The π-resonance in amides famously helped Pauling to his proposal of a helical structure for proteins. Here I explore some geometric properties of amides related to the C-N bond and the torsions about it. The key aspect of amides is that a lone pair of electrons on the nitrogen can conjugate with the C=O carbonyl only if the lone pair orbital is parallel to the C-O π-system.

Previously, I showed how conjugation in dienes and diaryls can be visualised by inspecting bond lengths as a function of torsions.

I am on a mission to persuade my colleagues that the statistical analysis of crystal structures is a useful teaching tool.

Sodium borohydride is the tamer cousin of lithium aluminium hydride (LAH). It is used in aqueous solution to e.g. reduce aldehydes and ketones, but it leaves acids, amides and esters alone. Here I start an exploration of why it is such a different reducing agent. Initially, I am using Li, not Na (X=Li), to enable a more or less equal comparison with LAH, with water molecules to solvate rather than ether (n=2,3,5) and R set to Me.

In 1923, Coster and von Hevesy[cite]10.1038/111079a0[/cite] claimed discovery of the element Hafnium , atomic number 72 (latin Hafnia, meaning Copenhagen, where the authors worked) on the basis of six lines in its X-ray spectrum. The debate had long raged as to whether (undiscovered) element 72 belonged to the rare-earth group 3 of the periodic table below yttrium, or whether it should be placed