Science is about making connections. And these can often be made between the most unlikely concepts. Thus in the posts I have made about pentavalent carbon , one can identify a series of conceptual connections.

In the previous two posts, I noted the recent suggestion of how a stable frozen S _N 2 transition state might be made. This is characterised by a central carbon with five coordinated ligands.

In this follow-up to the previous post, I will try to address the question what is the nature of the bonds in penta-coordinate carbon ? This is a difficult question to answer with any precision, largely because our concept of a bond derives from trying to define what the properties of the electrons located in the region between any two specified atoms are.

The bimolecular nucleophilic substitution reaction at saturated carbon is an icon of organic chemistry, and is better known by its mechanistic label, S _N 2 . It is normally a slow reaction, with half lives often measured in hours.