History of Curly Arrows
inventor of Curly Arrows is usually recognised to be Robert
Robinson (1886-1975), winner of the Nobel Prize for Chemistry in 1947.
main interests were in the study of the structures, properties,
and synthesis of plant dyestuffs (anthocyanins), sex hormones,
and alkaloids. His discoveries led to the successful production
of synthetic antimalarial drugs, and he contributed towards the
investigation of penicillin. He also took a great interest in
fundamental questions concerning the mechanisms of organic chemical
can read more about him at the FECS,
first use of curly arrows to represent the movement of electrons is
in a paper entitled An Explanation of the Property of Induced Polarity
of Atoms and an Interpretation of the Theory of Partial Valences on
an Electronic Basis, by William Ogilvy Kermack and Robert Robinson,
published in the Journal of the Chemical Society, 1922, 121,
Robinson had just recently come to adopt the then quite new idea,
first proposed by G.N. Lewis, that a (covalent) chemical
bond was formed by two shared electrons. The relevant part of the paper
is concerned with the observed addition reactions of conjugated dienes,
which it explains by noting that unsaturated atoms share more electrons
in common than saturated ones, and proposing that there will therefore
be a greater mobility of electrons.
term "primary conjugation" is used to denote a process
occurring in the course of a reaction resulting in addition
to the terminal members of an unsaturated system of more than
(a) Conjugation of Ethylene Linkings.The representation
of the active phase and conjugation of butadiene on the partial
valency theory is
on the Thomson and Lewis-Langmuir theory as now interpreted
the conjugation of three double bonds, supposing such to occur,
would be represented thus:
the notation which has been used in the development of the
theory of partial valency acquires a physical meaning if we
assume that the symbols imply
electrons to the number of four, three, two, and one, respectively,
held in common by two atoms.
[R. Robinson, J. Soc. Chem. Ind., 1924, 43, 1297] Robinson
again used arrows to explain why the nitroso group should be m-directing
in aromatic substitution reactions, and not o,p-directing, as
predicted by the opposing theory of the time. This example really does
begin to look much more like our common usage today.
an electron pair by a line, the following exhibits the covalency
changes leading to the negatively charged p-position.
figure is in strict accordance with the views on the electronic
explanation of conjugation which were expressed by Kermack
read more about the history of Curly Arrows in a recent article entitled
"Who really invented the curly arrow?", Education in Chemistry,
2001, 38, 102, and The Fontana History of Chemistry,
W.H. Brock, Fontana, London, 1992, gives more information about the
history of this period in the development of organic chemistry.
are two local connections for those of us at Aberdeen University. The
first is that the first phase of the building we presently occupy, the
Meston Building, was opened by Sir Robert Robinson in 1952.
second local connection is
William Ogilvy Kermack (1898-1970), Robinson's co-author on
the first "curly arrow" paper mentioned above. Kermack
was blinded in a laboratory accident in 1924, but nevertheless
succeeded in continuing with a career in science, although he
did not continue to collaborate with Robinson. He authored with
McKendrick two very important papers (1927
on the Mathematical Theory of Epidemics which are still regularly
cited to this day. Later, he joined Aberdeen University as Professor
of Biochemistry in 1948, and remained in this post until his retirement
in 1968. Students from his last years have vivid recollections
of his regular visits, with his assistant, to the laboratory classes
high in Marischal College, and of his inimitable lecturing style.