Martin D. Saltzman Providence College Providence, 131 02918
I
The Robinson-lngold Controversy
I
~recedencein the ekctronic theory of organic reactions
I
In his posthumously published autobiography, "Memoirs of a Minor Prophet" ( I ) , Sir Robert Robinson (1893-1975) makes the following comment about his role in the development of the electronic theory of organic reactions:
formulations such as shown in I, Thiele could account for 1,4 addition in dienes.
". . .these ideas constituted, in the writer's opinion, his most im-
Robinson differed from Thiele by proposing that the partial valencies were derived from normal valencies rather than added on t o as Thiele had suggested. By 1920 (6),Robinson had nerfected his notions about the role of ~ a r t i avalencies l in the reactions of conjugated systems.
portant contribution to knowledge.. ." (I).
A synoptic outline of Rohinson's system for the pathway of organic reactions can be found in a paper published in the Journal of the Chemical Society in 1926 (2). This paper summarizes ideas Robinson had been accumulatine and refining for almost a decade. In this chapter dealingUwiththe ddvelonment of the electronic theorv from a vantaee t .. .~ o i nof 50 years later, Rohinson makes some very serious charges concerning the a ~ ~ r o v r i a t i oofnhis pioneerine. - work hv Sir C. K. 1ngold(1893-i976). ' Ingold had published a paper several months after Robinson in the Journal of the Chemical Society (3)which contained similar ideas to that of Robinson, although, up to this point Ingold had heen operating from a totally different theoretical hasis. Robinson claims that with time the distinction of his work as beine first became clouded as Ineold throueh " his prolific writing and seminars appropriated all the credit for the work and rave none to Robinson. Indeed. in survevine texts in physical organic chemistry today both k e n are given equal credit for the foundations of reaction mechanism as we know i t today. Was Sir Robert correct and does he deserve singular recognition as the founder of modern electronic mechanistic thinking? One way to answer this question is to look at the intellectual developmint of these twoken and let the reader then assess the strength of the accusation, Sir Robert Ruhinson was horn Seotember 13. 1886. and received the whole of his chemical triiniug a t the university of Manchester. His graduate and Dosteraduate work was directed bv W. H. Perkin. Jr. ;190i-1912), and this association was probably responkble for his lifelong interest in organic synthesis especially directed toward natural products. He secured his first academic post a t the Vniversity of Sydney and remained there for three years. In 1915, he returned toBritain and wasmade Professor a t the Universitv of Liverpool. Robinson remained at Liverand came to feel that inadequate facilities pool for five and funding were stagnating him. In 1920 he accepted the directorship of research at the British Dyestuffs Corporation. He rapidly grew disillusioned of industry and returned to academia in 1921 with an appointment a t St. Andrews. In 1922, Robinson had the opportunity to return to Manchester and remained there for a period of six years. This appointment was followed in 1928 by two years at University College, London. Finally in 1930 he was offered the Waynflete Professorship at Oxford and stayed there until he retired in 1955. Robinson's first excursions into electronic theory date from 1916 (4). This paper and subsequent ones used as their basis of the interpr&a&on of reaction mechanism the concept of partial valency. This work was a departure from the partial valency theory of Thiele ( 5 )which was popular a t this time. Thiele had postulated that in conjugated systems the inner two atoms would saturate each other thus leaving all the chemical affinity at the outer one and four carbons. Thus by
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484 1 Journal of Chemical Education
;
n
;
c=c-c=c I
The necessary condition precedent to chemical change is the activation of one or more molecules taking part in the reaction; this is done by cohesion and rearrangement of valencies, most probably synonymous with changes in the position of electrons . . . . The activative molecules are further assumed to he polarized and to contain partially dissociated valeneies . .. .The representation of the phenomenon of conjugation and addition to conjugated systems is much simplified by the use of the theory of divisible and polar valency (6). Thus Robinson represented the addition of bromine to butadiene as follows: +
-
FH-CH
C,.. H-
.
+
. CH. , ~ ~ .
I l V B r
The dotted lines and the plus and minus signs were Rohinson's way of representing the quantity of rharge produced in the polarization to produce the partial valencies. The octet theorv of Lewisand Lanemuir at this time (1920) was very novel. ~ i o n with g other organic chemists Robinson had not assimilated its full import in terms of organic reaction mechanism. Robinson became aware of the utilitv of the octet -------~-~~~~~~~ concept after attending the lectures given by lrving Langmuir in 1921 a t the Edinbureh meetine of the British Association for the Advancement of Science. The year 1922 was a fateful one for Robinson, because it not only marked his return to Manchester and the opportunity t o become part of a premier center of chemical research, but also it marked the publication of his first paper to utilize Lewis-Langmuir theory (7). This paper was produced in collaboration with W. 0 . Kermack of the Royal College of Medicine, Edinburgh. I t was also the result of discussions that Robinson had had with his soon to be colleague Arthur Lapworth. The period that Robinson spent a t Manchester was to nrove to be so fruitful. because of the close association with Lapworth. Lapworth established the field of reaction mechanism studies with his classic investieations of cvanohvdrin formation and bromination using kinetics as a tool beginning in 1898. The paper published in 1922 entitled "An Explanation of the Property of Induced Polarity of Atoms and an Iuterpretation of the Theory of Partial Valencies on an Electronic Basis (7) had as its basis, the view that organic reactions are ionic in nature, a point contributed hy Lapworth's early work. In addition, movement of electron pairsas proposed by I.ewis and Langmuir was included. Key ideas advanced by Robinson in 1922 can be seen from the following passages: ~~
~
~
~~
~
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.~ ~
~~~
~
An atom is called negative which is surroundedby a stable octet, or which tends to attract electrons to make up a stable octet. The tendency to form an octet is greater the more nearly it is already
atom, over a long range seems to require the presence of double bonds, and usually in conjugated positions, consequently the principle must find ample scope in the aromatic series where conjugation is the rule (9).
formed. Conversely, adisintegrated octet tends to further disruption and atoms surrounded by such unstable systems tend to lose electrons and are positive in polar character (7). Robinson points out that polarity had a more profound impact on an unsaturated system than a saturated one, because of the mobility of electron pairs. If, now in the system
for some reason external or internal, the octet surrounding A becomes stable, this will automatically involve more or less the appropriation of the two electrons shared with B, the octet surrounding which is, therefore, unstable and tends to disintegrate. If, now another atom C is attached ta B, it will have to difficulty in appropriating two further electrons from B, and in doing so may form a stable octet. This again will preclude a fourth memher of the chain, D, from forminga stable octet. In other words the atoms, A, B, C, and D are respectively -, +, -,+.The case of allyl chloride may be cited as an example:
Here the stable &t surrounding the cblorine atom produces an unstable system about the adjacent carbon atom, and therefore, the formation of a stable system in the CH group is facilitated and occurs by the aid of two electrons held in common with the second unsaturated carbon acorn I t is accordingly quite natural that the product of the addition of H'Br- is trimethylene chlurobromide (7). Rohinson cautions that this view shows only what happens if a polar atom is present. but not the circumstances as to how theatom is induced to "assume its stable octet or to lose a n electron" (7). Robinson felt so comfortable with the concept of the mobility electron pairs and how this related to the seemingly unusual reactions of conjugated systems, that he produced the following electronic view of the Kekul6 structure of henzene:
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The relation of Kekule formula is seen to be aremarkable close one and to involve the movement of electrons,not from atom to atom, hut merely tonew positions in three octets. If, therefore, the benzene molecule is in fact, as manv chemists have assumed., subieet , to vibrations and in a dynamic condition, a relatively insignificant rearrangement is required in order to pas. from one Kekule formula to the other (7). Rohinson was the first person to use the term aromatic sextet (1925), in connection with investigations he had in progress on polynuclear heterocvclic aromatic svstems (8). Following this paper in 1922, ~ o h i n s d ndirected most of his effon toward the synthesis of natural ~roductsdurine the next six years at ~ a n r h e s w rHowever, . concurrent invekgations of aromatic suhatitution were o n e o i n ~in the laboratories at Manchester in which Robinson tried tb correlate orientation and reactivity with the electronic ideas he had developed. Arthur Lapworth (1872-1941), Robinson's colleague had also been developing ideas as to how to explain the course of oreanic reactions. The two men were inseoarable durine the ~ ~ k c h e s t e period. r Lapworth's ideas never achieved the sophistication of Robinson's. but the two alwavs seemed to be jumped together in any discussion of the ~ a k h e s t e school r of reaction mechanism bv their contem~oraries.Lanworth gave to polarity the key role in determining the course of reactions and his system is encompassed in the followine-. oassage:
.
~~~~~~~
~~-
The writer originally fell into the habit of labelling the atoms in a reaction molecule with +and -signs as the result of his applieations of ionic theory to the reactions of carbon compounds and especially to those of ketones and other carhonyl compounds.. . . The signs are applied merely as expressing the relative polar character which the atoms seem todisplay at the instant of chemical change. .. .The extension of the influenceof the directing, or key
Indeed, application of the key atom concept of Lapworth can predict the orientation in many simple substituted aromatic systems. Lapworth was never as adept as Robinson with Lewis-Langmuir concepts since he was essentially a product of the nineteenth century. In 1925, the first paper in a series entitled "The Nature of the Alternating Effects in Carbon Chains" (10) appeared from the pen of C. K. Ingold (1893-1970) of Leeds University. This paper was a direct challenge to the veracity of Robinson's electronic ideas in determining the c o m e of organic reactions. A rationale for the directive effect of the nitroso group in aromatic substitution completely opposed to the views of Robinson was discussed in this paper. To understand the basis for this challenge we should briefly review Ingold's career. Ingold was born Odober 28,1893, and he obtained his B.Sc. a t Southhampton in 1913. He then proceeded to Imperial College in London where he took his Ph.D. under the direction of Jocelyn Thorpe in 1918. It must be remarked that Ingold's first love during his undergraduate days was physics, but he found the subject, as it was taught in those days, static in comparison to chemistry which he then decided to study. This early bent toward physics probably led to his lifelong interest in the area of nhvsical . " oreanic chemistrv as comnared to Robinson's major and continuing interest in synthetic organic chemistrv. After leavine Imnerial. Ineold w e n t two years in the ~ h e ~ i cindustry al and then returned tddo postGaduate work with Thorpe at Imperial from 1920-3924. Thiscollaboration was so successful that hy 1924. Ingold, at the age of 31, was made a Fellow of the Royal Society and offered the Chair of Organic Chemistry heing vacated hy J. B. Cohen at Leeds. Ineold's stav at Leeds lasted until 1930. when he moved to ~ n i v & i t y ~ o h e g eLondon, , to occupy thk professorship vacated by Robinson's move to Oxford. During the latter period a t Leeds (1927-1930), much valuable work was done on refining the electronic theorv of reaction mechanism. Ineold had initiited the work on arodatic substitution as a res& of his application of Lapwonh's key ntom notions tosome synthetic projects he had conducted with Thorpe at Imperial. He had found that on occasion the produrt predirted hy Lapworth's experiformulation was not what was obtahed under mental conditions (10). Ingold throughout the period of 1924-1925 tended to lumn the work of Robinson and Lanworth as being in essenenie identical, though the former, ks we have indicated. was far more advanced in his sonhistication than his senior cdlleague. The basis of Ineold's interpretation of reaction mechanism was his reliance i n ideas that had been put forth beginning in 1902 bv Bernard Flurscheim (1874-1955). Flurscheim is an enigmatic figure in the history of organic reaction merhanism hecause, excent for brief perinds (190.51907: 192C1928) when he worked a t the ~ o y a Institution i in London, he held no formal post in the academic or industrial world. He, however, maintained a private laboratory at his home in which he worked till his death. Flurscheim studied with both Thiele and Werner. and no doubt his thinkine about valence was ereatlv. influenced by them. The basis of Flurscheim's thinkine was the concent of altemating affinity. Substituents could exert either a strong or weak affinity demand upon the carbon atom to which they were bound. This effect would then be transmitted along the chain in a n alternate manner. Implicit in Flurscheim's theoretical framework was the notion that affinity was continuously divisible and was partlv bound and partly free. Flursrheim never arrepted the not& ot covalen; bonding herawe to him the only strong force was electrostatic. In Flurscheim's system atoms whichcan increase their valency make large affinitydemands on the adjacent bound carbon atom whereils
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Volume 57, Number 7, July 1980 1 485
atoms already in a high valency state make little demand on adjacent carbon atoms. These affinity demands are then transmitted to alternate carbon atoms in a chain. Examples of Flurscheim's notions in the aromatic series are shown below where the phenolic group (11) represents a high affinity demand suhstituent and nitro (111) a low affinity demand group. This then leads to ortho. oara substitution in the former case and meta in the latter, agreeing very nicely with experimental reality.
he sketched out a counter argument to rebut the attack on his ideas by Ingold. Robinson argued that conjugation of the electron pair on nitrogen with the ring could also easily explain why o-, p-substitution should occur. Below is shown the representation that Rohinson drew in this short note to explain o-, p-substitution.
A further clarification of the views of Robinson aooeared in the May 1,1925 issueol'Chsmistrj ondlndustry (ij).The paper entitled "Polarization in Nitrosobenzene" heains - with the following statement: Flurscheim's speculations were very attractive since one did not have to dealwith such concepts as electron pairs, octets, as well as mobility of these species as Robinson had proposed. In almost all cases the use of Flurscheim's theories to oredict aromatic substitution worked extremely well, indeed as well as those of La~worth'skev atom concept. How lngold became enamoured with the notions of Flurscheim is difficult to establish. One can sav. with some cern s about tainty, that Flurscheim on numerous o ~ c a ~ i ospoke his ideas at meetings of the Chemical Society in London at which Ingold was i n attendance. They were good friends though life as witnessed by the obituary notice for Flurscheim by Ingold in the Journal of the Chemical Society (11).Ingold took the tact that what Robinson and Lapworth were really proposing was an alternation of electrical charges, whether real or latent, produced by the presence of a highly electroneeative atom. Ineold took Laoworth's theorv and a ~ n l i e dit in Yts most literal sense, assuming that ~ o b i n & nalsothought along similar lines. In the molecule nitrosobenzene, Ingold thought he had found a suitahle substituent that would produce one pattern of substitution using the concept of free and hound affinity of Flurscheim and a different one using Lapworth-Robinson ideas. In the nitroso group polarity would dictate that oxygen, being the most electronegative atom, according.to Lapworth's scheme, would produce an alternation of charge leading to an excess in the meta position (IV) and hence substitution at this ooint. On the other hand. Flurscheim's thinkine. as aoolied b y Ingold, assumed that the nitroso group -pos&ledj inore unbound affinitv than hvdmren and if attached to the benzene nucleus wili cause tl;e development of free affinity in the o- and p-positions; that is, they will he o- p-directing" (V) (10). The nitrogen was believed t o have a greater role to play than oxygen because of its ability to produce higher valence states.
The facts, as far as they have been ascertained, are that nitrosohenzene can he directly chlorinated, brominated, and nitrated; and that in each case the group enters mainly at the para-position; meta isomerides could not be detected (10). Thus, Ingold argued that substitution is controlled by alternation of the quantity of affinity and not by electropolar quantity and valency redistribution. The distinction here is significant and indicates that Ingold was thinking in a manner verv much different from Robinson in late 1924 and throughout 1925. Robinson knew of the nitrosobenzene results before thev appeared in print as they were communicated at a meeting of the Chemical Society in London. This practice was common as were written replies to points raised in opposition which were published in Chemistry and Industry. A letter appeared in the December 24,1924 issue (12) from Rohinson in which 486 1 J m l of Chemical Education
The reactions of nitrosohenzene and its derivatives have been much discussed, and in this short note it is proposed to consider the ean be aoolied manner in which an electronic theom of coniueation , .. to thrs remnrkahle group of ~uhrtancesand with special reference totheersoriation~rfthenitrosogroup with an unsaturated system
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(131.
Robinson then defines two major types of unsaturated svstems. which were called bv him crotenoid and crotonoid dased upon the reactions of crotenaldehyde and crotonic acid. The general tendency to acquire a more even distrihution of valency operates in the crotenoid types to facilitate polarization according to the annexed scheme in which arrows represent the changes in covalency functions of electrons necessarfto preserve the octets
(13).
*
"
VI
Thus, nitrasobenzene is an example of a crotenoid system and one would. therefore. usine these orincioles of coniueation. predict that o-, p-products-would de produced. ~ o t h i o in: n dicated that it was not always necessary for an atom to increase its covalency in an unsaturated system hut can in some cases actuallv decrease it. Rohinson called this a crotonoid system (VI).
M
In nitrosohenzene, both crotenoid and crotonoid systems coexist. Electroohilic suhstitution can be exolained best hv the crotonoid t h e of conjugation whereas n;cleophilic ardmatic suhstitution can be rationalized by the crotonoid pattern. Either mode leads to the same conclusion, that, o-, psubstitution will take place exclusively in nitrosobenzene. Furthermore, Robinson states that "application of what are loosely called the polarity theories demands first consideration of the-situation ofthe cohjugated systems (13)-a factor which Ingold obviously did not consider! T o counter the objections of Robinson that Ingold had completely neglected the role of the lone pair on nitrogen, which the latter did not think was important, he performed a study of the direction of aromatic suhstitution in n-methoxyvinyl benzene. Here he had a group where any objection based upon conjugation could be eliminated since the oxygen atom was now one removed from the aromatic rine. Again. lngold used the concept of free and hound affinity to pridict o-, p-substitution (VITI), and lumpinr Rohinson and 1 . a ~ worth together he predicted that meias;bstitution (IX) wouid result. 'l'hii suhititution is summarized below:
The outcome of the experiment was to show that in n-methoxylvinyl benzene the exclusive products of substitution are the ortho and para isomers ( 1 4 ) . A third and final paper which to Ingold's thinking would finally prove the superiority of his theoretical framework was a stud; of substit&on in benzvlalcohols and benzvlamines (15).1; this paper, Ingold sou& to dispel the ideas idvanced bv Robinson manv times and esneciallv in his studies of the nitration of m-meconin (16)that oxygen and nitrogen could upon occasion act as ouium ions. Formulations such as
and H @ C ~ were part of Robinson's rationale to explain the oath of nitration. This rationale would comdetelv change the predictions based upon polarity such as shown in ~ i g u r & IV and IX. In these systems not only were the nitrogen and oxygen atoms once removed from the ring, but also the formation of onium salts could be controlled according to Ingold. Ingold argued that in the benzylamines, because of the strong affinity demand of nitrogen be& tewalent in these compounds, meta substitution should result. In contrast benzylalcohols where t h e oxygen makes a weak affinity demand the pattern of aromatic substitution should be ortho-para. If salt formation took nlace. ortho-oara nroducts would also be formed in benzilalcohols. using pblarity principles of Robinson and Lapworth as interpreted by Ingold, the nitrogen atom in benzylamines would be feebly negative and indeed should produce ortho-para products. "Oxygen, owing to the greater pre-formation of its octet, should predominate over nitrogen as a negative key-atom, the theory of alternating free and bound affinity demands that the more unsaturated element tewalent nitrogen, should have greater influence (15). If benzvlamines were to exist in their onium form then oolarity principles of Robinson-Lapworth would predict that ortho.para substitution must result since nitrogen would he positively charged. Alternating polarity (Robinson-Lapworth) would predict that in all rases examined the same results would be obtained, whereas, free and bound affinity produces two nossible outcomes denendine on whether onium formationoccurred. Thus, lngold stat& "It follows that in comnarison of henzvl alcohols with benzvlamines we have a clear cut issue, from khich the theory of okium-action provides no exit" (15). ~e&lamine, methylbenzylamine and dibenzylamine were nitrated. These three compounds according to Ingold produced meta products and in addition a t low temperatures 0-20°C, also, some para isomer. These results were consistent with his analysis using free and bound affinity. For compounds such as acetobenzylamide, acetomethylbenzylamide, and a~etodibenz~lamide the assumption was made that these would form moderately stable salts. Substitutions here would be ortho-para, since these arnides were weaker bases than benzylamines. On the other hand, Ingold argued that diacetylbenzylamiue would be nun-basic and salt formation could not occur. This would lead to meta substitution in analow ..- to the benzvlamines where the tervalent nitrogen was responsihle for meta substitution. Thus, lngold predicted that I'm frec amincs substitution should produce heta, and salts would produce ortho-para suhs~itutiou products. Thus, wrote Ingold a t the conclusion of what he believed to he the definitive proof of the superiority of his analysis since he obtained all products predicted I t reems that thew ir only one comistpnt explanation of these facts, namely, that which has umformly and correctly forrwld ewnts thrwghout thisseriesof mvestrgations. Prwf has been given that the efficiences of negative key atoms stand, not in order of their electron affinities,hut in order of their unsaturation; and it seems fair, therefore, to conclude that unsaturation is the property transmitted. Thisis the essence of Flurscheim's form of the alter-
nating theory. We are aware that by identifying unsaturation with potentidy mobile electrons, and its alternating distribution with a similar propagated electronic displacement,a nearly equivalent theory may be formulated . . . . We suggest, therefore, without denying the possibility of polar alternation,that the factsthus far adduced constitute grounds for the conclusion that the propagation of alternating unsaturation is the prime directive process in ordinary aromatic substitution. I t must be remarked that between May and October 1925 when the series of three papers by Ingold appeared, a lively and vituperative dehate w& being conducted in the pages of Chemistry and Industry between Robinson, Ingold, Lapworth. and Flurscheim in terms of who was misinter~retina whom'with respect to aromatic substitution. The benz$lamine naner which was read a t the Chemical Societv~rior to ouhli.. cation provoked the most heated and hitter exchanges and was most resoonsible for the lifelonr - enmity between Robinson and 1ngAd. Robinson's initial answer to the results of Ingold was that there were two types of electronic displacemet& possible in aromatic svstems. One was the conjugative effect described in 1922 and in subsequent c o r n m ~ ~ c a t i o nasv '.involving changes in covalency functioning of electrons" and a second "due to electrostatir induction, the general effect requiring no changes in covalency" (17). The latter idea was a new addition to Robinson's theoretical framework. The ronceot of a general polar effect which could control the direction of substitution in an aromatic svstem could easilv- exdain - what happens when the pole itself is not conjugated with the ring. According to Robinson then:
..
... the relation to the case of the benzylamines was that a suffeiently positively charged ammonium group might so strongly attract electrons an to produce the effect of meta substitution when separated from the nucleus by a methylene group. A relatively greater proportion of the meta-isomeride is therefore expected in the case of benzylamine salts, the more powerful the base. In CH2Ph.NHCOMe and CHzPh.NEtPh the nitrogen will acquire a positive charge owing to its conjugation with the CO and Ph, respectively, and should therefore produce meta substitution (17). On the basis of the experiments performed which found that free amines cave meta nroducts and salts ~ r o d u c e d onho-para, Ingold completely dismissed the ideas of Robinson and held to the free and bound aftinitv notions of Flurscheim. Robinson in the Octoher 9,1925, issue of Chemistry and Industry made the following statement (18). The circumstances that Dr. Flur~cheimand Prof. Ingold do nor accept my own interpretation of the suggestimu of Kermack and Robinson relating to alternating stable and relatiwly unsrahle oetets is, I susped, of such small interest to the public that aeontinuation of the discussion can serve no useful purpose (18). Early in 1925 Robinson gathered together the whole of his theoretical framework in a paper submitted to the Journal of the Chemical Society (2). This paper contained a finely detailed discussion of hotb conjugation and general polarity and their application to the problem of orientation in aromatic systems. A pre-print of the manuscript of the paper was sent t o Iugold in hope of finally settling the dispute over iuterpretation between them. The Robinson paper was received bv the Journal on June 18.1925, and in a letter dated February I?, 1926, Ingold in returning the manuscript wrote the following to Robinson: They represent, in my opinion, avery fineeffort,especially on the theoretical side, and the theory is certainly one of organic chemistry and not of aromatic substitution only ( I ) . On Februaw.10.1926. a Daoer . . . bv. Innold .. was received by the Journal of the ~hernicolSociety; it appeared later in the same "ear and deals with the nitration of o-aminophenol derivatives i3). The explanation of the orientation is now based upon the concents that were found in Robinson's paper of 1926 (of whichlngold had received a pre-print). Ingold neatly rationalizes Flurscheim's free and bound aftin~tyconcepts in terms Volume 57, Number 7, July 1980 1 487
of Rohinson's superior electronic interpretation in a facesaving fashion. It will he obvious that the distribution of forces here involved is qualitatively the same as in Flurscheim's theory, the completed change corresponding with his figure for o- p- substitution.
In applying these suggestive ideas. . .we would regard the above formulae as expressing only the direction of imaginary gross changes which actually do not at any time proceed to more than a limited (in some cases exceedingly small) extent (3). T o exolain the activatine effect of a methvl erouD Iueold produced the following stricture very remin&nt o'f ~ o b i n son. Inrold had aooro~riated basically all the elements of .. . ohi ins on's system.
h oh ins on must have been extremely gratified that he had made a new convert to his theoretical views. His satisfaction must have been all the more complete when later in 1926, he (19)showed that Ingold's original work with benzylamines was completely wrong experimentally. The orientation in nitration was exactly opposite to that which Ingold had assigned and agreed totally with Rohinson's predictions of what would happen in these systems. It would~beinteresting to know what wuuld have happened if the experiments had not heen performed incorrectly and the results agreed with Robinson's notions and not the ones Ingold was so convinred were correct. Pruhahly the bitterness that developed between these two giants would not have resulted because lngold would have seen the superiority of Robinson's work and the rancorous exchanges over the henzylamines would never have occurred. The evidence aathered from the literature would certainlv .tend to indicate
