Imperial College London

Henry Rzepa

In 2012, I [wrote a
story](https://www.ch.imperial.ac.uk/rzepa/blog/?p=7234) of the first
ever reaction curly arrows, attributed to Robert Robinson in 1924. At
the time there was a great rivalry between him and another UK chemist,
Christopher Ingold, with the latter also asserting his claim for their
use. As part of the move to [White
City](https://www.ch.imperial.ac.uk/rzepa/blog/?p=19828) a lot of
bookshelves were cleared out from the old buildings in South Kensington,
with the result that yesterday a colleague brought me a slim volume they
had found entitled *The Journal of the Imperial College Chemical Society
(*Volume 6).^‡^ 

This journal is a record of lectures given to the chemistry department
by visiting speakers, this one dating from 1926, about two years after
the article by Robinson noted above.

[![](https://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2018/08/ingold2.jpg){.aligncenter
.size-full .wp-image-20000 decoding="async" width="540"
srcset="https://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2018/08/ingold2.jpg 622w, https://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2018/08/ingold2-300x142.jpg 300w"
sizes="(max-width: 622px) 100vw, 622px"}](https://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2018/08/ingold2.jpg)

There are a number of points of interest.

1.  Early on, Ingold introduces the topic of ***atoms in combination***.
    Lewis (who is acknowledged to have introduced this concept in 1916)
    is mentioned in parentheses, if not actually in passing, as
    *generalizing (Lewis) from this case, ...* As was the practice at
    the time, referencing one's sources was not always common, and you
    do not here get an actual citation for Lewis!
2.  Next comes the topic ***changes in molecular structure*** (which
    could be a synonym for **reactions**) and here you get this
    diagram[![](https://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2018/08/Ingold1.jpg){.aligncenter
    .size-full .wp-image-20001 decoding="async" width="540"
    srcset="https://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2018/08/Ingold1.jpg 621w, https://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2018/08/Ingold1-300x122.jpg 300w"
    sizes="(max-width: 621px) 100vw, 621px"}](https://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2018/08/Ingold1.jpg)A modern
    version is shown below, scarcely different!
    [![](https://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2018/08/Ingold-page001.svg){.aligncenter
    .size-large .wp-image-20002 decoding="async"
    width="300"}](https://www.ch.ic.ac.uk/rzepa/blog/wp-content/uploads/2018/08/Ingold-page001.svg)
3.  Whilst the first example has examples such as S~N~1 ionizations, the
    second is perhaps not as common as might be imagined. It would only
    work if atom C (assuming it to be carbon) was *e.g.* a carbene (with
    six valence electrons) converting to a vinyl carbanion (with eight).
    Although we may speculate that Ingold thought that the second
    example might relate to common reactions, in the event both curly
    arrows are still entirely valid by modern standards. There is no
    acknowledgement of Robinson's 1924 effort.
4.  Ingold goes on to discuss substitution patterns in benzene
    derivatives, and the *o/p* or *m*-directing abilities of
    substituents. He concludes that *the Dewar formula for benzene is
    the most satisfactory vehicle for expressing the theory that
    electrical disturbances readily reach the o- and p-position, whilst
    only a small second order effect can reach the m-position*. Here I
    think we can conclude that this approach has not survived into
    modern thinking. Robinson in his 1924 arrows had of course striven
    to explain the apparent propensity of nitrosobenzene towards
    electrophilic substitution in the *p*-position. Henry Armstrong some
    thirty years earlier in 1887\[cite\]10.1039/CT8875100258\[/cite\]
    had arguably already made a pretty decent start, without requiring
    the use of Dewar benzene.

I suspect those who have dug through the historical archives to cast
light on the Robinson/Ingold rivalry may not have appreciated that the
*Journal of the Imperial College Chemical Society* might have been an
interesting source!

------------------------------------------------------------------------

^‡^There were nine volumes produced during 1921-1930. It then morphed
into *The Scientific Journal of the Royal College of Science* which
continued for an unknown number of years.

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In 2012, I wrote a story of the first ever reaction curly arrows, attributed to Robert Robinson in 1924. At the time there was a great rivalry between him and another UK chemist, Christopher Ingold, with the latter also asserting his claim for their use.

Rogue Scholar Beiträge

Early “curly” (reaction) arrows. Those of Ingold in 1926.