Imperial College London

Henry Rzepa

The title of this post merges those of the two
[previous](http://www.ch.ic.ac.uk/rzepa/blog/?p=2144){target="_blank"}
ones. The tunable C-Cl bond brought about in the molecule
tris(amino)chloromethane by anomeric effects will be probed using the
[Laplacian of the electronic
density](http://www.ch.ic.ac.uk/rzepa/blog/?p=2183){target="_blank"}.

::: {#attachment_2211 .wp-caption .aligncenter style="width: 371px"}
![](http://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2010/07/app-1-0.67.jpg "Laplacian @0.67 for tris(amino)choromethane"){.size-full
.wp-image-2211 loading="lazy" decoding="async"
aria-describedby="caption-attachment-2211"
onclick="jmolInitialize('../Jmol/');jmolSetAppletColor('white');jmolApplet([450,450],'load wp-content/uploads/2010/07/app-1_0.67.jvxl;isosurface \"\" translucent;zoom 120;connect (atomno=1) (atomno=11) none;connect (atomno=1) (atomno=2) none;connect (atomno=1) (atomno=5) none;spin 3;');"
width="361" height="392"}

Laplacian @0.67 for tris(amino)choromethane. Click for 3D
:::

The figure above shows the Laplacian for a conformation of
tris(amino)chloromethane with one of the nitrogen lone pairs
antiperiplanar to the C-Cl bond, and the other two lone pairs
antiperiplanar to C-N bonds. The features visible at an isosurface of ±
0.67 include

1.  \(a\) The Laplacian here has a value of -0.67 (= red isosurface),
    which indicates an accumulation of (covalent) shared density along
    the C-N bond (underneath this surface, you can see the blue sphere
    representing depletions from the nitrogen atomic region). This bond
    has the lone pair antiperiplanar to a C-N bond.
2.  \(b\) Contrast this with the C-N bond which is antiperiplanar to the
    C-Cl bond. A greater volume of the covalent C-N region is bounded by
    this isosurface. More of the N lone pair on this atom is donating
    into the C-N, as more conventionally represented below.
3.  Notice how the red isosurface associated with the N lone pair and
    the region associated with the C-N bond are in fact contiguous, and
    not separated basins!

    ::: {#attachment_2215 .wp-caption .aligncenter style="width: 178px"}
    [![](http://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2010/07/ultimate_anomeric1.jpg "ultimate_anomeric1"){.size-full
    .wp-image-2215 loading="lazy" decoding="async"
    aria-describedby="caption-attachment-2215" width="168"
    height="140"}](http://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2010/07/ultimate_anomeric1.jpg)
    Anomeric donation
    :::
4.  \(c\) represents the lone pairs on the chlorine, which have been
    augmented by the donation from the nitrogen. Notice how they come
    out as a torus rather than the conventional double dot
    representations!
5.  Notice the absence of any features along the C-Cl bond! This would
    be typical of a fully or even partially ionic bond, but it also
    illustrates that with a property such as the Laplacian, one does not
    get a complete picture by inspecting at just one isosurface value.

The next isosurface chosen is 0.3. At this lower value, more depletions
(blue = electrophilic regions) are seen and a tiny feature now appears
along the C-Cl bond, which is the covalent accumulation of that bond, a
feature that grows @ 0.2. This nicely illustrates the variable
covalency/ionicity of the C-Cl bond. Notice also how the lhs is all red
(anionic) and the rhs is mostly blue (cationic), showing the formation
of in effect an ion pair.

<table data-border="0">
<colgroup>
<col style="width: 50%" />
<col style="width: 50%" />
</colgroup>
<tbody>
<tr class="odd">
<td><div id="attachment_2219" class="wp-caption aligncenter"
style="width: 193px">
<img
src="http://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2010/07/app-1-0.31.jpg"
title="app-1-0.3" class="size-full wp-image-2219" loading="lazy"
decoding="async" aria-describedby="caption-attachment-2219"
onclick="jmolInitialize(&#39;../Jmol/&#39;);jmolSetAppletColor(&#39;white&#39;);jmolApplet([450,450],&#39;load wp-content/uploads/2010/07/app-1_0.3.jvxl;isosurface &quot;&quot; translucent;zoom 120;connect (atomno=1) (atomno=11) none;connect (atomno=1) (atomno=2) none;connect (atomno=1) (atomno=5) none;spin 3;&#39;);"
width="183" height="171" />
<p>tris(amino)chloroethane @ 0.3</p>
</div></td>
<td><div id="attachment_2220" class="wp-caption aligncenter"
style="width: 192px">
<img
src="http://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2010/07/app-1-0.21.jpg"
title="app-1-0.2" class="size-full wp-image-2220" loading="lazy"
decoding="async" aria-describedby="caption-attachment-2220"
onclick="jmolInitialize(&#39;../Jmol/&#39;);jmolSetAppletColor(&#39;white&#39;);jmolApplet([450,450],&#39;load wp-content/uploads/2010/07/app-1_0.2.jvxl;isosurface &quot;&quot; translucent;zoom 120;connect (atomno=1) (atomno=11) none;connect (atomno=1) (atomno=2) none;connect (atomno=1) (atomno=5) none;spin 3;&#39;);"
width="182" height="182" />
<p>tris(amino)chloroethane @ 0.2</p>
</div></td>
</tr>
</tbody>
</table>

There are many other features which can be explored in these Laplacian
maps, but I leave those for the reader to indulge in. Just click on any
of the diagrams above,and start your exploration.

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


The title of this post merges those of the two previous ones. The tunable C-Cl bond brought about in the molecule tris(amino)chloromethane by anomeric effects will be probed using the Laplacian of the electronic density.

Messaggi di Rogue Scholar

Tunable bonds looked at in a different way