Ever since the concept of a shared two-electron bond was conjured by Gilbert N. Lewis in 1916,[cite]10.1021/ja02261a002[/cite] chemists have been fascinated by the related concept of a bond order (the number of such bonds that two atoms can participate in, however a bond is defined) and pushing it ever higher for pairs of like-atoms. Lewis first showed in 1916[cite]10.1021/ja02261a002[/cite] how two carbon atoms could share two, four or six electrons to achieve a bond order of up to three. It took quite a few decades for this to be extended to four for carbon (and nitrogen) and that only with some measure of controversy and dispute (for one recent brief summary, see[cite]10.1039/D1CP02056K[/cite]).
Archive for the ‘Hypervalency’ Category
Chasing ever higher bond orders; the strange case of beryllium.
Monday, February 7th, 2022Never mind main group “hypervalency”, what about transition metal “hypervalency”?
Sunday, March 18th, 2018I have posted often on the chemical phenomenon known as hypervalency, being careful to state that as defined it applies just to “octet excess” in main group elements. But what about the next valence shell, occurring in transition metals and known as the “18-electron rule”? You rarely hear the term hypervalency being applied to such molecules, defined presumably by the 18-electron valence shell count being exceeded. So the following molecule (drawn in three possible valence bond representations) first made in 1992 intrigues.[cite]10.1002/anie.199203231[/cite]
Hypervalent or not? A fluxional triselenide.
Saturday, February 24th, 2018Another post inspired by a comment on an earlier one; I had been discussing compounds of the type I.In (n=4,6) as possible candidates for hypervalency. The comment suggests the below as a similar analogue, deriving from observations made in 1989.[cite]10.1016/S0040-4039(00)99132-9[/cite]
Are diazomethanes hypervalent molecules? An attempt into more insight by more “tuning” with substituents.
Tuesday, December 26th, 2017Recollect the suggestion that diazomethane has hypervalent character[cite]10.1039/C5SC02076J[/cite]. When I looked into this, I came to the conclusion that it probably was mildly hypervalent, but on carbon and not nitrogen. Here I try some variations with substituents to see what light if any this casts.
Can any hypervalence in diazomethanes be amplified?
Saturday, December 23rd, 2017In the previous post, I referred to a recently published review on hypervalency[cite]10.1039/C5SC02076J[/cite] which introduced a very simple way (the valence electron equivalent γ) of quantifying the effect. Diazomethane was cited as one example of a small molecule exhibiting hypervalency (on nitrogen) by this measure. Here I explore the effect of substituting diazomethane with cyano and nitro groups.‡
Are diazomethanes hypervalent molecules? Probably, but in an unexpected way!
Saturday, December 23rd, 2017A recently published review on hypervalency[cite]10.1039/C5SC02076J[/cite] introduced a very simple way of quantifying the effect. One of the molecules which was suggested to be hypervalent using this method was diazomethane. Here I take a closer look.
Ammonide: an alkalide formed from ammonia and resembling an electride.
Sunday, December 17th, 2017Alkalides are anionic alkali compounds containing e.g. sodide (Na–), kalide (K–), rubidide (Rb–) or caeside (Cs–). Around 90 examples can be found in the Cambridge structure database (see DOI: 10.14469/hpc/3453 for the search query and results). So what about the ammonium analogue, ammonide (NH4–)? A quick search of Scifinder drew a blank! So here I take a look at this intriguingly simple little molecule.‡
Identification of a simplest hypervalent hydrogen fluoride anion.
Friday, December 8th, 2017An article with the title shown above in part recently appeared.[cite]10.1038/s41598-017-02687-z[/cite] Given the apparent similarity of HF1- to CH3F1- and CH3F2-, the latter of which I introduced on this blog previously, I thought it of interest to apply my analysis to HF1-.