4 NOV 0, F16,Journal of Chemical Physics

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1 OFFICE OF NAVAL RESEARCH II Contract N C-0647 TECHNICAL REPORT #51 Determination of the Minimum Energy Conformation of Allylbenzene and Its Clusters with Methane, Ethane, Water and Ammonia by P. J. Breen, E.R. Bernstein, Jeffrey I. Seeman and Henry J. Secor.2 "Prepared for Publication in the 4 NOV 0, F16,Journal of Chemical Physics Department of Chemistry Colorado State University Fort Collins, Colorado June 1, 1989 Reproduction in whole or in part is permitted for any purpose of the United States Government. This document has been approved for public release and sale; its distribution is unlimited


3 SECURITY CLASS.FCAT.ON OF THIS5 PAGE REPORT DOCUMENTATION PAGE r,%8n 408 'a REPORT SECjRITY CLASSFCA'ION!t RESTRICT,VE VAPI, NGS 2a SECURITY CLASSiFICAT'ON AUTHOR-TY 3 DSTRIBUTiON AVA LAB... OF R Acioroved for oublic release; distribution 2b DECLASSIFICATION;IDOVVNGRADING SCHEDULE unl imi ted Unclassified 4 PERFORMiNG ORGANIZATION REPORT NUMBER(S) S MONITORING ORGA%;ZATO% R--;ORP\' 5' N C a NAME OF PERFORMING ORGANIZATION 6b OFFCE SYMBOL?a NAME OF -VO.7R '.C 'D"C-~'A 7 Colorado State University (it applicable) 6( ADDRESS (City, Stare, and ZIP Code) 7o ADD7E SS 'Ciry State and ZIP C,-0e) Department of Chemistry Fort Collins, CO ' 0523 Ba NAME OF FUNDING isponsoring 3b OFF CE SYMBOL I PROCIUREM'vENT 'STR ORGANIZATION (if applicable) Office of Naval Research N C ( ADDRE SS (City, State, and ZIP Code) 10 SOURCE OF FUNDING LES.0RGGRPAM PpO.Ec- 1 VE"J Di'LV a 300 North Quincy Street EF.EMENr %O 1.O %i N1 0O Arlinqton. VA TITLE (include Security Classi~tcation) "Determination of the Minimum Enerqv Conformation of Allylbenzene and Its Clusters with Methane, Ethane, Wate.- and Ammonia" 12 PERSONAL AUTHOR(S) P. J. Breen. E. R. Brrnstein, Jeffrey 1. Seeman and Henry 'V. Secor '33 TYPE OF REPORT 1I3b TIME CO4vERED 114 DATE OF REPORT Year Month OiI,( Technical I ROM -O 70 Junel SUPP EMENTARY NOTATION 7 COSATI CODES 18 SU)BJECT TERMS (Continup on reverse if necessary ard 'denrirn by block numtber) L FIELD GROUP SUB-GROUP ll1vlbenzene, suoersonic jet.clusters, conformations 19 ABSTRACT (Continue on reverse if necessary and identifry by block number) SEE 4TTACHED ABSTRACT 20 DSTRIB, 'ON. AVAILABILITY Ut ABSTRACT 2' ABSTRACT SECUR- CA.S AO ),NC, ASSiFiETI"jNi ivited [E SAMF b"i RPT El DTIC USERS Unclassified 2a NAME OF RESPONSIBLE INDIVIDI)AL Z2 T re LE P HON E (Inc lude A rea Code) C2 1 L N 1E. R. Bernstein (303) DO Form 1473, JUN 86 Previous editions are obsolete S S( S,'N (9102- LF-01,

4 Abstract SupersonIc molecular Jet laser time of flight mass spectroscopy (TCFMS) is employed to determine the minimum energy conformation of the allyl group with respect to the henzene ring of allylbenzene, 1-allyl-2-methylbenzene and I- allyl-3-methylbenzene. The spectra are assigned and conformatinns are suggested with the aid of molecular orbital molecular mechanics (MOMM-85) calculations. Based on the experimental and theoretical results, the minimum energy conformer is found to have r1(cortho-cjpso-c&-co) = ca. 9 0 a (i.e., the allyl group is essentially perpendicular to the plane of the benzene ring) and 7 2 (Cipso-C&-Cd- C 7 ) = ± 2, (i.e., the olefin C=C bond is eclipsed with the Cd-Hj bond). The TOFMS of allylbenzene clustered with methane, ethane, water and ammonia are also presented. A Lennard-Jones potential energy atom-atom caiculation is used to characterize the structures of these clusters. Experiments and calculations demonstrate that the four different solvent molecules studied can form stable clusters with allylbenzene by coordinating to the f-system of the ally] substituent in addition to that of the aromatic ring. o i,, JI', - [,'

5 Determination of the Minimum Energy Conformation of Allylbenzene and Its Clusters with Methane* Ethane, Water and Ammonia P.J. Breen * and E.R. Bernstein Department of Chemistry Colorado State University Fort Collins, Colorado and Jeffrey I. Seeman and Henry V. Secor Philip Morris U.S.A. Research Center P.O. Box Richmond, Virginia REVISED * Present Address: Baker Performance Chemicals, 3920 Essex Lane, Houston, Texas 77027

6 Abstract Supersonic molecular Jet laser time of flight mass spectroscopy (TOFMS) is employed to determine the minimum energy conformation of the allyl group with respect to the benzene ring of allylbenzene, 1-allyl-2-methy]benzene and 1- allyl-3-methylbenzene. The spectra are assigned and conformations are suggested with the aid nf molecular orbital molecular mechanics (MOMM-85) calculations. Based on the experimental and theoretical results, the minimum energy conformer is found to have rl(cortho-cjpso-ca-co) = ca. 900 (I.e., the u 'yl group is essentially perpendicular to the plane of the benzene ring) and -2(Cipso-Ca - C 7 ) = ± 1200 (i.e., the olefin C=C bond is eclipsed with the Ca-Ha bond). The TOFMS of allylbenzene clustered with methane, ethane, water and ammonia are also presented. A Lennard-Jones potential energy atom-atom calculation Is used to characterize the structures of these clusters. Experiments and calculations demonstrate that the four different solvent molecules studied can form stable clusters with allylbenzene by coordinating to the n-system of the ally] substituent in addition to that of the aromatic ring.

7 L. Introductin Supersonic molecular jet laser spectroscopy has recently been proven to be remarkably capable technique for the observation and structural characterization of a wide variety of alkyl and heteroalkyl substituted benzenes. 1-6 For example, the minimum energy conformations of various ethyl, I propyl, 3 butyl 4 and methoxybenzenes 5, 6 and styrenes' nave been observed for the first time and their stable conformations have been experimentally determined. In addition, molecular jet laser spectroscopy has been able to characterize potential energy barriers, typically for aromatic methyl rotors, for some of these molecules in both their ground and excited 2,6,8 states. In this paper, we focus attention on the effects of a carbon-carbon double bond (an additional '-system) incorporated onto an aromatic ring in terms of the geometry of the minimum energy conformation(s) of the molecule and on the geometry of various van der Waals clusters. The specific sybtems studied are allylbenzene (1), the allyltoluenes (2 and 3), and the van der Waals clusters formed between allylbenzene and methane, ethane, water and ammonia. Even though the allylbenzene substructure is found in numerous natural products and has value in organic synthetic manipulations, its conformational properties have received little attention. 9 Indeed, there is a dearth of both experimental and theoretical information regarding the conformational preferences of allylbenzene and its derivatives. 1, R I = R 2 H 2, R 1 = CH 3 R 2 = H 3, R 1. H, R 2 = CH 3

8 Spectroscopic studies of these systems are obtained through supersonic molecular jet cooling and isolation of the various species in the gas phase, and one- and two-color time of flight mass spectroscopy (TOFMS) detection. Mass selected excitation spectra of isolated molecules and clusters are thus obtained. 1 0 In order to determine the conformations and cluster geometries associated with the individual mass selected spectra observed, model calculations of the isolated and clustered species are performed. 1 2 Five questions are addressed in this work: 1) can the stable conformations be isolated and spectroscopically observed for benzene and alkyl substituted allylbenzenes? 2) what are the minimum energy conformations of the allyl group in allylbenzenes? 3) what are the configurations of clusters of allylbenzenes with small solvent molecules? 4) does solvation influence the allylbenzene molecular geometry significantly? and 5) does the it-system of th9 allyl group influence significantly the solvation of the aromatic ring in substituted benzenes? The supersonic jet time of flight mass spectrometer is as described previously. 13 Expansion into the vacuum chamber is achieved with an R.M. Jordan pulsed valve. In the case of the allylbenzene van der Waals clusters, two-color photolonization spectra are obtained by using two Quanta-Ray Nd:YAG-pumped tunable dye lasers to generate the pump and ionization beams. The energy of the tunable pump beam (0.5 to 1.0 mj/pulse) is typically cm - 1 while that of the fixed wavelength ionizing beam (1.0 to 2.OmJ/pulse) is cm - 1. Under these experimental conditions no one-color spectra, due only to the pump beam, are observed. Complications due to fragmentation of higher order clusters are avoided by careful control of the allylbenzene and solvent concentrations so that, in general, higher order clusters are not oberved. Moreover, the -2-

9 ionization energy is determined to be jlust high -nouigh to ierve.p,,-i h t,, cause extensive fragmentat ion into lower mass chanr el s A ll peaks in, ai w, spectrum are found to have rhe sam- backi;g prpsslut' poqln,- Ground state potential energy profiles for the ally erie~reps AV-.,, using Kao's molecular nrbitali -mclciar mechani's MOMm -A5 a!gor thm theoretical appuoach which has found to he Applic'able t),romatw, m,lo,ules 14.16a The resolution p)respnt i;,vi. lble tn us (ca ) s not '07 : lent to determine the,etaild geometries of allylbenzene clusters from rotational spectroscopy Instead. potential energy Lannard-Jones (LI) atom-atom (6-12-1) calculations 1 7 are used in this endeavor These calculations are similar to others used in the past. and employ the same set of L. potential parametersi' 19 The partial electronic charges centered on each atom of allylbenzene are listed in Table I and are obtained from Ab initio STO-3G calculations. For allylbenzene clustered to methane and ethane, the use of partial charges has no effect on the calculated cluster geometry, and only a small effect (-3 cm - 1 ) on the calculated cluster binding energies. The partial charges are therefore omitted in these calculations Methane. ethane, water and ammonia are typically mixed with the expansion gas at a concentration of 2% in psig of helium. Allylbenzene (1) and!-allyl-2-methylbenzene 12) are purchased from Wiley Organics, Inc. and are used without further purification. The samples are all maintained at ca C during the experiment. I-AlIyJ-3-Iethylbenzene (3). 2 A solution of m-tolylmagnesium bromide, prepared from 3-bromotoluene (85 g, 49.7 mmol) and magnesium turnings (2 41 g, 99 mmol) in ether (20 ml). was added at room temperature to a mixture -3-

10 of allylisopi-opyisuit i'i- f -InV *IN g, 0 92 mmol) in (8I' :IIttoI Ither m II r. I I for 10 h. coo l ed. and quencheid w t i1n hyrlroch I(U I,!. e ~ra te d. I tpr-d.!.- 1{ - i um stlfite). ti lrl( ~rit~ 1 7 mm~4g) The I - ii Iy I-3-met h,,!bp.pl 3) wis the -n i t -. vv1t g iv 3 ;2,4 n~~ I 1 p 2 iig H N M R CflrD 224 NMR ( ') 2-61, 2 R 12F ( IT. Exper imentali Resu I ts A. A]lylbenzene and A] lyl toluenes. The time of flight mniss sptrum of the 00 band region fr, ' S*. trans t ton i of J P t-cooid ybenzpne ( is pr nied n in f gur The spectrum contains one origin. ".is located it cm I single origin indicates that only one eneirgy minimlim e-xists for the orientation of the rill T t e M, gn. flg 1 tp p,ru f te 0 b n o lo t,- h < group with respect to the ring in yund ayiybbnzene. as deined in 4a 4b PUMn 0( Umanc 4a 4b Figure 2 is the TOFMS of jet-cooled 1-allyl-3-methylbenzene (3). The spectrum exhibits what are assigned as two separate origins, at and cm -. belonging to different conformers. The origin at cm - appears weak because the laser output at this wavelength (LDS-698 doubled mixed with '-m) is quite low in intensity As has been commonly obserrved for

11 ~.1~-v!-3-rnethy ta -o, 1~-~'- in r- 1- n *..., 7 dr" : ' " ;r'sen i,' -','r ] r ati:" -'. " ' ' f' m: " S rv' ' -',JTL -2," - - -,' hv b,-':,','- 2' ": b,-h '7Iss - :C'or' - r - ; IC ' *he -il s-:bs*.. r "ssprnt,:t' hgonhl g - 1h o. 1' ]-'. he henz~ne rinlg :c f 4! Th;s :s ':"Pnt w: h "he exper:me'n i.-,i -,,t-icai i digs C r ' < yr - s I shs : "Comatoes ')f part III s r-ict"'re ArCHR 2 The N Pwrnin p ro ec t'ns t he -,onformat i>h ',i " a1 b c Ut -. C -C-" 3 -r r~pr~sent 'he 1,, er impor't t ;onform.i,-rn these compounds The s er:c 'nergy profi :e for r i ion 3botut 7, s -hown "n f;gure 4 As can be seen. Ihe viny 1 C1-C1 0 a->so " sed 5.rd C,-H 4:r.yJ oc Ipsed 6 (=7) conformations ire predic*cd to be t he energy m;r: m r iliylbenzene Because the Pnerg.y If ernc,betw(-n 5 1nd 6 7 ; ' kcil mol), certarinlv within the error range of the MOMM caicu )ations. wt cnot sper fy which of these is the global energy min;.mm Much morp rof:ni Calculatlons would be required before one could confidently predict Wh;ch f 5-7 is the most stable conformation and what the energy!j.ffrence between ther is For example, preliminary STO-3G cjlculati in, on the geometries of the MOMMderived energy minima found for I (i e. 5a xs 6a) led to a reversail )f *"hir potentiai energies (0 75 kcal mol by MOMM kcal o] by STO -5I The :mportant conclusion here is that the energy minimum is.a v nyl psed

12 , g on *tom,s n a b p -n U m-! C 3 UI B Al ]ylbenzene/methane -B(CH s prosen t 'd Three. vtv " v i rtenst f ' res *-cur, it ) mnd 1 (4r,3d 9 sh!fed from the )r igin i f dlilyibenzene by 4 O and 4 7 cm The first two shif's are similar to those observed for meth;,ne clusterod 1o other substituted benzenes such as propylbenzene 13 For this latter case, shifts of -51, and -26 cm - are found for m'-thane above and below the ring of the anti conformer fn order to perform the usual LJ cluster potential energy geometry search?alrulat;ons for the allylbenzene solvent clusters. i geomptry for the allylbenzene portion of the cluster must be assumed Cunformer 6a is chosen for the illylbenzene minimum onergy conf-rmor irguments in favor of this choice are presented In the Discussion Section and are consistent with the aforementioned spectra. Potential energy calculations for NB(CH 4, 1 yield the five cluster geometries illustrated in figure 6 Cluster binding energies are also presented in this figure. For only two of these geomptries is the methane molecule coordinated directly to the aromr3tic --system of the ring. These two structures are analogous to those observed for propylbenzene (CH ) and

13 presi:mib]y ire esk m 'hri 'e ".. *he ring) red shifted feart' f - The remaining thrr"' 'rc*:r r,;f>':r '.. t on to the,'-system f r iiin.mal effect on '7he of-" ",...,'.... ' - therefore 2t!past, kps,,,.-' :,,,:: y", c J'," *. - r, spons'ble f,.r he C. Allylbenzene/Ethane The TqFMS of "h t" ' ''" :,..'p W. '1 is presented in f'g:e T m,-st :2'e'se fe.t:2ef "hs,'1'" :m occ :rs c1 I and is r-d l -h,:'',..', 2 8 m i - : rr_ F-h cur -ieton :,~ '7 h1 1~ -, 4 5 Some of the otherr ft::sprp-" i':re? occur ot :. 2745:, and (:m wi'h... spcnd.ug shifs f, '.e:.en.e -. :g-in of -73.8, and 19 8 cm 1 LJ potential energy separate cluster gometries: 'heso Jqlculations of ail ybeiizenc(%hr,,.:i n:. a are depicted. in fgure 3 and I de.onge 5 first four of these th- familiar ">-rpend'u'ar"- nd 'par-il. configurations of the ethane molecule over the benzene r,z ndg.,'been observed for ethane coordinated to benzene* ind propyl.erz'2' Te "perpendicular" and "parallel" configurations of the ben7-re?c2h ', cluster produce red shifts of the 61 transition of 97 2 and 30 8 cm - i 0... resp ' Thus these cluster geometries for allylbenzene(c,h 6 ) 1 clusters are must likely responsible for the features it and cm - 1 (red shifts -f 71,3 -tnd 41 6 cm) in figure 7. The most intense features of the spectrum in figure 7 lie qiite c:'ose '.o the allylbenzene origin. Such small red shifts are to be expected fcr closters in which the aromatic i-system of the ring is not coordinated or so"ted -'7-

14 l:kely due to the coordin!'.,-, the. rn'>'- ': -. y 1,l subst itutent. D. A] I yibenzene/wat~r. Figur- 9 iep-:;s 'h T"FMq,',ily,lhrn/.,,P n ai!ylbenz-ne 0 0-fp tr ns: ":.. si ur i:' :ese ti:sshift; relative to, - e(zinp, : 8 of ') 'C I u:': - T potentia - l nery :-i1 our spp,ir.it i lylben,'nteh ) :oufigtor::rcns. as shc%&: : ' ogt:rt 10 Two of these invo!vk the,'m rdina- ;n of tho, woiter mn!,-cul t-' ''-systemn - above- and bf'?ow 'h9 :2 I,Lster of similar geometry pr,;dt::ps , cm -i blue shift of the P') t ): nra' n benzene 13 Th fe;iai:rs i- figure ) '.,hich ire blue shifted from e al ylbenzene origin by 5 1 and 10 3 m -1 are therefore most likely due to the cool lination of the water "nlerute to the i-system of the ring. Thp f-it arps which are blue-shifted by 10 1 and 47.8 cm are presumably!u, e,t c-'... of the water molecuo> to the :-system of the il!yl group E. A] lylbenzene/amuonla. The TOFMS of the 00 transition of aliylbenzene(nh3) 1 is pros~nt~d in fig'irp 1 Intense featnres occur at and cm shifted by and cm - 1. respectively from the origin of allylbenzprne L.I potential energy calculations predict the existence the four cluster ronfigurations Illustrated in figure 12. As for water, two of these clusters involve coordination of the ammonia molecule to the f-system of the ring, while the other two involve ammonia coordination to the 7- system of the ally! group. The TOFMS of ammonia coordinated to benzene is complex and difficult to interpret. 1 8 but an assignment of these data has been presented 18 The rod-most feature in -8-

15 " f -r,mmonia coordinated v v'. -1s:s tc"'d t,;nz7. s t: r", p.e. ' va i 1-i ble. \n ammoniai.. K :' -..:...,. "h- -1sy s -i:-om i tic ring nyionz of fne,i i I! --.7 e ne w. l: :.n r,'-,,, 2 T.. -. the clus*er O?r-ns tr;.i', ' ring -system *yp,; p'1il'i W'' :-,.>,:, "he ' e-,.lster ( ar sh. *S.issign the features :n ".u h ir" h ue.,,i e :1 n 2, "I ) the i l 1henz ne origin 1,) 7 ;s,ons bhpl r, g:ng t') 1:'isters :n h h 'h ammon! is i,,)sitioned '::'" y,v- '.- ring 'he The 2 0 cm 1 red shifted feature is most k~ly!':p to 1 :s r n qh,,-h the immonia mnoecule is 'iirectly coordinat ed to the i y 1 s'.s lrent IV. Discussion. A. Allylbenzene Conformation. in previous studies, w# have drmons*r,-ated that laser Jt spectros-py -an be employed to observe stable conformational isomers, even if the energy barriers for conformatienal interconversion ire very low 1-6 each spectrum, the origin transition is associated with a specific stable ground state conformation: conversely, each stable conformation corresponding to 3 potential energy minimum generates, at least in principle, its own spectroscop.c 0 transition. Hence, by examining the spectra of specifically substituted allylbenzenes, one can in principle "count" the number of stable ground state conformations and thereby establish their molecular geometries 17 For a!lylbenzenes, this may!ead to a distinction between 5 and 6'7. or the possible presence of both in the jet. As shown in figure 4. a variety of stable conformations can be proposed for 1-3: however. only conformations for which the ally] substituent is

16 ss,l perpe~di(':,,1'!.,' 'he -l, me of thp benzene ring ire Q':'': %re this discussion, since M(IMM - r,: i'.ns indic;it -1 n orientations are found ex ji) mp'7 11 Pd f y ai.,1(.1 thei 1 (.,,' for ill othr rylpt :,kyl I 1. -C 2 -RI :ompourdis Z "" - '.sohuty. neope t., etc 2 The MOMM : s spci:t 1 5P( 6 7 sta-b'e gr-)ind s' ite.. : f r.:. Si )nly I :-s: rinsi. i )nser is ' f'r I. '- 5a 6a but not both ccnf irm,." fis tl y benzene ini : s,., 5.gcis mixtu:r ' of r 6!: 71 'h' tins fr 2 n,,! 3, To dist ; nuish g,' w--n thes possibi 1 ities, w :s these s t- I y'd msy metrical!y subst i tu ed I, lylb- nzenes following the st te. p'-' previous ly by us to,,mn-over the -n n mim'nery conformations of alky! i id mwt,,xy s~ist tuted benzeres 16 Considtr 1-al lyl-2-i hyiser.z-iie 2- the TOFMS of this compound -wmild contain only one origi:" transition if conformation 5b were the energy minimum, while conformations f6b nd 7b would yield two distinct origins. S.ince the actual TOFMS of l-ul!yl-2-methylbenzene. presented in figure 3. contains two origins, at and cm - 1 conformation 5c is ru1ed out Thus conformations 6c and 7c are assigned as the stable conformations of 2. Similar logic obtains for l-allyl-3-methylbenzene (3) As shown in figure 2 and discussed above, two origin transitions are observed ind ass igned as 6c and 7c. Although we have made assignments linking specifir conformations with Individual transitions for other systems, as in the case of the anti 8 and two gauche 9a and 9b conformations observed for propylbenzene 3. we cannot :it this time assign the individual transitions observed for 2 and 3 to specific conformations 6 or 7, -10-

17 CHI~ 9b~. R' -. R B. AIIylbenzene Clusters Thp -- system OF '.r.bh. - hm,, :n i'l,'benz'ne -.an an cjp's :ompp*e.rfrctively with the -- s'. m :f 'he iromot>c ng to coordinate incor:n ; so!vent molecules. Cct :Inn n with this nlefinu c.-- system results ir" '*able clusters with various solver't molecult-- 'n a ( ddtion, the geometries Of clusters in which the solvent mu:lecn!l is cnordinated to the ring are influenced by the double bond of the,1.lyl g'rotp. which tends to pull the solvent mlec,:]e to the allyl side of the ring. Thus. the early (and perhaps litpr) st-iges uf nucleation and solvation of olefin-substituted benzene derivatives may well differ substantially from those of ailkane-substituted benzene derivatives. Allylbenzene water and ammonia clusters for which the solvent is coordinated to the aromatic ring apparently generate blue shifted 00 0 transitions with respect to the allylbenzene isolated molecule. This excited state reduced binding energy is probably r-lated in the fact that These solvent * molecules contain lone pairs of electrons which can destabilize the.7, state of the ring relative to the ground state. Very similar behavior is found and characterized for other aromatic systems. 1 2, 1 3, 1 7, 1 8,19 Finally, the fact that the coordination of solvent molecules to the allyl substituent generally has only minor effects on the energy of the ring - r transition indicates that the two,-electronic systems are indeed reasonably -Il-

18 isolated from each other V. Conclusions. We have observed sp, '--i of!.hp iso,t'! l y,,z.u 1 3. benzene itself solvite! 1,y vt:,iot;s smt 1 no.- c.. s,,... on both spectroscopic and, I,or res:'. Srind S 'ItO,''.. 7. geometry of isoloted ylh,'u!pr>. is ll ed bet"rmin bch 6a = 7a Fn - 2, conforma* ions 5a anr! 6b i:. I, P *, he _7-, ui,,a, sia',- rh-gy m. ' " S i lar!y, for 3, Confu:m..o:s 5c i'd i6c,rp ' he groo':id t~ite ene:' y ": r', l',y.benzene cl usters tpp ir I,) hive *wo v (ry ist nct typ-s of spe( tr: Ihose well shifted (red or bluie) f:-om "he comparahle,lilyibenzene feature and those relatively near the comparbl- allylbenzene foaature The former spectra we have associated with clusters in whi.h the solvet: is directly coordinated to "he aromatic ring and the latt-r spoctra we have associated with clu-ters in which the solvent is coordinated to the allyl group -- system. well removed from the ring and the 1-7 transition. Solvation does not appear to disrupt in any w.oy the conformation of the isolated allylbenzene molecule, as the spectral shifts characterized for the clusters are all rolatively small and well within the range found for other simple aromatic systems. And finally, since much of the cluster spectroscopic Intensity seems to be found in fatures associated with allyl group direct solvation (origin features with small cluster shifts), we suggest that the allyl n-system has a significant infliencp upon how allylbenzene interacts with and is solvated by small solvent molecules. Acknowledgments. We thank J. Kao for providing the STO-3G results and for developing and making available the MOMM-85 algorithm and associated CHMLIB software, R. Ferguson, B. LaRoy, and A. C. Lilly for helpful discussions and support, and Professor Paul v. R. Schleyer for providing the MNDO and.a4m results and for helpful discussions Parts of this effort were supported by ONR -12-

19 1. Breen, P. J.; Warren, J. A.; Bernstein, E. R.; Seeman, J. [. J. Am. Chem Soc. 1987, 109, Breen, P. J.; Warren, J. A.; Bernstein, E. R.; Seeman, J. 1. J. Chem. Phys 1987, 87, Breen, P. J.; Warren, J. A.; Bernstein, E. R.; Seeman, J. I. J. Chem. Phys. 1987, 87, Seeman, J. I.; Secor, H. V.; Breen, P. J.; Grassian, V. H.; Bernstein, E. R. J. Am.Chem. Soc., in press. 5. Seeman, J. I.; Secor, H. V.; Breen, P. J.; Bernstein, E. R. J. Chem Soc. Chem. Comm. 1988, Breen, P. J.; Bernstein, E. R.; Secor, H. V.; Seeman, J. I. J. Am. Chem. Soc., in press. 7a. Seeman, J. I.; Grassian, V. H.; Bernstein, E. R. J. Am. Chem. Soc. 1988, 110, b. Grassian, V. H.; Bernstein, E. R.. Secor, H. V.; Seeman, J. I. J. Phys. Chem. in press. c. Grassian, V. H.; Bernstein, E. R.; Seeman, J. 1. J. Phys. Chem., to be submitted. 8a. Okuyama, K.; Mikami, N.; Ito, M. J. Phys. Chem. 1985, 89, b. Oikawa, A.; Abe, H.; Mikaxni, N.; Ito, M. J. Phys. Chem. 1984, 88, c. Murakami, J.; Ito, M.; Kaya, K. Chem. Phys. Lett. 1981, 80, Schaefer, T.; Kruczynski, L. J.; Krawchuk, B.; Sebastian, R.; Charlton, J. L.; McKinnon, D. M. Can. J. Chem. 1980, 58, a. The name "one (and two) color time of flight mnss spectroscopy- is generally employed to describe the following experiment. A sample is Irradiated with a laser of energy,1. resulting in the generation of the first excited singlet state (S )_ A second photon 12 subsequently ionizes those molecules in S1 I-, I) The ions are detected in given masa channels by time of flight mass spectroscopy, such that only Ion current representing a chosen -/z is recorded. The energy of the, laser is changed, and a mass selected excitation spectrum is obtained b. In early pioneering work, Smalley and coworkers 1la.1ib and!to and coworkers lic-lie have reported the fluorescence excitation (FE) spectra and dispersed fluorescence spectra of various aromatic compounds. Because FE results are not mass selected, ambiguity may exist regarding the source of some of the transitions.

20 1 a. Hopkins, J. B.; Powers, D. E., Smalley, R. E. J. Chem. Phys. 1980, 72, b. Hopkins, J. B.; Powers, D. E.; Mukamel, S; Smalley, R. E. J. Chem. Phys. 1980, 72, c. Ebata, T.; Suzuki, Y.; Mikama, N.; Miyashi, T.; Ito, M. J. Phys. Chem. 1984, 88, d. Oikawa, A.; Abe, H.; Mikamni, N.; Ito, M. J. Phys. Chem. 1984, 88, e. Yamomoto, S.; Okuyama, K.; Mikami, N.; Ito, M. Chem. Phys. Lett. 1986, 125, Bernstein, E. R. Solute Solvent Clusters in Atomic and Molecular Clusters; Bernstein, E. R., Ed.; Elseiver, Bernstein. E. R.; Law, K.; Schauer, M. J. Chem. Phys. 1984, 80, 207, Kao, J.; Leister, D.; Sito, M. Tetrahedron Lett. 1985, 26, Kao, J. J. Am. Chem. Soc. 1987, 109, Seeman, J. I.; Pure Appl. Chem. 1987, 59, Wanna, I.; Bernstein, E. R. J. Chem. Phys. 1986, 84, Wanna, J.; Menapace, J. A.; Bernstein, E. R. J. Chem Phys. 1986, 85, Law, K. S.; Bernstein, E. R. J. Chem. Phys. 1985, 82, Laskina, E. D.; Devitskaya, T. A.; Koren, N. P.; Simanovskaya, E. A.; Rudoldfi, T. A. Zh. Orig. Khim. 1972, 8, 611; Chem. Abst. 1972, 77, 4623t. 21. Okamura, H.; Takei, H. Tetrahedron Lett. 1979, a. 5ki, N. Applications of Dynivnic NMR Spectroscopy to Organic Chemistry; VCH, b. Berg, U.; Liljefors, T.; Roussel, C.; Sandstrom, J. Acc. Chem. Res. 1985, 18, 80. c. Berg, U.; Sandstrom, J. Adv. Phys. Org. Chem., in press. d, Pettersson, I.; Rang, K.; Sandstrom, J. Acta Chem. Scand. 1986, B40, For allylbenzene,.ndo calculations reveal a minimum at r2 = 1200 ind maxima at r 2 0 and 1800, while AN1 calculations reveal a global minimum at r a less stable minimum at '2 xo W4OMM MNDO. and ANI are reasonably consistent in that each predicts the energy minimum to be ca.?? 1200 We thank Professor Paul v.r. Schleyer for providing!he MNDO and A1 results.

21 Partial Electronic C r 4harg-s "n Atomb 1 I (C) -0 1) 2 (C) 4 (C) r (C) (C) (C (C) H 17 2 ( -0 O28 H (H) (H) (H) H is 13 (H) (H) (H) (H) (H) 0, (H) (H) a From STO-3G calculations using the MOMM-85 derived energy minimum Other attached atoms, not shown In diagram, are 2-12, , 5-15, and 6-16.

22 Figure Capt ions Figure 1 One-color Tf)FMS of the 00 rogon S, - C~ I -co'i,' benzene The slngle n.onse featire :s ass1onet i and occurs t. Q2 - Thp weak f-i-,ros to h:gy, 7 -ner,' of the origin ipt -- es(:red 9 l e o o i l,oon of the ally' '-,,,:p h-,olliary origin demonstrates thar only one molecular confcrmatimn exsts as (n energy minimum for this molecule. Figure 2 One-color TFMS of The O region of S 1 - S 0 for jet-cooled 1-00 allyl-3-methylbenzene. The spectrum contains two origins, at and 37O66 9 c' - I The origins appear as doublets due to transitions between internal rotational states of the ring methyl group. Figure 3 One-color TOFMS of the 00 region of - for jet-cooled 1-0 S 1 allyl-2-methylbenzene. The spectrum contains two intense features at and cm - 1 which are assigned as origins. The presence of two origins eliminates the conformation 5 as the correct geometry of the energy minimum. Figure 4 MOM-derived steric energy profile for allylbenzene for rotation about r 2. I

23 Figure 5 Two-color TCFMS of the O'j r-gion of allylbenzene(ch 4 ) The three ntprst piks c, 1 cm to liwer -nergy of the -l Phon2',,:,t, r g,,. to three differp" u2nster configurations Figure 6 M n nl, or y ":'nr configj:t :gus.ind b n.>7l.g g'g, " allylbcnz~ne(rh,) obtained frnm.he L.,r -'o::-s po.n ii en -rgy caic ila ion Figure 7 Two-color TOFMS of the 00 region of S 1 - for jet-cooled allylbenzene(c 2 H6) 1. The intense features center-d around cm - I are within 20 cm - I of the allylbenzene origin and are due to clustering of the ethane molecule on the allyl substituent. Figure 8 Minimum energy configurations and binding energies for allylbenzene(c 2 H 6 ) 1 obtained from LJ potentia' calculations. (A) Complexatlon of ethane with aromatic i-system. (B) Complexation of ethane with olefin T-system. Figure 9 Two-color TOFMS of the 00 region of S 1 allylbenzene(h 2 0) 1. The spectrum contains four intense features at , , and cm - corresponding to four different cluster configurations. Figure 10 Minimum energy configurations and binding energy for allylbenzene(h 2 0) 1 obtained from LJ potential calculations.

24 Figure 11 Two-color T3FMSl of the nl) rog- n) allylbenzvne(nmh. 3 i 7he i n ten s et ps i I -I duv'c j rp d i F igu~re 12 %f n m r n q s 'I:' d - ar bm

25 ~0 ~0 0Z Q ", u Fiur I I I I I I I

26 0 4.)j z Lu rioure 2

27 fie %&a C >mp LU figur

28 I -K -L ( I DE 50E0 H 2H P O5 d g LFiur 4

29 Figuro 3 L)

30 ~/Xc S-~\_ s-60 - T.a I t x... \, , -388 Figure 6

31 WII Jz LU LU 8C 00 Figure 7

32 ~f \-'--('t-678 I r/" -827 Figure 8a

33 143 f /-, _ ,-, < Fisure 8b

34 0 ro z LUJ =L Figure 9

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38 1 DL/1113/89/1 TECHNICAL REPORT DISTRIBUTION LIST, GENERAL No. Copies No. Copies Office of Naval Research 3 Dr. Ronald L. Atkins Chemistry Division, Code 1113 Chemistry Division (Code 385) 800 North Quincy Street Naval Weapons Center Arlington, VA China Lake, CA Commanding Officer 1 Chief of Naval Research Naval Weapons Support Center Special Assistant Attn: Dr. Bernard E. Douda for Marine Corps Matters Crane, IN Code 00MC 800 North Quincy Street Dr. Richard W. Drisko 1 Arlington, VA Naval Civil Engineering Laboratory Code L52 Dr. Bernadette Eichinger Port Hueneme, California Naval Ship Systems Engineering Station Defense Technical Information Center 2 Code 053 Building 5, Cameron Station high Philadelphia Naval Base Alexandria, Virginia quality Philadelphia, PA David Taylor Research Center 1 Dr. Sachio Yamamoto Or. Eugcne C. Fischer Naval Ocean Systems Center Annapolis, MD Code 52 San Diego, CA Dr. James S. Murday 1 Chemistry Division, Code 6100 David Taylor Research Center Naval Research Laboratory Dr. Harold H. Singerman Washington, D.C Annapolis, MD ATTN: Code 283