Molecules with very large dipole moments: cyclopropenium acetylide
Occasionally, someone comments about an old post here, asking a question. Such was the case here, when a question about the dipole moment of cyclopropenylidene arose. It turned out to be 3.5D, but this question sparked a thought about the related molecule below.
Of the two resonance forms show above, the one on the left is a zwitterion resulting in the formation of an aromatic cyclopropenium ring, with the charge balanced by the acetylide anion.‡ The calculated structure (ωB97XD/Def2-TZVPP/SCRF=chloroform, Data DOI 10.14469/hpc/8399 ) shows a short terminal CC bond which indicates a significant degree of delocalisation of the three membered ring.
Molecular electrostatic potential
The molecular electrostatic potential (above) agrees with a large dipole moment of 11.9D. This is certainly up there with the molecule suggested in 2016 as being the most polar molecule neutral compound synthesised[cite]10.1002/anie.201508249[/cite] and is a fair bit smaller than that candidate. A brief search of the literature (Scifinder) suggest that the molecule is currently unknown. Anybody fancy making it?
The Data DOI by the way gives you access to the other outputs from the calculation, which would include the molecular orbitals and the molecular vibrations which I have not shown here.
‡ Such zwitterions are known as unstable intermediates. See e.g. [cite]10.1039/D1CP02056K[/cite] for examples.
Related
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