2 Physical Methods Part (i) Mass Spectroscopy By R. T. APLlN The Dyson Perrins 1aboratory Oxford University DURING 1970 the number of papers on this topic has further increased," notably in areas of applied mass spectrometry particularly in the natural product and biochemical fields. There has also been an increase in the number of papers concerned with detailed studies of the kinetics and mechanisms of fragmentation processes. Two new techniques ion cyclotron resonance' (ICR) and ion kinetic energy spectroscopy' (IKES) have been employed in the interpretation of various fragmentation processes. This Report will attempt to cover the more generally interesting aspects of both the detailed and applied papers. General Methods of Interpretation.-The quasi-equilibrium theory (QET) whose validity for small molecules is well established has been shown to give rate constants which agree well with those observed from a study of substituent effects on normal and metastable ion abundances as well as ionisation and appearance potentials of 1,2-diphenylethane~.~ A probability distribution of internal energies has been derived4 for those aromatic molecular ions which undergo decomposi- tion to afford a single product whose relative abundance and appearance potential are each functions of Hammett sigma constants.This approach provides a rationalisation for the unexpected relationship between sigma constants and the loss of substituents from biphenyl molecular ions.5 Both +I and -Z substituents are capable of increasing the migratory aptitude of aryl groups in the spectra of diary1 sulphones.This rearrangement also affords a Hammett correlation with total ion abundances at 20 eV.6 Zon Energies and Structure. The production and subsequent decomposition of benzoyl ions (m/e 105) derived from N-(substituted pheny1)benzamide (1) are related to the energy distribution in the molecular ion.' The substituent effects ' G. C. Goode R. M. O'Malley A. J. Ferrer-Correia and K. Jennings Chem.in Britain 1971 7 12. ' J. H. Beynon R. M. Caprioli W. E. Baitinger and J. W. Amy Internut. J. Muss Spectrometry Ion Phys. 1969 3 313. F. W. McLafferty T. Wachs C. Lifshitz G. Innorta and P. Irving J. Amer. Chem. SOC.,1970 92 6867. ' R. P. Buck and M. M. Bursey Org. Mass Spectrometry 1970 3 387.M. M. Bursey and P. T. Kissinger Org. Mass Spectrometry 1970 3 395. T. Nagai T. Maeno. and N. Tokura Bull. Chem. SOC. Japan 1970,43,462. ' R. H. Shapiro J. Turk and J. W. Serum. Org. Muss Spectrometry 1970 3 171. * Many of the papers are mentioned in the first volume of 'Mass Spectroscopy' ed. D. H. Williams (Specialist Periodical Report) The Chemical Society London 197 1. R. T. Aplin NH' co+ ~NH!~'" -+ + \ -+ C,H,+ 6 Y Y (1) mle 105 observed in the spectra of NN'-diarylethylenediamines (2) are best interpreted as affording the fragments (a)and (b)with open-chain rather than the closed structures + Y0 (2) a b shown.* Electron-withdrawing substituents increase the abundance of the mol- ecular ion in the spectra of substituted styrene ozonides; the intensities of the fragments XC6H4CHO+'follow a Hammett relationship.' Ground-state bond- orders in molecular ions derived from MO analysis can be used as a reliable guide to the low-energy (ground-state) fragmentation of heterocycles.The subsequent decomposition of the M -42 ions derived from methoxy- and dimethoxy-phenyl acetates' ' suggests that these ions have the structure of the corresponding phenols. '3CLabelling has established that the [C6H60]+' ion in the spectrum of C,H,OC,H has the same structure as the phenol molecular ion.'2 Steric effects suggest that the [YC,H,N] +.ions from phenyl-substituted acetanilides have the structure of the corresponding aniline. A study of appear-ance potentials and metastable ion abundances has shown that the m/e 165 ions 0 C6H 5 C6HS c6H5vc6H5 0 0 (5) (6) * H.Giezendanner M. Hesse and H. Schmid Org. Mass Spectrometry 1970 4 405. J. Carles Y. Rousseau and S. Fliszar Canad. J. Chem. 1970 48 2345. lo R. C. Dougherty R. L. Foltz and L. B. Kier Tetrahedron 1970 26 1989. l1 C. B. Thomas J. Chem. SOC.(B) 1970 430. P. D. Woodgate and C. Djerassi Org. Mass. Spectrometry 1970 3 1093. l3 A. A. Gamble J. R. Gilbert and J. G. Tillett Org. Mass Spectrometry 1970 3 1223. Physical Methods-Part (i)Mass Spectroscopy (C,,H,+) from fluorene and phenalene do not have the same structure^;'^ similarly the ions C ,H and C 2H,N+ from 1-(benzy1ideneamino)benzo-+ triazole do not have the fluorenyl or carbazole structures.’ p-Fluoro-labelling has established that the (C,Ar,)+’ ions derived from tetracyclone (3) and tetra- phenylquinone (4)are produced after complete scrambling in the molecular ion that partial scrambling occurs in pentaphenylcyclopentadienol(5) and that there is virtually no scrambling in tetraphenylthiophen SS-dioxide (6).l6 A detailed study of the fragmentation of tetralin and related heterocycles [(7) and (8)] has shown that only isothiochroman (7 ;X = S) gives a true retro-Diels- Alder (RDA) fragmentation.In the series (7; X = 0 NH and S) the ion of (7; X = CH, 0,NH S) (8; X = CH, 0,NH S) m/e 104 is produced almost exclusively by process (i). However for tetralin only 45‘xis produced by this route the remainder by (ii).In the series of compounds mx’+’ -+ a’+’ + CH =X (1) + CH = X (ii) (8) the RDA fragmentation is not important.” The spectra of the related systems (9) and (10)are dominated by processes equivalent to (i).18 The full details of the ICR study of the double McLafferty rearrangement reported last year” have appeared.20 The subsequent decomposition of the enol J. H. Bowie and T. K. Bradshaw Austral. J. Chem. 1970 23 1431. U. Rapp H. A. Staals and C. Wunsche Org. Mass Spectrometry 1970 3 45. l6 M. K. Hoffman T. A. Elwood P. F. Rogerson J. M. Tesaret M. M. Bursay and D. Rosenthal Org. Mass Spectrometry 1970 3 891. A. G. Loudon A. Maccoll and S. K. Wong J. Chem. SOC.(B) 1970 1727. A. G. Harrison M. T. Thomas and I. W. J. Still Org. Mass. Spectrometry 1970 3 899.l9 G. Eaden J. Dickmann and C. Djerassi J. Amer. Chem. SOC.,1969 91 3986. G. Eaden J. Dickmann and C. Djerassi J. Amer. Chem. SOC.,1970 92 6205. R. T. Aplin ions (ll) (12) and (13) produced in the McLafferty rearrangement of simple ketones is via initial ketonisation.21 (1 1) (12) (13) The technique of ion kinetic energy spectroscopy (IKES) has been applied to study the processes involved and the energetics of the spectra of a series of aromatic hydrocarbons,22 and also used to study the triply charged molecular ion of biphenyl.23 The release of 4.5 eV in its decomposition C12H1O3++ CI1H7'++ CH3+ suggests the charge-separated structure (14) for this ion. Conventional spectra have also been used to study similar processes in other condensed aromatic corn pound^.^^ Fragmentation and Rearrangement Processes.-The studies of carbon and hydrogen randomisation reported last year2 have been continued this year by the use of deuterium and '3C-labelled systems.The spectrum of the 13C- labelled benzene (15) shows complete carbon scrambling in the molecular ion prior to the loss of C2H2.26 The spectrum of the doubly labelled benzene (16) D (15) * = I3C (16) (17) showed that ca. 30% of the ions C3H3+and C4H4+arise by paths in which the carbon atoms are scrambled without breaking C-H bonds. In the remaining 70 % the hydrogens are scrambled over and beyond whatever carbon scrambling ' D. J. McAdoo F. W. McLafferty and J. S. Smith J. Amer. Chem. Soc. 1970,92,6343.22 J. H. Beynon R. M. Caprioli W. E. Baitinger and J. W. Amy Org. Mass Spectrometry 1970 3 455. '' J. H. Beynon R. M. Caprioli W. E. Baitinger and J. W. Amy Org. Mass Spectrometry 1970 3 661. 24 P. Nounou Internat. J. Mass Spectrometry Ion Phys. 1970 4 219. 25 R. T. Aplin Ann. Reports (B) 1969 66 5. 26 I. Hormon A. N. Yeo and D. H. Williams J. Amer. Chem. Soc. 1970 92 2131. Physical Methods-Part (i) Muss Spectroscopy 11 occurs.27 The loss of methyl radicals from m/e 168(M") and m/e 167(M" -H') in the spectra of diphenylmethanes is preceded by a complete hydrogen and carbon scrambling.28 Complete loss of positional identity of both a- and ring- hydrogen atoms has also been established for the simple molecular ion fragmenta- tions (M -H' M -H, M -CH,' and M -CH,) of triptycene and tri- ~henylmethane.~~ The spectrum of the benzo[b]thiophen (17) showed that car- bon scrambling also occurs before or during the formation of many of the fragments.,' Randomisation of all nine hydrogens uia ring expansion occurs in methylquinolines prior to fragmentati~n.~' In the dimethylquinolines ring expansion precedes loss of H' and CH,'.Expansion in the benzenoid ring is favoured over the pyridine ring.32 The molecular ions of fluoro- and chloro- toluenes like those of substituted chlor~benzenes,~ undergo ring-expansion rearrangement prior to fragmentation ;in contrast the bromo- and iodo-toluenes do not rearrange prior to fragmentati~n.~~ The loss of HCN and C2H2 from the phenylnitrenium ion generated from [2,4,6-'H3]phenyl azide is preceded by H-D rand~misation.~~ Hydrogen scrambling in the molecular ion is also observed between the two phenyl rings in halogenated diphenyla~etylenes.~' In contrast evidence of hydrogen randomisation has been found to be absent from the spectra of hydr~cinnamaldehyde,~ the triphenyl/tetraphenyl derivatives of the Group IV and V elements,,' and 1,2,2a,3-tetrahydrocyclobuta[b]quin-oxaline (18).39 Similarly p-fluoro-labelled penta-arylpyridine and related CH,(CH,),OCH = CH H (19) (18) compounds show little or no randomisation prior to fragmentation of their molecular ions.40 In the 70 eV spectra of normal4' and bran~hed-chain~~ ali-phatic ketones hydrogen randomisation has been shown to occur prior to a-cleavage.Extensive carbon rearrangement precedes the loss of CH,' and C,H,' '' W. 0.Perry J. H. Beynon W. E. Baitinger J. W. Amy R. M. Caprioli R. N. Renaud L. C. Leitch and S. Meyerson J. Amer. Chem. Soc. 1970 92 7236. " T. K. Bradshaw J. H. Bowie and P. Y. White Chem. Comm. 1970 537. 29 S. Meyerson Org. Mass. Spectrometry 1970 3 119. 3n R. G. Cooks and S. L. Bernasek J. Amer. Chem. SOC. 1970 92 2129. " P. M. Draper and D. B. Maclean Canud. J. Chem. 1970 48,747. 32 P. M. Draper and D. B. Maclean Canud. J. Chem. 1970 48 738. 33 P. Brown Org. Muss. Spectrometry 1970 3 639. 34 A. N. H. Yeo and D. H. Williams Chem. Comm. 1970 886. 35 D. G. I. Kingston and J. D. Henion Org. Muss. Spectrometry 1970 3 413. 36 S. Safe Org. Mass Spectrometry 1970 3 239.37 A. Venema N. M. M. Nibbering and Th. J. de Boer Org. Muss Spectrometry 1970 3 583. 38 J. H. Bowie and B. Nussey Org. Muss Spectrometry 1970 3 933. 39 C. W. Koch and J. H. Markgraf J. Heterocyclic Chem. 1970 7 235. 40 M. M. Bursey and T. A. Elwood J. Org. Chem. 1970 35 793. 41 A. N. H. Yeo Chem. Comm. 1970 987. 42 G. Eadon and C. Djerassi J. Amer. Chem. SOC.,1970,92 3084. R. T.Aplin from various isomeric hexane~.~~ A further example of the rare triple hydrogen transfer observed in the higher esters of trimellitic anhydride,25 is present in the spectra of alkyl vinyl ethers (19; n >4);deuteriation has established the sequence shown in Scheme 1 for the loss of C2H60.44Skeletal rearrangements have been Scheme1 observed in the following systems acetylenic sulphoxides and s~lphones,~’ acetylenic ethers of cyclic p0lyols,4’-~~ thiobenzoates and thio- acetates,’ thionyl[1-’3C]aniline,52 nitrophenyl hydrazones of aldehydes and tetrasila-adamantane~,~~ ketones,53 chroman~,~~ 3-phenylnitropropane and 3-phenylpropyl nitrite,56 2-methyl-2-hydroxy(or 2-amino)-propane~,~’ phenyl-ox as tannin^,^ and diaryl thiosulphinates and diaryl thio~ulphonates.~~ In spite of further evidence for the migration of trimethylsilyl groups in the spectra of TMS ethers of aldonic and deoxyaldonic acids,60 these derivatives have proved invaluable in the study of ketoses and aldoses,61 sugar phosphates,62 and inositols 43 C.Corolleur S. Corolleur and F. G. Gault Bull. SOC. chim. France 1970 158.44 M. Katoh and C. Djerassi J. Amer. Chem. SOC.,1970 92 731. 45 T. H. Kinstle W. R. Oliver and L. A. Ochtymowycz Org. Muss Spectrometry 1970 3 241. 46 R. T. Aplin and R. Mestres Org. Mass Spectrometry 1970 3 1067. 47 R. T. Gray J. Diekman G. L. Larson W. K. Musker and C. Djerassi Org. Mass Spectrometry 1970 3 973. 48 J. Winkler and H.-Fr. Griitzmacher Org. Mass. Spectrometry 1970 3 11 17. 49 A. Casper G. Teller and R. E. Wolff Org. Mass spectrometry 1970 3 1351. 50 P. D. Woodgate R. T. Gray and C. Djerassi Org. Mass Spectrometry 1970 4 257. 5‘ A. Ohno T. Koizumi Y.Ohnishi and G. Tsuchihashi Org. Mass Spectrometry 1970 3 261. 52 A. S. Siegel Org. Mass Spectrometry 1970 3 875. s3 J. Seibl Org. Mass Spectrometry 1970 3 417. 54 J. R.Trudell S. D. Sample Woodgate and C. Djerassi Org. Muss Spectrometry 1970, 3 753. 55 R. S. Gohlke and R. J. Robinson Org. Mass Spectrometry 1970 3 967. 56 N. M. M. Nibbering and Th. J. de Boer Org. Mass Spectrometry 1970 3 487. 57 A. S. Siegel Org. Mass Spectrometry 1970 3 1417. 58 I. Lengyel and M. J. Aaronson Chem. Comm. 1970 129. 59 S. Kozuka H. Takahashi and S. Oae Bull. Chem. SOC.Japan 1970 43 129. ‘O G. Peterson Tetrahedron 1970 26 3413. 61 S. Karady and S. H. Pines Tetrahedron 1970 26 4527. 62 M. Zinbo and W. R. Sherman J. Amer. Chem. SOC.,1970,92 2105. Physical Methods-Part (i) Mass Spectroscopy by the combined g.c.-m.s. te~hnique,~~ and show promise for the sequencing of nucleoside~.~~ Although the spectra of the bicyclic alcohols (20) (21) and (22) (20) (21) (22) are complex involving extensive rearrangements a characteristic ion m/e 57 (X = H) m/e 58 (X = D) is produced without rearrangement; the ion can be used to analyse the amount of migration occurring during the solvolysis of various deuteriated derivatives of these alcohols.65 The predicted potentialb6 of mass spectrometry for stereochemical studies has been realised in two papers.The endo esters (23) eliminate methanol through a seven-membered transition state ;the stereoisomeric exo diesters (24) do not appreciably eliminate methanol but eliminate MeO' instead. The trans diesters (25) eliminate methanol via a five-membered transition state.b7 Deuteriation has shown that the loss of water ,C02Me (23) (24) (25) (n = 14) from the cis-and trans-4-isopropylcyclohexanol proceeds as shown in Scheme 2.68 Similar differences are apparent in the spectra of the isomeric 3,4-diethyl- muconic acid dimethyl esters.69 trans cis Scheme 2 '' W.R. Sherman N. C. Eilers and S. L. Goodwin Org. Muss Spectrometry 1970 3 829. 64 J. J. Dolhun and J. L. Wiebers Org. Muss Spectrometry 1970 3 669. 65 H. Kwart and T. A. Blazer J. Org. Chem. 1970,35 2726. " E. L. Eliel H. L. Allinger S. J. Angyal and G. A. Morrison 'Conformational Analysis' Interscience New York 1965 p. 1878. " J. Deutsch and A. Mandelbaum J. Amer. Chem. SOC.,1970 92 4288. " M. M. Green and R. B. Ray J. Amer. Chem. SOC.,1970 92 6368. 69 E. Gil-Av J. H. Leftin A. Mandelbaum and S.Weinstein Org. Mass Spectrometry 1970 4 475. 14 R. T Aplin Application of Various Techniques.-Field ion spectroscopy has been employed to examine substituent effects in aryl-O-gluco~ides~~ and to determine the sequence of small peptides. Chemical ionisation (CI) spectroscopy as antici-~ated,~’ is proving a valuable structural tool and has been used to examine amino-acid~,~~ alcohols,73 alkaloids,74 and sensitive photodimer~.~’A very promising application is in combined g.c.-m.s. analysis where the carrier gas is the ionising gas eliminating the need for a separator between the gas chromato-graph and the mass spe~trometer.~~ The CI spectra of a series of substituted benzophenones have been investigated with several reactant gases methane ethane propane and butane.77 Amino-acid derivative^^^.^^ and peptides have been further examined by mass spectrometry and spectacular success has been achieved in determining the structure of the antibiotic cycloheptamycin via sequencing of the permethylated derivative (26).80 The insecticidal cyclodepsi-peptides Destruxin A and B have also been successfully sequenced.8 Mass sequence ions M.W.1092 142 271 462 547 674 817 1061 H C-MeVal; MeThr MeTyr I MeAIa MeaIlel /3-hydroxyMeNva I.5-methoxyMeTrp IOMe 0 I I I I Me Me Me Me spectrometry has also established that synthetic L-pyroglutamyl-L-histidyl-L-prolinamide is identical to the natural thyrotropin-releasing hormone (TRH).~ Structural elucidation of antibiotics including two new heptaene macrolides from StreptomycesB3and the macrolide primycin whose polyether (27) afforded a molecular ion,84has been greatly facilitated by analysis of the mass spectra of degradation products.Mass spectrometry was also successful in the elucidation ’O G. 0. Phillips W. G. Filby and W. L. Mead Chem. Comm. 1970 1269. 71 P. Brown and G. R. Pettit Org. Muss Spectrometry 1970 3 67. 72 G. W. A Milne T. Axenrod and H. M. Fales J. Amer. Chem. SOC.,1970 92 5170. i3 F. H. Field J. Amer. Chem. SOC.,1970 92 2672. ” H. M. Fales H. A. Lloyd and G. W. A. Milne J. Amer. Chem. SOC.,1970,92 1590. ” H. Ziffer H. M. Fales G. W. A. Milne and F. H. Field J. Amer. Chem. SOC.,1970 92 1597. 76 G. P. Arsenault J. J. Dolhun and K. Biemann Chem. Comm.1970 1542. ” J. Michnowicz and B. Munson Org. Mass Spectrometry 1970 4 481. 78 M. S. Manhas R. S. Hsiech and A. K. Bose J. Chem. Sac. (C) 1970 116. ’’ I. Lengyel R. A. Salomone and K. Biemann Org. Mass Spectrometry 1970 3 789. 8o W. 0.Godtfredson S. Vangedal and D. W. Thomas Tetrahedron 1970 26 4931. A. Suzuki N. Takahashi and S. Tamura Org. Mass Spectrometry 1970 4 175. 82 D. Gillessen A. M. Felix W. Lergier and R. 0.Studer Helv. Chim. Acta 1970,53,63. x3 F. Bohlmann E. V. Dehmlow H.-J. Neuhahn R. Brandt and H. Bethke Tetrahedron 1970 26 2199. 84 J. Aberhart T. Fehr R. C. Jain P. de Mayo 0.Motl L. Baczynskyg D. E. F. Gracey D. B. Maclean and I. Szitagyi J. Amer. Chem. SOC.,1970 92 5816. Physical Methods-Part (i) Mass Spectroscopy of the structures of other complex antibiotics including Roridin H8' and E,86 Phomine,87 Aranciamycin,88 and the Mitomycin~,~~~~~ Bun OR' H OR' R4 (27; R' = RZ = R3= Me R4 = COMe) M.W.1319 The A"6'-aromatic Erythrina alkaloids [(e.g.(28)] undergo the characteristic fragmentation shown," which has been applied to identify new members of this group." Mass spectrometry was largely responsible for determining the structures 1" -+ Me0 OH of the highly complex bis-indole alkaloids amataine goziline and ~werreine.'~ The characteristic cleavage of the side-chain of the unusual marine sterol gorgo- sterol (29)94 was used to determine the absence of the 23-methyl group in the related sterol (30).95 The characteristic fragmentation of the insect moulting hormones has been utilised in determining the structures of related '' P.Traxler and Ch. Tamm Helv. Chim. Acta 1970 53 1846. 86 P. Traxler W. Ziircher and Ch. Tamm Helv. Chim. Acta 1970 53 2071. " N. Rothweiler and Ch. Tamm Helv. Chim. Acta 1970 53 696. 88 W. Keller-Schierlein J. Sauerbier V. Vogler and H. Zahner Helv. Chim. Acra 1970 53 779. " G. E. Van Lear Tetrahedron 1970 26 2587. 90 G. 0. Monton G. E. Van Lear and W. Falmor Tetrahedron 1970 26 2588. 9' R. B. Boar and D. A. Widdowson J. Chem. SOC.(B) 1970 1591. 92 D. H. R. Barton P. N. Jenkins R. Letcher D. A. Widdowson E. Hough and D. Rogers Chem. Comm. 1970 391. 93 V. Agwada M. B. Patel M. Hesse and H. Schmid Helv. Chim. Acta 1970,53 1567. 94 R. L. Hale L. Leclerq B. Tursch C.Djerassi R. A. Gross jun. A. J. Weinheimer K. Gupta and P. L. Scheuer J. Amer. Chem. SOC.,1970,92 2179. 95 F. J. Schmitz and T. Pattabhiraman J. Amer. Chem. Soc. 1970 92 6074. R. T. Aplin (29; R = Me) (30; R = H) compounds.96-100 The potential of mass spectrometry in the sequencing of oligo-saccharides has been demonstrated by the use of 1-phenylflavazole peracetates to sequence di- to penta-saccharides. lo The spectra of peracetylated cardenolides similarly give information about both the aglycone and sugar moietie~.'~~*'~~ Methoxymercuration-demercuration followed by combined g.c.-m.s. analysis has been developed as a general method for the location of olefinic links in long- chain esters as shown in Scheme 3.'04 Further papers on the use of computers R'-CH=CH-R2 Me0 HgOAc 4 MeOH AcOHg OMe II I1 R'-CH-CH-R2 R'-CH-CH-R~ 1NaBH 1NaBH OMe I 1 1 + + + MeO+ OMe OMe OMe I1 II II II RICH + CHCH,R2 R'CH2CH + CH-R2 Scheme 3 96 H.Hikino. K. Nomoto and T. Takemoto Terralredron. 1970. 26 887. 97 A. Faux M. N. Galbraith D. H. S. Horn E. J. Middleton and J. A. Thomson Chem. Comm. 1970 243. 9a M. Koreeda and K. Nakanishi Chem. Comm. 1970 351. 99 S. Imai E. Murata S. Fujioka T. Matsuoka M. Koreeda and K. Nakanishi Chem. Comm. 1970 352. loo Y. K. Chong M. N. Galbraith and D. H. S. Horn Chem. Comm. 1970 1217. lo' G. S. Johnson W. S. Ruliffson and R. G. Cooks Chem. Comm. 1970 587. lo' B. Blessington and I. M. Morton Org. Mass Spectrometry 1970 3 95.B. Blessington Y. Nakagawa and D. Sotoh Org. Mass Spectrometry 1970 4 215. Io4 D. Abley F. J. McQuillin D. E. Minnikin K. Kusamran K. Maskens and N. Polgar Chem. Comm. 1970 348. Physical Methods-Part (i) Mass Spectroscopy for the interpretation of mass spectra have appeared from the Djerassi-Lederberg group; these are concerned with the spectra of saturated arnine~'~~~'~~ and iso- meric ketones of the composition C,H,00.'07 Two small on-line computer systems have also been described in detail.' 08*'O9 lo' A. Buchs A. B. Delfino A. M. Dufield C. Djerassi B. G. Buchanan E. A. Feigen-baum and J. Lederberg Helu. Chim. Acfa 1970 53 1395. A. Buchs A. M. Duffield G. Schroll C. Djerassi A. B. Delfino B. G. Buchanan G. L. Sutherland E. A. Feigenbaum and J.Lederberg J. Amer. Chem. Soc. 1970 92,6831. lo' V. M. Shiekh A. Buchs A. B. Delfino G. Schroll A. M. Duffield C. Djerassi B. G. Buchanan G. L. Sutherland E. A. Feigenbaum and J. Lederberg Org. Mass Spectro- metry 1970 4 493. Io8 R. J. Himowski R. Venkataraghaven F. W. McLafferty and F. B. Delany Org. Mass Spectrometry 1970 4 17. '09 H. S.Hertz D. A. Evans and K. Biemann Org. Mass Spectrometry 1970 4 453.