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Home , Henry Edward Armstrong, Martin Lowry

1 ll t Ch (1997

THOMAS AND THE MIXED MULTIPLE BOND

Mrtn . Sltzn, rvdn Cll

h Mrtn r (17-193 n flr nfln f nr Edrd Artrn (1-1937 n t ll ht prrl fr h thr f d nd b nlt thr nd rrhr Artrn n r- l dvrd nd nd ldtd th h- n ht bt rbrd fr h ntr fr- n f trttn ll bn pnr n th l fr bnzn; bt h l dd nfnt r n td f ptl rttr dprn pl ntrtd n th htr f htr h pblhd dl d txt Historical Introduction to hh nt thrh thr dtn (1 rnd rnll n r- n ht h ntrt rvttd t phl h- tr r n f th pnr n th dvlpn hbrd dpln f phl rn htr Wth h tdnt Wll Al Wtr (193-195 h pr- dd n 1935 th frt b n th r Physical As- pects of Organic Chemistry. Othr b rbrt n Wtn (19-1975 tt (19-197 nd Grld rnh (19-195 nd Mlvn Clvn (1911-997 flld n 1937 19 nd 191 rp- tvl On f r t nfnt ntrbtn t phl rn htr h rl dv f th f -nr thr n th ntrprttn f rn rtn ( h ppr ll rv nd - th nfn f h rl n th frtv prd f phl rn htr r brn Otbr 17 n rdfrd Enlnd fthr Mthdt ntr hd bn nrtn f r bfr lf d- ntd b p dvtn t h rln; nd h b- rphr Allp nd Wtr (3 tt tht h ntf M r rr l dd b h dvtn t h rl- n A l t h r ld rvtt t ph- th trhtr f ntrl prdt nd hl l rn htr fr h d trn- rtllrph Artrn n f th frt t r n In 193 h ntrd th Cntrl hnl Cll th trdtnl bndr btn phl nd rn f th Ct nd Gld Inttt n ndn t br htr On h rdtn n 19 r b pn h hl trnn hr h ndr th Artrn tnt nd rnd ntl 1913 r- n th prd h btnd h S dr (199 nd Bull. Hist. Chem. 20 (1997) 11 taught himself physical chemistry (4). He held a series the Advancement of Science meeting in Edinburgh, J.J. of teaching positions in this period which culminated in Thomson had over the years modified his views from a 1912 in a Lectureship in Chemistry at the Guy's Hospi- strictly electropolar approach to accommodate tal Medical School. His reputation as an innovative re- sharing and covalence. These ideas were to appear in searcher led to his election as a Fellow of the Royal papers in 1907 (5), 1914 (6), and in 1921 (7). Thomson Society (1914) and his promotion to the rank of Profes- could not envision bonding as a gradation of the extent sor. In 1920 the newly created physical chemistry chair of electron pair sharing. To him polar and nonpolar bonds at Cambridge was offered to Lowry, and he spent the were distinctly different. Lowry's first contribution to rest of his life at Cambridge. In summarizing his work the electronic theory occurred in 1922, when he read a his biographers have written (3): paper before the Faraday Society on November 20, en- titled "The Electronic Theory of Valency. Part I. Intramo- Lowry gained scientific eminence as a physical chem- lecular Ionization" (8). This paper appeared in the Feb- ist, and for the last twenty years of his life held one of the senior professorships of physical chemistry in ruary, 1923, issue of the Transactions of the Faraday ; but at the outset of his scientific career he Society. Most of the paper is devoted to examples from was an experimental organic chemist busily engaged inorganic chemistry, with a few examples from organic in elementary teaching. His early work in both these chemistry. The key premise is that "a condition of in- directions deeply influenced his outlook throughout tramolecular ionization exists in a large number of com- his whole life, for his approach to physical chemis- pounds, where nothing of the sort has been suspected try was always that of the experimenter rather than previously" (8). With respect to amine oxides Lowry that of the theorist, possibly because his mathemati- writes (8): cal knowledge was limited, though in this direction he was enthusiastic in stimulating the efforts of col- It therefore really looks as if the obvious method of laborators. representing this compound; as one in which the oxy- gen is linked to the nitrogen by a mixed double bond, Lowry became one of the most enthusiastic advocates including one covalency and one electrovalency, thus of the Lewis-Langmuir theory. His original contribu- may perhaps be novel. tions to the field were to occur in the period only from 1923-1925, but his impact was to be long lasting. The characterization of the electron by J. J. Thomson of Cambridge University (1856-1940) in 1897, as a fundamental sub-atomic particle in 1897 was fol- lowed by initial speculations on the role of the electron in chemical bonding. Thomson's first paper on the sub- ject appeared in 1904, but it seemed to have had little Lowry suggested this structure in response to that pos- impact on the British chemical community. Thomson's tulated by-Langmuir for amine oxides (8): conception of bonding was a modern revival of Langmuir states definitely that in this compound the Berzelius's dualism. His ideas were enthusiastically nitrogen is quadricovalent, and it is entirely unnec- adopted by a group of American organic chemists who essary to assume a quinquivalent nitrogen. It is diffi- attempted to explain chemical properties as well as re- cult to believe that Langmuir can have overlooked action mechanism based upon the Thomson model. This the fact that in this system the nitrogen atom is posi- American effort was doomed to failure and would in tively charged (and thereby converted into a kation), turn in the United States retard the adoption of the newer whilst the oxygen is negatively charged, and so con- ideas developed by the American chemists G. N. Lewis verted into a bound anion. (1875-1946 in 1916 and Irving Langmuir (1881-1957) On November 27, 1922, shortly after the Faraday Soci- in 1919. American organic chemists with a few excep- ety meeting paper, Lowry wrote to G.N. Lewis. The let- tions such as James B. Conant (1893-1978) and Howard ter was an acknowledgment by Lowry of reprints of re- Lucas (1885-1963), did not get involved in the applica- cent work by Lewis. Plans to confirm a visit by Lewis tion of Lewis-Langmuir theory. British chemists who to England in the summer of 1923 were also included. had not been bruised by the battles fought earlier in The post-script is the most important part of the letter America were far more receptive to new ideas. and is reproduced below (9): Lowry's interest in the Lewis-Langmuir theory be- gan sometime after 1921. Langmuir had spoken at length I should be interested to know your opinion in refer- on his octet theory at the 1921 British Association for ence to Langmuir's electronic formula for N. My 1 ll t Ch (1997

own view is that it is an anomaly for which I cannot On the other hand, the group of eight in find any sufficient justification; and I certainly pre- which the pairs are symmetrically placed about the fer the interpretation which you gave in your 1916 center gives identically the model of the tetrahedral paper. I have also been interested myself in the dis- carbon atom which has been of such single utility covery of electric charges on the atoms in the elec- throughout the whole of organic chemistry. tronic formulae of quite a lot of simple compounds, e.g. methylethylaniline oxide. h in thr r thr bnd th x nbr blvd ld xt nd h rprntd th l- l nr d nvr t hv trd th dff- lt nd prbl f n th bl t n r plx ttn n rn htr 1919 p- pr rplt th ttpt t th bl t n- All this appears very obvious, but I cannot find that it has been published before, and it certainly leads to td f dt frl t rprnt trtr r some interesting results both in inorganic and in or- was dpt nh t th pnt t tht b n th ganic chemistry. ltrn-pr nd tt npt t nt pbl t rt frl fr n xd tht frl p- n h n hnd rt th flln trtr tv nd ntv hr nvr dptd r tn lthh h nt n h 193 n rph n "ln nd th Strtr f At nd Ml- l" fll (13 Presumably such a substance as amine oxide is there- fore considerably polarized.

vll Sd (173-195 n 197 t d- prbbl lth t n b t ld rb th bndn n n xd rdnt - l l rvvl f th ltrplr thr h hd vlnt (r dtv bnd rt "th th -p- thrhl drdtd r rprnttn f n lr ln f r nd thr hh rttn xd f r d n ll txtb td Ovr th nxt f nth r xtndd h d A— or A— (10). Lowry never d th tr n th ltrn ntrprttn f ltpl bnd n r- "rdnt" r "dtv" n h rtn n pnd h r t b h t sig- nr hd prntd rthr dd trtr fr nificant ntrbtn In lttr dtd nr 3 193 th ntrn ll n h 1919 ppr "Arrnnt t r t frth h d n th ntr f th f Eltrn n At nd Mll" (11 Sn t bnd fr vn h rtnlztn fr ltpl th bl t h prntd th trtr bnd h rtrnd t th prbl f frl hr n hn bl n hh n ltrn pair is bddd n n xd (1 th tt tht rrnd th t ntrn t n rdr If so, you will see that the electric charges that I have t dt th 1 ltrn f th t ntrn postulated are arrived at by dividing equally between t h n n drpl bnd the two atoms the duplet which constitutes the bond been the oxygen and nitrogen in the amine oxides. The mere balancing of the electrons against the nuclear charges then gives evidence of an excess or a deficiency of electrons on the individual atoms. With rrd t ltpl bnd h tt th flln (1

As regards the formula for I am inclining more hd rlzd n 191 tht n th bl and more towards the view that unsaturation nearly t npt ld t pbl t rprnt always means the presence of electrovalencies, usu- trpl bnd r t h th npt f fr rttn ally in the form of a 'mixed' double or triple bond b tnt f trhtr tt (1 containing at least one valency of each type. Thus the unsaturation of ethylene and acetylene can be ascribed to the association of one electrovalency with Bull. Hist. Chem. 20 (1997) 13

one or two covalencies, respectively, as in CHI -CH 2 became saturated from the residual affinity on C and C3 leaving partial valencies on the terminal carbons to and CH=CH2 . On the other hand, the saturated produce enhanced reactivity

character of 02 and N2 would be ascribed to the pres- ence of double and triple covalencies. Lewis in his structure for ethylene which he presented

in 1916 has two formulas: H:C::C:H and H C:C:H. In Hugo Kaufmann (1870-?) in a 1908 paper in the a cryptic note Lewis writes, "I shall postpone a discus- Physikalische Zeitshrift (17) interpreted Thiele's theory sion of the important bearing of such formulae upon the in terms of the electron theory of valence. He argued problem of the conjugate bond" (15). Unfortunately this that valence was divisible and that the lines of force as- seemed to have been a permanent postponement! Cer- sociated with the electron were divided among three at- tainly Lowry's conception was different from Lewis' as oms. Thus although three atoms A1, AAandshared3 a to the nature of the double bond. pair of electrons to form a bond, the valence was dis- Who were some of the persons and the ideas that tributed over three atoms. influenced Lowry to produce his "novel" conception of unsaturation? Certainly J.J. Thomson was one. On Janu- ary 6,1923, Lowry wrote to Thomson the following con- cerning a lecture Thomson had recently given in which he discussed the electronic nature of unsaturation and conjugation. Thomson presented a model in which the reactivity of the double bond was the result of dividing the bond equally, in essence producing a septet at each Kauffmann's electronic structures bear strong similari- carbon atom. Thomson used the cubic model of Lewis ties to those of Thiele. His dashed and dotted lines were to show how this happened (16). equivalent to an electron bond in the former and a par- tial bond in the latter. To explain the reactivity of unsat- I was interested to hear your references to conjugated urated molecules which was not obvious from the struc- compounds in your lecture on Thursday morning. tural formula, Kaufmann proposed that in these systems There are two possibilities as regards the opening of there were more numerous lines of force more widely the hinge between two doubly bound carbon atoms. extended out in space, thus creating enhanced reactiv- I think your scheme involved the formation of two ity. Kauffmann's interpretation did not seem in retro- septets: but I have been following up the alternative hypothesis that one carbon atom takes both electrons spect to elicit much support or use in the chemical com- giving rise to an octet and a sextet. This makes the munity. It was only a small step for Lowry to translate alternate atoms positively and negatively charged so the formula of butadiene of Thiele to the one he pro- that the formula for butadiene becomes posed to J. J. Thomson. In a paper received on March 14, 1923, by the Chemical Society and appearing in the April, 1923 is- sue, Lowry expanded on his view of the double bond in organic chemistry. The paper opens as follows (18): J. J. Thomson in reply seemed to accept this idea of Lowry as a possible electronic interpretation of the The object of this paper is to suggest that, whilst a double bond. This is one of the earliest known examples single bond may be either a covalency or an electro- of what became known as the electromeric effect. valency, a double bond in organic chemistry usually reacts as if it contained one covalency and one elec- Another important influence was the work of trovalency. Acetaldehyde is therefore written as Johannes Thiele (1865-1918). Thiele, as distinct from most German organic chemists of his time, was very much interested in the theory of organic reactions. In Bonds of this character are described as mixed double 1899 he proposed his theory of partial valencies to ex- bonds.... Each (-) sign then indicates an excess of one plain the phenomenon of conjugation and the apparently planetary electron above the net nuclear charge, and anomalous chemistry that results. All atoms had inher- each (+) sign a deficit of one electron. ently some residual affinity for reaction, according to Thiele. Thus in butadiene the inner two carbon bonds According to Lowry an electrovalency enhanced the reactivity of any substance, regardless of the elements.

21771M 14 Bull. Hist. Chem. 20 (1997)

The enhanced reactivity of double bonds versus single Lowry to task in a short note received by the Journal of bonds is the result of the mixed bond in the former. the Chemical Society on June 21, 1923, entitled "Elec- Thiele's ideas of partial valencies are easily translatable tron Valency Theory and Stereochemistry" (19). Sugden on an electronic basis by using the mixed bond: points out that Lowry's conception of the double bond The superposition of an electrovalency on a cova- would lead to free rotation and the lack of geometrical lency therefore provides a convenient explanation of the isomerism. Lowry quickly replied on July 10, 1923 and subdivision of affinity, which Thiele indicated by dot- this followed Sugden's note ( ted lines in unsaturated groups such as In rdn ppr n h lrt f bl nd I ld ndrbl tr n th ft tht th frl thr t t rprntd th rtn f th vr pnd rthr thn th rtn-tt These may be written as C=C, C=O, and C=N, where f th ll h tphr d tht th oxygen and nitrogen are usually negative relatively to frl rprntd th d tndn p nd br- carbon, and oxygen relatively to nitrogen. n nd tht h ht vr dffrnt tt- Perhaps the most important insight Lowry had in td hn rld p nd t rt this paper deals with conjugated compounds. These were In cases such as the amine oxides there n d- the subject of much theoretical speculation in the 1920's tntn between the ground and activated tt r by the British chemists Arthur Lapworth (1872-1941), implied that the mixed double bond is only prtv in Robert Robinson (1886-1974), and Christopher Ingold the activated state and until a molecule is activated or- (1893-1970) (18): dinary considerations will apply. The use of the ± signs Crtnldhd nd btdn r frltd by Lowry and his qualification in this reply to Sugden created confusion. Lowry recalled in a letter dated May 9, 1935, to William Albert Noyes (1857-1941) of the It ll b n tht ndr th h th dtntn University of Illinois (21): btn nl nd dbl bnd n njtd - h prpl t th h fr pptn tht t dppr pltl hr thrfr n fr r t n t rt + r - n n lnr n nd t ptlt ndrn f th th blbrd f th Chl St fr fr f dbl bnd hn btdn brntd n th pn rdl b Inld nd thr ntrl dbl bnd lrd n ptn In the midst of writing these papers Lowry rnz- From our present perspective we could read into this n ht to become a landmark conference in the statement the concepts of mesomerism as well as application of electronic theory to organic chemistry. A electromerism. These would become part of the system two-day meeting on July 13-14, 1923 was held at Cam- of tautomeric effects involving polarization and polar- bridge under the auspices of The Faraday Society. The izability that Ingold was to develop beginning in 1926. symposium entitled "The Electronic Theory of Valency" Similarly Lowry's explanation of the structure of the consisted of three sessions. G. N. Lewis gave the intro- of carboxylic is very much as used today. For ductory address entitled "Valence and the Electron" (22). example in sodium formate "The distinction between Among those attending were J.J. Thomson, William the single and double bonds disappears, just as in the Bragg, William Albert Noyes, Arthur Lapworth, Robert case of conjugation" (18). Robinson, R. G. W. Norrish, Jocelyn Thorpe, Ian Heilbron, George Norman Burkhardt, and Bernard Flurscheim. Many of these were already the leaders or soon to be leaders in British organic chemistry. In pr- Other applications were made by Lowry by using tlr Lapworth and Robinson had been very active in the mixed bond which were to lead to controversy. the area under discussion. Lowry firmly believed that there were formal charges Lowry presented the introductory address to th in the systems he discussed and he compared his ± sign second part of the symposium which dealt with applica- as the same as that used in compounds such as sodium tions to organic chemistry. Lowry defended his concept chloride. Statements of this kind were bound to cause of the mixed bond as a convenient way to explain the Lowry problems. Samuel Sugden (1892-1950) of reactions but probably not the structure of a variety of Birkbeck College, , almost immediately called unsaturated compounds and conjugated systems (23): Bull. Hist. Chem. 20 (1997) 15

For good or evil, it possesses one feature which dis- some internal or external agent. This would lead to an tinguishes it from some other electronic theories, alternation of polarities represented by + and - signs. Thus, although it was definitely suggested by and is These signs were not to be taken in the same light as firmly based upon the electronic theory of valency, it Lowry's. For example, allyl chloride could be repre- is capable of being expressed by familiar symbols, sented in the following way (27): the meaning of which is readily grasped by all chem- ists. It therefore presents a specially easy target for criticism, of which it has received at least a full share. These criticisms appear to me to have done no dam- age to the target; and, whilst questions may be raised as to the conditions under which the structure that I Here the stable octet surrounding the chlorine atom have discussed is developed, I am confident that the produces an unstable system about the adjacent carbon mixed double bond represents a real alternative to atom, and therefore the formation of a stable system in the well-recognised double covalency. the CH group is facilitated by the aid of two of the elec- Lowry's original contributions to the symposium were trons held in common with the second unsaturated car- two papers: "Intramolecular Ionisation in Organic Com- bon atom. It is accordingly quite natural that the prod- pounds" (24) and "The Transmission of Chemical Af- uct of the addition of H Br is trimethylene chlorobromide finity By Single Bonds" (25). In the former he presented Cl—CH—CH-CHBr. evidence showing that a polar catalyst is required to In discussing chemistry of conjugated systems such cause ethylene to react with bromine which was in line as hexatriene, Kermack and Robinson chose the follow- with the idea of an activated double bond being a mixed ing representation by incorporating the curved arrow: bond. In the latter paper he addressed the question of the types of valency and methods for the transmission of these. All the papers presented at the symposium, including the discussion that ensued, were printed in The Transactions of The Faraday Society. Robinson's view of multiple bonds was far more In many of the papers and the discussions which general than that of Lowry. He viewed the enhanced followed exception was taken to Lowry's interpretation reactivity in terms of the mobility of the octet, not an of the double bond. Lowry proposed that the mixed bond implicit electrovalency. For this and other reasons has to be thought of in the context of the problem of Robinson proved to be far more successful. Colin structure and reactivity. In the ground state the electron Russell, in his classic study of valence, best summa- pair will be equally shared, but during the reactive phase rizes the contributions made by Robinson and Lowry; there may be an ionization of the bond to produce the (28): mixed bond. Lowry stated (26): Thus the covalent bond was no longer conceived as At the end of the discussion I am still convinced that a rigid entity with two electrons symmetrically shared the mixed double bond, in which one of the links has between the atoms. A molecule was subject to strains been completely ionised, really exists and plays an and stresses unimagined twenty years previously, and important part in many branches of organic chemis- the valency bonds were more dynamic than static, trY. responding to the demand of a reagent to assist a re- action. At this point it would be instructive to compare the ideas of Lowry with those of Robinson, who was also ini- Lowry's involvement with further developments in the tially influenced by Thiele's residual affinities concept electronic theory of valency after 1923 was to be pe- as well as by the alternating polarities of his colleague ripheral in nature. In a brief paper published in the Philo- Arthur Lapworth. In a 1922 paper written in collabora- sophical Magazine in 1924 entitled "The Origin of - tion with William O. Kermack (1898-1970) entitled "An ity," he stated his definition of acidity as follows (29): Explanation of the Property of Induced Polarity of At- An acid may be defined as a hydride from which a oms and an Interpretation of the Theory of Partial Va- proton can be detached, e.g. on dissolution in an - lencies on an Electronic Basis" (27), the attempt was izing solvent, on electrolysis, or by displacement by made to translate Thiele's and Lapworth's ideas by us- a metallic ion. ing Lewis-Langmuir theory. In discussing the reactions To explain the order of acidity in the series CH , NH3 , of conjugated systems Kermack and Robinson produced OH , and HF, Lowry adopted ideas from the Bohr model the concept of the mobility of the octet in response to 16 Bull. Hist. Chem. 20 (1997) of the atom. He invoked the idea that the electrons in a bond. Sugden's parachor was succeeded by more so- molecule are in what he called looped orbits which ex- phisticated physical measurements; indeed, the optical ecute a figure eight between the nuclei in a molecule. In activity of the sulfinates is based on an entirely differ- molecules like methane the loops are for removed from ent explanation. Nevertheless, Lowry certainly tried to the nucleus. There is little probability of repulsion be- use all the experimental evidence of his day to validate tween electrons in these orbits and thus the chances of his ideas. losing a hydrogen as a proton are minimal. However in To his credit, Lowry was one of the f university hydrogen fluoride for example (9 lecturers in Britain in the 1920's who dealt with the elec- tronic theories of valency in his courses. His student W. th h llr lp n hh th prtn f h- A. Waters reminisced (32): drn flrd hld t brn t nrr t th nl nd l brn t nr tht t n b At Cbrd n t (193 h v d t drvn td th lp b th trn rpln t f ltr n rnt thr f t nd l- hh t bjtd lr trtr flln hr nd nr hn h xpl h fr rn fr In order to explain the transmission of acidity through a nrn htr nd vn th rl ptr- carbon chain, such as in halogenated aliphatic carboxy- p vdn tht ld t th nt thr f lic acids, the suggestion was made by Lowry that atoms t nd llr rbtl like chlorine tend to change the size of the orbits of the electrons they share with other atoms. Thus in a dy- Although Lowry's contributions to the electronic theory namic way this will cause alterations of properties along of valency may be considered only as a footnote to the a chain whose effect will diminish with distance. Groups work of others, through his prestige he certainly was that enhance basicity will function in the opposite man- influential in setting the state for the remarkable devel- ner. These novel suggestions indicated the way that opments that occurred in Britain in the era between 1919- Lowry, essentially a product of the nineteenth century, 1939. so eagerly embraced new ideas. Although few chemists were to adopt Lowry's con- cepts of the mixed or semi-polar bond, his faith in these REFERENCES AND NOTES ideas persisted through 1925. For example, in a discus- 1 M r Historical Introduction to Chemistry, sion at the British Association meeting in Southhampton Mlln & C ndn 1915 19 193 on September 1, 1925, devoted to "The Alternating Ef- Cprhnv htr f vln b fnd n fect in Carbon Chains," Lowry offered what he believed CA ll The History of Valency, tr Unvr- was new evidence for his views (30). Sugden had de- t r tr 1971 nd A Strn Electrons veloped a concept in 1924 (31) called the parachor, a & Valence, x A & M Unvrt r Cll St- measurement of molecular volume by use of surface ten- tn 19 r htrl td f ntrtn sion, density measurements of liquid and vapor phases, A A r r Unsaturation in Organic Chemis- try, htn Mffln tn MA19 and molecular weight [P = M 1/4]. Parachor measure- 3 C Allp nd W A Wtr "h Mrtn r" ments, according to Lowry, were inconsistent with a n A ndl nd W Mll Ed British Chemists, nonpolar double bond in such systems as nitro, for ex- Chl St ndn 197 pp -1 ample. There must be a nonpolar as well as a polar bond, rvt Cntn fr W A Wtr brr and a group such as the sulfoxide contains only a polar 3 193 bond. 5. J. hn Corpuscular Theory of Matter, Chrl In 1925 Phillips reported resolution of the com- Srbnr Sn Yr 197 pound ethyl toluenesulfinate into a pair of enantiomers. hn "h r tn At nd Ch- Lowry saw in this report conclusive evidence for the l Affnt" Phil. Mag., 1914, 7 757-71 7. J. J. hn "On th Strtr f th Mll nd semipolar bond. As Lowry stated, the S=0 bond in these Chl Cbntn" Phil. Mag.,, 1921, 41, 51-5 compounds must be semipolar since only when repre- M r "Std f Eltrvln rt I Intr- sented by the symbol llr Inztn" Trans. Faraday Soc.,1923, 18, 285- 95 9 ttr n th G ppr h nrft brr could the existence of optical activity be possible. Unvrt f Clfrn rl Sugden's measurement of the parachor for this com- 1 Sd The Electronic Theory of Valency, pound also offered additional evidence for the semipolar Clrndn r Oxfrd 197 p Bull. t Ch (1997 17

11. I. Langmuir, Arrangement of Electrons in Atoms and 24. T. M. Lowry, "Intramolecular Ionization in Organic Molecules," J. Am, Chem. Soc., , 41, 868-934. Compounds," Trans. Faraday Soc., 2, 19, 488-496. 12. G. N. Lewis, "The Atom and the Molecule," J. Am. 25. T. M. Lowry, "The Transmission of Chemical Affinity Chem. Soc., 6, 38, 762-785. by Single Bonds," Phil. Mag., 24, 47, 10I3-1020. 13. G. N. Lewis, Valence and the Structure of Atoms and 26. T. M. Lowry, "The Électronic Theory of Valency: Dis- Molecules, The Chemical Catalog Company, New York, cussion on Part II," Trans. Faraday Soc., 2, 19, 537. I923, p. 134. 27. W. O. Kermak and R. Robinson, "An Explanation of the 14. Letter in the G. N. Lewis papers, The Bancroft Library, Property of Induced Polarity of Atoms and an Interpre- University of California, Berkeley. tation of the Theory of Partial Valences on an Electronic 15. Ref. 12. Basis," J. Chem. Soc., 22, 121, 427-440. 16. Letter in the J. J. Thomson papers, Cambridge Univer- 28. C. A. Russell, The History of Valency, Leicester Uni- sity Library. versity Press, Leicester, 1971, p. 290. 17. H. Kaufmann, "Electronen and Valenzlehre," Phys. Z., 29. T. M. Lowry, "The Electronic Theory of Valency," Phil. 08, 9, 311-314, 334-42, 539-541. Mag., 24, 47, 1021-1024. 18. T. M. Lowry, "Studies of Électrovalency. Part I. The 30. T. M. Lowry, "Polarity and Activation," J. Chem. Soc., Polarity of Double Bonds," J. Chem. Soc., 2, 123, 1925, 44, 970-972. 822-831. 31. S. Sugden, "A Relation between Surface, Tension, Den- 19. S. Sugden, "Electron Valency Theories and Stereochem- sity, and Chemical Composition," J. Chem. Soc., 24, istry," J. Chem. Soc., 2, 123, 1861-1867. 125, 1177-1189. 20. T. M. Lowry, "Note on the Theory of Free Rotation," J. 32. Ref. 4. Chem. Soc., 2, 123, 1866-1877. 21. Letter in the W. A. Noyes papers, University of Illinois Library, Urbana, IL. ABOUT THE AUTHOR 22. G. N. Lewis, "Valence and the Electrons," Trans. Fara- day Soc., 2, 19, 452-458. r Sltzn rfr f trl Sn t rv- 23. T. M. Lowry, "Introductory Remarks to Part II: Appli- dn Cll rvdn I 91 nd prt- cations in Organic Chemistry, The Electronic Theory of lrl ntrtd n th dvlpnt f phl rn Valency," Trans. Faraday Soc., 2, 19, 485-487. htr n th th ntr n rtn nd Ar

Letter to the Editor

In 15/1 f th Bulletin, th ppr b rr zl "Gr rzn (157- 195 Invntr nd Inlt" p 59- rrd b t nfrtnt dt- rl ddtn t n t n t htr th El plthn hdd b Grn nrl Evn thh th hrrbl t rrtd n th prf Mr Mrph r th vnfl Gd lft t fr ll t — rr zl