The classic anomeric effect operates across a carbon atom attached to oxygens. One (of the two) lone pairs on the oxygen can donate into the σ* orbital of the C-O of the other oxygen ( e.g. the red arrows) tending to weaken that bond whilst strengthening the donor oxygen C-O bond. Vice versa means e.g. the blue arrows weakening the other C-O bond.

I noted in an earlier post the hypothesized example of (CO) ₃ Fe⩸C[cite]10.1039/d0cp03436c[/cite] as exhibiting a carbon to iron quadruple bond and which might have precedent in known five-coordinate metal complexes where one of the ligands is a “carbide” or C ligand. I had previously mooted that the Fe⩸C combination might be replaceable by an isoelectronic Mn⩸N pair which could contain a quadruple bond to the nitrogen.

Following from much discussion over the last decade about the nature of C ₂ , a diatomic molecule which some have suggested sustains a quadruple bond between the two carbon atoms, new ideas are now appearing for molecules in which such a bond may also exist between carbon and a transition metal atom.

The quote of the post title comes from R. B. Woodward explaining the genesis of the discovery of what are now known as the Woodward-Hoffmann rules for pericyclic reactions.[cite]10.1021/ja01080a054[/cite] I first wrote about this in 2012, noting that “ for (that) blog, I do not want to investigate the transition states”. Here I take a closer look at this aspect.

Metaldehyde is an insecticide used to control slugs.

With the current global lockdown, and students along with everyone else staying at home, I have noticed some old posts of mine are getting more attention than normal.

My previous two posts on the topic of strongest bonds have involved mono and diprotonating N ₂ and using quantum mechanics to predict the effect this has on the N-N bond via its length and vibrational stetching mode. Such species are very unlikely to be easily observed for verification.

In the news this week is a report of a molecule whose crystal lattice is capable of both storing and releasing large amounts of hydrogen gas at modest pressures and temperatures. Thus “NU-1501-Al” can absorb 14 weight% of hydrogen. To power a low-polluting car with a 500 km range, about 4-5 kg of hydrogen gas would be need to be stored and released safely.

A reaction can be thought of as molecular dancers performing moves. A choreographer is needed to organise the performance into the ballet that is a reaction mechanism. Here I explore another facet of the Michael addition of a nucleophile to a conjugated carbonyl compound.

Here is another selection from the Molecules-of-the-Year shortlist published by C&E News, in which hexagonal planar transition metal coordination is identified.