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The molecular structure and conformational behaviour of 3-methyl-3-phenyl-cyclopropene
Jooum~l of Mol. :ular Structure, 126 (1985) 207-216 Elsevier Science Publishers E-V., Am~sterdam - Printe.?
in The h’etherknds
TEE MOLECULAR STRUCTUI?aE X.X-D CONFOFLMATIONAL BEHAVIOUP, OF 3-METHYL3-PHEh”iTLCYCLOPROPENE
M. TRLW-J?‘FESERG Deparimenf
of Chernistq.
University
of Trondheim,
AVH,
hi-7003
T-ondireim
(Xorway)
-4. DE MEIJERE Fackbereich Chemie, Liniversitir D-2000 Hamburg 23 (B.R.D.)
Hcrnburq,
dl~rh’n-Luth~.-h-iing-Plan
6.
I. N. DOM:MN Irstifufe of Chemistq, ~U.S.S.R.)
University
of Leningrcd,
Srednijpr.
41.
1920&!
Leningad
B-4
ABSTRACT The moiecular structure and conform,ti,~nal propert.ies of 3-methyi-3-phenyl
Interactions between the cyclopropane Walsh e_,-orbit& and T-slbstituents have been studied by a v&e* of methods and for many cliffereni jTpes of x-accept0l-s e,-orbital
as well as T-donors [l-4) znd substituent x-orbitais
_ Maximum is obtained
overlap
between
the Walsh
Zor the scl-called biszckd favourable when the substituent
conformer, which is found to be parkicdarly is a I;-accEptor i 5-73 . With T-donor substituenls the bisec’keci conformer also norm&y the preferred one, but the preference over other conformers not so pronour.ced
as for z-acceptor
substxtients
is
is
[S, 91.
In 3substituted cyclopropenes a r-substituen;; has possiblities of interacting with the Walsh e_.-orbi’kl of the cyclopropen.? ring and with the z-orbital of the cyclopropene double bond. Inter&ion -with the Walsh e,-orbital is espected +A favour a bisected cotiorrner, while interaction Titan cydcpropene z-c3rbitals of the double bond will favour a perpendicular conformer. According to MNDO cakulated heats of -Formation for various 3. substituted cyclopropenes 1.~51nonbisected conform; &ions rue preferred for I;-accep’tor (methorycarbonyl) as weil as for ;: -donor (phenyl) substituent: . Temperature dependent NMR chemical shifts 143 seemed to confkm t’hk behaviour for the 5ee molecules, while X-ray structure studies [4] of 1$,3-tziphenyl0022-286c/S5/$03.30
G 1985
Else\
B.V.
205
,.2,3-triphenykyclopropene showed that cyclopropene and 3-isopropyl-l these molecules adopt bisected ccnformations r&h respect to the Sphenyl groups. The .aim of the present study of 3-nie~yl-3-~lheny’,-cycropIopene (PHCP) is to contibute ‘to the gathering of the experimenti evidence that is necessary in order to reach an understtding of the fcrces operating between ‘;he cyclopropene ring akd a 3-s~ibstitu~ rr-system. EXPERIMENTAL
The sample of 3-methyl-3-phznylcyclopropene was prepared from a--methylstyrene by dibromocarbene addition, monodebromination and dehydrobromination ilO] _ The electron diffraction scattering da&&from the gas were recorded cn the Oslo apparatus 1113 with nozzle-to-plate distances of 435.27 (6 plates) and 205.27 mm (5 plates). Kodak Electron image plates were used and the nozzle tip temperature was 69”‘J during the exposures. The electron wavelength was C.06461 A, as calibrated against diffraction patterns of gaseous benzene, using ro(C-C> - 1.3975 A ss a standard. The estimated standard deviation in the determination of the wavelength is 0.1% Xanges of scaiAering data were 1.000-19.375 and 6.25-43.0 (A-l), with Z s increments of 0.125 and 0.250 (A-l), respectively. The experiienkl data werl processed in the usual way 1123. The intensities were modified by s[fYl -z, and the scattering ampiitudes (f’) were calculated by the partial-wave method 1133, using YartreeFock atomic potentj& 1143 _ The inelastic sca%ering factors used were those of Tavard et *aI. 1151. STRUCTURE
XXXLYSIS
The geometry and conformation23 properties of PtiCP were studied by lesnt-squares intensity refinements, combined with information ob+kined from radial distribution (RD) cmes. The geometry was calculated on the basis of ra pammeters, which in.Aude corrections for ski&age effects [16]. Root-mean-square ainplitudes of vibrations (u) and perpendicular correction coeificients (K) v-era calculateti [Z7] for the bisected and the _~rppndicular FHCP co&ormex, based on the valence force field presented in Table 1. The calculated u and R values for the most important interatomic PHCP chstsnces are g&n in Table 2. Figure 1 shoss models for tbe bisected and perpendicular conformers of PEEP, as well as tbe numbering of the atoms. The following asnunptions aoout t.he geometry were mu d e : hexagonal symmetry 13f the phenyl ring; local f& symmetry of tie methyl group; the Cs-Cz-& plane bisects the cycbpropece ring. The geometry of one PHCP canformer could then be described by the follovkg twelve psram&ezs: r(C=C), rI&-C3), r(C3-C4),
209
TABLE
1
Valence force xmstants (in mdyn A-’ and calc!&tioEE on 3-methyl-3-phenyl-yclopropene
Str.
Valence coordinate
Velue
c=c
8.770 4.152 4600 6.115 5.066 4.696
CL-C, G--c. CW C,=-H C SP3-E BeEd
C-W C,-C_ C--H C:--c,-C, C,-C,-H C,-C,-H H-C-H
TOES.
“3 Es ($4: C-C(a)
r(Cs-&),
r(CW),
mdyn
A
ra d-‘)
used
ir
11ornal
coordina’k
Value
Valence coordinate
1.028 0.753 0.515 0.75 0.8 0.642 9.535
c).o.pi
C--H c--C
SP./Str.
C,-G/C,-G CW/CW(o) C-/C-(m) C=C/C=c(p) C=C/C,--c,
0.45* 0.502 0.364 0.7716 -0.3189 0.2895 0.2506
Str.;Eend
0.270 0.163 0.642 0.1187 0.186 0.0518
0.272 G.19 0.05 0.3
r(C,---H).
r(Cs,-‘--E),
LC,.-C,-3’
= LP, IC5-C3-C?,
LC=C-5, 8 (3’-C3-C5-C6) = 8 (C,---C,), L&-C,-H. The bisected conformer (0 ( CJ-C~) = 0” ) and. the perpendicular conformer (6’1&--CA,) = 90”) were at first tested individually. Figure 2 shows the theoretical R.D curves for the best fits obtained for bl&ected azd perpendic~;lar conformers, respectively. The perpendicular conformer is fond to be unacceptable, while f&e bisected conformer is in fairly good accordance with the experimenti data. The main p,vblem in accepting a bkected conformer (0 (C,-C,) = 0” ) is being tied +a the thee? e&al area at 3.1-3.7 A, which is too small. The theoretical peak for the btiezted corxormer is in this region solely due to r:on-bonded C- - - H distancrs, especialiy to the ten 1,4 n?;fi with;& the phenyl ring. T’II,* vznsiderably C - - - U di&ances larger in the 3.1-3.7 A region in-rlicates ti;t F-cm-bonded CC
area
sxpezimenti
c3,stances
also
contrbibuteto some extent. The bisected cor?former was further studied, and by Aaxing the condition imposed upon @(C,--C,,) a much more satkfying RD curve wzs obtzined (se2 Fig. 3). 0 (&-C&j refmed ;O 3S.O”, while at the same ikne the R-fat-tar was greatly improved, Eom 0.9943 to 0.0548. Lfi changed fiorn 125.7” to 121.4”, while t’ne other pzzueterswere only slightly influenced jsee Table 3). The RDxme for the relaxed biseckd mode! described above is shuwn in Fig. 3. It fits tire experime;ltel R-D c-zve nicely, except perhaps for the peak
il0
Rcot-rrean5quare amplitudesoivib~a~ion(uij)andper3endic~lar CprdatiOQcoefficiEQts (S,j for the most promkent interaAamicdistancesin bisectidand pEiaeadica!arconforr;lsrs of 3~e~yl-8-phe~yi-Evclopror=ne.Resukkfrom norm.alcoordirz~te analyses Confc_matisnallyindependent distance:; uy (A) Diet.(i-_j)(Rg) Kij (-4 1 c=c
Q-C, C,S, G-G C_ C v z--H C .cp3--H 5-7(2.42) e-5(2.55) 3-6i2.52)
0.0415 0.0494 0.0466 0.0490 0.0455 0.0771 0.0786 0.0545 0.0699 0.0632
0.00753 o.oos15 0.01ck80 0.00846 0.00351 0.01755 0.05064 0.0027E 0.00730 0.00282
Dist.(i-j)(RU)
UG (A)
Kc- (A)
4-2(2.60) 2-5(2.60) 5-s[2.80) 3-7(3.60) 3-6(4.30) 4-8(5.16) 2-a(5.21) 5-16(2.16) 5-17(3.41) 5-lS(3.89)
o.c750 0.0672 0.0602 a.0637 0.0650 O-r,956 C.0898 0.0995 0.0957 0.0941
0.01130 0.00524 0.00416 0.00136 0.00185 0.00295 0.00094 0.01212 0.00790 0.01006
0.1053 0.1239 O-0815 0.1083 0.1239 0.0845 0.1078 0.1178 O.OSl=? 0.1073 0.1178 0.0817
0.00529 0.00399 0.00291 0.00529 o.co399 0.00291 0.00328 3.00196 0.001i4 0.00328 0.00196 0.00114
Conformatior!-dependegtdistances Bisxted
Perpendicular
4-lO(2.88) 1-6(3.G2) 2-6(3.02) 4-6(3.86) 2-10(3_83 l-10(3.83 4--9(?.53) i-7(4.39) 2-7(439) 4-7(4 99) Z-9(4.98) '1+(4.98)
4-lO(3.33) l-6(3.15) 2-6(3_62) 4-6(3.33) 3-10(3_15 l-lC(3.62 ; r-9(4.55) l-7(4.46) Z-7(4.60) 4-7(4.55) 2+(4.46) l--9(4.80)
0.1046
0.00852
0.0595
0.00594 0.00594
0.08S5 0.0714 0.0631 0.0831 0.1085 0.0923 0.0923 c.07s7 O-G669 0.0869
0.00361 0.00204 0.00204 0.005ii 0.00257 0.00257 0.09165 0.00069 O.OOC69
at ca. 5.2 A, which ticludes co~Lritutio~~~ from the C4 - - - CS and Cz - - - C8 distances. When ‘Lhe vibrational amplitudes of r(Cr, - - - C,) and r[C= - - - C,) were included as variables in the least-squares refkements, they increased by ca. !I.027 A while the R-factor improved to 0.0528 and the discrepancies between theoretical and expe,rimenti RD curves almost vmrished. With this change in refinement scheme the G-CA, dihedral angle was reduced Tom 38 to 36.8”, whZe the other geometrical parx-meterz were not influenced noticeably. Throughout the study al! vibrational amplitudes vieye fixed at the calsula+kd values. For the sake cf consistency the~G&r results zre therefore not included in Table 3. Figure 3 shows that ttia increased ueain the RD 3.1-3-7 A-region for the relaxed bisected mode1 is due to some contributions horn distances between the unsaturated cyclopiopene atoms and the ortizo carbons of the phenyl ring.
211
Fig. 1. Xodels
for tie Lkec’&d and perpendiculzr confo:mer
of 3-methyl-3-~~e--.yl-c~clo-
propene.
The perpendicular F’HCP conformer gives sut&antia.l contribution to t.he RD curve in the 3.1-3.7 .il region (see Fig. 2). Kven if this conformer is rot compatible with t.he ssperimentzl ED data wherl treated separately, it might eventually contribute ti a conformational mixture. A model consisting of variable amounts of +&a btiec-,-led(f?(C,-C,j = 0”) and the perpendicuIx ) = 90”) conformers was therefore te?;ted. All gecmetical parair.(0 (G--c, eters except LB, LC5-C,S, and 0 (C,-C,) were assumed to be identical 5x the two conformers. The results of the refinements for the PHCE’ conformational mistxre is shown i3 Table 3, wMe the theoreticA RD cm.e for this model is-shown in Fig. 3. The R-factor determined for the bisected. + perpesdfcular conformaLional mixture is rzearly as good as that obtzined for the relax& Sisected conformer. The theoretical molecukr intensitjr function for the relaxed bisec’kd model is shown in Fig. 4 tugether wit’h t.he corresponding experimental funtion. The theoretical intensities caktiated for the conformational compotitian given in Table 3, are not shoxn, ;is it is not easy to visually Minguish them from those of the relaxed bisected model.
T---
-
PER?
Pig. 2. Experimental RD-&we for PHCP znd theoretical former (@(C,-C~) = CP) and a perpendicular conformer ence curves. k = 0.0012 A’.
I
RI3 cunies Ear a bisected con(ff(C,-C, j = 9i)” j and differ-
A model based on free rotation around the CS--C_Q bond ~-as also tested, but was clearly inferior to the relaxed bisected model and to the bisected + perpendicukr conformational mixture, and was t.herefors rejected.
Two models were found k~ be in accordance witi the experiment& 3-methyl-3-phenykyc~opropene ek%Lron diffr-zctiort, data. One GZ these ax-responds i;c a relaxed bisecQd model, with a C3SXr dihedral angle of ca. 38”, while t’ne other is a conforrnationai m&Cure composed of 64% of t,he bisected conformer (0 (C,-C,) = 0”) and 36% of tke perpendicular conformer (6’(C3--;=_k) = 30”). It should be noted that the standard deviation for the molar fractions is unuslraUy smaB, co~espond~g tt, I .7% One cannot, drav~ d&.&e comlusions from the present study as to how the kkmctiocs heheen the substituent x-system and ei’;her the cydopropene C=C Double bond or the W&h e,-orbital OCCXLI-. However, the results indicate that, the sUbstif,ueqi I-b r-system interacti more stron~y with the la%er_
213
:,ll,.:,, D
,,,1ll,,! 1
,l'l,lI,i 2
,.:,I::,:i,I!,l.,,r 3
L
,lrl,,,,,~ 5
r(A)
c
Fig. 3. Experimerzti RD curve for PZCP and theoreticai RD curves for tht tno fu-d mode’ti: relaxed b%ecSd (o(C5-Clx) = 3s’); bisected (64%) + perpendiculv (36%) and difference curves. R = 0.0012 A’.
Tne relaxed Sisected conformer model might he descrihd as a compromise between the two kinds of interaction, corresponding to minirnxum total energy. The conformational composition model (64% bisected i 36% perpendicular) interaction might similarly be interpreted as the x-substituent Walsh e,-orbital being ca., 0.36 kcal mol-’ more favomable than the interaction x&h the C:=& x-orbiti. In Table 5 ‘be results obtained for PNCP are compared with some of the very few data available for structura2y related molecules. The PHCP cycloprcpene C=C bond appears to be slightly larger than in unsubstituted cyclopropene [IS], while the Cz-Cs bond is fo;md $0 be practically the same in the ‘&WCcompounds. An increased C=C bond length is in accordance with t!~e generally accepted ideas about the effect of ,m ir:tzraction between a xdonor and *he Walsh e-%-orbital [I93 _ The difference in bond lengt!xs is, however, not large eno-ugh, when t’ne error of the measur2ment.s is taken intc accoun$, to justify a statement to this effect. The C- C bond. in PHCP appears ‘to be larger than in the twc lriohengl-substituted cyclopropenes (bisected conformers) shown in Table 2. X-ray studies do, however, consistently give shorter C=C bonds than do electron difZraction .snd microwave spectroxopy studies. This will therefore probably be th e case also for strained cyclopropene rings.
TABLE3
Results Distarces
:‘rom
leaskquzres
(r,j ii-t_&, arigles
for 3-methyl-3-phenyl-cyclopropane. intensiQ. refklement in degrees. Standard deviationsin parentisses
Perp. r(C=C;
l-335(11) 1_515(16j l-502(26; :.3x3(10) 1.4Gljl) 1.110(6) 1.1376
tiCCt-C,I r(C,-w W,+G) r(C_) T(CSPZ--H) r(C,g-H) @ (bis.) LC,-c,-c, (bk.) LC=C--II L c,-z,-X e:?'x,+z,x,) = siC,<_ti)(bis.)
i5C!.Yla.)
Bis.
BiS_
Bis. t Pcrp.
l-317(7) l.-514(7) l-533(14) 1.503(6) 1.399(l) 1.099(4) 1.125d 125.7(5) 116.2(6) 15o.qrrs.) 113_5(ass.) c).qass)
1.308<*) 1.51@3) 1.545(6) l-513(3) 1.399(0,) l.'i95(2) 1.122~ 12X.4(4) 117.8(3) 150.0(=.) 113_5(ass.; 3&O(9)
1.31i(4) X517(6) 1.53?(12) 1.502(3) 1_839(1j .1.0X(2) 1;124d 122.9(4) 116-l(5) 150_0(aaz) 113.5(ass.j 3_G(us)
~oo.~(sss.) O.XJQS
119.0c 111.1= 90.0(X%) 64.Cy1.8) G-0561
117.6(1.?) 113.0(1.1) 90_0(ass.)
LB (i%-P-j LC,-Cj-CG(perp.) i9
O(a-2-j
lOO.O(ass.)
0.1685
0.0943
^ jwi~ss-]L~~_ CDetermined by wrying the =See Fig. 1 for definition. “R = 1s iwi(I~c)2/r. parameter over an expected parameter range. and for each fixed garameter value doing a Ieast-cqaares analy~khAssu~ed to be O-027 A larger thar! r(C,---H).
0
5
?O
15
20
Fig. 4. Experimental ard keoretical (relaxed and ,he diffewnces between rhe XO.
25
30
bisectedmodel)
35 5 :&-I:
xl
molecular
ictecsity functions
215
Correlation (COII. coeff.
TABLE Tbe
matrix 100).
x
for the bisected Only coefficients
i
perpendicular iarger thm 0.30
cnnform&ional misture (>I 100) are included
of
PIlCP
5
present PHCP reculk dcrivrtives
compved
with
other
sknckulal
resu!ts
for cyclopropene
2nd
its slmp!e
COLTlpZIr;rld
Rci.
Me-Aod
c=c
(A)
1.308(4) 1.312(C) 1.2959(G) 1.254(10)
l.slo(;) 1.51?(a) 1.509(l) l-52(1)
X.513(3) 1.509c3;
ia 20
ED ED MW Mm
4
xii
l-293(4)
1.515,,_(3)
1.470(4)
4
X9
1398C5)
1.516,,-.(6)
1_EOS{7)
rsCPi3L.) PHCP (Sz. +?trp.) CJc;opr~:~-r~e 3.3-~:~':2~-;-1cyd@~o;.Pne 1.2.3~izip~cr~rI-
c,-q
ti)
q--c_-
(A)
C,-CH,
.G
X.545(6) l-531(12)
121.4(4) 122.9(4)
1.52(l)
CYClOpL-OZXlC
t-'sopro=yl-1.2.3tiphCTl~:-C?dOZlroPenc
The corc&tlon matris (Table 4) shows t-hat the G--Z3 and C,-G bond len@hs arc most extensively correlated wi’rh the other parameters. The standard deviation for i(C2-C3) is, however, quite low, and this bond is probably fairly accuratzly determined. The correlation mat& calculzkd for +he re!axed bisected PHCP model is fairly similar to the one in Table 4, b& the correlation coefficient r( Cz-G3 )/LB is reduced -to -0.08. 13(C,--C,) shows si&-nifitxat correlation only with L 5(-0.31). ACKNOR‘LEDGES5EXTS
We are grate-&l to Rag&i!d Seip and Arne _tixenningen for measm-ing the ED intensities and ‘;o Snetid Guxdersen and I%kko Bakken for technical assistence. This eollaoorative effort was made possible by the Admmistration of the University of Letigrad er,d the DAAD (German Academic Exchange Service) O‘II the basis of the cooperation programme 1382-55 between t.he Universities of Leningrad and Hamburg.
1NFEREXCES
.1 F. H. Allen, Acta Crystallogr., Sect. B, 36 {1980) 81. 2 F. II. _Ulen, Acta Crysttogr., Sect-B, 37 (1961) 890. 3 F. H. AUen, Acta Cryst=llogr., Sect. B, 3’7 (1981) 900. 41. N. Domnin, J. Kopf, S. Keyaniyan and h de Meijsre, Tetnzhedron (in press) and references therein. 5 L S. Bartell and 3. P. Guilieroy, J. Chern. Phys., 43 (1965) 647. I 6 I-i. N. Vollhauer and R. H. Echwendemen, J. C&em. Phys., 54 (1,971) 260,268. 7 L. S. Bartell, J. ?. Guilleroy and A. T. Parks, J. Pigs. Chem., 69 (1965) 3043. 8M. Trxttcberg, to be published. 9 G. L. Clozs and H. B_ Khnger, J. Am. Chem. Soc.. 66 (1964) 908. 10 N_ V. Bovin. L. S. Surmina. N. I_ k-akushkina and L G. Bolesov, J. Org. Chem. LJSSR (En& transl-). 13 (1977) 1749. 110. Bastiznsen, 0. Hasse! and F. Risberg, -4~~a Chem. Stand., 9 (1955) 232. 12 8. Andemen, H. M. Seip, T. G. Strand and R. St$levih, Acta Chem Stand., 23 (i969) 322&. 13 A C_ Yxes, Comput. Phys Commur~. 2 (1971) 175. 14T. G. Strand and R. A. Bon&m, J. Chem. PhyL, 40 (1964) i686. 15 C. Tavarc, D. Nico‘& and 31. Roeatit, J. Chim. Phys., 64 (1967) 580. 16 K. Kuchitsu and S. J. Cyvin, in S. J. Cyvin (Ed.), Molecu’ar Structures and Vibrations, Elsevier, Amsterdam, 197 2. Chap. 12. 17R:Stdlevik, H. M. Seip ar.d S. J. Cyvin, Chem. Phys. Lett., 15 (1972) 263. 18 W. M. Stigliani, V. IV. La\ rie and J. C. Li, J. Chem. Phys., 62 (1975) 1890. 19R. Hoffmann, Tetrahedrcn Ltt., (1970) 2907;H. Giinther, ibid., (1970) 5173. 2_ K. B. Wiberg, G. B. EUis:~n, J. J. Wendolsky, X. E. Pratt 2nd M:. D_ Harmony, J. Am. Chem. Sot., 100 (1978) “837.
in The h’etherknds
TEE MOLECULAR STRUCTUI?aE X.X-D CONFOFLMATIONAL BEHAVIOUP, OF 3-METHYL3-PHEh”iTLCYCLOPROPENE
M. TRLW-J?‘FESERG Deparimenf
of Chernistq.
University
of Trondheim,
AVH,
hi-7003
T-ondireim
(Xorway)
-4. DE MEIJERE Fackbereich Chemie, Liniversitir D-2000 Hamburg 23 (B.R.D.)
Hcrnburq,
dl~rh’n-Luth~.-h-iing-Plan
6.
I. N. DOM:MN Irstifufe of Chemistq, ~U.S.S.R.)
University
of Leningrcd,
Srednijpr.
41.
1920&!
Leningad
B-4
ABSTRACT The moiecular structure and conform,ti,~nal propert.ies of 3-methyi-3-phenyl
Interactions between the cyclopropane Walsh e_,-orbit& and T-slbstituents have been studied by a v&e* of methods and for many cliffereni jTpes of x-accept0l-s e,-orbital
as well as T-donors [l-4) znd substituent x-orbitais
_ Maximum is obtained
overlap
between
the Walsh
Zor the scl-called biszckd favourable when the substituent
conformer, which is found to be parkicdarly is a I;-accEptor i 5-73 . With T-donor substituenls the bisec’keci conformer also norm&y the preferred one, but the preference over other conformers not so pronour.ced
as for z-acceptor
substxtients
is
is
[S, 91.
In 3substituted cyclopropenes a r-substituen;; has possiblities of interacting with the Walsh e_.-orbi’kl of the cyclopropen.? ring and with the z-orbital of the cyclopropene double bond. Inter&ion -with the Walsh e,-orbital is espected +A favour a bisected cotiorrner, while interaction Titan cydcpropene z-c3rbitals of the double bond will favour a perpendicular conformer. According to MNDO cakulated heats of -Formation for various 3. substituted cyclopropenes 1.~51nonbisected conform; &ions rue preferred for I;-accep’tor (methorycarbonyl) as weil as for ;: -donor (phenyl) substituent: . Temperature dependent NMR chemical shifts 143 seemed to confkm t’hk behaviour for the 5ee molecules, while X-ray structure studies [4] of 1$,3-tziphenyl0022-286c/S5/$03.30
G 1985
Else\
B.V.
205
,.2,3-triphenykyclopropene showed that cyclopropene and 3-isopropyl-l these molecules adopt bisected ccnformations r&h respect to the Sphenyl groups. The .aim of the present study of 3-nie~yl-3-~lheny’,-cycropIopene (PHCP) is to contibute ‘to the gathering of the experimenti evidence that is necessary in order to reach an understtding of the fcrces operating between ‘;he cyclopropene ring akd a 3-s~ibstitu~ rr-system. EXPERIMENTAL
The sample of 3-methyl-3-phznylcyclopropene was prepared from a--methylstyrene by dibromocarbene addition, monodebromination and dehydrobromination ilO] _ The electron diffraction scattering da&&from the gas were recorded cn the Oslo apparatus 1113 with nozzle-to-plate distances of 435.27 (6 plates) and 205.27 mm (5 plates). Kodak Electron image plates were used and the nozzle tip temperature was 69”‘J during the exposures. The electron wavelength was C.06461 A, as calibrated against diffraction patterns of gaseous benzene, using ro(C-C> - 1.3975 A ss a standard. The estimated standard deviation in the determination of the wavelength is 0.1% Xanges of scaiAering data were 1.000-19.375 and 6.25-43.0 (A-l), with Z s increments of 0.125 and 0.250 (A-l), respectively. The experiienkl data werl processed in the usual way 1123. The intensities were modified by s[fYl -z, and the scattering ampiitudes (f’) were calculated by the partial-wave method 1133, using YartreeFock atomic potentj& 1143 _ The inelastic sca%ering factors used were those of Tavard et *aI. 1151. STRUCTURE
XXXLYSIS
The geometry and conformation23 properties of PtiCP were studied by lesnt-squares intensity refinements, combined with information ob+kined from radial distribution (RD) cmes. The geometry was calculated on the basis of ra pammeters, which in.Aude corrections for ski&age effects [16]. Root-mean-square ainplitudes of vibrations (u) and perpendicular correction coeificients (K) v-era calculateti [Z7] for the bisected and the _~rppndicular FHCP co&ormex, based on the valence force field presented in Table 1. The calculated u and R values for the most important interatomic PHCP chstsnces are g&n in Table 2. Figure 1 shoss models for tbe bisected and perpendicular conformers of PEEP, as well as tbe numbering of the atoms. The following asnunptions aoout t.he geometry were mu d e : hexagonal symmetry 13f the phenyl ring; local f& symmetry of tie methyl group; the Cs-Cz-& plane bisects the cycbpropece ring. The geometry of one PHCP canformer could then be described by the follovkg twelve psram&ezs: r(C=C), rI&-C3), r(C3-C4),
209
TABLE
1
Valence force xmstants (in mdyn A-’ and calc!&tioEE on 3-methyl-3-phenyl-yclopropene
Str.
Valence coordinate
Velue
c=c
8.770 4.152 4600 6.115 5.066 4.696
CL-C, G--c. CW C,=-H C SP3-E BeEd
C-W C,-C_ C--H C:--c,-C, C,-C,-H C,-C,-H H-C-H
TOES.
“3 Es ($4: C-C(a)
r(Cs-&),
r(CW),
mdyn
A
ra d-‘)
used
ir
11ornal
coordina’k
Value
Valence coordinate
1.028 0.753 0.515 0.75 0.8 0.642 9.535
c).o.pi
C--H c--C
SP./Str.
C,-G/C,-G CW/CW(o) C-/C-(m) C=C/C=c(p) C=C/C,--c,
0.45* 0.502 0.364 0.7716 -0.3189 0.2895 0.2506
Str.;Eend
0.270 0.163 0.642 0.1187 0.186 0.0518
0.272 G.19 0.05 0.3
r(C,---H).
r(Cs,-‘--E),
LC,.-C,-3’
= LP, IC5-C3-C?,
LC=C-5, 8 (3’-C3-C5-C6) = 8 (C,---C,), L&-C,-H. The bisected conformer (0 ( CJ-C~) = 0” ) and. the perpendicular conformer (6’1&--CA,) = 90”) were at first tested individually. Figure 2 shows the theoretical R.D curves for the best fits obtained for bl&ected azd perpendic~;lar conformers, respectively. The perpendicular conformer is fond to be unacceptable, while f&e bisected conformer is in fairly good accordance with the experimenti data. The main p,vblem in accepting a bkected conformer (0 (C,-C,) = 0” ) is being tied +a the thee? e&al area at 3.1-3.7 A, which is too small. The theoretical peak for the btiezted corxormer is in this region solely due to r:on-bonded C- - - H distancrs, especialiy to the ten 1,4 n?;fi with;& the phenyl ring. T’II,* vznsiderably C - - - U di&ances larger in the 3.1-3.7 A region in-rlicates ti;t F-cm-bonded CC
area
sxpezimenti
c3,stances
also
contrbibuteto some extent. The bisected cor?former was further studied, and by Aaxing the condition imposed upon @(C,--C,,) a much more satkfying RD curve wzs obtzined (se2 Fig. 3). 0 (&-C&j refmed ;O 3S.O”, while at the same ikne the R-fat-tar was greatly improved, Eom 0.9943 to 0.0548. Lfi changed fiorn 125.7” to 121.4”, while t’ne other pzzueterswere only slightly influenced jsee Table 3). The RDxme for the relaxed biseckd mode! described above is shuwn in Fig. 3. It fits tire experime;ltel R-D c-zve nicely, except perhaps for the peak
il0
Rcot-rrean5quare amplitudesoivib~a~ion(uij)andper3endic~lar CprdatiOQcoefficiEQts (S,j for the most promkent interaAamicdistancesin bisectidand pEiaeadica!arconforr;lsrs of 3~e~yl-8-phe~yi-Evclopror=ne.Resukkfrom norm.alcoordirz~te analyses Confc_matisnallyindependent distance:; uy (A) Diet.(i-_j)(Rg) Kij (-4 1 c=c
Q-C, C,S, G-G C_ C v z--H C .cp3--H 5-7(2.42) e-5(2.55) 3-6i2.52)
0.0415 0.0494 0.0466 0.0490 0.0455 0.0771 0.0786 0.0545 0.0699 0.0632
0.00753 o.oos15 0.01ck80 0.00846 0.00351 0.01755 0.05064 0.0027E 0.00730 0.00282
Dist.(i-j)(RU)
UG (A)
Kc- (A)
4-2(2.60) 2-5(2.60) 5-s[2.80) 3-7(3.60) 3-6(4.30) 4-8(5.16) 2-a(5.21) 5-16(2.16) 5-17(3.41) 5-lS(3.89)
o.c750 0.0672 0.0602 a.0637 0.0650 O-r,956 C.0898 0.0995 0.0957 0.0941
0.01130 0.00524 0.00416 0.00136 0.00185 0.00295 0.00094 0.01212 0.00790 0.01006
0.1053 0.1239 O-0815 0.1083 0.1239 0.0845 0.1078 0.1178 O.OSl=? 0.1073 0.1178 0.0817
0.00529 0.00399 0.00291 0.00529 o.co399 0.00291 0.00328 3.00196 0.001i4 0.00328 0.00196 0.00114
Conformatior!-dependegtdistances Bisxted
Perpendicular
4-lO(2.88) 1-6(3.G2) 2-6(3.02) 4-6(3.86) 2-10(3_83 l-10(3.83 4--9(?.53) i-7(4.39) 2-7(439) 4-7(4 99) Z-9(4.98) '1+(4.98)
4-lO(3.33) l-6(3.15) 2-6(3_62) 4-6(3.33) 3-10(3_15 l-lC(3.62 ; r-9(4.55) l-7(4.46) Z-7(4.60) 4-7(4.55) 2+(4.46) l--9(4.80)
0.1046
0.00852
0.0595
0.00594 0.00594
0.08S5 0.0714 0.0631 0.0831 0.1085 0.0923 0.0923 c.07s7 O-G669 0.0869
0.00361 0.00204 0.00204 0.005ii 0.00257 0.00257 0.09165 0.00069 O.OOC69
at ca. 5.2 A, which ticludes co~Lritutio~~~ from the C4 - - - CS and Cz - - - C8 distances. When ‘Lhe vibrational amplitudes of r(Cr, - - - C,) and r[C= - - - C,) were included as variables in the least-squares refkements, they increased by ca. !I.027 A while the R-factor improved to 0.0528 and the discrepancies between theoretical and expe,rimenti RD curves almost vmrished. With this change in refinement scheme the G-CA, dihedral angle was reduced Tom 38 to 36.8”, whZe the other geometrical parx-meterz were not influenced noticeably. Throughout the study al! vibrational amplitudes vieye fixed at the calsula+kd values. For the sake cf consistency the~G&r results zre therefore not included in Table 3. Figure 3 shows that ttia increased ueain the RD 3.1-3-7 A-region for the relaxed bisected mode1 is due to some contributions horn distances between the unsaturated cyclopiopene atoms and the ortizo carbons of the phenyl ring.
211
Fig. 1. Xodels
for tie Lkec’&d and perpendiculzr confo:mer
of 3-methyl-3-~~e--.yl-c~clo-
propene.
The perpendicular F’HCP conformer gives sut&antia.l contribution to t.he RD curve in the 3.1-3.7 .il region (see Fig. 2). Kven if this conformer is rot compatible with t.he ssperimentzl ED data wherl treated separately, it might eventually contribute ti a conformational mixture. A model consisting of variable amounts of +&a btiec-,-led(f?(C,-C,j = 0”) and the perpendicuIx ) = 90”) conformers was therefore te?;ted. All gecmetical parair.(0 (G--c, eters except LB, LC5-C,S, and 0 (C,-C,) were assumed to be identical 5x the two conformers. The results of the refinements for the PHCE’ conformational mistxre is shown i3 Table 3, wMe the theoreticA RD cm.e for this model is-shown in Fig. 3. The R-factor determined for the bisected. + perpesdfcular conformaLional mixture is rzearly as good as that obtzined for the relax& Sisected conformer. The theoretical molecukr intensitjr function for the relaxed bisec’kd model is shown in Fig. 4 tugether wit’h t.he corresponding experimental funtion. The theoretical intensities caktiated for the conformational compotitian given in Table 3, are not shoxn, ;is it is not easy to visually Minguish them from those of the relaxed bisected model.
T---
-
PER?
Pig. 2. Experimental RD-&we for PHCP znd theoretical former (@(C,-C~) = CP) and a perpendicular conformer ence curves. k = 0.0012 A’.
I
RI3 cunies Ear a bisected con(ff(C,-C, j = 9i)” j and differ-
A model based on free rotation around the CS--C_Q bond ~-as also tested, but was clearly inferior to the relaxed bisected model and to the bisected + perpendicukr conformational mixture, and was t.herefors rejected.
Two models were found k~ be in accordance witi the experiment& 3-methyl-3-phenykyc~opropene ek%Lron diffr-zctiort, data. One GZ these ax-responds i;c a relaxed bisecQd model, with a C3SXr dihedral angle of ca. 38”, while t’ne other is a conforrnationai m&Cure composed of 64% of t,he bisected conformer (0 (C,-C,) = 0”) and 36% of tke perpendicular conformer (6’(C3--;=_k) = 30”). It should be noted that the standard deviation for the molar fractions is unuslraUy smaB, co~espond~g tt, I .7% One cannot, drav~ d&.&e comlusions from the present study as to how the kkmctiocs heheen the substituent x-system and ei’;her the cydopropene C=C Double bond or the W&h e,-orbital OCCXLI-. However, the results indicate that, the sUbstif,ueqi I-b r-system interacti more stron~y with the la%er_
213
:,ll,.:,, D
,,,1ll,,! 1
,l'l,lI,i 2
,.:,I::,:i,I!,l.,,r 3
L
,lrl,,,,,~ 5
r(A)
c
Fig. 3. Experimerzti RD curve for PZCP and theoreticai RD curves for tht tno fu-d mode’ti: relaxed b%ecSd (o(C5-Clx) = 3s’); bisected (64%) + perpendiculv (36%) and difference curves. R = 0.0012 A’.
Tne relaxed Sisected conformer model might he descrihd as a compromise between the two kinds of interaction, corresponding to minirnxum total energy. The conformational composition model (64% bisected i 36% perpendicular) interaction might similarly be interpreted as the x-substituent Walsh e,-orbital being ca., 0.36 kcal mol-’ more favomable than the interaction x&h the C:=& x-orbiti. In Table 5 ‘be results obtained for PNCP are compared with some of the very few data available for structura2y related molecules. The PHCP cycloprcpene C=C bond appears to be slightly larger than in unsubstituted cyclopropene [IS], while the Cz-Cs bond is fo;md $0 be practically the same in the ‘&WCcompounds. An increased C=C bond length is in accordance with t!~e generally accepted ideas about the effect of ,m ir:tzraction between a xdonor and *he Walsh e-%-orbital [I93 _ The difference in bond lengt!xs is, however, not large eno-ugh, when t’ne error of the measur2ment.s is taken intc accoun$, to justify a statement to this effect. The C- C bond. in PHCP appears ‘to be larger than in the twc lriohengl-substituted cyclopropenes (bisected conformers) shown in Table 2. X-ray studies do, however, consistently give shorter C=C bonds than do electron difZraction .snd microwave spectroxopy studies. This will therefore probably be th e case also for strained cyclopropene rings.
TABLE3
Results Distarces
:‘rom
leaskquzres
(r,j ii-t_&, arigles
for 3-methyl-3-phenyl-cyclopropane. intensiQ. refklement in degrees. Standard deviationsin parentisses
Perp. r(C=C;
l-335(11) 1_515(16j l-502(26; :.3x3(10) 1.4Gljl) 1.110(6) 1.1376
tiCCt-C,I r(C,-w W,+G) r(C_) T(CSPZ--H) r(C,g-H) @ (bis.) LC,-c,-c, (bk.) LC=C--II L c,-z,-X e:?'x,+z,x,) = siC,<_ti)(bis.)
i5C!.Yla.)
Bis.
BiS_
Bis. t Pcrp.
l-317(7) l.-514(7) l-533(14) 1.503(6) 1.399(l) 1.099(4) 1.125d 125.7(5) 116.2(6) 15o.qrrs.) 113_5(ass.) c).qass)
1.308<*) 1.51@3) 1.545(6) l-513(3) 1.399(0,) l.'i95(2) 1.122~ 12X.4(4) 117.8(3) 150.0(=.) 113_5(ass.; 3&O(9)
1.31i(4) X517(6) 1.53?(12) 1.502(3) 1_839(1j .1.0X(2) 1;124d 122.9(4) 116-l(5) 150_0(aaz) 113.5(ass.j 3_G(us)
~oo.~(sss.) O.XJQS
119.0c 111.1= 90.0(X%) 64.Cy1.8) G-0561
117.6(1.?) 113.0(1.1) 90_0(ass.)
LB (i%-P-j LC,-Cj-CG(perp.) i9
O(a-2-j
lOO.O(ass.)
0.1685
0.0943
^ jwi~ss-]L~~_ CDetermined by wrying the =See Fig. 1 for definition. “R = 1s iwi(I~c)2/r. parameter over an expected parameter range. and for each fixed garameter value doing a Ieast-cqaares analy~khAssu~ed to be O-027 A larger thar! r(C,---H).
0
5
?O
15
20
Fig. 4. Experimental ard keoretical (relaxed and ,he diffewnces between rhe XO.
25
30
bisectedmodel)
35 5 :&-I:
xl
molecular
ictecsity functions
215
Correlation (COII. coeff.
TABLE Tbe
matrix 100).
x
for the bisected Only coefficients
i
perpendicular iarger thm 0.30
cnnform&ional misture (>I 100) are included
of
PIlCP
5
present PHCP reculk dcrivrtives
compved
with
other
sknckulal
resu!ts
for cyclopropene
2nd
its slmp!e
COLTlpZIr;rld
Rci.
Me-Aod
c=c
(A)
1.308(4) 1.312(C) 1.2959(G) 1.254(10)
l.slo(;) 1.51?(a) 1.509(l) l-52(1)
X.513(3) 1.509c3;
ia 20
ED ED MW Mm
4
xii
l-293(4)
1.515,,_(3)
1.470(4)
4
X9
1398C5)
1.516,,-.(6)
1_EOS{7)
rsCPi3L.) PHCP (Sz. +?trp.) CJc;opr~:~-r~e 3.3-~:~':2~-;-1cyd@~o;.Pne 1.2.3~izip~cr~rI-
c,-q
ti)
q--c_-
(A)
C,-CH,
.G
X.545(6) l-531(12)
121.4(4) 122.9(4)
1.52(l)
CYClOpL-OZXlC
t-'sopro=yl-1.2.3tiphCTl~:-C?dOZlroPenc
The corc&tlon matris (Table 4) shows t-hat the G--Z3 and C,-G bond len@hs arc most extensively correlated wi’rh the other parameters. The standard deviation for i(C2-C3) is, however, quite low, and this bond is probably fairly accuratzly determined. The correlation mat& calculzkd for +he re!axed bisected PHCP model is fairly similar to the one in Table 4, b& the correlation coefficient r( Cz-G3 )/LB is reduced -to -0.08. 13(C,--C,) shows si&-nifitxat correlation only with L 5(-0.31). ACKNOR‘LEDGES5EXTS
We are grate-&l to Rag&i!d Seip and Arne _tixenningen for measm-ing the ED intensities and ‘;o Snetid Guxdersen and I%kko Bakken for technical assistence. This eollaoorative effort was made possible by the Admmistration of the University of Letigrad er,d the DAAD (German Academic Exchange Service) O‘II the basis of the cooperation programme 1382-55 between t.he Universities of Leningrad and Hamburg.
1NFEREXCES
.1 F. H. Allen, Acta Crystallogr., Sect. B, 36 {1980) 81. 2 F. II. _Ulen, Acta Crysttogr., Sect-B, 37 (1961) 890. 3 F. H. AUen, Acta Cryst=llogr., Sect. B, 3’7 (1981) 900. 41. N. Domnin, J. Kopf, S. Keyaniyan and h de Meijsre, Tetnzhedron (in press) and references therein. 5 L S. Bartell and 3. P. Guilieroy, J. Chern. Phys., 43 (1965) 647. I 6 I-i. N. Vollhauer and R. H. Echwendemen, J. C&em. Phys., 54 (1,971) 260,268. 7 L. S. Bartell, J. ?. Guilleroy and A. T. Parks, J. Pigs. Chem., 69 (1965) 3043. 8M. Trxttcberg, to be published. 9 G. L. Clozs and H. B_ Khnger, J. Am. Chem. Soc.. 66 (1964) 908. 10 N_ V. Bovin. L. S. Surmina. N. I_ k-akushkina and L G. Bolesov, J. Org. Chem. LJSSR (En& transl-). 13 (1977) 1749. 110. Bastiznsen, 0. Hasse! and F. Risberg, -4~~a Chem. Stand., 9 (1955) 232. 12 8. Andemen, H. M. Seip, T. G. Strand and R. St$levih, Acta Chem Stand., 23 (i969) 322&. 13 A C_ Yxes, Comput. Phys Commur~. 2 (1971) 175. 14T. G. Strand and R. A. Bon&m, J. Chem. PhyL, 40 (1964) i686. 15 C. Tavarc, D. Nico‘& and 31. Roeatit, J. Chim. Phys., 64 (1967) 580. 16 K. Kuchitsu and S. J. Cyvin, in S. J. Cyvin (Ed.), Molecu’ar Structures and Vibrations, Elsevier, Amsterdam, 197 2. Chap. 12. 17R:Stdlevik, H. M. Seip ar.d S. J. Cyvin, Chem. Phys. Lett., 15 (1972) 263. 18 W. M. Stigliani, V. IV. La\ rie and J. C. Li, J. Chem. Phys., 62 (1975) 1890. 19R. Hoffmann, Tetrahedrcn Ltt., (1970) 2907;H. Giinther, ibid., (1970) 5173. 2_ K. B. Wiberg, G. B. EUis:~n, J. J. Wendolsky, X. E. Pratt 2nd M:. D_ Harmony, J. Am. Chem. Sot., 100 (1978) “837.