chain alkane might be before dispersive interaction start to fold it (the answer appears to be C17).


Dynamic effects in nucleophilic substitution at trigonal carbon (with Na+).

Thursday, July 19th, 2012

In the preceding post, I described a fascinating experiment and calculation by Bogle and Singleton, in which the trajectory distribution of molecules emerging from a single transition state was used to rationalise the formation of two isomeric products 2 and 3.  In the present post, I explore possible consequences of including a sodium cation (X=Na+ below) in the computational model.


More joining up of pieces. Stereocontrol in the ring opening of cyclopropenes.

Thursday, July 12th, 2012

Years ago, I was travelling from Cambridge to London on a train. I found myself sitting next to a chemist, and (as chemists do), he scribbled the following on a piece of paper. When I got to work the next day Vera (my student) was unleashed on the problem, and our thoughts were published[1]. That was then.



  1. M.S. Baird, J.R. Al Dulayymi, H.S. Rzepa, and V. Thoss, "An unusual example of stereoelectronic control in the ring opening of 3,3-disubstituted 1,2-dichlorocyclopropenes", Journal of the Chemical Society, Chemical Communications, pp. 1323, 1992.