Thomas Martin Lowry and the Mixed Multiple Bond
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1 ll t Ch (1997 THOMAS MARTIN LOWRY 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 Chemistry 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 electron 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 England; 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 electrons 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 N2 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.