Christopher Kelk Ingold lived a life that reminds us that not every historical figure received prominent signs of destiny from childhood. Indeed, his first sign of brilliance was not recognized until he was ready to graduate from college. Later, when he was making major discoveries, acceptance of his authority was not naturally offered as it would have been to a recognized genius. Still, he had great influence in the field of organic chemistry, offering the landmark explanation of organic reactions. Furthermore, he addressed issues of methodology and, thus, had a crossover effect in physical chemistry in spite of the tendency for scientists to resist influence from outside their specialty. He is credited with systematizing modern organic chemistry because he clarified many issues through his prolific, comprehensible writings.
As quiet and unassuming as his research career was, it still contained some elements of a classic story of the struggle for success. (William Brock even suggests that a 1930 novel was partially based on Ingold's life.) Many classical novels include characters such as the loyalty- inspiring teacher and the ever-faithful wife. For Ingold, his teacher, J. F. Thorpe, inspired him long after their association. Ingold's wife Edith, an accomplished researcher herself, often helped in her husband's work. Ingold's drama also included the long-term friend (collaborator Edward David Hughes) and an unrelenting rival (Robert Robinson). The main point of this drama was that success was achieved through perseverance and self- confidence in the face of adversity.
Christopher Ingold was born in London in 1893. He lived an obscure childhood on the Isle of Wight. There was nothing remarkable about his youth and education. He entered Hartley University College of Southhampton in the year 1910 at age seventeen. He was very much interested in physics, but was drawn to chemistry by the enthusiasm shown for the subject by one of his teachers, David R. Boyd. Ingold wanted so much to impress Boyd that, when he achieved second honors in the class, he felt it was not good enough. However poorly he felt he did in that class, he made chemistry his life long obsession. Friends report that, until he turned sixty, he appeared to have no other interest.
After graduating from Southhampton, Ingold began graduate studies toward a Ph.D. at Imperial College. There, he was student and research assistant of Jocelyn Field Thorpe. Thorpe was on the breakthrough of important research dealing with tautomerism and the structure of compounds. Ingold was thrown immediately into the thick of this study. This collaboration was a mutually beneficial relationship. Ingold trusted Thorpe as mentor so much that when Thorpe arranged for him to work at a chemical company for over two years, Ingold considered the job as part of his studies. After the two years was over, Ingold returned to Imperial College and to collaborating with Thorpe. Only this time, Ingold was at college, not as student, but as lecturer. He had earned a Doctorate of Science (rather than a Ph.D.) based on his writings.
After three years as lecturer, Ingold took at turn in his life and in his career. He married his skillful research assistant, Edith Hilda Usherwood. The next year, 1924, Ingold was elected Fellow of the Royal Society and received a Chair of the Chemistry department at the University of Leeds. Ingold's wedding may have influenced his research interests. His wife Edith had already begun her own career in organic chemistry research. Around the time of his marriage, Ingold was turning from classical theoretical research, influenced by Thorpe, toward the physical studies from which he gained his international reputation. At this time, he also became serious (from a classical point of view) about overturning Robinson's (electron-based) theories of organic reactions. It was just the beginning of a long-term, sometimes uncivil, rivalry between the two.
In 1930, Ingold was offered second Chair of Chemistry at the University College of London. The position was vacant because of the promotion of Robinson who, incidentally, opposed Ingold's nomination. One of the lecturers in the department was Edward David Hughes who was to collaborate on Ingold's research for over thirty years. When F. G. Donnan retired from UCL in 1937, Ingold was made head of the Chemistry department where he stayed until his retirement in 1961. After his retirement, he accepted a fellowship at Vanderbilt University where he updated his well-known textbook on organic chemistry. He died in 1970 in Middlesex, England.
The debate between Robinson and Ingold centered on the applicability of the principles of physical chemistry to organic chemistry. When the personalities were extracted from the debate, it became clear that there were two major issues with Ingold or Robinson on the wrong side of either. Both were growing into an electron-based theory but from different paradigms. Robinson, before Ingold, recognized the value of attributing organic reactions to exchanges at the particle level. However, it was Ingold who stressed that the laws of organic reactions (when and if found) would hold true generally for all compounds and any differences seen within individual compounds are due to alternative influences. Ingold delivered 14 long experimental papers in 18 months on this issue. With almost all, Robinson challenged his findings in person or with critical papers. Both made embarrassing mistakes until they began to modify their stances through accepting points from each other.
In studying tautomerism, Ingold accepted that certain compounds must exist in two different forms. The question arose: "Which form was most descriptive of the properties of the compound"" Ingold studied the developing reactions of these compounds and recognized that there was an intermediate state before these compounds divided into their various forms. This intermediate state he called the mesomeric state. The most organized and useful description of the compound, he argued, was this mesomeric state. Through further study of the mesomeric state, Ingold reached one of his most important contributions to organic chemistry. This was the concept that there were four different types of reactions possible in elimination and substitution based on bimolecular or unimolecular reactions. Bimolecular elimination occurs through the influence of a base. Unimolecular elimination does not involve interaction with the base. Bimolecular substitution occurs when two reactants join to form a mesomeric ion. Unimolecular substitution is a two-step process involving the forming of an ion to react immediately with an anion. Ingold stressed that it was important to identify which type of reaction was occurring to best define and predict the effects of the reaction.
While others were making similar observations, Ingold was the first to elucidate all observations in a practical model. He, thereby, explained many different phenomena in a comprehensive manner. Ingold found the means to develop the models because he held to his belief that the mechanisms in organic chemistry were generally applied across all compounds. (Others experimented based on the concept that each compound followed principles of individual mechanisms.) Ingold was also one of the first to use the apparatus and methods of physical chemistry in the study of organic chemistry. These included the use of isotope effects and molecular spectroscopy.
It should be noted that Ingold's loyalty to Thorpe delayed his acceptance of an electron-based theory. Ingold's delay, in turn, influenced the delayed acceptance of the theory. When he finally accepted, he gave a most comprehensive explanation of the implications of the theory outshining proponents such as Robinson. One wonders how much organic chemistry could have been advanced if only these two giants of theory could have worked together. Ingold's refusing to acknowledge Robinson's influence on his work led to Robinson's accusations of plagiarism. This accusation probably influenced Ingold's not winning the Nobel Prize when he was nominated. However, Ingold did receive many honors, including a knighthood, for his work.
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