Nuclear Magnetic Resonance Spectroscopy Cyclopropane Derivatives Citation Patel, Dinshaw Jehangir (1963) Nuclear Magnetic Resonance Spectroscopy Cyclopropane Derivatives. Master's thesis, California Institute of Technology. doi:10.7907/MXFQ-9281. https://resolver.caltech.edu/CaltechTHESIS:04302010-094941787 Abstract Chemical shifts and coupling constants have been determined from the analysis of proton nuclear magnetic resonance spectra for a series of cyclopropane derivatives . The geminal and vicinal cyclopropyl couplings have opposite signs. Additional ^(13)C-H coupling constants have been obtained for cyclopropanes which support the conclusion that the hybridization in cyclopropanes is close to sp^2. The chemical shifts for several cyclopropanes seem consistent with a ring-current effect. 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 1963 Record Number: CaltechTHESIS:04302010-094941787 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:04302010-094941787 DOI: 10.7907/MXFQ-9281 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 5760 Collection: CaltechTHESIS Deposited By: Tony Diaz Deposited On: 16 Jul 2010 16:24 Last Modified: 08 Jan 2024 23:59 Thesis Files Preview PDF - Final Version See Usage Policy. 1MB Repository Staff Only: item control page

NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY CYCLOPROPANE DERIVATIVE Thesis by Dinshaw J. Patel, In Partial Fulfillment of the Requirements for the Degree of Master of Science California Institute of Technology Pasadena, California 1963 The author is thankful to Professor John D. Roberts for introducing him to the problem and his patient guidance during its solution. It has been a great pleasure to have been a member of the Roberts group. The finer details of computer analysis were patiently explained by Mr. Ken Servis; Mr. George shitesides spent much time on the n.m.r. machine on behalf of this v search, c The financial support of the California Institute of Sechnology and the Tata Foundation during my stay at the California Institute of Technology is sratefully acknowledged. I thank my parents for their encouragement and counsel, and Mr. KF. BP. Vazifdar for making my stay in the United States possible. ABSTRACT Chemical shifts and coupling constants have been determined from the analysis of proton nuclear magnetic resonance spectra for a series of cyclopropane derivatives . The geminal and vicinal cyclopropyl couplings have opposite signs. Additional 13 oy coupling constants have been obtained for cyclopropanes which support the conclusion that the hybridization in cyclopropanes is close to sp*. The chemical shifts for several cyclopropanes seem consistent with a ring-current effect. OFFICE OF NAVAL RESEARCH Contract Nonr 220(26) Task No, NR 055-386 TECHNICAL REPORT NO. 21 Nucleay Magnetic Resonance Spectroscopy. Cyclopropane Derivanvyes: : PR NE a el RON lt A NaN Dinshaw J. Patel, M. E. H. Howden and John D. Roberts Prepared for publication in the Journal of the American Chemical Society California Institute of Technology Division of Chemistry and Chemicai Engineering Pasadena, California April 1963 Reproduction in whole or in part is permitted for any purpose of the United States Government { Contribution No. 2964 from the Gates and Crellin Laboratories of Chemistry, California Institute of Technology, Pasadena, California] Par lg al” oe fs 1 Cyclopropane Derivatives. (1) Supported in part by the Office of Naval Research and the National Science Foundation. 2 By Dinshaw d. Patel,” M. E. H. Howden and John D. Roberts (2) J. N. Tata Fellow, 1961-1963. Chemical shifts and coupling constants have been determined from the analysis of proton nuclear magnetic resonance spectra for a series of cyclo- propane derivatives. The geminal and vicinal cyclopropyl couplings have opposite signs. Ad-~ ditional =C-H coupling constants have been obtained fer cyclopropanes which support the conclusion that the hybridization of the carbon bonding orbitals in eyclopropanes is close to sp?. The chemical shifts for several cyclopropane hydrocarbons seem con- sistent with a ring-current effect. 3 . 4 Proton n.m.r.”~ and fluorine n.m.r. ~ spectroscopy have been (3) G. L. Closs, R. A. MossandJ. J. Coyle, J. Am. Chem. Soc., 84, 4985 (1962). (4) W. Mahler, J. Am. Chem. Soc., 84, 4600 (1962). utilized for structure determinations of substituted cyclopropanes. Coupling constants and chemical shifts of cyclopropane derivatives”? 6 (5) H. M. Hutton and T. Schaefer, Can. J. Chem., 40, 875 (1962). (6) J. D. Graham and M. T. Rogers, J. Am. Chem. Soc., 84, 2249 (1962), have recently been reported and interpreted in terms of substituent effects and molecular geometries. 6 In the present research, the spin-spin splittings in the proton n.m.r. spectra of several substituted cyclopropanes have been 7,3 analyzed using standard methods ’’~ with results shown in Table I. (7) J. D. Roberts, ‘An Introduction to the Analysis of Spin- Spin Splitting in Nuclear Magnetic Resonance," W. A. Benjamin, Inc., New York, 1961. (8) J. A. Pople, W. G. Schneider and H. J. Bernstein, "High-resolution Nuclear Magnetic Resonance, '' McGraw-Hill Book Company, Inc., New York, 1959. 10 The Wiberg, 9 the Bothner-By and the Swalen”” computer (9) K. B. Wiberg and B. J. Nist, "The Interpretation of NMR Spectra, '"' W. A. Benjamin, Inc., New York, 1962. (10) J. D. Swalenand C. A. Reilly, J. Chem. Phys., 37, 21 (1962). 3 programs were used to obtain the best agreement between the observed and the calculated spectra. The AB cyclopropyl proton patterns in the n.m.r. spectra cf tetrasubstituted cycloproganes yielded the cyclopropyl coupling directly. The trans-cyclopropy! couplings in the ABX type spectra of trans -3-(trans-2'-carboxyprdépenyl)-2, 2-dimethylcyclopropane- i-carboxylie acid and its dimethyl ester were determined directly from the AB portion of the spectrum, the dowrfield part of which was split by the adjacent vinyl hydrogen. The n.m.r. spectra of neat samples of 1, 1-dimethylceyclopropanecarboxylic acid, dimethyl 1-methylcyclopropane- cis ~1, 2-dicarboxylate and dimethyl 1-rnethylcyclopropane-trans-1, 2- dicarboxylate were analyzed as ABC systems. Identification in the ob- served spectrum of the three quartets and repeated spacings between lines gave approximate values of the chemical shifts and coupling con- stants, respectively. Best calculated frequency fits for the four possible combinations of relative signs of couplings were then obtained 10 The best fit between observed and calcu- using the Swalen program. lated intensities was found for the assignments with geminal coupling having an opposite sign to the vicinal couplings in the three ABC systems studied. The analysis of the n.m.r. spectrum of dimethyl] i1-methyl- cyclopropane-trans -1, 2-dicarboxylaie in benzene gave magnitudes and Signs Of couplings in agreement with the neat compound. The C satellite n,m.r. spectra of 1, i-dichlorocyclopropane, i, i-dimethylcyclopropane, spiropentane and spirohexane were analyzed as AA'TAR’ systems. ' The center of each multiplet of the *C satellites was determined by the moment method. i Similar calculated spectra in (11) W. Anderson and H. M. McConnell, J. Chem. Phys., 26, 1496 (1957). agreement with the observed spectrum were found with two geminal couplings having different magnitudes and different signs in each AA'XX" system studied. However, the best fit to the intensities was found for 1,1-dichlorocyclopropane with the geminal and vicinal couplings having opposite signs and this sign assignment is also assumed for the other three AA'XX' systems. The cis and trans couplings which have the same sign are interchangeable without affecting the spectrum and have been assigned assuming the cis coupling has the greater magnitude. The errors involved in the determination of coupling constants are large due to a low signal- to-noise ratio in the }3C satellite spectra, and also because small changes in the geminal coupling do not have much effect on the calculated spectra. The AA'BB' type proton n.m.r. spectrum of neat 1-phenyl-1- bromocyclopropane was solved with the aid of the Swalen program. The only satisfactory fit was obtained with the geminal coupling taken to have the opposite sign to the vicinal couplings. Interchange of the two cis couplings and interchange of the geminal and trans couplings does not affect the calculated spectrum. The assignment of geminal and trans couplings with opposite signs appears to be definite and is supported by analysis of the spectrum of 1-phenyl-1-bromocyclo- propane in chloroform (where the chemical shifts are different). Gutowsky and co-workers!” on the basis of valence-bond calcu- (12) H. S. Gutowsky, M. Karplus and D. M. Grant, J. Chem. Phys., 31, 1278 (1959). lations have predicted a positive geminal coupling for H-C-H angles less than 120°. However, a recent publication!® on the proton n.m.r. (13) E. Lustig, J, Chem, Phys. , 37, 2725 (1962). spectra of small-ring compounds, indicates that the geminal coupling has an opposite sign to the vicinal couplings in cyclobutane derivatives. 14 With the aid of spin decoupling, Anet”~ has shown that the geminal (14) F. A. L. Anet, J. Am, Chem. Soc., 84, 3767 (1962). proton-proton coupling in CHDOH is opposite in sign to the “C-H coupling. Since the latter coupling is almost sure to be positive!” (15) M. Karplus, J. Am. Chem. Soc., 84, 2458 (1962). the geminal coupling must have a negative sign. On the basis of this evidence we have assigned the geminal coupling a negative sign and the cis andtrans vicinal couplings positive signs in cyclopropanes. It is very interesting that in ethylene oxides, the coupling constants have been reported to have the same relative sign. 16 (16) C. A. Reilly and J. D. Swalen, J. Chem. Phys., 32, 1378 (1960); C. A. Reilly and J. D. Swalen, J. Chem. Phys., 36, 1522 (1961). The geminal H-C-H angles in cyclopropanes appear to fall goll in the vicinity of 114.5 -11 and, for this range of angles, the (17) E. Goldish, J. Chem. Ed., 36, 408 (1959). 6 theoretical valence-bond curve of Gutowsky and co-workers?” predicts H-C-H spin-spin couplings of +4.5to+7 cps. We have investigated the coupling constants in a number of cyclopropanes with different kinds of substituent groups and find the geminal coupling constants between -3. 1 to -6.0 cps (Table I). These results contrast with those of Weitkamp and co-workers!® who report geminal couplings of 7.0 (18) H. Weitkamp, U. Hasserodt and F. Korte, Chem. Ber., 95, 2280 (1962). to 9.0 eps for substituted 1, 1-dichlorocyclopropanes. In monosubsti- 6 tuted epoxides, the geminal coupling constants have been reported! to fall in a narrow range of +5. 0 to +6. 3 cps for the compounds studied. In ethylene oxides, the H-C-H angle is around 116° and similar geminal couplings in cyelopropanes and ethylene oxides would be expected due to the dependence of the coupling on H-C-H angle. The valence-bond $ 20 calculations of Karplus! and the molecular- orbital treatment of Conroy (19) M. Karplus, J. Chem. Phys., 30, 11 (1959). (20) H. Conroy, Advances in Organic Chemistry, Vol. 2, Interscience Publishers, Inc., New York, 1960. predict for sp? hybridization, a dependence of the vicinal coupling constant on the dihedral angle between the C-H bonds. For the geminal H-C-H angles of 114.5 -118° for cyclopropanes* ! the corresponding dihedral angles are calculated to be 131 -134° for trans cyclopropyl hydrogens and 0° for cis cyclopropyl hydrogens. The Karplus equations predict for these dihedral angles, a cis coupling of +8. 2 cps andatrans coupling of +3.8 to +4.3 cps, while the Conroy curve predicts cig andtrans couplings of +8.0 cps and +6. 4 to +7. 0 eps, respectively. The vicinal cyclopropyl coupling constants (Table I) are found to be +8.0to+11.2 cps for cis hydrogens and +5. 2 to +8. 0 for trans hydrogens in cyclopropanes. The cis coupling was found to pe greater than trans in cyclopropanes in agreement with theory. 16 the cis andtrans couplings In monosubstituted ethylene oxides, have smaller magnitudes than in cyclopropanes being +4. 0 to +5. 2 cps and +1. 86 to +2. 51 cps for cis andtrans protons. The cis hydrogens in both cyclopropanes and ethylene oxides are eclipsed and the difference in couplings cannot be accounted for on the basis of dihedral angle. The differences in vicinal couplings may be due to the electronegativity of oxygen in the oxides. Lynden~Bell and Sheppard”? (21) R. Lynden-Bell and N. Sheppard, Proc. Roy. Soc. (London), A269, 385 (1962). have analyzed the proton n.m.r. spectra of =C-labeled acetylene, ethylene and ethane and found the 8C-H coupling to be 249, 156.3 and 125 cps respectively. The fact that the C-H values for cyclo- propanes (Table I) fall between 157, 8 and 166.5 cps rein~ 22 forces the suggestion“ that the hybridization of the carbon bonding (22) N. Muller and D. E. Pritchard, J, Chem. Phys., 31, 768 (1959). orbitals in cyclopropanes is close to sp?. The #%C~H couplings in cyclopropanes may be compared with those observed for allenes° (23) E. B. Whipple, J. H. Goldstein and W. E. Stewart, J. Am. Chem. Soc., 81, 4761 (1959); E. I. Snyder and J. D. Roberts, J. Am. Chem. Soc., 84, 1582 (1962). which are in the range 166-168 cps and with those for three-membered 24 heterocycles” which are in the range 168-176 cps. The @C-F (24) F. S. Mortimer, J. Mol. Spect., 5, 199 (1962). 25 coupling in octafluorocyclobutane~~ is 298.0 cps. We find for the (25) R. K. Harris, J. Phys. Chem., 66, 768 (1962). 19 F spectrum of hexafluorocyclopropane a 3C-F coupling of 328.7 cps and a 6.4 cps upfield 18C isotope effect on the fluorine line positions. Not enough data is available to use the magnitude of 8C-F coupling in fluorocyclopropanes to indicate the hybridization of the carbon-bonding orbitals. A study of chemical shifts in cyclopropanes offers the possi- bility of giving new insight into the electronic structure of the cyclo- propane ring. A large body of evidence has accumulated which sup- ports the concept that the cyclopropane ring system possesses double- 26 bond character. The evidence is based on measurements of dipole (26) See, for example, E. Vogel, Angew. Chem., 72, 4 (1960). moments, ultraviolet and infrared spectra, and ionization potentials as well as on chemical reactivity. Cyclopropane has been suggested 9 BS et 27 N, by Walsh” to have bonding corresponding to a three-centered ethylene-- (27) A. D. Walsh, Trans. Faraday Soc., 45, 179 (1949). the C-C bonds being formed by overlap in the plane of the ring of p orbitals on neighboring carbon atomis and by overlap of three sp? orbitals on adjacent carbon atoms directed towards the center of the ring (Figure 1). The Walsh model assumes that two electrons occupy the central hybrid orbitals while four electrons occupy the molecular orbitals formed by overlap of the p-atomic orbitals. Some localized bond character was predicted for cyclopropane leading to hybridization between sp? and sp? but closer to sp’. On the basis of a pure valence-state model with perfect pairing, Coulson and Moffitt” (28) C. A. Coulson and W. E. Moffitt, Phil. Mag., 40, 1 (1949), formulate the carbon-carbon bonds of cyclopropane to involve hybrid orbitals which lie outside the internuclear angles. It was shown that the most favorable hybridization angle corresponds to having the C-C bond-forming orbitals at an angle of 104° which make the difference hetween internuclear lines and the hy brid orbitals be 22° (Figure 1). The Coulson-Moffitt model predicts the C-H bond orbitals in cyclo- propane to have less p-character than normal tetrahedrai bonds and hence be more like ethylene than ethane. Despite the fact that the theoretical models indicate that the C-H bonds in cyclopropane should be more closely akin tc those of ethylene than those of ethane, the cyclopropyl resonances come very 10 Significautly upfield from the vinyl resonances. Clearly some factor (s) other than carbon nypridization determine tc chemical shifts of cyclo- Comparison of the cyciooropyl chemical shifts for 1, 1-dimethylcyclopropane, spiropentane and spirohexane indicate that as the external C-C-C bond angie is decreased the cyclopropyl resonances are shifted to lower field. (see Table I). y The contribution of magnetic anisotropy” of the C-C bonds in (28) Ho M. McConnell, J, Chem. Phys., 27, 226 (1957). “ eyclopropanes to the proton shielding has been calculated by Wiber¢: paer®O a ua is . 4 and Nist'” tobe 15 cps. The greater mobility of the carbon electrons (30) K. B. Wiberg and B. J. Nist, J. Am. Chem. Soc., 83, 1228 (1% Oty yciopropane predicted on the basis of the theoretical models compared to ordinary saturated compounds suggests that part of this anomalous diamagnetic shift may be due to a cyclopropane ring-current effect This could either oppose or reinforce the field of the magnet depending on the position of the attached hydrogen atom relative to the ring. Johnson and Bovey” ot have calculated the chemical shift changes in (31) C. E. Johnson, Jr., and F. A. Bovey, J. Chem. Phys. 29, 1012 (1958). aan aromatic systems due to ring current effects by considering the circular precession of the 7 electrons in two regions above and below the viane of the aromatic ring under the influence of the component of the applied field which is perpendicular to this plane. ii 2 , was applied te the calculation The Johnson and Bovey method” of expected chemical shifts for ring and side-chain hydrogens in several cyclopropanes. The mobile electrons, four for the Walsh model and six for the Coulson and Moffitt model, were assumed to precess in the plane of the cyclopropane ring. Molecular parameters given by Goldisn?! were used. Calculations were carried out for (Case A) the radius of the ring current equal to that of the circle circumscribing the ring (0.88 A for cyclopropane) and (Case B) of a circle passing ras) rough the center of maximum electron density (assumed to 0.5 5 A from the carbon atom) of a p orbital oriented as in the Walsh model (1.01 A for cyclopropane). The results are summarized in Table and compared with observed shifts. Tne calculated values are in no more than qualitative agreement with the observed chemical-shift differences. Since some degree of localization of the C-C bond electrons in cyclopropane is likely, the calculated influence of ring currents probably representsupper limits of such effects. itis to be expected that the C-C and C-H bond aniso- tropies also make substantial contributions to the observed chemical shifts. The assumed ring-current for cyclopropane suggests tnat a hydrogen located near the equatorial plane of the ring will experience a paramagnetic effect on its resonance position and a diamagnetic effect is predicied for hydrogens inside the ring, or somewhere above it and reasonably close to its three-fold axis. The comparison between experi- gt ment and theory shown in Table II cannot be taken as establishing the existence of ring current in cyclopropanes, but the trends are reasonably consistent with a ring-current effect which has aiso been invoked to 1 ty explain the unusually large molar diamagnetic susceptibility of cyclo- propane. 42 (32) J. R. Lacher, J. W. Pollock and J. D. Park, J. Chem. Phys., 20, 1047 (1952). 13 8°88 Leh yer 1°63 «6 "86 py 'SIT C°Lb 6b 6S % ER pl OL Tes -- (H (2)H (DH x sdo sytyg [eorumayo GOFSO+ —-groFg et == BOFS FH Z-oFE 9+ = & “OFO "Bt 8 OFLb- € 'OF9 “G+ € ‘OFG “G+ & OFS “Pe GOFO'L+ = gOFGOI+ = BOF GG - SUB STO, was, sdo squrjeuog sundress "9°09 (DHY | (€) aN tntgg’ 7 (2) HO (I) H "HQ He (8) WEN *HO%00/ 1 (2) *HO*O (1)H “HQ = (g) MON woo! 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The chemical shifts on the V-4300B were measured by means of a Hewlett-Packard Model 200AB audio oscillator and Model 521C frequency counter. Line positions have been measured to an accuracy of O.l cps. Tetramethylsilane was used as an internal reference in the study of AB systems and as an external reference for other systems. Proton and fluorine “C satellite n.m.r. spectra were taken for °C in natural abundance. “C-H coupling constants were obtained as the difference between the chemical shifts of the centers of the low- and high-field satellites, Hexaflucrocyclopropane was a sample generously supplied by Dr. D. C. England of the DuPont Company. The positions of the C- satellite peaks were determined at 56.4 Mc, using side bands from the parent difluoromethylene peak. The chemical shift of the latter peak was measured by interpolation with a 50% solution of hexafluorocyclopropane ‘in fluorotrichloromethane, by generating an approximately 600-cps side band and sweeping rapidly through to the fluorotrichloromethane peak. 1, 1-Dichlorocyclopropane was obtained by photochlorination of cyclopropane. It was distilled through a center-rod fractionating column and the fraction b.p. 74.5° (744.5 mm), np 1, 4373 (it. °° b.p. 74 -75°, (33) J. D. Roberts and P. H. Dirstine, J. Am. Chem. Soc., 67, 1281 (1945) np 1. 4400) was used. al 1,1-Dimethyleyclopropane was prepared by Cox*4 and was (34) E. F. Cox, Ph.D. Thesis, California Institute of Technology, 1955. used without further purification. Spiropentane of b. p. 36-38° was obtained from Professor D. E. Applequist. It had been distilled after treatment with bromine and dried over calcium hydride. Spirohexane was furnished by Professor D. E. McGreer. 35 (35) D. E. McGreer, Can. J. Chem., 38, 1638 (1960). 1-Phenyl-1-bromocyclopropane was prepared in these labor- atories by Dr. D. I. Schuster. Dimethyl 1-Methylcyclopropane-cis-1, 2-dicarboxylate. - The parent diacid, m.p. 139-141°, was provided by Professor L. L. McCoy, 36 (36) L. L. McCoy, J. Am. Chem. Soc., 80, 6568 (1958). and was esterified with an excess of diazomethane in benzene. The product was microdistilled at 3 mm. with a bath at 80°. Dimethyl 1-Methyleyclopropane-trans-1, 2-dicarboxylate. - The parent diacid, m.p. ca. 170° from Professor L. L. McCoy, was esterified with excess diazomethane. The resulting dimethyl ester was microdistilled at 2mm. with a bath at 65-70°. Nortricyclene was a pure sample obtained from Professor H. Hart. The spectrum showed a smal) broad CH peak, large CH, 22 peak and a cyclopropyl peak at 114.6, 70.8 aud 57. 60 cps respectively with areas 1:6:3. The chemical shift for the cyclopropyl peak was measured by side-band superposition frora tetramethylsilane, and that for the CH,.ani CH peaks by interpolation from two tetramethylsilane side bands. Since the chemical shifts were critical, they were obtained from the maxima or geometric center of each resonance for volume fractions of nortricyclene in carbon tetrachloride of approximately 1,0. 25,0. 06, 0.016 and extrapolating to infinite dilution. 1 ; 3 ; 4, 5- Tetramethy]- 2~methylene-bicyclo| 3.1.0 hex- 3-ene was obtained from Dr. L. deVries. 37 two side bands from the vinyl (37) L. deVries, J. Am. Chem. Soc., 82, 5242 (1960). peak were used to obtain the frequencies of the cyclopropyl peaks by interpolation, the chemical shift difference between the cyclopropyl hydrogens being 3.9 cps. The chemical shift of the center of the cyclopropyl methylene quartet was measured by interpolation from side bands from tetramethylsilane for a 5% w/v solution of the hydrocarbon in carbon tetrachloride and found to be 31. 2 cps. 2-Oxa-7, 7-dichloronorearane of b.p. 50-52° (1. 6-1. 9 mm. ) PPRAPARAAAARRARR ALR ADAP PAOD 22. ™D 1.4981 was provided by Professor W. E. Parham. 38 The n. m.r. (38) E. E. Schweizer and W. E. Parham, J. Am. Chem. Soc., 82, 4085 (1960). spectrum of a 5% w/v solution of 2-oxa-7, 7-dichloronorcarane in carbon tetrachloride showed two main groups of peaks, the larger group at high- field being assigned to the methylene hydrogens at C4, C5 and the cyclo- 23 propyl methine hydrogen at C6; and the smaller group at low -field to the methylene hydrogens at C3 and the c yclopropyl methine hydrogen at Cl. The latter gave a prominent unsymmictrical doublet on the low- field side of the lower group of peaks, due to cis: -vicinal spin coupling with the cyclopropyl methine hydrogen at C6. The frequencies of the peaks in this doublet were determined by side-band superposition from tetramethylsilane. Dicycloprop yimethane was provided by Professor H. Hart. 39 (39) H. Hart and O. E. Curtis, J. Am. Chem. Soc., 78, 112 (1956). SO The acyclic methylene resonance appeared as a broadened doublet near the cyclopropyl methine peaks. The chemical shift for the center of this doublet was obtained by extrapolation to infinite dilution and found to be 65. 4 eps downfield from tetramethylsilane. i-carboxylic acid was the dextrorotatory enantiomer, m.p. 164-165", obtained from Professor Y. Inouye. 40 The line positions were measured (40) Y. Inouye, Bull. Inst. Chem. Res., Kyoto Univ., 35, 49 (1957); C.A., 52, 11759 (1958). by superimposing side bands from chloroform. Methyl trans-3- (trans -2'-carbomethoxypropenyl)- 2, 2-dimethyl- cyclopropane-l-carboxylate, m.p. 80° was also provided by Professor Y. Inouye. 24. 2, 2-Dimethyl-trans-3~phenylcyclopropane-1-carboxylic acid RRP INP lel Moa PPA AA PNA LOLOL NL LOS PAPAS ANA ASN ANS Pet was provided by Professor F. Sorm?! and had m.p. 102°. Approximate (41) J. Karkas, P. Kourim and F. Sorm, Chem. listy, 52, 695 (1958); C.A., 52, 13651 (1958). chemical shifts (accurate to + 1 cps) were obtained for the methyl and cyclopropyl hydrogens by interpolation from a tetramethyisilane peak (internal reference) and the low-field cyclopropyl doublet, which has been accurately calibrated. The chemical shift differences were thus found to be 48 cps between the cyclopropyl hydrogens and 31 cps between the gem dimethyl groups. . 2, 2~ Dimethyl-cis -3-phenylcyclopropane-i-carboxylic acid was also provided by Professor Sorm and had m.p. 124°. The chemical shift between the cyclopropyl hydrogens was 39 cps, and between the gem_ dimethyl groups only 2 cps. 2, 2~Dimethyl-trans-3-phenylcyclopropane-1-carboxamide was 2 obtained from Professor G. W. Perold. —f Ay (42) G. W. Perold, |g, S. African Chem. Inst., 10, 11 (1957), The chemical shifts were approximately 55 cps between the cyclopropyl hydrogens and 27 cps between the gem dimethyl groups. Dimethyl 2, 2-dimethylcyclopropane-trans- 1, 2-dicarboxylate-- LRN ANN at NNN NA A NL ALP AAA AD NP ll NP lO ae APP PRP The parent diacid was obtained from Professors Y. Inouye and M. Matsui, who report m.p. 210-212° and 212-213° respectively. The combined samples were esterified with excess diazomethane, and the product was 25 microdistilled at 14 mm. with a bath at 125-130° and gave diester of n24p 1,4434. The high-field cyclopropyl “C satellite was a slightly unsymmetrical doublet. The resonances were calibrated by side-~band superposition from the carbomethoxyl peak. Dimethyl 1, 2-dimethylcyclopropane-cis-1, 2-dicarboxylate was provided by Proiessor L. L. McCoy and contained 7% of the trans isomer. Two side bands from the methyl peaks were placed on either side of the upfield cyclopropane doublet and the splitting determined by interpolation. The analysis of the cyclopropyl methylene quartet indi- cated that the chemical shift between the cyclopropyl hydrogens was 79, 0 cps. Acknowledgement. - Besides the generous gifts of samples of cyclopropane derivatives mentioned above, we are deeply grateful to Drs. A. A. Bothner-By, J. D. Swalen and Professor K. B. Wiberg for supplying us with program decks for the calculation and fitting of n.m,r. spectra for use with the IBM 7090 computer. Mr. K. Servis and Mr. L. Sloan provided extensive help with the computatiors .