Previously, I explored the Graham reaction to form a diazirine. The second phase of the reaction involved an Sn2′ displacement of N-Cl forming C-Cl. Here I ask how facile the simpler displacement of C-Cl by another chlorine might be and whether the mechanism is Sn2 or the alternative Sn1.

There is a predilection amongst chemists for collecting records; one common theme is the length of particular bonds, either the shortest or the longest.

Last year, this article[cite]10.1038/nchem.2716[/cite] attracted a lot of attention as the first example of molecular helium in the form of Na ₂ He. In fact, the helium in this species has a calculated ^‡ bond index of only 0.15 and it is better classified as a sodium electride with the ionisation induced by pressure and the presence of helium atoms.

I analysed the bonding in chlorine trifluoride a few years back in terms of VSEPR theory. I noticed that several searches on this topic which led people to this post also included a query about the differences between it and the bromine analogue. For those who posed this question, here is an equivalent analysis.

Allotropes are differing structural forms of the elements. The best known example is that of carbon, which comes as diamond and graphite, along with the relatively recently discovered fullerenes and now graphenes. Here I ponder whether any of the halogens can have allotropes. Firstly, I am not aware of much discussion on the topic.