Tautomerism Ingold

In his 1933 paper on "tautomerism," Ingold began discussion with references to the physics of the electron, citing a 1923 paper by J. J. Thomson and a recent book by John H. Van Vleck.62 He noted Lewis s contributions (1923) to the notion of inductive effect ( ) in which electrons remain bound by their original atomic nuclei Lowry (1923) to the notion of electromeric effect, in which there is a displacement of a duplet, shifting from one pair of atoms to... 

General accounts of prototropic tautomerism have been presented by Ingold and Baker" these include an outline of the historical development of the subject in which heteroaromatic compounds are discussed incidentally, and, therefore, such a historical account will not be given here. Of historical interest are Eistert s book on tautomerism and mesomerism which was published in 1938, a review on — NH-CO— tautomerism by Arndt and Eistert published in 1938, and Heller s account of heterocyclic tautomerism which appeared in 1925. Although more recent works on heterocyclic chemistry (e.g., references 9-11) have dealt incidentally with tautomerism, no unified... 

However, within the next few years, Ingold s dominance in the field of organic reaction mechanisms theory became clearly established, following a 1933 paper on tautomerism in which he introduced the terms "nucleophilic" and "electrophilic" and a 1934 article in Chemical Reviews systematizing "Principles of an Electronic Theory of Organic Reactions." Burkhardt, one of Lapworth s collaborators, said, "ft was a complete takeover of terminology at the right time. "129... 

Burkhardt, "Arthur Lapworth and Others," 143. C. K. Ingold, "The Significance of Tautomerism and of the Reactions of Aromatic Compounds in the Electronic Theory of Organic Reactions," JCS (1933) 1120 and C. 

While at Leeds from 1924 to 1930, Ingold s laboratory focused on three main topics of research (1) the nature and mechanism of orienting effects of groups in aromatic substitution (mainly nitration) (2) the study of prototropic rearrangements (shifts of H+) and aniontropic rearrangements (shifts of anions) as the ionic mechanisms of tautomerism and (3) the effect of polar substituents on the velocity and orientation of addition reactions to unsaturated systems. One of Ingold s students at Leeds, John William Baker, wrote a widely read book on tautomerism. 16... 

Cambridge University Press, 1954) 146. On Ingold s move to UCL, J. W. Baker was appointed "Reader in the Mechanism of Organic Reactions" and F. Challenger was appointed "Professor of Organic Chemistry" at Leeds. Baker s book is Tautomerism (London Routledge, 1934), with an appendix by Ingold. 

Quoted in Seddon, (1972 41), from C. K. Ingold, E. A. Perren, and J. F. Thorpe, "Ring-Chain Tautomerism. Pt. III. The Occurrence of Tautomerism of the Three-Carbon (Glutaconic) Type between a Homocyclic Compound and Its Unsaturated Open-Chain Isomeride," JCS 121 (1922) 17651789. 

The beauty of the Dewar structure, Ingold remarked, lay in the fact that it explains quinoid transformations and aromatic tautomerism as well-established principles of aliphatic and alicyclic chemistry, that is, it provided a rationale for the unification of aliphatic and aromatic chemistry. 

In 1934 Ingold defined the chemical term "mesomerism" to mean stable intermediate states explained physically by quantal resonance.41 He stressed a preference for the word "mesomerism" over the term "tautomerism" or "resonance" on the grounds that it did not lead to the false impression that alternate structural formulas are passing into each other very rapidly, like tautomerides. If such rapid motion were going on, he argued, every molecule must spend most or all of its time in transforming itself, and the term molecular "state" simply loses its meaning.42... 

Charles Shoppee, Ingold s student, who wrote a paper with Ingold and Thorpe in 1926 on the mechanism of tautomeric interchange,48 later claimed... 

Busy with the move from Leeds to London in 1930, Ingold afterward was in residence at Stanford University in California in 1932, with some leisure to work out generalizations of the results already at hand. He soon published two widely read pieces "Significance of Tautomerism and of the Reactions of Aromatic Compounds in the Electronic Theory of Organic Reactions," in the Journal of the Chemical Society, and the essay review, "Principles of an Electronic Theory of Organic Reactions," in Chemical Reviews.58... 

Ingold, "Significance of Tautomerism," pp. 312313 in Baker, citing Lewis, Valence, 139 Lowry,... 

Ingold, Edith Hilda. "The Correlation of Additive Reactions with Tautomeric Change. Pt. IV. The Effect of Polar Conditions on Reversibility." JCS 127 (1925) 469475. 

As Ingold s version of the electronic theory developed, NH2, NR2 and NHAcyl groups were classified as —/ and +7" in their electronic effects, signifying electron attraction through the Inductive Effect and electron release by the Tautomeric Effect59. Later the latter was subdivided into the Mesomeric Effect M (polarization) and Electromeric Effect E (polarizability)60. The NO group was also classified as —I and +T in its electronic effect, while NO2 was classified as —I and —T. 

Ingold, C. K. The structure of the benzene nucleus. I. Intra-nuclear tautomerism. Trans, chem. Soc. [London] 1922, 1133. 

Ascorbic acid was, therefore, shown to be a y-lactone, conveniently represented as in Figure 3.5 although other tautomeric forms may exist in small quantities. The configuration at C-5 is l- (or S-, using the Gahn-Ingold-Prelog system). The acidic nature in aqueous solution derives from the ionisation of the enolic OH on C-3 (pA a 4.25), the... 

The assumption of very similar transition states for substitution of benzenes and addition to ethylenes gives the foregoing theory some of the characteristics of those theories that assume preliminary addition. Except for the assumption of an o-p-directing effect from the dehydrogenation of a nuclear carbon atom, we have closely followed Ingold s theories of the inductive and tautomeric (resonance) effects of groups on the favored positions of substitution. 

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