Car transmissions come in two types, ones with fixed ratio gears, and ones which are continuously variable. When it comes to chemical bonds, we tend to think of them as being very much of the first type. Bonds come in fixed ratios; single, aromatic, double, triple, etc. OK, they do vary, but the variations are assumed as small perturbations on the basic form. Take for example the molecule shown below.

Stereo-induction is, lets face it, a subtle phenomenon. The ratio of two stereoisomers formed in a reaction can be detected very accurately by experiment, and when converted to a free energy difference using ΔG = -RT Ln K, this can amount to quite a small value (between 0.5 – 1.5 kcal/mol). Can modelling reproduce effects originating from such small energy differences?

A conjugated, (apparently) aromatic molecular trefoil might be expected to have some unusual, if not extreme properties. Here some of these are explored. The first is the vibrational spectrum. With 144 atoms for this molecule, it has 426 vibrational modes, but one is highlighted below. This is the mode that moves the atoms in accord with the Kekulé resonance. If real, this mode resists such alternation.

Something important happened in chemistry for the first time about 100 years ago. A molecule was built (nowadays we would say synthesized) specifically for the purpose of investigating a theory.

In the first part of the post on this topic, I described how an asymmetric sulfoxide could be prepared as a pure enantiomer using a chiral oxygen transfer reagent. In the second part, we now need to deliver a different group, cyano, to a specific face of the previously prepared sulfoxide-imine.

The assembly of a molecule for a purpose has developed into an art form, one arguably (chemists always argue) that is approaching its 100th birthday (DOI: 10.1002/cber.191104403216) celebrating Willstätter’s report of the synthesis of cyclo-octatetraene. Most would agree it reached its most famous achievement with Woodward’s synthesis of quinine (DOI: 10.1021/ja01221a051) in 1944.

In this previous blog post I wrote about one way in which we have enhanced the journal article. Associated with that enhancement, and also sprinkled liberally throughout this blog, are links to a Digital Repository (if you want to read all about it, see DOI: 10.1021/ci7004737). It is a fairly specific repository for chemistry, with about 5000 entries.

Peter Murray-Rust in his blog asks for examples of the Scientific Semantic Web, a topic we have both been banging on about for ten years or more (DOI: 10.1021/ci000406v). What we are seeking of course is an example of how scientific connections have been made using inference logic from semantically rich statements to be found on the Web (ideally connections that might not have previously been spotted by humans, and lie overlooked and unloved in

Since I have gotten into the habit of quoting some of my posts in other contexts, I have started to also archive them using WebCite. One can quote the resulting archive as: Rzepa, Henry. Quintuple bonds.  2010-04-18. URL:http://www.ch.ic.ac.uk/rzepa/blog/?p=1722. Accessed: 2010-04-18. (Archived by WebCite ^® at http://www.webcitation.org/5p5BtuzSH) There is one issue though.

Some molecules, when you first see them, just intrigue. So it was with carbobenzene, the synthesis of a derivative of which was recently achieved by Remi Chauvin and co-workers (DOI: 10.1002/chem.200601193). Two additional carbon atoms have been inserted into each of the six C-C bonds in benzene. Carbobenzene The structure shows two resonance forms, which remind one of Kekulé and of course benzene itself.