Following on from my re-investigation of close hydrogen bonding contacts to the π-face of alkenes, here now is an updated scan for H-bonds to alkynes. The search query (dataDOI: 10.14469/hpc/2478) is similar to the previous one: QA is any of N,O,F,Cl. X is any atom, including metals and non-metals.

Previously, a mechanistic twist to the oxidation of imines using peracid had emerged. Time to see how substituents respond to this mechanism. With X = NO ₂ 100% oxaziridine and no nitrone is obtained experimentally;

The story so far. Imines react with a peracid to form either a nitrone (σ-nucleophile) or an oxaziridine (π-nucleophile).[cite]10.1016/S0040-4039(00)98582-4[/cite] The balance between the two is on an experimental knife-edge, being strongly influenced by substituents on the imine.

Compounds with O-O bonds often have weird properties. For example, artemisinin, which has some fascinating stereoelectronics. Here is another such, recently in the news and known as HMTD (hexamethylene triperoxide diamine). The crystal structure was reported some time ago[cite]10.1021/jp0123841[/cite] and the article included an inspection of the computed wavefunction.

In this post, I pondered upon the C=O infra-red spectroscopic properties of esters, and showed three possible electronic influences: The red (and blue) arrows imply the C-O bond might shorten and the C=O bond would lengthen; the green the reverse. So time for a search of the crystal structure database as a reality check.

The previous post explored the structural features of amides. Here I compare the analysis with that for the closely related thioamides. Here is the torsional analysis around the C-N bond. The “diff” (difference) is that almost all the hits are concentrated into angles of 0° or 180°; the twist about the C-N bond from co-planarity is much less if S is present.