Imperial College London

Henry Rzepa

[Steve Bachrach has just
blogged](http://comporgchem.com/blog/?p=510){target="_blank"} on a
recent article (DOI:
[10.1002/anie.200903969](http://dx.doi.org/10.1002/anie.200903969))
claiming the isolation of a compound with a C≡S triple bond;

::: {#attachment_1211 .wp-caption .aligncenter style="width: 211px"}
![A compound with a CS triple
bond](http://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2009/12/CSCC.jpg "CSCC"){.size-full
.wp-image-1211 loading="lazy" decoding="async"
aria-describedby="caption-attachment-1211" width="201" height="101"}

A compound with a C≡S triple bond
:::

Steve notes that Schreiner and co claim a "structure with a rather
strong CS double bond or a weak triple bond". With this size of
molecule, the proverbial kitchen sink can be thrown at the analysis of
the bonding. But one technique that was NOT applied is ELF (see the
[earlier
post](http://www.ch.ic.ac.uk/rzepa/blog/?p=1183){target="_blank"} using
ELF to analyze the bonding in MgPh~2~). So here is such an analysis,
computed for the CCSD/cc-pVTZ wavefunction at the geometry reported in
the publication (see also DOI:
[10042/to-2980](http://hdl.handle.net/10042/to-2980){target="references"}).
The (centroids of the) synaptic basins are the small purple spheres.

::: {#attachment_1213 .wp-caption .aligncenter style="width: 360px"}
![ELF analysis of the bonding in HOCCH. Click for
3D](http://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2009/12/CSCC-elf.jpg "CSCC-elf"){.size-full
.wp-image-1213 loading="lazy" decoding="async"
aria-describedby="caption-attachment-1213"
onclick="jmolInitialize('../Jmol/');jmolSetAppletColor('yellow');jmolApplet([450,450],'load wp-content/uploads/2009/12/CSCC-elf.mol;zoom 120;spin 3;set fontscaling TRUE; font label 14;select atomno=10;label %A 2.36;select atomno=11;label %A 2.0;');"
width="350" height="238"}

ELF analysis of the bonding in HOS≡CH. Click for 3D
:::

The key (disynaptic) basin is labelled **10**, and it integrates to 2.36
electrons, rather far from the 6 electrons which might be expected for a
triple bond! Its centroid is also significantly off-centre from the S-C
bond. Basin **11** integrates to 2.01 electrons; it resembles a lone
pair on the carbon, although the ELF analysis actually labels it a S-C
disynaptic basin. It approximately maps to the HOMO orbital.
Monosynaptic basin **9** encompases the two formal lone pairs on the
sulfur, and it integrates to 3.59e (quite often, what we regard as
separate, *rabbit-ear*, lone pairs on an atom manifest only as a single
monosynaptic basin). Completing the analysis are two further
monosynaptic basins **6** and **7**, which represent lone pairs on the
oxygen (2.45e each) and the disynaptic basin **8** (1.1e).

Bonding, much like the Humpty-Dumpty meaning, is very much what you want
it to be! But in this case, one has to ask whether the description of
the bonding in the C≡S region really is best described as a weak triple
bond, or even a strong double bond, or whether the nominal six electrons
of the triple bond split into two regions, one clearly bonding, the
other more non-bonding.

::: {.wp_orcid_field}
[https://orcid.org/0000-0002-8635-8390](https://orcid.org/0000-0002-8635-8390){target="_blank"
rel="author"}
:::


Steve Bachrach has just blogged on a recent article (DOI: 10.1002/anie.200903969) claiming the isolation of a compound with a C≡S triple bond; A compound with a C≡S triple bond  Steve notes that Schreiner and co claim a “structure with a rather strong CS double bond or a weak triple bond”. With this size of molecule, the proverbial kitchen sink can be thrown at the analysis of the bonding.

Messaggi di Rogue Scholar

The nature of the C≡S triple bond