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Magnetic circular dichroism studies—XLVI2
MAGNETIC
CIRCULAR
DICHROISM
STUDIES-XLVI’
STRCCTURE AND THE MAGKETIC CIRCULAR DICHROISM TRANS-~-I>EC‘AI,ONES AND BI(‘YCI.O(~.~.2jOC’I’AN-2-ONES’
OF
Kf;tiT MORRII.I.. ROHFR’I E. I.INI)I~.R.Emff .W. HRU’KYA~~N.~ (;ilslER RARTff. b4aRI) ~l;KYf:SflERG ;Ind CAR1 L)IERASSI* Ikpartmcnr
of (‘hemicrr).
Sbnford
L’nrter\lI).
Stanford.
C.4 94305. L’ S .4
~btract-The m+xneIrc C‘I) \prcIra of a numtw of MC wh\~~tu~ed rronr~!~decalonc~ and b~cyclo[X !)ocIanZ. unc\ were mcawred The rcwlb &.wed ;I large. .rnd wmcrlme\ dommanf. conInbuIion IO rhc MUD inlerbrl) u hrch could he iorrclaled wIh OK presewx of a.subWtuenl\ lying oulsidc of lhc plane of lhc carbon)1 chromophorc
The magnetic sucular dichroism (MCD) spectra of saruratcd ketones have been the subject of sonsidcrablc interest. ’ Exher work correlated the structures of a large numher of saturated ketones with the B-values obtained from Ihc MCD spectra for their n -+ rr* transitions. In arriving a~ Ihcsc correlations one utilired the fact that the MC’D spectrum for the electric dipole forbidden n - rr* transition of a saturated ketone is rero cncepr in Ihc presence of vibrational or structural perturbations that are nontotally symmetric as regards the local (‘>. symmetry of Ihc carbonyl chromophore. In order IO clarify Ihc correlations and further test the proccdurcs involved, it was desirahlc IO obtain a series of closely related compounds in which vihrdtional variations and conformational ambiguities would be minimized. In rrans-!-decalone (1). the rr~n.I ring juncture prevents either of the IWO h-membered rings from Ripping from one chair conformation IO the other; calculations and electron diffraction studies” indicate that the major species is in the chair-chair conformationS Hic~clol!.~.Z)ocIan-!-one (12) is a conformationally unambiguous compound since the IWOcarhjn bridge across the &membered rmg locks it mto a boa1 conformation Therefore. we have synthcsired a series of methyl suhstitutcd Irons-Z-decalones and hicyclo[ ?X]ocIan-!-ones. measured their YC’D spectra. and subjected the data IO the correlative analysis presented earlier.’ -_. .-..-
._-.
-..
-
The MCI) and UV data for the ketones studied arc summarized in ‘T;lble I. The H-values for ~hc methyl substituted Irons-2-decalones and bicycloI!.~.!llK-IiIn-?ones may be compared IO the R-values for the parent compounds of the two respective series in the manner previously described.’ and which is illustrated in Fig I The perturbing atoms. i.e. those which are not part of the (‘0 chromophore. are projected onto quadrant diagrams. The 1oIa1 structural pcrturabtion is thereby decomposed into its various components. each of which transforms :I\ a different nontotally symmetric representation of the C:. point group. Each such component. if nonzcro. has associated with it a signed partial H-value. and the pertinent signs here are: H(A,j>O.
BIR,)>O.
HIB:l
The totally symmetric component R(A,) since only an oreroll nonloIally symmetric
.
0
is neglected perturbation
-,
-.. * ‘..
-. . .
-
“l’.ikcn m p;trI from Ihc Ph.11 ‘Thew of KenI Morrdl. IO Ix whmrrfcd IO Sr.mfurd Cnrvcr~rl) I.AACW Yo\rdocloraI Fcllou 19’1-2 IForce field c.dcularwn\ for rhc I- and J.rr1~1 MC wh\IrIurcd rron~~!ilec.tlonc~ mdrcarcd rn encrp) dlffcrcncc bcrwccn the chau rnd bwl ;onf~>rm.llan\. for rhc nnp conlammg lhe (‘0. of rxr 6 ks;d/molc U AS :t rcferec h.t\ pomrcd WI. recent ub inrfio srlsulaltont” indlcarc .I corre~pondmp energy difference of 2 92 and 069 kc;dlmole far rhc 1. and !~~ual mcrhyl compound%. rc~pccl~~el) Ihux rhc ih.ur-zh,ur wnformcr I\ ;~\wmcd IO tx lhc more popul.r~cdone m each caw ( TYpn,for IS). and - ‘59 for 101
Fig. I Symmetry opcraImn\ and projecrmn drapram\ for saIurared kcIonc~. .A pcrturkr Iwlid circle) constitute\ .m atorn which. for a piben incducrble repreunIarmn. doe\ not la11 on J nodal plane and I\ nor cancelled hy a conrribuflon of cqu;tl .md opp)silc mapnilude from anolher atom. (The 5rRn of Ihc rw cflccl of all pcrlurbmg aIom\ for a &en tneduclhle rcprcsen. Irlron IS dcIermrncd from the incqualrrier g\cn in the 1~x1 \incc Ihc phavx given rn ~hc projcclron diagrams arc arhrtrar! I
K
WI
-
8 9 10
II 12 13 14 15 16 II I8
‘Tahk
I MCI) and
-
(‘ompound .-.---.-
abuxpfion
data’
MOURNI
cf ol
for ~ronr~!decalone~
Ahwrpfmn” A ,.lf I
fNn 4 3.1
x 10’
frun~~?~kcalonc I(cq~~Mcfhyl~rmnr2Jccalone’ ~cqLYeth)l-frunr. 2.decalone lceq).3(eq~l)lmeth~l~ fmns -2decalolK Ilax)~Mcthyl~fmn~~ !Jecalone ~ax~~Mefhyl-fmnr~ !-dccalonc I.l-Dimcrhyl.rmns. 2.decalone I .I.3tcq)~Tnmcrhylfruns.2dccalonc XXlf~Tnmcfh~l. fruns~!&calonc’ ~feq~.l0-l)lmcfh~l~ frun> .!dccalone’ 5.5.%arFTnmethylrrunx-!.dccalonc’ H,cyclo[ 2 !.!)cK.l;m. !.onc I-Mcrh~l.brcyclo. (2.2 2)octan-Zone !~Mcfh\l-bicbclo. [Z 2.!kK-ran-!-one Ul)lmcrh)l.h~c~cloI! 2 !kxtan-!-one 4-Methyl-blcyclo. (2.2 !]o&tn~!-one ‘(endol~hleth)I.blcyclo. [? 2 !)oclan-!-one
MCV
L...clel,
!loctan-!.oncs B0l-B
* IO’)
8’1’
x IO-
Prcd (oh\)’ --
23 25
-I
2.x
‘(_)
3.1 34 3.2 3.0
m
6)
313&j ?l?(- 4) 300(1X) \2w2)
?l2 OC - 4t.5 X0
1
-(=I -(
1
-(-I
- 12.0
24
3wll) \2$!( 3, 30791 ?m 5) ZULU- II)
‘In
2n3( - hj
22.3
‘(
2.6
29tn
6)
30.2
‘f-1
36
3cr-
18)
72 6
3s
2n3f-
IO
73.4
(=)
34
2X)(-.
lb)
fl< 5
+c- )
41
2’
30014)
35
!flOl-2) !Uh- I!)
4.2 3’
o(cndo).Mcth!l.blc!clo. 12 2.2hxlan.2.one
and bicyclol!.!
306(6) !60( - 24) x97(- ?I)
37 n
- 9.9
- (- 1 -(
1
- C-1
)
?(-I
46x
?( .)
70.4
+(-I
IM.0
- (+I
‘Spccfrogrz~dc c):lohcnanc “Wa\cknp!h m nm: molar etfmcllon coefficcenr m 1000cm mol ’ . Dipole \trenpth in (dcbycl’. ‘Yagnc~~c molar ell~pl~s~ty m dcg cm’dmol ’ (; ‘; s = shoulder. ‘H.\aluc in unit\ of (debye)’ bohr magnclonlcm ’ ‘Predicted lobwr~cdl chanpc [JB(n -* n’l] m H(n + a*) relafrve IO the parent compound for the \crtc\ ‘See ref. 13 ‘G. OhIoIT. F 4;.11, R Dccorzanl. W Thommen and E. Sundf. ffdt. Ckm Acfu 56. 1414 119?3) ‘E Pier\ and M 13 (icraphf). Can 1. Chrm 51. 2166 (19731
can induct YCD mlensily values are uddillve.’
Further.
these partial
B-
* H(R:) (\lructural pcrlurhation) Thus one is able to cstlmale the sign of the ddTcrcncc m H(n + rr*)-values. A&n - rr*). bclwccn a compound and a reference parent compound hy noting the differences in the comributions of their partial B-values from the projection diagrams. The projection diagrams for several of the ketones studied arc illustrated in Figs. 2 and 3: predicted and oh\crvcd signs for M(n + n’) arc given there also. The result\ for the entire series of compounds are listed m Table I. In the GM of the Irons-2-decalones. the bulk of Ihe predicted and observed sign\ of A&n -+ n*l arc in agrccmcnl. However. thcrc is one especially notable exception. The compound 3~;~n)-methyl-~runs-2-decalone
(6). exhibits a change in B-value of appreciable magnitude cis-ri-ris (I I. and of Ggn opposite IO that predicted. Similarly, four of the hicyclo[22.?]oclan-‘-ones show changes in the R-value\ which clearly disagree with the predicted resuhs. In addition. rhc differences between the R-values for 3.3dimethyl-blcycloIZ.Z.?Joctan-?-one (15) and those of Ihe other bicyclo(2.2.2)octan-2~~ncs arc far larger than would be predicted if they arose simply from the same ~ypc of static structural perturbations assumed IO he the cause of the variations in R-values among the other hicyclol2.2.2jocran-!-ones. The discrepancies just noted have forced us IO reexamine the basis of our analysis, and we recognize now the potential importance of an effect as&atcd with the fordly s.wfmefrir structural pcrturbalions previously ncplected. AS noted above. a totally symmetric cr~ctunl perturbation cannot per se provide any MCD inrcnsity. However. a royally symmetric structural perturbation can exert a marked syncrgistrc. or amiencrgislic. effect on the MCI> intensity assoclatcd wuh nonrotally symmetric
Magnetic
cucular
dlchrolsm
r1ud1cs-.XI.V1
:.
CL.
. .
.I
‘J . . ._
I’
IL
a,
.’ I
.
.
.?A I..
D
‘: 1
po
-y
I
r.J .i
slruclural perturbations are alw;~y\ t~periilivc, ;ind lhcw may contribute 10 rhc MCD intensit) in ;I dIrection opposite IO that of rhc a-alkyl effect noted. In such instances. manifestation of the out-of-pl;mc a-alkyl effect in the raw data may tend IO bc obscured. For cnamplc. the positive component in rhc MCD curs cs is less prominent in I5 (Fig. C) than in 6 or 7. :Ind is oscrridden m 14 by
Fig. 3 Prqccrtnn diagrams for UK bicyclol! ! !JcKti-!+ncs. The reference compound for M(n 4 rr’) I\ 12. Now lhal an unusual degree of cancellation CXISI~ in ~hc B: partial B.value diagrams. leadmp In cerlam cases lo ambtgurlg In lk predtclwns.
vihratlonal pcrrurb;&ons. The mechanism for the syncrgistic cffcc~ opcra~cs by allcrinp the efficacy of the vibronic coupling through which ii forbidden tmncition borrows YCD intensity. The details of these coopcr;ttive vibralionill-srrucrurlll effecls :trc clah%iled in separate publications.’ We nolc here only th;it \uch effects arc dependent upon the relative stereochemistry of the perturbing atoms ris-d-cis the CO group, and that the stereochemistry of outufplane a-substituents IS p;utlcularl) conducive IO them. This is already manifest in some of the raw MCD data. For example, among the decalones, the MCD curves for 6 ;md 7 (Fig. 4) exhibit very prominent positive MCD componenls that are absent in I. 3 ;Ind 4 where there are no out-of-plane a-alkyl substituents. Of course. the ~rar~~
..
.. Frg ( Rcprewxauvc clo[! ? ?kxxan.!.oncs mdlcales
_
_;
.
MCI) qtcc~r~ of mclh)l-wb\trtuted b~c). and OK parcnl compound ‘I’hc wrwal bar ftw crpertmentrl no~sc k\el
\tn)ng &A:) and R(R,). and diminished H(H:) static conrrihurions (see projection diagrams). Thus although rhc raw da!a arc at time\ instructive, a more mformatiw structural interpretation is provided by analyris of the B-vafues, Such analyses’ must take into acfounl both static structura1 and v~b~~i~~l-~~~~~ur~l tfkfs.
the dddiftonal &Me \uh\fliucnf fool; place during the uork.up of the rcacrion mixrurc. (Found: C. Iu).?I: It. II Ox Calc for
(‘,Jf,:O~
C’. Ml.35; H.
IL4l’kl.
!..Hcrkrf.k~efcfrI!.?.?lorran 4onr (141 was prepared aa” cording to the m&od described ht Tich$ PI ei:” Sff’ mic 13X; NSiR 6 1 10 (d. J - h fft,.
7%~ m,tgnetic circular dfchromctcr and experrmenfal procedure have been dcscrthed eirewhcrc.’ ’ 1%~ sourCc\ of the C~)rn~lund~ which were not synrhe\ired in these lahoralorics lrrt Iced m ‘l‘ahic I. l’hc NMRq~~traweremeasured nn a Vat&n T-ho NUK ~pccfrnmercr using CC& as rht rotvenf. Recau~ fht W’D fs weak for tafurafed kctonex. if ~a\ n~etsar)to monitor all of the compounds-~!nthcrwed \)r dunrtcd-for fhc prc%cncc of impuritw some of uhlch dommafcd fbe MCD spectra 31 \ery small conccnfralion\ (c.g. a\ hltlc ;s\ 0.1% of an a&un\pturdfed kelane). Thi\ ua\ done h) ctaminmg rhe G1.C truces and L’V spectra of Ihe srmptcc a\ ucll t-.Merkyf. (13) and &mefkj&yfof? 2 ?]orfon-?-mt t 10. a\ the MCff ipecfr;t them~elncs When ncce\\itry. fh+ compound\ ‘lhr tffhmm reduction of totuene in liqurd smmonu” pvc wcrc purified as much s porsibk urmg 6l.C and hrgh prev.ure I-mah)l-t.QcyckthesadKnt. The unconjugated JRnc was liquid ~hr~~rn3fc~~r~phy 1HPI.C! Esen wtfh rhc~e precauttonx equtldxiafed h) rt@uting o+trnight with bBuf)H and t.RuOK” to pike a cotorlc%s liquid which on di~~fll~f~n had an odor however. MIictcnr impurities rematncd to pre+ent fk nepat~vc hand\ in the high frequency regmnx of man) of the MCD tpecfra rc~emhhng that of i.~~ycI~)~~adicnc. Thir liquid uas placed in from reIurnin~ fo the haceltnc {F&q. 4 and 5). In these cavx the a flask and wcces~~ve small amount\ of mrktc anh}drfdc added. curve\ wcrc extrapolated 10 fhe bavline so that thr) couid be An NMR xpccfrum of the crude ddduif dspla)td 4 \harp singlet interprlfed and rhe 21.values dtwrmincd. al 154ppm. The matcnai from fk t%eb.Alder reacfton *a% karg . Sf&$10 nntf kcql - mffhyf . trm5 . ? =dmden~ hydrogenafed in Tlif: using 18% Pdj<’ until H, uprakc ccartd. t3t ‘li~nr4~xx%&n w&r prepared frc3m~ujnt~nc~nd t.?-huiarftcnc The NSfR +cctrum of rhc ~~dr~~ge~linn prorfurr con&cd a occordrnp to the method of Minn tf a(.’ with *light alteration\ in Tharp smgkt ai I.12 ppm and a tcr) *mall douhkt centered at the ;ondifr)n\ of fhe IkebAlder re&on’” and in the srpdralivn 0 9U ppm Tbc h)droprnalh)n product was placed u~fh Ii2 cquik KHCO, m w;rler and lcff on a \ream bath for \c\cral hr Thr of ~ttc w and fmns &omer\:” h’%iR 6 5.6 (unrc+.olvcd mr~ow binllrc mulfiplef). The octalin wz\ reacted In chloroform uifh rcAoc. affcr removal of rhc uafcr. *;I\ hi+dccarhor)lafcd u\mp mcfu~chloroprrtKnroic rctd m the u>ual manner lo form Ihe led fcfrJ;)ccf;(Ic in pjridinc:“’ EMR 6 I.I fst. 6 I cm). cpoxidc. The reacf~~n WB followed u\tng NMR hp fhc H~dro~r~~fon yielded an alcohol u-hich U’JI otidilcd h) u&m di\appE%ranCt of the &tylic protons of the oclahn and the dtchrom& m a mixture of HI%f,. %iFcr axi ether. After seueraf appearance of a new peak at 3.Oppm. The cfoxwit u-n\ treated hours. she xotn was t?ltmCted wtfh crhcr 10 gibe a ketone mix&WC. under nitrogen with 54cI.i in reffuxfng hctsnc to form the aicohof The component\ of the mtlturt wcrc vzparatcd by G1.C (~xid~~~)n of the alcohol using chromic acid in acclfc actd” pave fdic~h~-lcne~~l~col~~difr~c croxs.linked on ~‘hrt~mo~orb WI tnro the desired 3tar~methyl.fmnr-?~ecalone (61: F;MR 6 I 18(d. two fracftonx. ‘I’hc fir\t fracrton proved to be 13, M’ m/e 1%; I = h.5 HI); report& 1.2 (d, J h 5Htr The equatort4 Lomcr 3 NMR 6 0.83 (\. 3H1, 1.61 is, RHf ? 1’ (5, ?H). rePOrted” 0 X2 t\. wax produsccd by cp~mcri7~tion of the axial i\omcr C in methrnolrc fraciion wa\ I&? !ftl. 1.52 1%. XII). 2.17 t\, _‘Hg. The frond KOH JS dtrcrtbed by Siion er at.:’ !iUR 6 0 Cy cd. f -160 Hz): S?‘n& 13%. ?ISjR 6 0.93 15. ?Xi. t 9(1& 2Wt. 2.13 fm. ift). reponed m t .O(d, J - 6.5 Hrf. ltur)_iltfk~~--I~ns.?.drrolonf (St. Compound 2” ua\ cpimcritcd IO a 50: 50 mtxlure of rhc axiai and cquatornl tu)mcr\ ArLnclrf~d~~~lcnlr-Wc fhank th. (i Ohloff f FtrmcntchS:1. $1~. the pyrrohdmc cnaminc mtcrmedia!c lnof bolafcd) h) (;cncva. Su-lizcrland) and Profr f; Stork I(‘olumhl.~ Cm\cr\il! L refluxing wlfh pyrrolidinc in xylenc over 3 A moleoular Gcvc~ for E Piers IUnivcrqif) of HriIl\h (‘olumbla\. and I HudcC one day. The IWO isomcrr wcrc xparafcd using HD1.C: SMR 4 tfJni\er\ily of Sourhampton) for providmg II\ utth ketone I.@3 fd. J = 6.5 Hz): reported’ 1.03 fd, J - 6.5 Hz). sample% and L. Sctifcr It’ni\er\ifg of 4rkan\a\I for hl\ lfcy~,3~e~ft-~mrr~~l-tranr~?-tf~rafonr f4i. Utfhyl isopropcn!l cakufrtionr on she conf~~rrn~~jon~ of tbe rronr-?-decalones. We ketone and fk pynoiidint cnamine of cyclohcx;;nune were arc atso grateful fo !&s. Ruth Record< for tcchnrcaf a%%sIancc reacted in the manner drscnbed by Stork zr ” to produce dnd fo fhc National Science Foundation ff;rant So. CHE~~~fh~i.~‘~.~~~~lo~ (M’ mfr 1641 whtch wa\ reducfi\cly ?M5!541 and the h;rfional In~ilfufe~ of Health Grants No. (i% 20276 and HI, 168331 for financial aid. fhnc of UI (E.M.R.) wicks aIkylafcd using Uel and K in liquid arnrn~~~i~~~to give 4 as fhc major product: MS m/r 180; NS4R 6 0.92 (two overlapping Me to thank rhc .American Axroctatron of Cni\er\rt! Women for an doohkr\. I - hHz). fFound: f‘, 80 14, 11. Il.&. falc. for X.AI:W infernational postdoctoral fellowship. C,:H& f, “294; H, II.t8%tt. I,f.Dimrrkyf17) end i,I,Werjrrrim~khj-tran~-~~decu~on~ tit. I.Mtthyt-5”-!+cv,Jont wa\ synfhcsited md reductircl) ;rfk* ‘Paper XI.VI tn our scricr M;rgncric (‘ircular Dichrcri\m Studits. viared usmn K and Mel in 1xGd ammonia and THF ;LI dcxribed Iiw Parf XLV xc Ci. Barth, R. E. Ijndcr. !i Wacspe-Scrcevlc. h) Stork ‘et cl.“” The AAfanf only liquid obtained on E. Runnenberg. I’. D)erass~. Y S. Aronclwlf7 md %t(.(ioulcr. hulb~~d~~lb disfillafion oonfamcd IWO cumpnncnl~ which wcrc man, 1. (‘kern. .‘hc Pcrkm II. In prcx\ qdrahk usin HP1.C. One component proved IO k 7: M’ m!e ‘A. 1. McCaBcr). G Iri. Henning P %. Schatz. A H. RitchK. H. 180; NMR d 1(10(5);reported” 0.99 (si). ‘fhe rccond componrn! P. Peczzmcw~ki, 0. R. R&g, ,A. W. Sorxlle. Jr and f’, J. had ;t mast \pectrai motccukr ton of m/c 1% fndtcatinp the Strpkns, (In. fbmmm. 5% fWb&t prclcscnceof an rddifionaf Me group. A Iarge h’hfWsin&t f6 0 991 ‘6. Byrh, E. ~u~ncn~rg and i‘ IIjcra\d. Ibid. 1% (?%%I dnd an ovcriapping doubkr fd 0.9?! mdicated Ibe pre%cncc nf a ‘G. Barth, E. Hunncnkrg. (‘. DjcrarG, II. Eldrr rnd R. ~m.dirnclh~~ and an eqwforia1 Me group, 0f the two pov Ghilities. l.I.!~rqt_f~mcrhyl-rmn~-2-dccatone and 3.3.lfeqb trlmerhyl-rrPnr-2-declrtnc. rhe former is the only one whfch ‘1.. .%m& A. Moscouitr. G Barth, E. Hunnenkrg and E’. could result from the reductive mefhylstion of I-meth)LA’ *I Qerassi. 1. .4m. f_‘kcm SW 94. b#A I I93 ocfan-Z-one. EG%eatly. a base cafiilyrrd methylation produsing
af
K
WORNI
-W. Schubert. 1.. .Scbfer and (i. H. Pauli. 1. .4b/ Sfrwf 21. 53 I 1974). ‘L. Schafer. private communcatlon. . M. Askari. !i. S (hrlund and I. Schifer. 1. Am (‘hrm .GK whmtrlcd for puhhcarmn ‘L. Seamans and A. Moscowitz. 1. Chow Phyr 56. lO9Y (IV7!l. “L. &mans. A. MoscowiIr. R. E Imdcr. K Merrill. J S Dixon. G Hanh. E Runrwnbcrg and C D]erassl. J .4m Chum .Soc. accepted for puhhcalbn: ‘K E Imdcr. K Mornll. J S Dwn. G Barth. F. Hunnenlxrg. (’ I))erasst. I. Seaman\ .md .A Mmcou117. Ibtd accepted for puhlicaflon. ‘I.. Mlon. A. Casadcvall and E. (‘asadcsall. Bull Sot-. (‘him. pr 3s. 29so (IWR); 36. 3199 (IW9) ‘“I.. F Flew. J Am Chrm. .5x- 70. 316.5 (1%). ‘u’ S Johnson. V J Hducr. J 1. Margrave. M A Fnsch. 1. tf Drcpcr and w’ S. Huhhard. Ibid 83. 606 Cl%11 “G. Swrk. A Hnzzolara. H. landc\man. J Srmusrkovrcr rnd R Tcnell. Ibrd. U. 207 (lW31. “6. Stork. P. Rosen. S. Goldman. R. V Ctwmht and J T~JI. /hid 87. 275 (I%!) “I .A. Marshall .md K H Anderscn. J 0~. (‘hem 31. M’ (l9w
CI 01. “K. “H
911
54140~ and J Ct. Rcrger. J Am Chrm. .%c. 84. 19% t I%!). 1.. (iocrmg. K. u’ Grciner .snd M. F Sloan. Jhtj 83. 1391
I1961 b. “A. (h.~hosa~s. M Tichj and J Stchcr. Co/l. (‘xc-h Chrm Commun. 3S. X3g ( 1970). “K R Stephens. J H. Slothers and C T ‘Tan. .Wors Sptcrmmet~ and SMR .‘$wc~mrcopv tn I’rr~trrdc (‘hrmirrr?_. (EdlIed hy R. Haquc and F J Biros). p I79 Plenum Press. Sets York (IV11 “M Tlchj. A Orahovals and J Slcher. (‘o/l (‘xrh (‘hem (bmmun 35. 459 I IY?O) “A. I.. Wild\ and K. A. Nelson. J .4m (‘hn SCM-. 75. 5% (IYC31 ‘-1 Alfaro. H’ Ashlon. K 1. Kahone and N .A 1. Rogers. T’ttmhrdmn Iy. (59 (19741 “(’ .4 Grub. $1 Ohb E Rcnk and A. WCI\S. Htlc (‘hem .41-u 41. IIYI IIYw) “u’ Krdux. (‘ (‘hasw and R (‘hassIn. Tifrohtdmn 25. W18l (I%YI
CIRCULAR
DICHROISM
STUDIES-XLVI’
STRCCTURE AND THE MAGKETIC CIRCULAR DICHROISM TRANS-~-I>EC‘AI,ONES AND BI(‘YCI.O(~.~.2jOC’I’AN-2-ONES’
OF
Kf;tiT MORRII.I.. ROHFR’I E. I.INI)I~.R.Emff .W. HRU’KYA~~N.~ (;ilslER RARTff. b4aRI) ~l;KYf:SflERG ;Ind CAR1 L)IERASSI* Ikpartmcnr
of (‘hemicrr).
Sbnford
L’nrter\lI).
Stanford.
C.4 94305. L’ S .4
~btract-The m+xneIrc C‘I) \prcIra of a numtw of MC wh\~~tu~ed rronr~!~decalonc~ and b~cyclo[X !)ocIanZ. unc\ were mcawred The rcwlb &.wed ;I large. .rnd wmcrlme\ dommanf. conInbuIion IO rhc MUD inlerbrl) u hrch could he iorrclaled wIh OK presewx of a.subWtuenl\ lying oulsidc of lhc plane of lhc carbon)1 chromophorc
The magnetic sucular dichroism (MCD) spectra of saruratcd ketones have been the subject of sonsidcrablc interest. ’ Exher work correlated the structures of a large numher of saturated ketones with the B-values obtained from Ihc MCD spectra for their n -+ rr* transitions. In arriving a~ Ihcsc correlations one utilired the fact that the MC’D spectrum for the electric dipole forbidden n - rr* transition of a saturated ketone is rero cncepr in Ihc presence of vibrational or structural perturbations that are nontotally symmetric as regards the local (‘>. symmetry of Ihc carbonyl chromophore. In order IO clarify Ihc correlations and further test the proccdurcs involved, it was desirahlc IO obtain a series of closely related compounds in which vihrdtional variations and conformational ambiguities would be minimized. In rrans-!-decalone (1). the rr~n.I ring juncture prevents either of the IWO h-membered rings from Ripping from one chair conformation IO the other; calculations and electron diffraction studies” indicate that the major species is in the chair-chair conformationS Hic~clol!.~.Z)ocIan-!-one (12) is a conformationally unambiguous compound since the IWOcarhjn bridge across the &membered rmg locks it mto a boa1 conformation Therefore. we have synthcsired a series of methyl suhstitutcd Irons-Z-decalones and hicyclo[ ?X]ocIan-!-ones. measured their YC’D spectra. and subjected the data IO the correlative analysis presented earlier.’ -_. .-..-
._-.
-..
-
The MCI) and UV data for the ketones studied arc summarized in ‘T;lble I. The H-values for ~hc methyl substituted Irons-2-decalones and bicycloI!.~.!llK-IiIn-?ones may be compared IO the R-values for the parent compounds of the two respective series in the manner previously described.’ and which is illustrated in Fig I The perturbing atoms. i.e. those which are not part of the (‘0 chromophore. are projected onto quadrant diagrams. The 1oIa1 structural pcrturabtion is thereby decomposed into its various components. each of which transforms :I\ a different nontotally symmetric representation of the C:. point group. Each such component. if nonzcro. has associated with it a signed partial H-value. and the pertinent signs here are: H(A,j>O.
BIR,)>O.
HIB:l
The totally symmetric component R(A,) since only an oreroll nonloIally symmetric
.
0
is neglected perturbation
-,
-.. * ‘..
-. . .
-
“l’.ikcn m p;trI from Ihc Ph.11 ‘Thew of KenI Morrdl. IO Ix whmrrfcd IO Sr.mfurd Cnrvcr~rl) I.AACW Yo\rdocloraI Fcllou 19’1-2 IForce field c.dcularwn\ for rhc I- and J.rr1~1 MC wh\IrIurcd rron~~!ilec.tlonc~ mdrcarcd rn encrp) dlffcrcncc bcrwccn the chau rnd bwl ;onf~>rm.llan\. for rhc nnp conlammg lhe (‘0. of rxr 6 ks;d/molc U AS :t rcferec h.t\ pomrcd WI. recent ub inrfio srlsulaltont” indlcarc .I corre~pondmp energy difference of 2 92 and 069 kc;dlmole far rhc 1. and !~~ual mcrhyl compound%. rc~pccl~~el) Ihux rhc ih.ur-zh,ur wnformcr I\ ;~\wmcd IO tx lhc more popul.r~cdone m each caw ( TYpn,for IS). and - ‘59 for 101
Fig. I Symmetry opcraImn\ and projecrmn drapram\ for saIurared kcIonc~. .A pcrturkr Iwlid circle) constitute\ .m atorn which. for a piben incducrble repreunIarmn. doe\ not la11 on J nodal plane and I\ nor cancelled hy a conrribuflon of cqu;tl .md opp)silc mapnilude from anolher atom. (The 5rRn of Ihc rw cflccl of all pcrlurbmg aIom\ for a &en tneduclhle rcprcsen. Irlron IS dcIermrncd from the incqualrrier g\cn in the 1~x1 \incc Ihc phavx given rn ~hc projcclron diagrams arc arhrtrar! I
K
WI
-
8 9 10
II 12 13 14 15 16 II I8
‘Tahk
I MCI) and
-
(‘ompound .-.---.-
abuxpfion
data’
MOURNI
cf ol
for ~ronr~!decalone~
Ahwrpfmn” A ,.lf I
fNn 4 3.1
x 10’
frun~~?~kcalonc I(cq~~Mcfhyl~rmnr2Jccalone’ ~cqLYeth)l-frunr. 2.decalone lceq).3(eq~l)lmeth~l~ fmns -2decalolK Ilax)~Mcthyl~fmn~~ !Jecalone ~ax~~Mefhyl-fmnr~ !-dccalonc I.l-Dimcrhyl.rmns. 2.decalone I .I.3tcq)~Tnmcrhylfruns.2dccalonc XXlf~Tnmcfh~l. fruns~!&calonc’ ~feq~.l0-l)lmcfh~l~ frun> .!dccalone’ 5.5.%arFTnmethylrrunx-!.dccalonc’ H,cyclo[ 2 !.!)cK.l;m. !.onc I-Mcrh~l.brcyclo. (2.2 2)octan-Zone !~Mcfh\l-bicbclo. [Z 2.!kK-ran-!-one Ul)lmcrh)l.h~c~cloI! 2 !kxtan-!-one 4-Methyl-blcyclo. (2.2 !]o&tn~!-one ‘(endol~hleth)I.blcyclo. [? 2 !)oclan-!-one
MCV
L...clel,
!loctan-!.oncs B0l-B
* IO’)
8’1’
x IO-
Prcd (oh\)’ --
23 25
-I
2.x
‘(_)
3.1 34 3.2 3.0
m
6)
313&j ?l?(- 4) 300(1X) \2w2)
?l2 OC - 4t.5 X0
1
-(=I -(
1
-(-I
- 12.0
24
3wll) \2$!( 3, 30791 ?m 5) ZULU- II)
‘In
2n3( - hj
22.3
‘(
2.6
29tn
6)
30.2
‘f-1
36
3cr-
18)
72 6
3s
2n3f-
IO
73.4
(=)
34
2X)(-.
lb)
fl< 5
+c- )
41
2’
30014)
35
!flOl-2) !Uh- I!)
4.2 3’
o(cndo).Mcth!l.blc!clo. 12 2.2hxlan.2.one
and bicyclol!.!
306(6) !60( - 24) x97(- ?I)
37 n
- 9.9
- (- 1 -(
1
- C-1
)
?(-I
46x
?( .)
70.4
+(-I
IM.0
- (+I
‘Spccfrogrz~dc c):lohcnanc “Wa\cknp!h m nm: molar etfmcllon coefficcenr m 1000cm mol ’ . Dipole \trenpth in (dcbycl’. ‘Yagnc~~c molar ell~pl~s~ty m dcg cm’dmol ’ (; ‘; s = shoulder. ‘H.\aluc in unit\ of (debye)’ bohr magnclonlcm ’ ‘Predicted lobwr~cdl chanpc [JB(n -* n’l] m H(n + a*) relafrve IO the parent compound for the \crtc\ ‘See ref. 13 ‘G. OhIoIT. F 4;.11, R Dccorzanl. W Thommen and E. Sundf. ffdt. Ckm Acfu 56. 1414 119?3) ‘E Pier\ and M 13 (icraphf). Can 1. Chrm 51. 2166 (19731
can induct YCD mlensily values are uddillve.’
Further.
these partial
B-
* H(R:) (\lructural pcrlurhation) Thus one is able to cstlmale the sign of the ddTcrcncc m H(n + rr*)-values. A&n - rr*). bclwccn a compound and a reference parent compound hy noting the differences in the comributions of their partial B-values from the projection diagrams. The projection diagrams for several of the ketones studied arc illustrated in Figs. 2 and 3: predicted and oh\crvcd signs for M(n + n’) arc given there also. The result\ for the entire series of compounds are listed m Table I. In the GM of the Irons-2-decalones. the bulk of Ihe predicted and observed sign\ of A&n -+ n*l arc in agrccmcnl. However. thcrc is one especially notable exception. The compound 3~;~n)-methyl-~runs-2-decalone
(6). exhibits a change in B-value of appreciable magnitude cis-ri-ris (I I. and of Ggn opposite IO that predicted. Similarly, four of the hicyclo[22.?]oclan-‘-ones show changes in the R-value\ which clearly disagree with the predicted resuhs. In addition. rhc differences between the R-values for 3.3dimethyl-blcycloIZ.Z.?Joctan-?-one (15) and those of Ihe other bicyclo(2.2.2)octan-2~~ncs arc far larger than would be predicted if they arose simply from the same ~ypc of static structural perturbations assumed IO he the cause of the variations in R-values among the other hicyclol2.2.2jocran-!-ones. The discrepancies just noted have forced us IO reexamine the basis of our analysis, and we recognize now the potential importance of an effect as&atcd with the fordly s.wfmefrir structural pcrturbalions previously ncplected. AS noted above. a totally symmetric cr~ctunl perturbation cannot per se provide any MCD inrcnsity. However. a royally symmetric structural perturbation can exert a marked syncrgistrc. or amiencrgislic. effect on the MCI> intensity assoclatcd wuh nonrotally symmetric
Magnetic
cucular
dlchrolsm
r1ud1cs-.XI.V1
:.
CL.
. .
.I
‘J . . ._
I’
IL
a,
.’ I
.
.
.?A I..
D
‘: 1
po
-y
I
r.J .i
slruclural perturbations are alw;~y\ t~periilivc, ;ind lhcw may contribute 10 rhc MCD intensit) in ;I dIrection opposite IO that of rhc a-alkyl effect noted. In such instances. manifestation of the out-of-pl;mc a-alkyl effect in the raw data may tend IO bc obscured. For cnamplc. the positive component in rhc MCD curs cs is less prominent in I5 (Fig. C) than in 6 or 7. :Ind is oscrridden m 14 by
Fig. 3 Prqccrtnn diagrams for UK bicyclol! ! !JcKti-!+ncs. The reference compound for M(n 4 rr’) I\ 12. Now lhal an unusual degree of cancellation CXISI~ in ~hc B: partial B.value diagrams. leadmp In cerlam cases lo ambtgurlg In lk predtclwns.
vihratlonal pcrrurb;&ons. The mechanism for the syncrgistic cffcc~ opcra~cs by allcrinp the efficacy of the vibronic coupling through which ii forbidden tmncition borrows YCD intensity. The details of these coopcr;ttive vibralionill-srrucrurlll effecls :trc clah%iled in separate publications.’ We nolc here only th;it \uch effects arc dependent upon the relative stereochemistry of the perturbing atoms ris-d-cis the CO group, and that the stereochemistry of outufplane a-substituents IS p;utlcularl) conducive IO them. This is already manifest in some of the raw MCD data. For example, among the decalones, the MCD curves for 6 ;md 7 (Fig. 4) exhibit very prominent positive MCD componenls that are absent in I. 3 ;Ind 4 where there are no out-of-plane a-alkyl substituents. Of course. the ~rar~~
..
.. Frg ( Rcprewxauvc clo[! ? ?kxxan.!.oncs mdlcales
_
_;
.
MCI) qtcc~r~ of mclh)l-wb\trtuted b~c). and OK parcnl compound ‘I’hc wrwal bar ftw crpertmentrl no~sc k\el
\tn)ng &A:) and R(R,). and diminished H(H:) static conrrihurions (see projection diagrams). Thus although rhc raw da!a arc at time\ instructive, a more mformatiw structural interpretation is provided by analyris of the B-vafues, Such analyses’ must take into acfounl both static structura1 and v~b~~i~~l-~~~~~ur~l tfkfs.
the dddiftonal &Me \uh\fliucnf fool; place during the uork.up of the rcacrion mixrurc. (Found: C. Iu).?I: It. II Ox Calc for
(‘,Jf,:O~
C’. Ml.35; H.
IL4l’kl.
!..Hcrkrf.k~efcfrI!.?.?lorran 4onr (141 was prepared aa” cording to the m&od described ht Tich$ PI ei:” Sff’ mic 13X; NSiR 6 1 10 (d. J - h fft,.
7%~ m,tgnetic circular dfchromctcr and experrmenfal procedure have been dcscrthed eirewhcrc.’ ’ 1%~ sourCc\ of the C~)rn~lund~ which were not synrhe\ired in these lahoralorics lrrt Iced m ‘l‘ahic I. l’hc NMRq~~traweremeasured nn a Vat&n T-ho NUK ~pccfrnmercr using CC& as rht rotvenf. Recau~ fht W’D fs weak for tafurafed kctonex. if ~a\ n~etsar)to monitor all of the compounds-~!nthcrwed \)r dunrtcd-for fhc prc%cncc of impuritw some of uhlch dommafcd fbe MCD spectra 31 \ery small conccnfralion\ (c.g. a\ hltlc ;s\ 0.1% of an a&un\pturdfed kelane). Thi\ ua\ done h) ctaminmg rhe G1.C truces and L’V spectra of Ihe srmptcc a\ ucll t-.Merkyf. (13) and &mefkj&yfof? 2 ?]orfon-?-mt t 10. a\ the MCff ipecfr;t them~elncs When ncce\\itry. fh+ compound\ ‘lhr tffhmm reduction of totuene in liqurd smmonu” pvc wcrc purified as much s porsibk urmg 6l.C and hrgh prev.ure I-mah)l-t.QcyckthesadKnt. The unconjugated JRnc was liquid ~hr~~rn3fc~~r~phy 1HPI.C! Esen wtfh rhc~e precauttonx equtldxiafed h) rt@uting o+trnight with bBuf)H and t.RuOK” to pike a cotorlc%s liquid which on di~~fll~f~n had an odor however. MIictcnr impurities rematncd to pre+ent fk nepat~vc hand\ in the high frequency regmnx of man) of the MCD tpecfra rc~emhhng that of i.~~ycI~)~~adicnc. Thir liquid uas placed in from reIurnin~ fo the haceltnc {F&q. 4 and 5). In these cavx the a flask and wcces~~ve small amount\ of mrktc anh}drfdc added. curve\ wcrc extrapolated 10 fhe bavline so that thr) couid be An NMR xpccfrum of the crude ddduif dspla)td 4 \harp singlet interprlfed and rhe 21.values dtwrmincd. al 154ppm. The matcnai from fk t%eb.Alder reacfton *a% karg . Sf&$10 nntf kcql - mffhyf . trm5 . ? =dmden~ hydrogenafed in Tlif: using 18% Pdj<’ until H, uprakc ccartd. t3t ‘li~nr4~xx%&n w&r prepared frc3m~ujnt~nc~nd t.?-huiarftcnc The NSfR +cctrum of rhc ~~dr~~ge~linn prorfurr con&cd a occordrnp to the method of Minn tf a(.’ with *light alteration\ in Tharp smgkt ai I.12 ppm and a tcr) *mall douhkt centered at the ;ondifr)n\ of fhe IkebAlder re&on’” and in the srpdralivn 0 9U ppm Tbc h)droprnalh)n product was placed u~fh Ii2 cquik KHCO, m w;rler and lcff on a \ream bath for \c\cral hr Thr of ~ttc w and fmns &omer\:” h’%iR 6 5.6 (unrc+.olvcd mr~ow binllrc mulfiplef). The octalin wz\ reacted In chloroform uifh rcAoc. affcr removal of rhc uafcr. *;I\ hi+dccarhor)lafcd u\mp mcfu~chloroprrtKnroic rctd m the u>ual manner lo form Ihe led fcfrJ;)ccf;(Ic in pjridinc:“’ EMR 6 I.I fst. 6 I cm). cpoxidc. The reacf~~n WB followed u\tng NMR hp fhc H~dro~r~~fon yielded an alcohol u-hich U’JI otidilcd h) u&m di\appE%ranCt of the &tylic protons of the oclahn and the dtchrom& m a mixture of HI%f,. %iFcr axi ether. After seueraf appearance of a new peak at 3.Oppm. The cfoxwit u-n\ treated hours. she xotn was t?ltmCted wtfh crhcr 10 gibe a ketone mix&WC. under nitrogen with 54cI.i in reffuxfng hctsnc to form the aicohof The component\ of the mtlturt wcrc vzparatcd by G1.C (~xid~~~)n of the alcohol using chromic acid in acclfc actd” pave fdic~h~-lcne~~l~col~~difr~c croxs.linked on ~‘hrt~mo~orb WI tnro the desired 3tar~methyl.fmnr-?~ecalone (61: F;MR 6 I 18(d. two fracftonx. ‘I’hc fir\t fracrton proved to be 13, M’ m/e 1%; I = h.5 HI); report& 1.2 (d, J h 5Htr The equatort4 Lomcr 3 NMR 6 0.83 (\. 3H1, 1.61 is, RHf ? 1’ (5, ?H). rePOrted” 0 X2 t\. wax produsccd by cp~mcri7~tion of the axial i\omcr C in methrnolrc fraciion wa\ I&? !ftl. 1.52 1%. XII). 2.17 t\, _‘Hg. The frond KOH JS dtrcrtbed by Siion er at.:’ !iUR 6 0 Cy cd. f -160 Hz): S?‘n& 13%. ?ISjR 6 0.93 15. ?Xi. t 9(1& 2Wt. 2.13 fm. ift). reponed m t .O(d, J - 6.5 Hrf. ltur)_iltfk~~--I~ns.?.drrolonf (St. Compound 2” ua\ cpimcritcd IO a 50: 50 mtxlure of rhc axiai and cquatornl tu)mcr\ ArLnclrf~d~~~lcnlr-Wc fhank th. (i Ohloff f FtrmcntchS:1. $1~. the pyrrohdmc cnaminc mtcrmedia!c lnof bolafcd) h) (;cncva. Su-lizcrland) and Profr f; Stork I(‘olumhl.~ Cm\cr\il! L refluxing wlfh pyrrolidinc in xylenc over 3 A moleoular Gcvc~ for E Piers IUnivcrqif) of HriIl\h (‘olumbla\. and I HudcC one day. The IWO isomcrr wcrc xparafcd using HD1.C: SMR 4 tfJni\er\ily of Sourhampton) for providmg II\ utth ketone I.@3 fd. J = 6.5 Hz): reported’ 1.03 fd, J - 6.5 Hz). sample% and L. Sctifcr It’ni\er\ifg of 4rkan\a\I for hl\ lfcy~,3~e~ft-~mrr~~l-tranr~?-tf~rafonr f4i. Utfhyl isopropcn!l cakufrtionr on she conf~~rrn~~jon~ of tbe rronr-?-decalones. We ketone and fk pynoiidint cnamine of cyclohcx;;nune were arc atso grateful fo !&s. Ruth Record< for tcchnrcaf a%%sIancc reacted in the manner drscnbed by Stork zr ” to produce dnd fo fhc National Science Foundation ff;rant So. CHE~~~fh~i.~‘~.~~~~lo~ (M’ mfr 1641 whtch wa\ reducfi\cly ?M5!541 and the h;rfional In~ilfufe~ of Health Grants No. (i% 20276 and HI, 168331 for financial aid. fhnc of UI (E.M.R.) wicks aIkylafcd using Uel and K in liquid arnrn~~~i~~~to give 4 as fhc major product: MS m/r 180; NS4R 6 0.92 (two overlapping Me to thank rhc .American Axroctatron of Cni\er\rt! Women for an doohkr\. I - hHz). fFound: f‘, 80 14, 11. Il.&. falc. for X.AI:W infernational postdoctoral fellowship. C,:H& f, “294; H, II.t8%tt. I,f.Dimrrkyf17) end i,I,Werjrrrim~khj-tran~-~~decu~on~ tit. I.Mtthyt-5”-!+cv,Jont wa\ synfhcsited md reductircl) ;rfk* ‘Paper XI.VI tn our scricr M;rgncric (‘ircular Dichrcri\m Studits. viared usmn K and Mel in 1xGd ammonia and THF ;LI dcxribed Iiw Parf XLV xc Ci. Barth, R. E. Ijndcr. !i Wacspe-Scrcevlc. h) Stork ‘et cl.“” The AAfanf only liquid obtained on E. Runnenberg. I’. D)erass~. Y S. Aronclwlf7 md %t(.(ioulcr. hulb~~d~~lb disfillafion oonfamcd IWO cumpnncnl~ which wcrc man, 1. (‘kern. .‘hc Pcrkm II. In prcx\ qdrahk usin HP1.C. One component proved IO k 7: M’ m!e ‘A. 1. McCaBcr). G Iri. Henning P %. Schatz. A H. RitchK. H. 180; NMR d 1(10(5);reported” 0.99 (si). ‘fhe rccond componrn! P. Peczzmcw~ki, 0. R. R&g, ,A. W. Sorxlle. Jr and f’, J. had ;t mast \pectrai motccukr ton of m/c 1% fndtcatinp the Strpkns, (In. fbmmm. 5% fWb&t prclcscnceof an rddifionaf Me group. A Iarge h’hfWsin&t f6 0 991 ‘6. Byrh, E. ~u~ncn~rg and i‘ IIjcra\d. Ibid. 1% (?%%I dnd an ovcriapping doubkr fd 0.9?! mdicated Ibe pre%cncc nf a ‘G. Barth, E. Hunncnkrg. (‘. DjcrarG, II. Eldrr rnd R. ~m.dirnclh~~ and an eqwforia1 Me group, 0f the two pov Ghilities. l.I.!~rqt_f~mcrhyl-rmn~-2-dccatone and 3.3.lfeqb trlmerhyl-rrPnr-2-declrtnc. rhe former is the only one whfch ‘1.. .%m& A. Moscouitr. G Barth, E. Hunnenkrg and E’. could result from the reductive mefhylstion of I-meth)LA’ *I Qerassi. 1. .4m. f_‘kcm SW 94. b#A I I93 ocfan-Z-one. EG%eatly. a base cafiilyrrd methylation produsing
af
K
WORNI
-W. Schubert. 1.. .Scbfer and (i. H. Pauli. 1. .4b/ Sfrwf 21. 53 I 1974). ‘L. Schafer. private communcatlon. . M. Askari. !i. S (hrlund and I. Schifer. 1. Am (‘hrm .GK whmtrlcd for puhhcarmn ‘L. Seamans and A. Moscowitz. 1. Chow Phyr 56. lO9Y (IV7!l. “L. &mans. A. MoscowiIr. R. E Imdcr. K Merrill. J S Dixon. G Hanh. E Runrwnbcrg and C D]erassl. J .4m Chum .Soc. accepted for puhhcalbn: ‘K E Imdcr. K Mornll. J S Dwn. G Barth. F. Hunnenlxrg. (’ I))erasst. I. Seaman\ .md .A Mmcou117. Ibtd accepted for puhlicaflon. ‘I.. Mlon. A. Casadcvall and E. (‘asadcsall. Bull Sot-. (‘him. pr 3s. 29so (IWR); 36. 3199 (IW9) ‘“I.. F Flew. J Am Chrm. .5x- 70. 316.5 (1%). ‘u’ S Johnson. V J Hducr. J 1. Margrave. M A Fnsch. 1. tf Drcpcr and w’ S. Huhhard. Ibid 83. 606 Cl%11 “G. Swrk. A Hnzzolara. H. landc\man. J Srmusrkovrcr rnd R Tcnell. Ibrd. U. 207 (lW31. “6. Stork. P. Rosen. S. Goldman. R. V Ctwmht and J T~JI. /hid 87. 275 (I%!) “I .A. Marshall .md K H Anderscn. J 0~. (‘hem 31. M’ (l9w
CI 01. “K. “H
911
54140~ and J Ct. Rcrger. J Am Chrm. .%c. 84. 19% t I%!). 1.. (iocrmg. K. u’ Grciner .snd M. F Sloan. Jhtj 83. 1391
I1961 b. “A. (h.~hosa~s. M Tichj and J Stchcr. Co/l. (‘xc-h Chrm Commun. 3S. X3g ( 1970). “K R Stephens. J H. Slothers and C T ‘Tan. .Wors Sptcrmmet~ and SMR .‘$wc~mrcopv tn I’rr~trrdc (‘hrmirrr?_. (EdlIed hy R. Haquc and F J Biros). p I79 Plenum Press. Sets York (IV11 “M Tlchj. A Orahovals and J Slcher. (‘o/l (‘xrh (‘hem (bmmun 35. 459 I IY?O) “A. I.. Wild\ and K. A. Nelson. J .4m (‘hn SCM-. 75. 5% (IYC31 ‘-1 Alfaro. H’ Ashlon. K 1. Kahone and N .A 1. Rogers. T’ttmhrdmn Iy. (59 (19741 “(’ .4 Grub. $1 Ohb E Rcnk and A. WCI\S. Htlc (‘hem .41-u 41. IIYI IIYw) “u’ Krdux. (‘ (‘hasw and R (‘hassIn. Tifrohtdmn 25. W18l (I%YI