Imperial College London

Henry Rzepa

An extensive discussion developed regarding [my
post](http://www.ch.imperial.ac.uk/rzepa/blog/?p=9322){target="_blank"}
on a fascinating helical \[144\]-annulene. Topics included the nature of
the ring current sustained by the π-electrons and in particular the
bond-length alternation around the periphery and whether this should
alter if the electron count were to be changed to that of a 4n+2 system
(*i.e.* a dication). Whilst the \[144\]-annulene itself is hypothetical,
it emerged that some compounds known as expanded porphyrins have very
similar (albeit smaller scale) helical structures. X-ray structures for
two such provide useful reality checks on the calculations. Here^‡ ^I
include the (3D) coordinates of these two systems so that you can
explore for yourself their helicity.

::: {#attachment_9513 .wp-caption .aligncenter style="width: 461px"}
![SELQUW. Click for
3D.](http://www.ch.imperial.ac.uk/rzepa/blog/wp-content/uploads/2013/02/SELQUW.jpg){.wp-image-9513
loading="lazy" decoding="async"
aria-describedby="caption-attachment-9513"
onclick="jmolInitialize('../Jmol/','JmolAppletSigned.jar');jmolSetAppletColor('white');jmolApplet([450,450],'load wp-content/uploads/2013/02/SELQUW.cif;');"
width="451" height="278"}

SELQUW. Click for 3D X-ray structure
:::

 

::: {#attachment_9514 .wp-caption .aligncenter style="width: 476px"}
![HIYTAL. Click for
3D.](http://www.ch.imperial.ac.uk/rzepa/blog/wp-content/uploads/2013/02/HIYTAL.jpg){.wp-image-9514
loading="lazy" decoding="async"
aria-describedby="caption-attachment-9514"
onclick="jmolInitialize('../Jmol/','JmolAppletSigned.jar');jmolSetAppletColor('white');jmolApplet([450,450],'load wp-content/uploads/2013/02/HIYTAL.cif;');"
width="466" height="211"}

HIYTAL. Click for 3D X-ray structure
:::

I include below Δ~r~^meso^, being the mean unsigned difference in bond
length (Å) at the [meso positions of the
porphrin](http://www.ch.ic.ac.uk/rzepa/talks/acs09-comp/){target="_blank"}
ring, the calculations being at the 6-311G(d,p) level using the DFT
procedure indicated below. The linking number
analysis\[cite\]10.1021/ja710438j\[/cite\] for such systems will be
reported elsewhere.\[cite\]10.1021/ol703129z\[/cite\]

|                   |                                                                            |                                                                            |
|-------------------|----------------------------------------------------------------------------|----------------------------------------------------------------------------|
| Method            | SELQUW                                                                     | HIYTAL                                                                     |
| X-ray             | 0.048                                                                      | 0.045                                                                      |
| B97D/6-311G(d,p)  | [0.025](http://hdl.handle.net/10.6084/m9.figshare.156475){target="_blank"} | [0.015](http://hdl.handle.net/10.6084/m9.figshare.156394){target="_blank"} |
| B3LYP/6-311G(d,p) | [0.047](http://hdl.handle.net/10.6084/m9.figshare.156532){target="_blank"} | [0.017](http://hdl.handle.net/10.6084/m9.figshare.156528){target="_blank"} |

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^‡^[The WordPress system operated here does not enable 3D coordinates to
be inserted into the comment section of a post, only the main
body.]{style="font-size: x-small;"}

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


An extensive discussion developed regarding my post on a fascinating helical [144]-annulene.

Messaggi di Rogue Scholar

Helically conjugated molecules. A follow-up to [144]-annulene.