In 1900 when Arts subjects dominated Oxford, Lincoln College decided to offer a Fellowship in either chemistry or physiology. N. V. Sidgwick was elected in April 1901 and came to Oxford from Germany where he had been learning about the application of physical principles to organic chemistry.
Sidgwick worked on kinetics (studying the rates of isomerisation of triphenylmethane dye intermediates and the hydration of carboxylic anhydrides), thermodynamics (investigating phase equilibria and the solubility of organic acids and bases), as well as investigating the colour of copper complexes.
In 1910, Sidgwick published what was to be an incredibly successful book "The Organic Chemistry of Nitrogen" which was revised and reprinted many times. In the preface he stated that "it is becoming generally recognised that organic chemistry cannot be treated satisfactorily without reference to those questions of physical chemistry which it involves. To attempt a separation of the two is to refuse all the assistance which can be derived from what is the quantitative side of chemistry"
World War I, changed the course of Sidgwick's work and he became an unpaid consultant to the Department of Explosive Supplies of the Ministry of Munitions. He was set to work on the process suggested by Perkin and developed by Lambert for the production of acetone (propanone) from ethanol, via acetaldehyde and acetic acid. The final conversion of acetic acid to acetone was never achieved satisfactorily, but the process was used throughout the war for the production of acetic acid. He worked on many other wartime projects, such as the production of phenol from benzene.
In 1916, Sidgwick moved into the Organic Chemistry Laboratory (now the Dyson Perrins Laboratory) where he continued his work after the war on the solubility of organic compounds in water. The anomalous low solubility and high vapour pressure of ortho-nitrophenol compared to the meta- and para- isomers was representative of a puzzle that Sidgwick had been wrestling with for some time, and in 1924 he published a paper which described the solution to the problem.
The ortho-nitrophenol is able to make an intramolecular hydrogen bond. This is stronger than any hydrogen bond to water and so the solubility is low; there is little favourable energy available when ortho-nitrophenol dissolves in water in comparison to para- and meta-nitrophenol which can make hydrogen bonds to the water molecules. The anomalously high vapour pressure of ortho-nitrophenol can be explained in a similar way; para- and meta-nitrophenol can make intermolecular hydrogen bonds which must be broken before molecules can evaporate into the vapour phase. These intermolecular hydrogen bonds are not present in the case of ortho-nitrophenol and so there are relatively more molecules of ortho-nitrophenol in the vapour phase (giving rise to a greater vapour pressure).
In 1922 Sidgwick was elected as a Fellow of the Royal Society (FRS) and two years later, the University made him a Reader. It was not until 1935 that the University made him a professor.
Sidgwick book "The Electronic Theory of Valency" was published in 1927 as a culmination of many years' interest in the nature of covalent and (what we now call) dative bonds. This interest was no doubt sparked by discussions Sidgwick had had with Rutherford in 1914, and given further impetus by Bohr's publications on atomic structure. In 1923, just as Sidgwick was beginning to publish papers in this area of research, G. N. Lewis visited him in Oxford and later in that same year published "Valence and the Structure of Atoms and Molecules."
"The Electronic Theory of Valency" made Sidgwick famous and when he was awarded the Royal Medal in 1937, it was said that this book had a more widespread influence on the views of chemists in this country than any other of this generation. He had brought together organic and inorganic chemistry by concluding that the covalency of the carbon-carbon bond was essentially no different to the co-ordinate link (dative bond) and so provided a firm basis for the general electronic theory of valency, including the concept of a lone pair of electrons.
Cornell University invited Sidgwick to be a visiting lecturer and in 1931 he accepted the offer and spent a semester there which resulted (in 1933) in the publication of "Some Physical Properties of the Covalent Link in Chemistry." In this book, Sidgwick described how data which had emerged from the newly refined techniques to measure dipole moments could help to understand valency and structure. During his travels in America, Sidgwick met Linus Pauling and became interested in the concept of "resonance" suggesting in "Some physical properties..." that the hydrogen bond could be explained by resonance. We now know this to be only a part of the truth, but it represented a significant insight at the time.
On his return to England, Sidgwick intended to resign from all of the committees he had been serving on in order to concentrate on writing 4 new books. Unfortunately, this was not to be and Sidgwick was drawn into more and more administrative tasks, including President of the Chemical Society (1935-37).
Sidgwick's wish to publish 4 new books and volume 2 of "The Electronic Theory of Valency" was sadly never realised, mainly due to his other commitments, but in part due to the rate at which experimental results from new techniques were being reported. The onset of World War II restricted Sidgwick's opportunities to travel, even visits to London were rare and the blitz made these visits unappealing. The war also meant that the flood of new data slowed down such that he could begin with the task of digesting the invaluable information that had been mounting up in the previous years. During this time Sidgwick consulted thousands upon thousands of papers and what was intended to be volume 2 of The Electronic theory of Valency became a two volume 750,000 word book containing almost 10,000 references which he entitled "The Chemical Elements and their Compounds." Sidgwick's health was failing by this time and he became vexed at the delays in publication, but after submission to the Clarendon Press in early 1948, the two volumes were eventually published in 1950 when he was 77.
"The Chemical Elements and their Compounds" has been described as a monumental work of scholarship and his exhaustive survey of the literature coupled with his prodigious memory and systematic way of thinking made Sidgwick perhaps the only person able to achieve it with such success.
Fighting ill health, Sidgwick visited America again in 1950 and 1951 and on the way back from his last trip he fell, or collapsed, and nearly died in Southampton where he taken from his ship. After a brief recovery, he returned to Oxford where he died during the night of 15th March 1952.
Sidgwick's rooms in Lincoln College were said to be part of his aura. He occupied the same rooms (now the Senior Common Room) from 1906 until his death. It was unimportant to him that the furniture was old and worn and that his personal possessions always seemed to be in a jumble. His extensive chemistry library and the thousands upon thousands of reference cards were systematically ordered (though it may not have appeared so to the observer).
Although they are now somewhat dated, Sidgwick's books will be treasured in the college library and we will remember the incredible achievements of Lincoln's first Chemistry Fellow.
Former Praelector in Organic Chemistry, Lincoln College