摘要:

2060 J.C.S. Perkin I1Molecular Polarisability. A Conformational Study of Some SubstitutedArylcyclopropanesBy Manuel J. Aroney," Kingsley E. Calderbank, and Heather J. Stootman, School of Chemistry, Universityof Sydney, Sydney, New South Wales, AustraliaThe dipole moments and molar Kerr constants of the following substituted cyclopropanes have been measured incyclohexane solution : 1 ,I -dichloro-2-p-chlorophenyl-2-methylcyclopropane, 1 ,I -dichloro-2-p-tolylcyclopro-pane, 1 ,I -dichloro-2-mesitylcyclopropane, 1 ,I -dichloro-2,2-diphenylcyclopropane, 1 ,I -dichloro-2,2-di methyl-3-phenylcyclopropane, 1 ,I -dichloro-2,2,3,3-tetra~ethylcyclopropane, hexabromocyclopropane, 1 ,I -dibromo-2-phenylcyclopropane, 1 ,I -dibromo-2-p-tolylcyclopropane, 1 ,I -dibromo-2-p-bromophenylcyclopropane, and 1 ,I -dibromo-2.2-diphenylcyclopropane.The data are analysed to deduce the preferred solution state conformations.IN arylcyclopropanes the conjugative interactionbetween the C, nuclear electrons and the li electronsystem of the aromatic substituent group is maximal forconformations in which the aromatic and cyclopropylgroup planes are mutually ~rthogonal.l-~ The reson-ance stabilisation of geometric forms of this type hasbeen experimentally verified in the case of phenylcyclo-p r ~ p a n e . ~ It was shown by Le Fevre et al.,5 however,that insertion of a vicinal (cis) chloro-substituent inphenylcyclopropane causes a steric deflection of thephenyl group away from the preferred ' orthogonal ' dis-position.In this work we explore further the com-petitive steric and mesomeric influences in a variety ofsubstituted phenylcyclopropanes.EXPERIMENTALMaterials, Apparatus, etc.-The solutes were preparedby standard procedures 677 and were purified immediatelybefore use to give : l,l-dichloro-2-p-chlorophenyl-2-methyl-cyclopropane, b.p. 135-136" at ca. 8-5 nimHg; 1,l-di-chloro-2-p-tolylcyclopropane, b.p. 138-139" a t ca. 31mmHg ; l,l-dichloro-2-mesitylcyclopropane, b.p. 89-9 1"at ca. 0-7 mmHg ; 1, l-dichloro-2,2-diphenylcyclopropane,m.p. 110-1 12"; 1,l-dichloro-2,2-dimethyl-3-phenylcyclo-propane, b.p. 111-112" at GU. 7 mmHg; 1,l-dichloro-* G. L. Closs and H. B. Klinger, J . Amer. Chem. SOC., 1965, 87,4 L. V. Vilkov and N. I. Sadova, Doklady Akad.Nauk.S.S.S.R., 1968, 162, 565.5 R. S. Armstrong, M. J. Aroney, A. Hector, P. Hopkins,R. J. W. Le Fbvre, and W. Luttke, J . Chem. SOC. ( B ) , 1971, 1499.6 M. Makosza and M. Wawrzyniewicz, Tetrahedron Letters,1969, 53, 4659.W. A. Bernett, J . Chem. Educ., 1967, 44, 17.J. P. Pete, Bull. SOC. chim. France, 1967, 357.3265.2,2,3,3-tetramethylcyclopropane, n1.p. 51-5-52' ; hexa-bromocyclopropane, n1.p. 193-195" ; l,l-dibromo-2-phenylcyclopropane, b.p. 86-87" at GU. 1 mmHg; 1,l-dibromo-2-~-tolylcyclopropane, b.p. 151-153" at ca. 29nimHg ; l,l-dibrorno-2-p-bromophenylcyclopropane, m.p.69-7 1" ; and l,l-dibromo-2,2-diphenylcyclopropane, m.p.15 1-1 52". Cyclohexane, as solvent, was dried oversodium, distilled, and then stored with sodium. Thefollowing constants apply for the solvent a t 25": E~ =2.0199, dl = 0.77389, (nl), = 1.4235, 107(B,), = 0.054,1014(,K1) = 1.35.The apparatus, techniques, symbolsused, and methods of calculation have been describedbefore.*-ll The experimental results are summarised inTable 1.DISCUSSIONConformations of the 2-Aryl-1 ,l-dichlorocyclopropalzes.-With each of the 2-aryl-1 , l-dichlorocyclopropanesexamined, theoretical molar Kerr constants were calcu-lated for conformations defined by angles of rotation 4 ofthe phenyl group from the reference ' orthogonal ' modelshown in Figure 1 for which 4 = 0". The sense of therotation is away from the CCl, grouping as indicated bythe arrow in Figure 1. The computational procedure is7 S. W. Tobey and R.West, J . Amev. Chem. SOC., 1964, 86,1459.8 C. G. Le Fbvre and R. J. W. Le Fbvre, Rev. Pure Appl.Chem., 1955, 5, 261.9 R. J. W. Le Fbvre, ' Dipole Moments,' Methuen, London,3rd edn., 1953.10 C . G. Le F h r e and R. J. \V. Le Fkvre, in ' Physical Methodsof Organic Chemistry,' ed. A. Weissberger, Interscience, NewYork, 3rd edn., vol. 1, ch. XXXVI, p. 2459.11 R. J. W. Le Fevre and G. L. D. Ritchie, J . Chem. Soc.,1963, 49331973 2061summarised in ref. 12. For each conformational formstudied the elements of the molecular polarisabilitytensor matrix bss, by,, etc., were calculated, with referenceto the system of axes, X,Y,Z of Figure 1, from additivityof component group parameters. The following bondand group polarisability data * were used: b,(cyclo-propane) = b,(cyclopropane) = 6.00, b3(cyclopro-pane) = 4.55; l3 br,(C-H) = bT(C-H) = bv(C-H) =0'65; l4 bL(C-cl) 3-44, bT(C-C1) = bv(c-c1) 2.05;and each of the bonds C(cyc1opropane)-C1 and C( cyclo-propane)-Me was taken l9 in each case as 56" while thecorresponding angle with the C(pheny1)-C(cyclopropy1)bond was assumed to be 51.5" (from ref.4). Trialcalculations were made to show that small variations(zfr2") in these angles do not significantly affect theconclusions. A test application of the group polaris-ability data was made in calculating the molar Kerrconstant of phenylcyclopropane using an electric momentTABLE 1Molar poiarisations and refractions, dipole moments, and molar Kerr constants (from observations on cyclohexanesolutions a t aso)ConcentrationrangeSolute 105w,1 , 1 -l>ichloro-2-p-chlorophenyl-2-methylcyclo-1,l -Dichloro-2-~-tolylcyclopropane 579-48291 , l-Dichloro-2-mesitylcyclopropane 388-291 1l,l-Dichloro-2,2-diphenylcyclopropanc 1295-45311 , 1 -Dichloro-2,2,3,3- tetramethylcyclopropane 3 19-2 189Iiexabromocyclopropane 411-1437I , l-Dibromo-2-phenylcyclopropane 506-70291,l-Dibromo-2-~-tolylcyclopropane 1148-46961 , 1 -Dibromo-2,2-diphenylcyclopropane 770-1 42061 1-3074propaneI , l-Dichloro-2,2-dimethyl-3-phenylcyclopropane 11 97-41 39I , I -Dibronio-2-t)-bromophenylcyclopropane 914-3467ME1 *2.002.201.831.602.193.150.231.361.611.1 11.15P *0.3940.3400.3200.3710.3260.2790.7860.5660.5340.6290-514Y *0.0510.0530.0560.0750.0530.0220.0490.0540.0550.0550.0698 *- 21.86-358.49- 18.931.020.22.43020.7- 17.2- 9.37150 54.0 2.13152 63-8 4-04155 73-8 1.95161 58.9 2.20166 43-3 2.43130 54.0 1.89150 59.9 2.06138 62-4 1.88153 79.9 1-8464-7 61.2 015.925.4- 67.988.643.617.2- 1.179.5- 83.8- 45.3* Incremciital changes in the dielectric constants, densities, refractive indices, and Kerr constants (AE, Ad, An, and AB, respec-tively) were measured for solutions having solute weight fractions w,.The coefficients, ME,, f5, y, and 6, were derived from therelations: C ( E ~ = C ~ E / C W , ; (3 = ZAd/d,Cw,; y = CAn/u,Xw,; 8 = CAB/B,Cw,. t Calculated on the basis that DP = 1.05 RD.$ The term x(mKa) refers to the solute molar Kerr constant at infinite dilution.ClFIGURE 1 Orthogonal model for conformations ofsubstituted phenylcyclopropanesb[,(C,r-CH,) = 3.4, b~(Car-CH3) = 2.0, bv(Car-CH3) =2.3; l6 bIJ(C2,r-CI) 4.3, bT(Car-Cl) = 2-05, bv(Ca,-Cl) =1.5; l7 bl(mesity1) = bT(mesity1) = 16.4,, bv(mesity1) =1l-G8.l8 The angle between the cyclopropane ring plane* The polarisability semi-axes of molecules b,, b,, or b,, or ofbonds and groups bL, bT, or bv are quoted in A3 units.If R.J. W. Le Fhvre, Adv. Phys. Org. Chem., 1965, 3, 1.l3 &I. J. Aroney, R. J. W. Le Fhvre, W. Luttke, G. L. D.Ritchie, and P. J. Stiles, Austral. J . Chem., 1968, 21, 2551.l4 R. J. W. Le Fbvre, B. J. Orr, and G. L. D. Ritchie, J .Chem.SOC. ( B ) , 1966, 273.of 0.46 D (from dielectric loss measurements 20) directedalong the C(cyclopropy1)-C(pheny1) bond axis. The,K(calc.) thus derived €or this molecule has a spread ofonly four units, (21-25) x 10-l2, so that it is not possibleto differentiate between the various allowable conform-ations; the experimental oo(mK2) is 26 (& 2) x 10-l2.The direction of action of the measured molecular dipolemoment was taken along the bisector axis of the C1-C-C1grouping except in the case of 1 ,l-dichloro-2-~-chloro-phenyl-2-methylcyclopropane and 1,l-dichloro-2-p-tolyl-cyclopropane. For each of these two molecules thelocation was calculated on the basis that p(resu1tant) isthe vector sum of the components pa and pb (as shown inFigure 1) where pa equals, in turn, 1-91 D (the momentof 1 ,l-dichloro-2-phenylcyclopropane) and 2.05 D (themoment of l,l-dichloro-2-methyl-2-phenylcyclopropane).The vector components pb thus derived are respectively1.64 and -0.52 D.The former is 0.43 D lower than themoment reported by Nishida et for P-chlorophenyl-cyclopropane and this we attribute to an inductivewithdrawal of electrons from the phenylcyclopropanel5 M. J. Aroney, K. E. Calderbank, R. J. W. Le Fbvre, andR. I<. Pierens, J . Chem. SOC. ( B ) , 1969, 159.l6 R. J. W. Le Fbvre and L. Radom, J . Chem. SOC. ( B ) , 1967,1295.l7 K. J. W. Le Fbvre and B. P. Rao, J . Chem. SOC., 1958, 1465.P. H. Gore, J. A. Hoskins, R. J. W. Le Fkvre, L. Radom,19 J . M. O'Gorman and V. Schomaker, J .Amer. Chewz. SOL,*O M. J. Aroney, S. Filipczuk, and H. J. Stootman, unpublished2 1 S. Nishida, I. Bloritani, and T. Sato, J. Amer. Chem. Soc.,and G. L. D. Ritchie, J . Chern. SOC. ( B ) , 1969, 485.1946, 68, 1138.data.1967, 89, 68852062 J.C.S. Perkin I1system by the CC1, group. The calculations for 1,l-dichloro-2-~-chlorophenyl-2-methylcyclopropane, 1,l-dichloro-2-$-tolylcyclopropane, and 1,l-dichloro-2-mesitylcyclopropane are summarised in Figure 2 whereinthe variation in ,K(Calc.) with angles of rotation0" < + < 180" is shown for each case. Also included in15Ot,..''. , IFIGURE 2 Plot of 101zmI< against 4 for A, l,l-dichloro-%p-tolylcyclopropane ; B, 1 , l -dichloro-2-mesitylcyclopropane ; C,1,l -dichloro-2-p-chlorophenyl-2-methylcyclopropane ; and D,l,l-dichloro-2-~-chlorophenylcyclopropaneFigure 2 are the corresponding calculations for 1,l-dichloro-2-$-chlorophenylcyclopropane for which LeF h r e et aL5 had reported an experimental 03(mK2) inCCl, of -104 x though they did not attempt atheoretical interpretation of this datum.From Figure 2 we see that accord between theoreticalmolar Kerr constants and those from experiment isachieved when + equals 53 or 177" for l,l-dichloro-2-$-chlorophenylcyclopropane, 60 or 166" for 1, l-dichloro-2-$-chlorophenyl-2-methylcyclopropane, 65 or 160" forl,l-dichloro-2-~-tolylcyclopropane, and 76 or 150" forl,l-dichloro-2-mesitylcyclopropane. Examination ofscale molecular models shows clearly that, in each case,the larger 4 value describes a conformation which isprecluded on steric grounds. This is indicated also bycalculation using the appropriate geometric parametersfrom refs.4 and 19 and standard van der Waals radii.,,Our conclusions are summarised in Table 2 togetherwith the results of previous work from ref. 5.HCIAThe mean value of + for the five 1,l-dichloro-2-phenylcyclopropanes is 60" ( 4 3 " standard deviation).This is larger than the estimate of 30" reported byArbuzov et for 1 , 1-dichloro-2-phenylcyclopropane.If the ortho-hydrogen atoms of the phenyl are replacedby methyl groups the steric deflection by the chlorineUniversity Press, New York, 3rd edn., p. 260.Izuest. Akad. Nauk S.S.S.R., Sev. Khim., 1972, 21, 461.22 L.Pauling, 'The Nature of the Chemical Bond,' Cornell23 B. A. Arbuzov, A. N. Vereshchagin, and S. G. Vul'fson,atoms is greater and the angle of rotation 4 rises to ca.76". The degree of conjugative interaction between theTABLE 2Preferred solution-state conformations of molecules AR1 R2 Solvent 4 (") Ref.Ph H CCl, 56 * 5Ph Me CCI, 65 5P-ClCeH, H CCl, 53 Present workP-C1C,H, Me C6H12 60 Present workp-MeC6H4 H C6H12 65 Present workMesityl H C6H12 76 Present work* From curve A of Figure 3 in ref. 5.phenyl and cyclopropyl ring systems is progressivelylowered as 4 increases though it has been shown byBernett that, on the basis of the bent bond model forbonding in cyclopropane, overlap between ~ $ 5 hybridorbitals with the $ orbital of an adjacent aromaticcarbon atom is appreciable even for 4 as large as 60".In the case of l,l-dichloro-2,2-diphenylcyclopropanethe variation of ,K(C~~C..> with angles of rotation + isshown in Figure 3.The unbroken curve refers to thesymmetric case in which each phenyl ring is rotated byFIGURE 3 Plot of 1012,K against 4 for A and C, 1,l-dichloro-2,2-diphenylcyclopropane ; and B, l,I-dichloro-2,2-dirr,ethyl-3-phenylcyclopropanethe same angle + away from the CCl, grouping while thebroken line applies to (equal) rotations q5 in which onephenyl ring is rotated away from the CCl, group and theother phenyl ring is rotated towards it. Four values oi + are theoreticallv allowable but of these only + = ca. 70"(symmetric) corresponds to a sterically permissibleconformation. De Lacy and Kennard 24 have recentlyreported an X-ray structure analysis for 1, l-dichloro-2,2-bis-fi-chlorophenylcyclopropane ; they show thateach aromatic ring has a disposition 4 of ca.80" in thesolid state configuration.Finally we consider l,l-dichloro-2,2-dimethyl-3-phenylcyclopropane for which theoretical ,K values areplotted against 4 in Figure 3. The contribution of theC (cyclopropyl) Me, group to the overall molecular24 T. P. De Lacy and C. H. L. Kennard, J.C.S. Perkin 11, 1972,21411973 2063polarisability anisotropy is uncertain. An attempt wasmade to extract an estimate of this from measurementson the model compound l,l-dichloro-2,2,3,3-tetramethyl-cyclopropane. The observed molar Ken constant(43.6 x 10-l2) when analysed in terms of the permanentelectric moment (2.43 D) and the cyclopropane, C-H,and C-C1 group polarisabilities quoted earlier, leads to anear equal polarisability contribution of the two CMe2groups along the X,Y,Z directions.This was assumedalso to be the case with the CMe, group in 1,l-dichloro-2,2-diniethyl-3-plienylcyclopropane. Two conformersare tlieorctically possible with + ca. 100 or alternativelyca. 134". The former value is preferred since it corre-sponds to a conformation which is much less hinderedsterically than the latter.Hexa bromocyclopropane Polarisabilities .-The principalpolarisability semi-axes of hexaklromocyclopropane maybe derived from the experimental molar Kerr constantand the t.lectron polarisation EP using equations (1)and (2) since, for this molecule, b, = b, =I= b, where b,is located along the three-fold symmetry axis.ThemK = 47Cfv$(b, - b3)2/405kT~PE P = 4xN(2b1 + bJ/9(1)(2)term 1)E' is the distortion polarisation which equals themeasured a;Pz (64-7 cm3). In the absence of relevantrefractivity dispersion data we assume that E P =0-95RD -- 58.1 cm3. Solution of the equations leads totwo mathematically possible sets of bi values : b, = b, =25.02, b, = 19.17, or, alternatively, b, = b, = 21-12,b, = 26.97. From these molecular parameters can bederived estimates of the polarisability semi-axes of theC(cyc1opropane)-Br bond by a procedure similar to thatused in ref. 5 to specify the C(cyc1opropane)-C1 polaris-abilities.The Br-C-Br angle was assumed to be 112"by analogy with the corresponding Cl-C-C1 and F-C-Fbond anglcs.1g~25~26 Two sets of C(cyc1opropane)-Brbond data emerge: bL(C-Br) = 2.65, &(C-Br) =bv(C-Br) = 4.04, corresponding to bl(C3Br6) > b,(C3Br6),and, alternatively, bL(C-Br) = 5.09, bT(C-Br) =bv(C-Br) = 2.82 when b,(C,Br,) < b3(C3Br6). TheDc(C-Br) : bT(C-Br) ratios are respectively 0.66 and 1.80;the latter alone is of the order of magnitude expected fora C-Br bond from previous determinations of C-Brpolarisabilities in a variety of molecular e~~ironments(see Table 22 on p. 50 of ref. 12 and p. 4936 of ref. 11).Thus we deduce that the C(cyc1opropane)-Br bondsemi-axes are best specified as bL(C-Br) = 5.09,hT(C-Br) = bv(C-Br) = 2.82 and these values are usedi n the subscquent calculations.Conformations of 2-Ar3~1-1,1-dibromocyclo~ro~anes.-The procedure is analogous to that used for the dichloro-derivatives.The following additional polarisabilitydata are required: bL(C,,-Br) = 6.3, bT(C,,-Br) = 2.5,bv(C,,-Br) = 2.2.l' The Br-C-Br angle was retainedas 112" throughout. The dipole moment vectors ofl,l-dibromo-2-phenylcyclopropane and of 1, l-dibromo-2,2-diphenylcyclopropane (1 -89 and 1-54 D respectively)were located along the bisector of the CBr, angle. With1 ,l-dibromo-2-$-tolylcyclopropane and l,l-dibromo-2-@-bromophenylcyclopropane the moment directions werederived vectorially on the basis that p(observed) iscomposed of p( l,l-dibromo-2-phenylcyclopropane) and asecond vector component directed along the phenylI,4-axis. The theoretical molar Kerr constants thusobtained were compared with the appropriate experi-mental values of Table 1; accord was achieved when4 = 72 or 158" for 1 ,l-dibromo-2-phenylcyclopropane,67 or 149" for 1 ,1-dibromo-2-$-to1y1cyc10propane1 61 or168" for 1 ,l-dibromo-2-~-bromophenylcyclopropane. A5in the case of the chloro-analogues, the larger 4 estimatescorrespond to structures which are precluded on stericgrounds.The mean value of $ for the three 1,l-di-bromo-2-phenylcyclopropanes is 67 (56") ; this isappreciably larger than that (40") reported for 1,l-dibromo-2-phenylcyclopropane by Arbuzov et aZ.= Theapparent small difference in the conformational para-meter $ between the dichloro- and the dibromo-phenyl-cyclopropanes is probably not related to the size of thehalogen as the phenyl ring does not occupy spaceadjacent to either the C1 or Br group when 4 is of theorder of 60". Most likely the phenyl group is deflectedby the cis-halogen atom away from the resonancefavoured bisected disposition (4 = 0') and it is, in turn,further rotated through steric interaction between thephenyl ortho-hydrogen atoms and the (cyclopropyl)methylene group. Finally we note that for 1,l-dibromo-2,2-diphenylcyclopropane four values of 4 are theoretic-ally possible from analysis of the molar Kerr constant:69 or 161" (symmetric) and 46 or 134" (asymmetric).The 4 (symmetric) estimate of 69" alone is stericallqreasonable and agrees closely with the conformatior[ca. 70" (symmetric)] for l,l-dichloro-2,2-diplienylcyclo-propane.The award of a Commonwealth Postgraduate Studcnt-ship to H. J. S. and suppoi-t from the Australian ResearchGrants Committee are gratefully acknowledged.[3/817 Received, 16th .4pvil, 1973125 P. 1'. Rarzdain, N. I . Gracheva, and N. V. Alekseev, Zhzw.26 J. F. Chiang and W. A. Bernett, Tetrahedron, 1971, 27, 975.Stvukt. Khinz., 1972, 13, 717

ISSN:1472-779X    

DOI:10.1039/P29730002060

出版商:RSC    

年代:1973

数据来源: RSC