Nuclear Magnetic Resonance Studies of Some 1,1-Difluoro-3-Phenylcyclobutane Derivatives Citation Takahashi, Masaaki (1962) Nuclear Magnetic Resonance Studies of Some 1,1-Difluoro-3-Phenylcyclobutane Derivatives. Master's thesis, California Institute of Technology. doi:10.7907/481A-5Q94. https://resolver.caltech.edu/CaltechTHESIS:05062010-112117806 Abstract 1-Difluoro-2, 2-dichloro-3-methy1-3-phenylcyclobutane has been prepared by the cycloacidition of a-methylstyrene to 1,1-difluoro2, 2-dichloroethylene. A 2 cps long-range H-F spin-spin coupling has been observed over five consecutive saturated bonds in 1,1-difluoro2, 2-dichloro-3-methyl-3-phenylcyclobutane, involving one of the fluorines at the 1-position and the protons of the 3-methyl group. Analysis of the spectrum and that of the stereospecifically labeled 4-deutero derivatives suggest that the fluorine involved is the one cis to the methyl group. The n. m. r. studies of 1,1-difluoro-3-bromo-3-phenylcyclobutane which was obtained by bromination of 1,1-difluoro-3-phenylcyclobutane with N-bromosuccinimide indicate that this molecule has on the average a more nearly planar cyclobutane ring than that of 1,1- difluoro-2, 2-dichloro-3-methyl-3-phenylcyclobutane. The four protons of the 2- Etna 4-positions are nearly magnetically equivalent, so that the spectrum of this compound is almost that of an ABX_4 system rather than an ABX_2Y_2 system. The theoretical calculations suggest that the chemical shift difference between X and Y is on the order of 1-2 cps. The chemical shift difference between the fluorines decreases in 1,1-difluoro-2, 2-dichloro-3-methy1-3-phenylcyclobutane and 1,1- difluoro-3-bromo-3-phenylcyclobutane with increasing temperature, suggesting that rapid ring-inversion is taking place. Item Type: Thesis (Master's thesis) Subject Keywords: (Chemistry) Degree Grantor: California Institute of Technology Division: Chemistry and Chemical Engineering Major Option: Chemistry Thesis Availability: Public (worldwide access) Research Advisor(s): Roberts, John D. Thesis Committee: Unknown, Unknown Defense Date: 1 January 1962 Record Number: CaltechTHESIS:05062010-112117806 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:05062010-112117806 DOI: 10.7907/481A-5Q94 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 5777 Collection: CaltechTHESIS Deposited By: Tony Diaz Deposited On: 10 Aug 2010 18:33 Last Modified: 21 Dec 2023 21:58 Thesis Files Preview PDF - Final Version See Usage Policy. 829kB Repository Staff Only: item control page

NUCLEAR MAGNETIC RESONANCE STUDIES OF SOME i, leDIFLUORO-3-PHENYLCYCLOBUTANE DERIVATIVES Thesis by Masaaki Takahashi In Partial Fulfillment of the Requirement For the Degree of Master of Science in Chemistry California Institute of Technology Pasadena, California 1962 ABSTRACT 1, 1-Difluoro-2, 2-dichloro-3-methyl-3-phenylcyclobutane has been prepared by the cycloadcition of a-methylstyrene to 1, 1l-difluoro- 2,2-dichloroethylene. A 2 cps long-range H-F spin-spin coupling has been observed over five consecutive saturated bonds in 1,l-difluoro- 2, 2edichloro-3-methyl-3-phenylcyclobutane, involving one of the fluor- ines at the l-position an<d the protons of the 3-methyl group. Analysis of the apectrum and that of the stereospecifically labeled 4-ceutero derivatives suggest that the fluorine involved is the one cis to the methyl group. The n.m.r. studies of 1,1-difluoro-3-bromo-3-phenylcyclo- butane which was obtained by bromination of 1,1-difluoro-3-pheny1- cyclobutane with N-bromosuccinimide indicate that this molecule has on the average a more nearly planar cyclobutane ring than that of 1,1- difluoro-2, 2-dichloro-3-methyl-3-~phenylcyclobutane. The four protons of the Z- anu 4-positions are nearly magnetically equivalent, so that the spectrum of this compound is almost that of an ABX , system rather than an ABX,Y, system. The theoretical calculations suggest that the chemical shift difference between X and Y is on the order of 1-2 cps. The chemical shift difference between the fluorines decreases in 1, l-difluoroeZ, 2-dichloro-3 -methyl-3-phenylcyclobutane and 1, 1- difluoro-3-bromo-3-phenylcyclobutane with increasing temperature, suggesting that rapid ring-inversion is taking place. ACKNOWLEDGMENT I would Mke to express my sincere appreciation and gratitude to Dr. John D. Roberts for his patlent guidance of all the research. I am indebted to the Kureha Chemical Inc, Cs. (Japan) for fellowships and other financial supports throughout my graduate work at the California Institute of Technology. TABLE OF CONTENTS Page Introduction . e e . e e e e e . e e 1 1, |-Difluoro-2, 2-dichloro-3~- methyl-3-phenylcyclobutane . . . . . ‘ 4 Reaction of 1, 1-ifluoro-2, 2«dichloro-3- methyl-3-phenylcyclobutane with 1, 1-Difluoro-3 -bromo-3-phenylcyclobutane . . . . i2 Temperature Dependence of the Fluorine Chemical Shift in i, 1-Difluoro-3-pheny!l- cyclobutane Derivatives ° . ‘ . . . . ié Experimental ° . . . . ‘ . . . ° . 20 References. . . : . . . . . . . . 25 INTRODUCTION Cycloaddition reactions of alkene to alkene and alkene to alkyne are important synthetic pathways to four -membered carbon ring systems (1, 2,3). Particularly, the cycloaddition of fMuoroalkenes to alkenes give fluorinated cyclobutane derivatives that would ke very difficult to syn- thesize by conventional methods. (3,4). 1,1-Difluoro-2, 2-dichloro-3- phenylcyclobutane has been prepared by cycloaddition of styrene to 1, l-difluoro-2, Z2-dichloroethylene. (4). CH CHeCH, + C1,C=CF ——> H 2 2 2 The structure of I for the adduct has been well established (3,4), The orfentation produced in this reaction has been explained on the basis of a diradical mechanism by Roberts and Sharte (3). C HCH=CH, + cig 2G nd , S ed Cc Cc 7” FON / C.HCH Ta F, or Cc eG Cc °C § 2 ) \ ta Ib YZ Hq, Cc ,HCH CF 2 ccl 2 I Po . ¥ Be The intermediate diradical Ia 1s considered to be more favorable than Ib, since a difluoromethyl radical should be less stable than a dichloro- methyl radical. (5). Substituted styrenes also undergo cycloaddition reactions. In the present work, 1, 1-difluoro-2, 2-dichloro-3-methy!l-3-phenylcyclo- butane and cis- and trans-4-deutero derivatives have been prepared by addition of a-methylstyrene and cis- and trans-{--deutero-a-methyl- styrene to 1,1-difluoro-Z, 2-dichloroethylene. C.H.¢*CH, + Cl CH, 2 Cecr, —p Cl 2 CH, F C .H,¢ #CHD + C1,Cscr, amma cH, 2 CH 3 HD cia-~ and trana- cis- andtrans- [iI Structures IJ and II for the adducts have been assigned on the basis of n.m.F. spectra and analogy with the formation of 1, l-difluoro-2, 2- dichloro~-3-phenylcyclobutane. The theoretical caiculationse of n.m.r. spectra have proved extremely useful for analysis of complex spectra. A program suitable for use with an IBM 7090 computer has been developed by Wiberg and Nist (6), which produces theoretical energies and intensities for all of the possible transitions corresponding to a given set of chemical shifts and coupling constants for up to seven nuclei with spin of 1/2. A satie- factory match between calculated and experimental spectra was achieved for 1, ledifluoro-2, 2-dichloro~-3 «methyl -3-phenylcyclobutane and 1,1- difluoro-+3-bromo-3-phenylcyclobutane. 1,1-Difluoro-2, 2-dichloro-3-methy]-3-phenylcyclobutane 1,1-Difluoro-2, 2-dichloro-3-methyl-3~-phenylcyclobutane (1) was prepared by heating a mixture of a-methylstyrene and 1,1-difluoro- 2, 2-dichloroethylene in a sealed tube at 130° for 24 hours. Structure IT for the adduct rather than 1, l-difluoro-Z, 2-dichloro-4-methyl-4- phenyleyclobutane is in good agreement with the magnitudes of the coupling constants between the methylene protons and the germ-fluorines. It is also supported by analogy to formation of 1, l-difluoro-Z, 2-dichioro- 3«phenylcyclobutane (3). cl, Cs Fs cH, a il The fluorine n.m.r. spectrum of IT shows the resonances of two none equivalent fluorines (3) and F,) with a chemical shift difference of 435 cps, each split by the FF, coupling (J,, * 187 cps) and couplings with the two nonequivalent methylene protons attached to the 4-carbon #1.9 and 9.5 cps, Sue #13.2 and 20.3 cps) (Fig. 1A). 2 In addition, the higher field fluorine resonance shows further splitting Gree 1 into 1:3:3:1 quartets with J 2 2.0 cps (Fig. 1C). This strongly implies a coupling with three equivalent protons, presumably with the protons Fig 18 Fig tA 4313.2 +326.44333.5 4346.7 I +330 cps Fig. 2A 500 400 300 200 Fig. 1. Fluorine n.m.r. spectra (56.4 Mc.) 1A. 1, 1-Difluoro-2, 2-dichloro-3-phenyl-3-methylcyclobutane (I) 1B. The low-field fluorine resonance of II. 1C,. The high-field fluorine resonance of II. Fig. 2A. Protonn.m.r. spectrum of II (60)Mc.) The calibration is cps downfield from tetramethylsilane oo of the methyl group at the 3-position and, indeed, the proton n.m.r. spectrum of II shows a doublet methyl resonance with J # 2.1 cps (Fig. 2A). Several long-range H-F spin-spin couplings have been re- ported (7,8) but couplings over five consecutive saturated single bonds appear to be previously unknown. This five-bond, H-F coupling is indicated to be a cis-interaction by the following rather involved argument. First, the methylene resonances consist of sixteen peaks as shown in Figure 2B. The sum of relative areas of the eight low-field peaks is equal to that of the eight high-field peaks and, therefore, each group haa been considered to represent separate methylene protons designated as H, (low-field) and H, (high-field), respectively. Three different coupling constants are found for each proton; i.e., 13.1, 9.4, and 20.5 cps for H, and 13.1, 1.8, and 13.7 cps for H,: A 3 series of theoretical calculations demonstrated that the spectrum is well fitted by taking Jy3 #9.4cpa, J. 14 z21.8cps, J J,,%20-5eps, J,, #13.7 24 cps, and J54 213.lcps (Fig. 2C). The theoretical calculations were set up for the two protons and two fluorines as an ABXY system having different combinations of observed chemical shifts and coupling constants using the program described by Wiberg and Nist (6) on an IBM 7090 computer. It ia possible to draw two conformers of II (a, and U,,) if itis assumed that the cyclobutane ring is nonplanar. These would be expected Fig 28 210 200 190 180 170 {60 150 140 Fig 20 Fo Sn a nr ar 3° 3 S82 of 5 8 2 $e @ & ge & BB55 $3 Fig. 2B. The methylene resonances of II (60 Mc.) Fig. 2C. The calibration is cps downfield from tetramethylsilane and the total chart width equal to 100 cps. Calculated methylene resonances of I. to have ‘'axtal'' and ‘equatorial’ groups Hke those of cyclohexane, and of the two, H. with the phenyl group "equatorial'' and the methyl group “asdal'' is Mkely to be favored. The degree of puckering of the ring is probably considerable since the chemical shift difference between the fluorines (435 cps) is about half of the 874 cps difference between the fluorines of 1,1-difluorocyclohexane when this substance undergoes slow ring-inveraion at «80° (16). 9 Cl F _. Sor — 3 H H a It has been observed that trans (axial-axial) couplings between protons on neighboring carbon atome in saturated ring systems are larger than gauche (axial -equatoxtal or equatorial-equatorial) couplings. (9). Similar arguments appear to apply to H-F couplings | (3). On this basis, one can take F 2 to be trans toH The whole argument hinges 3° on this point, if further analysis should show that trans H-f couplings tend to be smaller than the corresponding gauche couplings, then the assignment here has to be reversed. The stereochemical relationships of H, and H 4 with respect to 3 the pheny! group have been established by substitution of deutertium at the 4-position. Mixtures of Wand trans-4-deutero-l, l-difluoro-2, 2- dichloro-3-methyl-3-phenylcyclobutane (trans-II) and cis-4-deutero- 1, 1-difluoro-2, 2-dichloro+3-methyl-3-phenylcyclobutane (cis-III) have been synthesized by addition of trana~ and cis-,.-deutero-a-methylaty- rene (10) to 1,i-difluoro-2, 2-dichloroethylene. Cl Cl CliiH Cl r F CH, CH, FE trans -]I] cis II] The total area of the low-field methylene peaks was larger than that of the high-field methylene peaks for the mixture in which trans-Ill predominated. The high-field methylene proton Hy is therefore trans, and low-field methylene proton H, cis to the phenyl group. The come 3 plete assignment of chemical shifts is then as in Tr. and the long-range coupled fluorine (F,) is cia to the methyl group. The five-bond H-F coupling may well be exerted through space (8,11) instead of through the bonds, particularly because groups involved are expected to be rather close together in space. 10 Reaction of 1,1-Difluoro-2, Z2-dichloro-3-methyl-3-phenylcyclobutane with Lithium and t-Butyl Alcohol Winstein (12) has achieved smooth removal of chlorine in some cyclic systems by treating with lithium metal and t-butyl alcohol in tetrahydrofuran. The method has been applied to 1,1-difluoro-2, Z2-dichloro-3 -methyl- 3-phenylcyclobutane (I) in hepe of preparing 1, 1-difluoro-3-methyl- 3«phenylcyclobutane (Iv). Rather vigorous reaction occurred at 45°, and a colorless ofl of b.p. 40-40.5° was obtained. This product gave a positive unsaturation test, and its infrared spectrum also suggested the presence of a double bond. The protonn.m.r. spectrum showed phenyl-, vinyl-, methylene-, and methyl resonances in the approximate ratio of 5:1:2:3 (Fig. 3A). The fluorine n.m.r. spectrum showed only one flucrine resonance which was split into a broad 1:3:3:1 quartet (Fig. 3B). On this basis, the product is considered to be l-efluoro-3-methyl- 3-phenylcyclobutene-l (V). Cc Pea 5 Cc ge 5 CH CH Iv Vv ll Fig. 3A Fig. 3B i iv { 1 ¥ Fig. 3A. The protonn.m.r. spectrum of V (60 Mc.) Fig. 3B. The fluorine n.m.r. spectrum of V (56.4 Mc.) 12 1, 1-Difluoro-3-bromo-3+phenyleyciobutane Knutson (13) and Vogel (14) attempted the synthesis of 1,1- difluoro~3-bromo-3-phenylcyclobutane (VI) by bromination of 1,1- difluoro-3-phenylcyclobutane (VII) with N-bromosuccinimide in carbon tetrachloride, but they were unable to isolate Vi in pure form. A suc- cessful preparation was later achieved by Manatt (15). Ci C.H.CHsCH, Ss, <> C1,C#CF 2 HR C, H, OH 6 5 2 H Pd-C 1 KOH-C 2H, CH C, : NBS C 2 iH, cane 2 cc 65 2 ——~ Hs Br 4 vi vu The n.m.r. spectrum of VI has not been carefully analyzed heretofore. Manatt (15) only reported that the proton spectrum showed broad triplet methylene peaks. The fluorine n.m.r. spectrum was not - taken. In the present research, both proton and fluorine n.m.r. spec« tra of VI have been taken of pure samples under high resolution. The proton spectrum shows I:h1:1 quartet methylene resonances with the two 43 different coupling constants of 10.1 cps and 12.4 cps (Fig. 4A). The fluorine spectrum shows two pairs of quintets corresponding to two non-equivalent fluorines (F, and F,) with a chemical shift dliference of 225 cps. Each resonance is split by the FU-F, coupling (J # 192 cps) and coupling with the four nearly equivalent methylene protons of the ® 10.2 cps and Jur, = 12.2 cpa) (Fig. 43). The n.m.r. spectrum of VI was expected to be that of an 2 and 4 positions Cue, ABX Y, system, such that A,B represent the two nonequivalent fluorines eT and Boe and XW, represent two pairs of nonequivalent protons. However, the actual spectrum suggests that the chemical shift ciffer~- ence between X and ¥ is so small that the spectrum is very nearly that of an ABX, sy stem. & series of theoretical calculations has been rnade on the basis of an ABX,%, system varying the coupling constants and chemical shifts. Comparison of calculated and experimental spectra suggests that the degree of nonequivalence of X,Y is small and,since the H-F coupling constants are close to one another, the methylene resonances appear as quartets consisting of many closely spaced bands which cannot be resolved in the actual spectrum. The quintet splitting of the fluorine spectrum can be explained on the same basis. The chemicai shift difference between X and Y¥ is considered to be the order of l-2 cps; @.g. the spectrum is well fitted by taking Jax 2 9.9 cps, Jay = 10.3 *ouRlTIsS[AYJAUIBI}93 WOI pratyumop sdd sz uoWeaqriTes sy (°OoW 09) IA 30 umajoeds °1°ur°’u uojoud sy ve Sta sdo OO! 002 on i an | OOe OOv OOS T | T ym l4-a Vp big 14-b Fig. 4C | \ - 399 +399 -~-586 ~399 Oo +399 +586 cps Fig. 4B. The fluorine n.m.r. spectrum of VI (56.4 Mc.) Fig. 4C, The fluorine n.m.r. spectrum of 1, |-difluoro-3-phenylcyclobutane (56.4 Mc.) 15 cps, Jax = i2.3 cps, Jay = 12.5 cps, Jyy = 13.0 cps, and AV yy = 1.0 cps. From these observations, it may be deduced that the cyclobutane ring of VI is likely to be on the average nearly planar. This seems to be reasonable since the chemical shift difference between the flucrines (225 cps) is small compared with the 966 cps difference between the fluorines of 1, ] -difluoro+3-phenylcyclobutane (Fig. 4C). If we assume that the chemical shift difference between the fluorines is independent of whether a 3+bromine or 3-hydrogen is present in 1, i-difluoro-3- phenylcyclobutane except insofar as they might affect the conformational equilibria, then if the compound with the 3-hydrogen exists almost exclusively with the phenyl equatorial, the 3-bromo compound has the phenyl equatorial an average of 60% of the time. 16 Temperature Dependence of the Fluorine Chemical Shift in 1,1-Diflucro-3-phenyicyclobutane Derivatives The variation of the n.m.r. apectra with temperature can often distinguish between the slow and rapid ring-inversion of cyclic cone formers. Thus if the apparent chemical shifts are temperature de- pendent, rapid ring-inversion is indicated. (17) The temperature dependence of the fluorine chemical shift in 1,l-difluoro-2, 2-dichloro-3-methyl-3-phenylcyclobutane (1) and 1,1- difluoro-3-bromo-3-phenylcyclobutane (VI) has been investigated. In the both compounds, the chemical shift difference between the fluorines decreases considerably with increasing temperature. However, the fluorine-fluorine coupling constants are almost unchanged with tem- perature. Table 1 shows the chemical shift differences between the flucrines of several gem-difluoro compounds at various temperatures. Unsymmetrically substituted cyclobutane systems, for example, 1,l-difluoro-3-phenylcyclobutane derivatives, are likely to be nonplanar; there existe a ring-inversion between the two conformers, A and B. However, if the ring-inversion frequency is sufficiently high to average the environment of the fluorine atoms, one can only observe an average structure C in the fluorine n.m.r. spectrum. \7 Table 1 Compound Temperature, Fluorine Chemical P °c Shift Difference (cps) 1,1-Difluorocyclohexane -80 872 1, 1-Difluoro-3-phenyl- 25 966 cyclobutane (VIZ) 1,1-Difluoro-2, 2-dichloro- 31 435 3-methyl-3-phenyl- cyclobutane (I) 194 383 1,1-Difluoro-3-bromo-3- 31 225 phenylcyclobutane (VI) 99 168 1,1-Pifluoro-2, 2-dichloro-3- 25 550%* phenylcyclobutane (I) * at 56.4 Mec ** calculated from the fluorine spectrum of I taken at 40 Mc i8 ¢ : F — x ¢ X A B x = H,CH,. Br | Cc Then the chemical shift will be averaged over the two con- formers, 6 = c 18, +e,6, where c_, c, are the fractional populations. If the two conformers 1 2 have different energies, EY and E, -E /kT c } _ . ae 2 -&,/kT be where a, b are temperature independent coefficients. If it is assumed that E< E, 30 that c, 1.0 and cl, *0 in 1, i-difluoro-3-phenyl- 2 cyclobutane, one can calculate approximate fractional populations of YW and VI taking vy = 966 cps, v, = -966 cps for VI and vie 550 cps, 2 v= “550 cps for HI. i9 On this basis, there exist 90% of conformer A and 10% of conformer B inII, and 60% of conformer A and 40% of conformer B in VI at the room temperature. Thus the degree of nonplanarity of the average structure IIC is likely to be considerable, and, on the other hand, the average structure VIC appears as nearly planar. This 1s all wrong. Cl CLA H H H CH, F Br H F mc vic 20 EXPERIMENTAL 1, 1-Difluoro-2, 2-dichloro-3 -methyl-3-phenylcyclobutane (1).— A mixture of 59 g. (0.50 mole) of a-methylstyrene and 74 g. (0.55 mole) of 1, 1-difluoro-2, 2-dichloroethylene (Genetron 1112, General Chemical Division) was heated in a sealed glass tube at 130° for 24 hr. The. tube was cooled with Dry Ice, opened, and the light-yellow ofl dis- tilled through a 10-cm. Vigreux column. The yield of crude adduct was 66 g. (61%) of b.p. 91-98° (2.5-3.0 mm) waa collected, Redistil- lation through a 20-cm. Vigreux column gave 56 g. (52%) of product of b.p. 84-86° (1.5 mm). Anal. Caled. for C,H) FjCl,: C, 52.50; H, 3.98; Ci, 28.30. u-10 2°°2° Found C, 52.58; H, 4.01; Cl, 28.20. trans-))-Deutero-a-methylstyrene (10),.— In a 200-ml. round- bottomed three-necked flask equipped with a magnetic stirrer, helium inlet and dropping funnel, was placed 75 ml. of anhydrous ether. A flow of helium was passed through the flask and l.7 g. (0.25 mole) of Uthium wire was added, followed by 21 g. (0.12 mole) of trans-;:-bromo- a-methylstyrene (prepared from a-methylstyrene dibromide) (10) After a few minutes, the solution became cloudy red brown. The flask was then cooled and maintained between -30°- -40° for 40 min. A solution of 7.3 g. (0.12 mole) of deuteroacetic acid in 25 ml. anhydrous ether was 21 then added until the color disappeared. About 50% of the calculated amount of acid was required. The reaction mixture was poured into a beaker and combined with }00 ml. of pentane. The excess lithium was decomposed by water. The solution was separated from the solution of Uthium salts and dried overnight over anhydrous sodium sulfate. After the removal of solvent by evaporation, the residue was diluted with 2g. of pentane and chromatographed on 150 g. of acid-washed alumina . using pentane as eluent. The first 50 ml. of eluent was col- lected. After removal of the pentane, the product was distilled through a lQ-cm. Vigreux column. There was collected 5.0 g. (42%) of color. leas oll, b.p. 82-85%, 61-62 mm.), which consisted of 18% of a-methyl- styrene, 55% of trans-)-deutero-a-methylstyrene, and 27% of cis-5- deutero-a-methylstyrene, as judged by electronic integration of the appropriate peaks in itan.m.r. spectrum. cis; -Deutero-a+-methylstyrene was prepared from cis-j- bromo-a-methylstyrene (obtained by photo-isomerization of trans-f- bromo-a-methylstyrene) (10), The procedure was the same as for the trans-lsomer. Analysis by n.m.r. of the product gave 36% of ae methylstyrene, 21% of trans-) -deutero-a-methylstyrene, and 43% of cia. ~Ssdeutero-a-methylstyrene. trans -4-Deutero-l, l-difluoro-2, 2-dichloro-3-methyl-3-pheny!- cyclobutane (trans-III).— <A mixture (5.0 g., 0.04 mole) consisting of 18% a-methylstyrene, 55% of trans-)-deutero-a-methylstyrene and 22 27% of cis-() -deutero-a-methylstyrene was heated with 6.2 g. (0.05 mole) of 1,l-difluoro-2, 2-dichloroethylene at 130° for 20 hr. istillation gave 4.8 g. (45%) of adduct of b.p, 83-86° (1.5 mm). Integration of the n.m.r. peaks indicated that 45% of II, 36% of trans-IIl, and 18% of cis-I were formec. cis-4-Deutero-l, l-difluoro-2, 2-dichlora-3-methyl-3- phenylcyclobutane (cis-II).— A mixture of 0.4 g. (0.03 mole) of 36% of a-methylstyrene, 2l% of trans-js-deutero-a-methylstyrens and 43% of the cis isomer was heated with 1,1-difluoro-2, 2-dichloroethylene and gave 0.5 g. (59%) of adduct with b.p. 83-85° (1.5 rom) which by electronic integration of its n.m.r. spectrum was indicated to be 56% I, 12% trang- I, and 32% cis-Il. 1-F luoro-3-methyl-3-phenylcyclobutene-l (V).- Ina clean, dry 500-ml. three necked flask fitted with a condenser, stirrer and helium inlet were placed 150 ml. of dry tetrahydrofuran, 25.0 g. (9.10 mole) of I, and 14.8 g. (0.20 mole) of anhydrous t-butyl alcohol. A flow of helium was started and 2.8 g. (0.40 g. atom) of Mthium wire was added to the flask. No reaction occurred at the room temperature for 5 min. so the flask was warmed to 45° end then to 60°. The mixture began to veflux and became slightly cloudy. After 2 hr., the product was treated with a mixture of ice and water in order to decompose excess lithium. The solution was acidified with conc. hydrochloric acid and extracted four times with pentane. The pentane layer was washed with water and 23 dried over anhydrous magnesium sulfate overnight. After the removal of pentane and tetrahydrofuran, the residue was fractionated under reduced pressure and gave: Frac. 3.p.,°C (1 mm.) Wt.» ge 1 36-40 0.5 2 40-40. 5 1.9 3 42-65 i.5 4 65-83 7.1 Fractions 3 and 4 were identified as unreacted TI, Fraction 2 amounted to a 12% yield of dehalogenation product, which gave a positive permanganate test and also showed C-C in its infrared spectrum. The proton n.m.r. spectrum (Fig. 3A) showed four signals assigned as phenyl, vinyl, -CH,-, and CH 2 3 ratios of 5, 4:1.0:1.92:2.92, respectively. The fluorine n.m.r. spectrum - protons. Integration of the peaks gave showed only one fluorine resonance split into broad quartet of h3:3:1. 1, 1-Difluoro-3-bromo-3-phenylcyclobutane (VI).— 1, 1-Difiuoro- 3-phenylcyclobutane (VI) was prepared from I by elimination of hydrogen chloride followed by catalytic hydrogenation essentially as described by Manatt.(15). VI wae prepared from VII as follows. In a dry 100-ml. round-bottomed flasx fitted with a reflux con- denser were placed i0 g. (0.06 mole) of VI, i0.6g. (9.06 mole) of N-bromosuccinimide, 50 ml. of reagent grade carbon tetrachloride, and 0.5 g. of benzoyl peroxide. “When the mixture was heated a vigorous 24 exothermic reaction started, following which the reaction mixture was refluxed for !.5hr. The succinimide was removed by filtration, and the carbon tetrachloride distilled under reduced pressure. The residue was distilled through a '‘O-cm. Vigreux column using a magnetic stirrer to prevent pumping. The yield of VI was '0.5 g. (71%); b.p. 87-88° ('.5 mm), Le 2. 3. 7. 8. 9. 10. il. 12. 13. 14. i5. 25 REFERENCES D. D. Coffman, P. L. Barrick, R. D. Cramer and M. 5. Raasch, J. Am. Chem. Soc., 71, 490-496 (1946). C. M. Sharts, Ph. D. Thesis, California Institute of Technology, J. D. Roberts and C. M. Sharts, in A. C. Cope, Ed., “Organic Reactions," Vol. XII (in press). E. EF. Silversmith, ¥. Kitahara, M. C. Caserio and J. D. Roberts, J. Am. Chem. Soc., 80, 5840 (1958). CG. Walling, ‘Free Radicals in Solution,'’ John Wiley, New York, 1957, p. 253. K. B. Wiberg and B. J. Nist, ‘Theoretical NMR Spectra," W. A. Benjamin, Inc., New York, in press. J. D. Roberts, Nuclear Magnetic Resonance,’ McGraw-Hill Book Co., New York, 1959, Chap. 3. DO. R. Davis, R. P. Luts and J. D. Roberts, J. Am. Chem. Soc., 83, 246 (1961). J. A. Pople, W. G. Schneider and H. J. Bernstein, ‘‘High- resolution Nuclear Magnetic Resonance," McGraw-Hill Book Co., 1959, Chap. 8. , D. R. Davis and J. D. Roberts, J. Am, Chem. Soc., 84 (1962), in press. L. Petrakis and C. H. Sederholm, J. Chem. Phys., 35, 1243 (1961). _S. Winstein, et al., Chem. & Ind., (in press). Unpublished research of D. Knutson. Unpublished research of M. Vogel. S. Manatt, Ph. D. Thesis, California Institute of Technology, 1959. 1G. 26 Unpublished experiments by K. Nagarajan, J. Db. Roberts, Journal of Vsesouznoe Chemical Society, (in press). Reference 9, Chap. 13. The author is indebted to Mr. L. Sloan of the Jet Propulsion Laboratory for his assistance with the theoretical NMR spectra calculations on an IBM 7090 computer.